FREESCALE MC68HC908AZ32AVFU

MC68HC908AZ32A
Data Sheet
M68HC08
Microcontrollers
MC68HC908AZ32A
Rev. 2
10/2005
freescale.com
MC68HC908AZ32A
Data Sheet
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© Freescale Semiconductor, Inc., 2006. All rights reserved.
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List of Paragraphs
Chapter 1 General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Chapter 2 Memory Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter 3 RAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Chapter 4 Flash Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Chapter 5 EEPROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Chapter 6 Central Processor Unit (CPU). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Chapter 7 System Integration Module (SIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Chapter 8 Clock Generator Module (CGM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Chapter 9 Configuration Register (CONFIG-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
Chapter 10 Configuration Register (CONFIG-2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Chapter 11 Brake Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Chapter 12 Monitor ROM (MON) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Chapter 13 Computer Operating Properly (COP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Chapter 14 Low Voltage Inhibit (LVI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Chapter 15 External Interrupt Module (IRQ1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Chapter 16 Serial Communications Interface (SCI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Chapter 17 Serial Peirpheral Interface (SPI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Chapter 18 Timer Interface Module A (TIMA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Chapter 19 Timer Interface Module B (TIMB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Chapter 20 Programmable Interrupt Timer (PIT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Chapter 21 Analog-To-Digital Converter (ADC-15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .229
Chapter 22 Keyboard Module (KBD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Chapter 23 I/O Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Chapter 24 MSCAN Controller (MSCAN08). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Chapter 25 Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
Chapter 26 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
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List of Paragraphs
MC68HC908AZ32A Data Sheet, Rev. 2
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Freescale Semiconductor
Table of Contents
Chapter 1
General Description
1.1
1.2
1.3
1.4
1.4.1
1.4.2
1.4.3
1.4.4
1.4.5
1.4.6
1.4.7
1.4.8
1.4.9
1.4.10
1.4.11
1.4.12
1.4.13
1.4.14
1.4.15
1.4.16
1.4.17
1.4.18
1.4.19
1.4.20
1.5
1.5.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MCU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply Pins (VDD and VSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oscillator Pins (OSC1 and OSC2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Reset Pin (RST). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Interrupt Pin (IRQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog Power Supply Pin (VDDA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog Ground Pin (VSSA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Filter Capacitor Pin (CGMXFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Analog Power Supply Pin (VDDAREF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Analog Ground Pin (AVSS/VREFL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Reference High Voltage Pin (VREFH). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A Input/Output (I/O) Pins (PTA7–PTA0). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port B I/O Pins (PTB7/ATD7–PTB0/ATD0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port C I/O Pins (PTC5–PTC0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D I/O Pins (PTD7–PTD0/ATD8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E I/O Pins (PTE7/SPSCK–PTE0/TxD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port F I/O Pins (PTF6–PTF0/TACH2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port G I/O Pins (PTG2/KBD2–PTG0/KBD0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port H I/O Pins (PTH1/KBD4–PTH0/KBD3). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CAN Transmit Pin (CANTx) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CAN Receive Pin (CANRx) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MC Order Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
19
20
22
23
23
23
23
23
24
24
24
24
24
24
24
24
24
24
25
25
25
25
25
28
28
Chapter 2
Memory Map
2.1
2.2
2.3
2.4
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Additional Status and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vector Addresses and Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
31
36
38
Chapter 3
RAM
3.1
3.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
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Table of Contents
Chapter 4
Flash Memory
4.1
4.2
4.3
4.3.1
4.3.2
4.4
4.5
4.6
4.7
4.8
4.8.1
4.8.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Control and Block Protect Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Block Protect Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Block Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Mass Erase Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Page Erase Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Program Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
WAIT Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
STOP Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
43
44
44
45
46
47
47
48
49
49
49
Chapter 5
EEPROM
5.1
5.2
5.3
5.4
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
5.5
5.5.1
5.5.2
5.5.3
5.5.4
5.5.5
5.6
5.6.1
5.6.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Register Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Timebase Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Program/Erase Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Block Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Programming and Erasing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Array Configuration Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Nonvolatile Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Timebase Divider Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EEPROM Timebase Divider Nonvolatile Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
51
51
51
51
51
52
53
53
54
57
57
58
59
60
61
61
61
62
Chapter 6
Central Processor Unit (CPU)
6.1
6.2
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Index Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stack Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Program Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Condition Code Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
63
63
63
64
64
65
65
66
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6.4
6.5
6.5.1
6.5.2
6.6
6.7
6.8
Arithmetic/Logic Unit (ALU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instruction Set Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Opcode Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
67
67
67
67
68
73
Chapter 7
System Integration Module (SIM)
7.1
7.2
7.2.1
7.2.2
7.2.3
7.3
7.3.1
7.3.2
7.4
7.4.1
7.4.2
7.4.3
7.5
7.5.1
7.5.2
7.5.3
7.5.4
7.6
7.6.1
7.6.2
7.7
7.7.1
7.7.2
7.7.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Bus Clock Control and Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bus Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Startup from POR or LVI Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clocks in Stop Mode and Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset and System Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Pin Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Active Resets from Internal Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Counter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Counter During Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Counter During Stop Mode Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Counter and Reset States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Program Exception Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Status Flag Protection in Break Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Break Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Reset Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SIM Break Flag Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75
77
77
77
77
78
78
79
81
81
81
81
81
82
85
85
85
85
85
86
87
87
88
89
Chapter 8
Clock Generator Module (CGM)
8.1
8.2
8.3
8.3.1
8.3.2
8.3.3
8.3.4
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Crystal Oscillator Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phase-Locked Loop Circuit (PLL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Base Clock Selector Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CGM External Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
91
91
91
93
97
97
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Freescale Semiconductor
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Table of Contents
8.4
8.4.1
8.4.2
8.4.3
8.4.4
8.4.5
8.4.6
8.4.7
8.4.8
8.5
8.5.1
8.5.2
8.5.3
8.6
8.7
8.7.1
8.7.2
8.8
8.9
8.9.1
8.9.2
8.9.3
8.9.4
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Crystal Amplifier Input Pin (OSC1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Crystal Amplifier Output Pin (OSC2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
External Filter Capacitor Pin (CGMXFC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Analog Power Pin (VDDA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Oscillator Enable Signal (SIMOSCEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Crystal Output Frequency Signal (CGMXCLK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
CGM Base Clock Output (CGMOUT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
CGM CPU Interrupt (CGMINT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
CGM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
PLL Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
PLL Bandwidth Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
PLL Programming Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
CGM During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Acquisition/Lock Time Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Acquisition/Lock Time Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Parametric Influences on Reaction Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Choosing a Filter Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Reaction Time Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Chapter 9
Configuration Register (CONFIG-1)
9.1
9.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Chapter 10
Configuration Register (CONFIG-2)
10.1
10.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Chapter 11
Brake Module
11.1
11.2
11.3
11.3.1
11.3.2
11.3.3
11.3.4
11.4
11.4.1
11.4.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flag Protection During Break Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIM During Break Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COP During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
113
113
113
114
114
114
114
114
115
115
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11.5 Break Module Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
11.5.1
Break Status and Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
11.5.2
Break Address Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Chapter 12
Monitor ROM (MON)
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.1
Entering Monitor Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.2
Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.3
Echoing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.4
Break Signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.5
Commands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.6
Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3.7
Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
117
117
117
119
120
120
120
121
123
124
Chapter 13
Computer Operating Properly (COP
13.1
13.2
13.3
13.3.1
13.3.2
13.3.3
13.3.4
13.3.5
13.3.6
13.3.7
13.3.8
13.4
13.5
13.6
13.7
13.7.1
13.7.2
13.8
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CGMXCLK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
STOP Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPCTL Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power-On Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset Vector Fetch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COP Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COP Module During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
125
125
126
126
126
126
126
127
127
127
127
127
127
127
127
127
128
128
Chapter 14
Low Voltage Inhibit (LVI)
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.1
Polled LVI Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2
Forced Reset Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.3
False Reset Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
129
129
129
130
130
130
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Table of Contents
14.4 LVI Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5 LVI Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
131
131
131
131
132
Chapter 15
External Interrupt Module (IRQ1)
15.1
15.2
15.3
15.4
15.5
15.6
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Module During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
133
133
133
136
136
137
Chapter 16
Serial Communications Interface (SCI)
16.1
16.2
16.3
16.4
16.4.1
16.4.2
16.4.3
16.5
16.5.1
16.5.2
16.6
16.7
16.7.1
16.7.2
16.8
16.8.1
16.8.2
16.8.3
16.8.4
16.8.5
16.8.6
16.8.7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin Name Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI During Break Module Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PTE0/SCTxD (Transmit Data) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PTE1/SCRxD (Receive Data) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Control Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Control Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Control Register 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Status Register 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Status Register 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SCI Baud Rate Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
139
139
139
140
142
142
145
153
153
153
153
153
153
154
154
154
156
158
159
161
162
162
Chapter 17
Serial Peirpheral Interface (SPI)
17.1
17.2
17.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Pin Name and Register Name Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
MC68HC908AZ32A Data Sheet, Rev. 2
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Freescale Semiconductor
17.4 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.4.1
Master Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.4.2
Slave Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5 Transmission Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5.1
Clock Phase and Polarity Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5.2
Transmission Format When CPHA = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5.3
Transmission Format When CPHA = 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5.4
Transmission Initiation Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.6 Error Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.6.1
Overflow Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.6.2
Mode Fault Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.7 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8 Queuing Transmission Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.9 Resetting the SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.10 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.10.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.10.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.11 SPI During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.12 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.12.1
MISO (Master In/Slave Out). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.12.2
MOSI (Master Out/Slave In). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.12.3
SPSCK (Serial Clock) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.12.4
SS (Slave Select) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.12.5
VSS (Clock Ground) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.13 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.13.1
SPI Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.13.2
SPI Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.13.3
SPI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
166
168
168
169
169
170
170
171
173
173
174
176
177
178
178
178
178
178
179
179
179
180
180
181
181
181
182
185
Chapter 18
Timer Interface Module A (TIMA)
18.1
18.2
18.3
18.3.1
18.3.2
18.3.3
18.3.4
18.4
18.5
18.5.1
18.5.2
18.6
18.7
18.7.1
18.7.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMA Counter Prescaler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Compare. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pulse Width Modulation (PWM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMA During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMA Clock Pin (PTD6/ATD14/TACLK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMA Channel I/O Pins (PTF3/TCH5–PTF0/TCH2 and PTE3/TCH1–PTE2/TCH0) . . . . .
187
187
189
190
190
190
192
195
195
195
195
196
196
196
196
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Table of Contents
18.8 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.1
TIMA Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.2
TIMA Counter Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.3
TIMA Counter Modulo Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.4
TIMA Channel Status and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.5
TIMA Channel Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
197
197
199
199
200
203
Chapter 19
Timer Interface Module B (TIMB)
19.1
19.2
19.3
19.3.1
19.3.2
19.3.3
19.3.4
19.4
19.5
19.5.1
19.5.2
19.6
19.7
19.7.1
19.7.2
19.8
19.8.1
19.8.2
19.8.3
19.8.4
19.8.5
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Counter Prescaler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output Compare. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pulse Width Modulation (PWM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Clock Pin (PTD4/ATD12) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Channel I/O Pins (PTF5/TBCH1–PTF4). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Counter Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Counter Modulo Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Channel Status and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIMB Channel Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
207
207
207
207
209
209
210
213
213
213
213
213
214
214
214
214
214
216
217
217
220
Chapter 20
Programmable Interrupt Timer (PIT)
20.1
20.2
20.3
20.4
20.5
20.5.1
20.5.2
20.6
20.7
20.7.1
20.7.2
20.7.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PIT Counter Prescaler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PIT During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIM Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIM Counter Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TIM Counter Modulo Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
223
223
223
224
224
224
225
225
225
225
227
227
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Chapter 21
Analog-To-Digital Converter (ADC-15)
21.1
21.2
21.3
21.3.1
21.3.2
21.3.3
21.3.4
21.3.5
21.4
21.5
21.5.1
21.5.2
21.6
21.6.1
21.6.2
21.6.3
21.7
21.7.1
21.7.2
21.7.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Port I/O Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conversion Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Continuous Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accuracy and Precision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Analog Power Pin (VDDAREF)/ADC Voltage Reference Pin (VREFH) . . . . . . . . . . . . .
ADC Analog Ground Pin (VSSA)/ADC Voltage Reference Low Pin (VREFL) . . . . . . . . . . .
ADC Voltage In (ADCVIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Data Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Input Clock Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
229
229
229
229
230
230
231
231
231
231
231
231
232
232
232
232
232
232
234
234
Chapter 22
Keyboard Module (KBD)
22.1
22.2
22.3
22.4
22.5
22.5.1
22.5.2
22.6
22.7
22.7.1
22.7.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Module During Break Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Status and Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Interrupt Enable Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
237
237
238
239
239
239
240
240
240
240
241
Chapter 23
I/O Ports
23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.2 Port A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.2.1
Port A Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.2.2
Data Direction Register A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.3 Port B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.3.1
Port B Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.3.2
Data Direction Register B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
243
244
244
244
246
246
246
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Table of Contents
23.4
23.4.1
23.4.2
23.5
23.5.1
23.5.2
23.6
23.6.1
23.6.2
23.7
23.7.1
23.7.2
23.8
23.8.1
23.8.2
23.9
23.9.1
23.9.2
Port C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port C Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port F Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register F. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port G. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port G Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port H Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
248
248
248
250
250
251
252
252
253
255
255
256
257
257
258
259
259
260
Chapter 24
MSCAN Controller (MSCAN08)
24.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.3 External Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.4 Message Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.4.1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.4.2
Receive Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.4.3
Transmit Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.5 Identifier Acceptance Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.6 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.6.1
Interrupt Acknowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.6.2
Interrupt Vectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.7 Protocol Violation Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.8 Low Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.8.1
MSCAN08 Sleep Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.8.2
MSCAN08 Soft Reset Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.8.3
MSCAN08 Power Down Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.8.4
CPU Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.8.5
Programmable Wakeup Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.9 Timer Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.10 Clock System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.11 Memory Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.12 Programmer’s Model of Message Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.12.1
Message Buffer Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.12.2
Identifier Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.12.3
Data Length Register (DLR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
263
263
264
264
264
265
266
267
270
270
270
271
271
272
273
273
274
274
274
274
277
278
279
280
280
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24.12.4
Data Segment Registers (DSRn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.12.5
Transmit Buffer Priority Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13 Programmer’s Model of Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.1
MSCAN08 Module Control Register 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.2
MSCAN08 Module Control Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.3
MSCAN08 Bus Timing Register 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.4
MSCAN08 Bus Timing Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.5
MSCAN08 Receiver Flag Register (CRFLG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.6
MSCAN08 Receiver Interrupt Enable Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.7
MSCAN08 Transmitter Flag Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.8
MSCAN08 Transmitter Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.9
MSCAN08 Identifier Acceptance Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.10 MSCAN08 Receive Error Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.11 MSCAN08 Transmit Error Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.12 MSCAN08 Identifier Acceptance Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.13.13 MSCAN08 Identifier Mask Registers (CIDMR0–3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
281
281
281
283
284
285
286
287
289
290
291
292
293
293
294
295
Chapter 25
Electrical Specifications
25.1 Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.1
Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.2
Functional Operating Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.3
Thermal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.4
5.0 Volt DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.5
Control Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.6
ADC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.7
5.0 Vdc ± 0.5 V Serial Peripheral Interface (SPI) Timing . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.8
CGM Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.9
CGM Component Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.10
CGM Acquisition/Lock Time Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.11
Timer Module Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.12
RAM Memory Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.13
EEPROM Memory Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.1.14
FLASH Memory Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.2 Mechanical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
297
297
298
298
299
300
300
301
304
304
305
306
306
306
307
307
Chapter 26
Revision History
26.1
26.2
Major Changes Between Revision 2.0 and Revision 1.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Major Changes Between Revision 1.0 and Revision 0.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Glossary
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
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Table of Contents
MC68HC908AZ32A Data Sheet, Rev. 2
18
Freescale Semiconductor
Chapter 1
General Description
1.1 Introduction
The MC68HC908AZ32A is a member of the low-cost, high-performance M68HC08 Family of 8-bit
microcontroller units (MCUs). All MCUs in the family use the enhanced M68HC08 central processor unit
(CPU08) and are available with a variety of modules, memory sizes and types, and package types.
1.2 Features
Features of the MC68HC908AZ32A include:
• High-Performance M68HC08 Architecture
• Fully Upward-Compatible Object Code with M6805, M146805, and M68HC05 Families
• 8.4 MHz Internal Bus Frequency
• 32,256 bytes of FLASH Electrically Erasable Read-Only Memory (FLASH)
• FLASH Data Security
• 512 bytes of On-Chip Electrically Erasable Programmable Read-Only Memory with Security Option
(EEPROM)
• 1K byte of On-Chip RAM
• Clock Generator Module (CGM)
• Serial Peripheral Interface Module (SPI)
• Serial Communications Interface Module (SCI)
• 8-Bit, 15-Channel Analog-to-Digital Converter (ADC-15)
• 16-Bit, 6-Channel Timer Interface Module (TIMA-6)
• 16-Bit, 2-Channel Timer Interface Module (TIMB)
• Programmable Interrupt Timer (PIT)
• System Protection Features
– Computer Operating Properly (COP) with Optional Reset
– Low-Voltage Detection with Optional Reset
– Illegal Opcode Detection with Optional Reset
– Illegal Address Detection with Optional Reset
• Low-Power Design (Fully Static with Stop and Wait Modes)
• Master Reset Pin and Power-On Reset
• 5-Bit Keyboard Interrupt Module
• MSCAN Controller (Scalable CAN) implements CAN 2.0b Protocol as Defined in BOSCH
Specification September 1991
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
19
General Description
Features of the CPU08 include:
• Enhanced HC05 Programming Model
• Extensive Loop Control Functions
• 16 Addressing Modes (Eight More Than the HC05)
• 16-Bit Index Register and Stack Pointer
• Memory-to-Memory Data Transfers
• Fast 8 × 8 Multiply Instruction
• Fast 16/8 Divide Instruction
• Binary-Coded Decimal (BCD) Instructions
• Optimization for Controller Applications
• C Language Support
1.3 MCU Block Diagram
Figure 1-1 shows the structure of the MC68HC908AZ32A.
MC68HC908AZ32A Data Sheet, Rev. 2
20
Freescale Semiconductor
MC68HC908AZ32A Data Sheet, Rev. 2
USER RAM —1024 BYTES
USER EEPROM — 512 BYTES
COMPUTER OPERATING
PROPERLY MODULE
MONITOR ROM — 320 BYTES
TIMER A 6 CHANNEL
INTERFACE MODULE
USER FLASH VECTOR SPACE — 52 BYTES
TIMER B INTERFACE
MODULE
OSC1
OSC2
CGMXFC
RST
IRQ
CLOCK GENERATOR
MODULE
SERIAL COMMUNICATIONS
INTERFACE MODULE
SYSTEM INTEGRATION
MODULE
SERIAL PERIPHERAL
INTERFACE MODULE
POWER-ON RESET
MODULE
POWER
PROGRAMMABLE INTERRUPT TIMER
MODULE
AVSS/VREFL
VDDAREF
DDRA
PTA
DDRB
PTB
DDRC
PTC
PTD7
PTD6/ATD14/TACLK
PTD5/ATD13
PTD4/ATD12/TBCLK
PTD3/ATD11-PTD0/ATD8
PTE7/SPSCK
PTE6/MOSI
PTE5/MISO
PTE4/SS
PTE3/TACH1
PTE2/TACH0
PTE1/RxD
PTE0/TxD
PTF6
PTF5/TBCH1–PTF4/TBCH0
PTG2/KBD2–PTG0/KBD0
PTF3/TACH5-PTF0/TACH2
PTH1/KBD4–PTH0/KBD3
MSCAN MODULE
Figure 1-1. MCU Block Diagram for the MC68HC908AZ32A
CANRx
CANTx
21
MCU Block Diagram
VSS
VDD
VDDA
VSSA
KEYBOARD INTERRUPT
MODULE
IRQ MODULE
PTD
LOW-VOLTAGE INHIBIT
MODULE
PTE
USER FLASH — 32,256 BYTES
PTC5–PTC3
PTC2/MCLK
PTC1–PTC0
PTF
BREAK MODULE
PTG
CONTROL AND STATUS REGISTERS — 62 BYTES
PTB7/ATD7–PTB0/ATD0
PTH
ANALOG-TO-DIGITAL
MODULE
PTA7–PTA0
DDRD
VREFH
DDRE
ARITHMETIC/LOGIC
UNIT (ALU)
DDRF
CPU
REGISTERS
DDRH DDRG
Freescale Semiconductor
M68HC08 CPU
General Description
1.4 Pin Assignments
PTC1
PTC0
OSC1
OSC2
CGMXFC
VSSA
VDDA
VREFH
PTD7
PTD6/ATD14/TACLK
PTD5/ATD13
PTD4/ATD12/TBCLK
61
60
59
58
57
56
55
54
53
52
51
50
PTC4
1
PTH1/KBD4
PTC2/MCLK
62
49
PTC3
63
64
PTC5
Figure 1-2 shows the MC68HC908AZ32A pin assignments.
48
PTH0/KBD3
CANRx
9
40
PTB6/ATD6
CANTx
10
39
PTB5/ATD5
PTF5/TBCH1
11
38
PTB4/ATD4
PTF6
12
37
PTB3/ATD3
PTE0/TxD
13
36
PTB2/ATD2
PTE1/RxD
14
35
PTB1/ATD1
PTE2/TACH0
15
34
PTB0/ATD0
33
PTA7
PTA6 32
PTE4/SS 17
PTE3/TACH1 16
31
PTB7/ATD7
PTA5
41
30
8
PTA4
PTF4/TBCH0
29
PTD0/ATD8
PTA3
42
28
7
PTA2
PTF3/TACH5
27
PTD1/ATD9
PTA1
43
26
6
PTA0
PTF2/TACH4
25
VDDAREF
PTG2/KBD2
44
24
5
PTG1/KBD1
PTF1/TACH3
23
AVSS /VREFL
PTG0/KBD0
45
22
4
VDD
PTF0/TACH2
21
PTD2/ATD10
VSS
46
20
3
PTE7/SPSCK
RST
19
PTD3/ATD11
PTE6/MOSI
47
18
2
PTE5/MISO
IRQ
Figure 1-2. MC68HC908AZ32A 64 QFP Pin Assignments
NOTE
The following pin descriptions are just a quick reference. For a more
detailed representation, see Chapter 23 I/O Ports.
MC68HC908AZ32A Data Sheet, Rev. 2
22
Freescale Semiconductor
Pin Assignments
1.4.1 Power Supply Pins (VDD and VSS)
VDD and VSS are the power supply and ground pins. The MCU operates from a single power supply.
Fast signal transitions on MCU pins place high, short-duration current demands on the power supply. To
prevent noise problems, take special care to provide power supply bypassing at the MCU as shown in
Figure 1-3. Place the C1 bypass capacitor as close to the MCU as possible. Use a high-frequency
response ceramic capacitor for C1. C2 is an optional bulk current bypass capacitor for use in applications
that require the port pins to source high current levels.
MCU
VDD
VSS
C1
0.1 μF
+
C2
VDD
NOTE: Component values shown represent typical applications.
Figure 1-3. Power Supply Bypassing
VSS is also the ground for the port output buffers and the ground return for the serial clock in the Serial
Peripheral Interface module (SPI). See Chapter 17 Serial Peirpheral Interface (SPI).
NOTE
VSS must be grounded for proper MCU operation.
1.4.2 Oscillator Pins (OSC1 and OSC2)
The OSC1 and OSC2 pins are the connections for the on-chip oscillator circuit. See Chapter 8 Clock
Generator Module (CGM).
1.4.3 External Reset Pin (RST)
A logic 0 on the RST pin forces the MCU to a known startup state. RST is bidirectional, allowing a reset
of the entire system. It is driven low when any internal reset source is asserted. See Chapter 7 System
Integration Module (SIM) for more information.
1.4.4 External Interrupt Pin (IRQ)
IRQ is an asynchronous external interrupt pin. See Chapter 15 External Interrupt Module (IRQ1).
1.4.5 Analog Power Supply Pin (VDDA)
VDDA is the power supply pin for the analog portion of the Clock Generator Module (CGM). See
Chapter 8 Clock Generator Module (CGM).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
23
General Description
1.4.6 Analog Ground Pin (VSSA)
VSSA is the ground connection for the analog portion of the Clock Generator Module (CGM). See
Chapter 8 Clock Generator Module (CGM).
1.4.7 External Filter Capacitor Pin (CGMXFC)
CGMXFC is an external filter capacitor connection for the Clock Generator Module (CGM). See
Chapter 8 Clock Generator Module (CGM).
1.4.8 ADC Analog Power Supply Pin (VDDAREF)
VDDAREF is the power supply pin for the analog portion of the Analog-to-Digital Converter (ADC). See
Chapter 21 Analog-To-Digital Converter (ADC-15).
1.4.9 ADC Analog Ground Pin (AVSS/VREFL)
The AVSS/VREFL pin provides both the analog ground connection and the reference low voltage for the
Analog-to-Digital Converter (ADC). See Chapter 21 Analog-To-Digital Converter (ADC-15).
1.4.10 ADC Reference High Voltage Pin (VREFH)
VREFH provides the reference high voltage for the Analog-to-Digital Converter (ADC). See Chapter 21
Analog-To-Digital Converter (ADC-15).
1.4.11 Port A Input/Output (I/O) Pins (PTA7–PTA0)
PTA7–PTA0 are general-purpose bidirectional I/O port pins. See Chapter 23 I/O Ports.
1.4.12 Port B I/O Pins (PTB7/ATD7–PTB0/ATD0)
Port B is an 8-bit special function port that shares all eight pins with the Analog-to-Digital Converter (ADC).
See Chapter 21 Analog-To-Digital Converter (ADC-15) and Chapter 23 I/O Ports.
1.4.13 Port C I/O Pins (PTC5–PTC0)
PTC5–PTC3 and PTC1–PTC0 are general-purpose bidirectional I/O port pins. PTC2/MCLK is a special
function port that shares its pin with the system clock which has a frequency equivalent to the system
clock. See Chapter 23 I/O Ports.
1.4.14 Port D I/O Pins (PTD7–PTD0/ATD8)
Port D is an 8-bit special-function port that shares seven of its pins with the Analog-to-Digital Converter
module (ADC-15), one of its pins with the Timer Interface Module A (TIMA), and one more of its pins with
the Timer Interface Module B (TIMB). See Chapter 18 Timer Interface Module A (TIMA), Chapter 19 Timer
Interface Module B (TIMB), Chapter 21 Analog-To-Digital Converter (ADC-15) and Chapter 23 I/O Ports.
1.4.15 Port E I/O Pins (PTE7/SPSCK–PTE0/TxD)
Port E is an 8-bit special function port that shares two of its pins with the Timer Interface Module A (TIMA),
four of its pins with the Serial Peripheral Interface module (SPI), and two of its pins with the Serial
Communication Interface module (SCI). See Chapter 16 Serial Communications Interface (SCI),
MC68HC908AZ32A Data Sheet, Rev. 2
24
Freescale Semiconductor
Pin Assignments
Chapter 17 Serial Peirpheral Interface (SPI), Chapter 18 Timer Interface Module A (TIMA), and
Chapter 23 I/O Ports.
1.4.16 Port F I/O Pins (PTF6–PTF0/TACH2)
Port F is a 7-bit special function port that shares its pins with the Timer Interface Module B (TIMB). Six of
its pins are shared with the Timer Interface Module A (TIMA-6). See Chapter 18 Timer Interface Module
A (TIMA), Chapter 19 Timer Interface Module B (TIMB), and Chapter 23 I/O Ports.
1.4.17 Port G I/O Pins (PTG2/KBD2–PTG0/KBD0)
Port G is a 3-bit special function port that shares all of its pins with the Keyboard Module (KBD). See
Chapter 22 Keyboard Module (KBD) and Chapter 23 I/O Ports.
1.4.18 Port H I/O Pins (PTH1/KBD4–PTH0/KBD3)
Port H is a 2-bit special-function port that shares all of its pins with the Keyboard Module (KBD). See
Chapter 22 Keyboard Module (KBD) and Chapter 23 I/O Ports.
1.4.19 CAN Transmit Pin (CANTx)
This pin is the digital output from the CAN module (CANTx). See Chapter 24 MSCAN Controller
(MSCAN08).
1.4.20 CAN Receive Pin (CANRx)
This pin is the digital input to the CAN module (CANRx). See Chapter 24 MSCAN Controller (MSCAN08).
Table 1-1. External Pins Summary (Sheet 1 of 3)
Pin Name
Function
Driver Type
Hysteresis(1)
Reset State
PTA7–PTA0
General-Purpose I/O
Dual State
No
Input Hi-Z
PTB7/ATD7–PTB0/ATD0
General-Purpose I/O
ADC Channel
Dual State
No
Input Hi-Z
PTC5–PTC0
General-Purpose I/O
Dual State
No
Input Hi-Z
PTD7
General Purpose I/O
Dual State
No
Input Hi-Z
PTD6/ATD14/
TACLK ADC Channel
General-Purpose I/O
ADC Channel/Timer External Input Clock
Dual State
No
Input Hi-Z
PTD5/ATD13 ADC Channel
General-Purpose I/O
ADC Channel
Dual State
No
Input Hi-Z
PTD4/ATD12/T
BCLK ADC Channel
General-Purpose I/O
ADC Channel/Timer External Input Clock
Dual State
No
Input Hi-Z
PTD3/ATD11–PTD0/
ATD8 ADC Channels
General-Purpose I/O
ADC Channel
Dual State
No
Input Hi-Z
PTE7/SPSCK
General-Purpose I/O
SPI Clock
Dual State
Open Drain
Yes
Input Hi-Z
PTE6/MOSI
General-Purpose I/O
SPI Data Path
Dual State
Open Drain
Yes
Input Hi-Z
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
25
General Description
Table 1-1. External Pins Summary (Sheet 2 of 3)
Pin Name
Function
Driver Type
Hysteresis(1)
Reset State
PTE5/MISO
General-Purpose I/O
SPI Data Path
Dual State
Open Drain
Yes
Input Hi-Z
PTE4/SS
General-Purpose I/O
SPI Slave Select
Dual State
Yes
Input Hi-Z
PTE3/TACH1
General-Purpose I/O
Timer A Channel 1
Dual State
Yes
Input Hi-Z
PTE2/TACH0
General-Purpose I/O
Timer A Channel 0
Dual State
Yes
Input Hi-Z
PTE1/RxD
General-Purpose I/O
SCI Receive Data
Dual State
Yes
Input Hi-Z
PTE0/TxD
General-Purpose I/O
SCI Transmit Data
Dual State
No
Input Hi-Z
PTF6
General-Purpose I/O
Dual State
No
Input Hi-Z
PTF5/TBCH1–PTF4/TBCH0
General-Purpose I/O/Timer B Channel
Dual State
Yes
Input Hi-Z
PTF3/TACH5
General-Purpose I/O
Timer A Channel 5
Dual State
Yes
Input Hi-Z
PTF2/TACH4
General-Purpose I/O
Timer A Channel 4
Dual State
Yes
Input Hi-Z
PTF1/TACH3
General-Purpose I/O
Timer A Channel 3
Dual State
Yes
Input Hi-Z
PTF0/TACH2
General-Purpose I/O
Timer A Channel 2
Dual State
Yes
Input Hi-Z
PTG2/KBD2–PTG0/KBD0
General-Purpose I/O/
Keyboard Wakeup Pin
Dual State
Yes
Input Hi-Z
PTH1/KBD4 –PTH0/KBD3
General-Purpose I/O/
Keyboard Wakeup Pin
Dual State
Yes
Input Hi-Z
VDD
Chip Power Supply
N/A
N/A
N/A
VSS
Chip Ground
N/A
N/A
N/A
VDDA
CGM Analog Power Supply
VSSA
CGM Analog Ground
VDDAREF
ADC Power Supply
N/A
N/A
N/A
AVSS/VREFL
ADC Ground/ADC Reference Low Voltage
N/A
N/A
N/A
VREFH
A/D Reference High Voltage
N/A
N/A
N/A
OSC1
External Clock In
N/A
N/A
Input Hi-Z
OSC2
External Clock Out
N/A
N/A
Output
CGMXFC
PLL Loop Filter Cap
N/A
N/A
N/A
IRQ
External Interrupt Request
N/A
N/A
Input Hi-Z
RST
Reset
N/A
N/A
Output Low
MC68HC908AZ32A Data Sheet, Rev. 2
26
Freescale Semiconductor
Pin Assignments
Table 1-1. External Pins Summary (Sheet 3 of 3)
Pin Name
Function
Driver Type
Hysteresis(1)
Reset State
CANRx
CAN Serial Input
N/A
Yes
Input Hi-Z
CANTx
CAN Serial Output
Output
No
Output
1. Hysteresis is not 100% tested but is typically a minimum of 300mV.
Table 1-2. Clock Signal Naming Conventions
Clock Signal Name
Description
CGMXCLK
Buffered version of OSC1 from
Clock Generation Module (CGM)
CGMOUT
PLL-based or OSC1-based clock output from
Clock Generator Module (CGM)
Bus Clock
CGMOUT divided by two
SPSCK
SPI serial clock
TACLK
External clock input for TIMA
TBCLK
External clock input for TIMB
Table 1-3. Clock Source Summary
Module
Clock Source
ADC
CGMXCLK or Bus Clock
CAN
CGMXCLK or CGMOUT
COP
CGMXCLK
CPU
Bus Clock
FLASH
Bus Clock
EEPROM
CGMXCLK or Bus Clock
RAM
Bus Clock
SPI
Bus Clock/SPSCK
SCI
CGMXCLK
TIMA
Bus Clock or PTD6/ATD14/TACLK
TIMB
Bus Clock or PTD4/TBCLK
PIT
Bus Clock
SIM
CGMOUT and CGMXCLK
IRQ
Bus Clock
BRK
Bus Clock
LVI
Bus Clock
CGM
OSC1 and OSC2
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
27
General Description
1.5 Ordering Information
This section contains instructions for ordering the MC68HC908AZ32A.
1.5.1 MC Order Numbers
Table 1-4. MC Order Numbers
MC Order Number
Operating
Temperature Range
MC68HC908AZ32ACFU (64-Pin QFP)
–40°C to + 85°C
MC68HC908AZ32AVFU (64-Pin QFP)
–40°C to + 105°C
MC68HC908AZ32AMFU (64-Pin QFP)
–40°C to + 125°C
MC68HC908AZ32A Data Sheet, Rev. 2
28
Freescale Semiconductor
Chapter 2
Memory Map
2.1 Introduction
The CPU08 can address 64K bytes of memory space. The memory map, shown in Figure 2-1, includes:
• 32,256 Bytes of FLASH EEPROM
• 1024 Bytes of RAM
• 512 Bytes of EEPROM with Protect Option
• 52 Bytes of User-Defined Vectors
• 320 Bytes of Monitor ROM
The following definitions apply to the memory map representation of reserved and unimplemented
locations.
• Reserved — Accessing a reserved location can have unpredictable effects on MCU operation.
• Unused — These locations are reserved in the memory map for future use, accessing an
unused location can have unpredictable effects on MCU operation.
• Unimplemented — Accessing an unimplemented location can cause an illegal address reset
(within the constraints as outlined in the Chapter 7 System Integration Module (SIM)).
$0000
↓
I/O REGISTERS (80 BYTES)
$004F
$0050
↓
RAM (1024 BYTES)
$044F
$0450
↓
UNIMPLEMENTED (176 BYTES)
$04FF
$0500
↓
CAN CONTROL AND MESSAGE
BUFFERS (128 BYTES)
$057F
$0580
↓
UNIMPLEMENTED (640 BYTES)
$07FF
$0800
↓
EEPROM (512 BYTES)
$09FF
Figure 2-1. Memory Map (Sheet 1 of 3)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
29
Memory Map
$0A00
↓
UNIMPLEMENTED (30,208 BYTES)
$7FFF
$8000
↓
FLASH (32,256 BYTES)
$FDFF
$FE00
SIM BREAK STATUS REGISTER (SBSR)
$FE01
SIM RESET STATUS REGISTER (SRSR)
$FE02
RESERVED
$FE03
SIM BREAK FLAG CONTROL REGISTER (SBFCR)
$FE04
↓
RESERVED (5 BYTES)
$FE08
$FE09
Configuration Write-Once Register (CONFIG-2)
$FE0A
RESERVED
$FE0B
RESERVED
$FE0C
BREAK ADDRESS REGISTER HIGH (BRKH)
$FE0D
BREAK ADDRESS REGISTER LOW (BRKL)
$FE0E
BREAK STATUS AND CONTROL REGISTER (BSCR)
$FE0F
LVI STATUS REGISTER (LVISR)
$FE10
EEPROM DIVIDER HIGH NON-VOLATILE REGISTER
(EEDIVHNVR)
$FE11
EEPROM DIVIDER LOW NON-VOLATILE REGISTER
(EEDIVLNVR)
$FE12
↓
RESERVED (8 BYTES)
$FE19
$FE1A
EEPROM DIVIDER HIGH REGISTER (EEDIVH)
$FE1B
EEPROM DIVIDER LOW REGISTER (EEDIVL)
$FE1C
EEPROM NON-VOLATILE REGISTER (EENVR)
$FE1D
EEPROM CONTROL REGISTER (EECR)
$FE1E
RESERVED
$FE1F
EEPROM ARRAY CONFIGURATION REGISTER (EEACR)
$FE20
↓
MONITOR ROM (320 BYTES)
$FF5F
$FF60
↓
UNIMPLEMENTED (32 BYTES)
$FF7F
$FF80
FLASH BLOCK PROTECT REGISTER (FLBPR)
Figure 2-1. Memory Map (Sheet 2 of 3)
MC68HC908AZ32A Data Sheet, Rev. 2
30
Freescale Semiconductor
I/O Section
$FF81
↓
RESERVED (7 BYTES)
$FF87
$FF88
FLASH CONTROL REGISTER (FLCR)
$FF89
↓
RESERVED (7 BYTES)
$FF8F
$FF90
↓
UNIMPLEMENTED (48 BYTES)
$FFBF
$FFC0
↓
RESERVED (12 BYTES)
$FFCB
$FFCC
VECTORS (52 BYTES)
See Table 2-1
↓
$FFFF
Figure 2-1. Memory Map (Sheet 3 of 3)
2.2 I/O Section
Addresses $0000–$004F, shown in Figure 2-2, contain the I/O Data, Status and Control Registers.
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
$0000
Port A Data Register Read:
(PTA) Write:
PTA7
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
$0001
Port B Data Register Read:
(PTB) Write:
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
Port C Data Register Read:
(PTC) Write:
0
0
$0002
PTC5
PTC4
PTC3
PTC2
PTC1
PTC0
R
R
PTD7
PTD6
PTD5
PTD4
PTD3
PTD2
PTD1
PTD0
$0003
Port D Data Register Read:
(PTD) Write:
$0004
Data Direction Register A Read:
(DDRA) Write:
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
$0005
Data Direction Register B Read:
(DDRB) Write:
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
= Unimplemented
R
= Reserved
Figure 2-2. I/O Data, Status and Control Registers (Sheet 1 of 6)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
31
Memory Map
Addr.
$0006
Register Name
Data Direction Register C Read:
MCLKEN
(DDRC) Write:
$0007
Data Direction Register D Read:
(DDRD) Write:
$0008
Port E Data Register Read:
(PTE) Write:
$0009
Port F Data Register Read:
(PTF) Write:
$000A
$000B
Port G Data Register Read:
(PTG) Write:
Port H Data Register Read:
(PTH) Write:
$000C
Data Direction Register E Read:
(DDRE) Write:
$000D
Data Direction Register F Read:
(DDRF) Write:
$000E
$000F
Bit 7
Data Direction Register G Read:
(DDRG) Write:
Data Direction Register H Read:
(DDRH) Write:
$0010
SPI Control Register Read:
(SPCR) Write:
$0011
SPI Status and Control Read:
Register (SPSCR) Write:
$0012
SPI Data Register Read:
(SPDR) Write:
6
5
4
3
2
1
Bit 0
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
R
DDRD7
DDRD6
DDRD5
DDRD4
DDRD3
DDR2
DDRD1
DDRD0
PTE7
PTE6
PTE5
PTE4
PTE3
PTE2
PTE1
PTE0
PTF6
PTF5
PTF4
PTF3
PTF2
PTF1
PTF0
0
0
0
0
0
PTG2
PTG1
PTG0
R
R
R
R
R
0
0
0
0
0
0
PTH1
PTH0
R
R
R
R
R
R
DDRE7
DDRE6
DDRE5
DDRE4
DDRE3
DDRE2
DDRE1
DDRE0
DDRF6
DDRF5
DDRF4
DDRF3
DDRF2
DDRF1
DDRF0
0
0
0
0
0
DDRG2
DDRG1
DDRG0
R
R
R
R
R
0
0
0
0
0
0
DDRH1
DDRH0
R
R
R
R
R
R
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
OVRF
MODF
SPTE
MODFEN
SPR1
SPR0
0
R
0
R
SPRF
ERRIE
R7
R6
R5
R4
R3
R2
R1
R0
T7
T6
T5
T4
T3
T2
T1
T0
$0013
SCI Control Register 1 Read:
(SCC1) Write:
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
$0014
SCI Control Register 2 Read:
(SCC2) Write:
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
$0015
SCI Control Register 3 Read:
(SCC3) Write:
T8
R
R
ORIE
NEIE
FEIE
PEIE
R8
= Unimplemented
R
= Reserved
Figure 2-2. I/O Data, Status and Control Registers (Sheet 2 of 6)
MC68HC908AZ32A Data Sheet, Rev. 2
32
Freescale Semiconductor
I/O Section
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
SCI Status Register 1 Read:
(SCS1) Write:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
$0016
SCI Status Register 2 Read:
(SCS2) Write:
0
0
0
0
0
0
BKF
RPF
$0017
SCI Data Register Read:
(SCDR) Write:
R7
R6
R5
R4
R3
R2
R1
R0
$0018
T7
T6
T5
T4
T3
T2
T1
T0
SCI Baud Rate Register Read:
(SCBR) Write:
0
0
$0019
SCP1
SCP0
R
SCR2
SCR1
SCR0
IRQ Status and Control Read:
Register (ISCR) Write:
0
0
0
0
IRQF
0
$001A
IMASK
MODE
R
R
R
R
R
ACK
0
0
0
0
KEYF
0
IMASKK
MODEK
$001B
Keyboard Status and Control Read:
Register (KBSCR) Write:
ACKK
$001C
PLL Control Register Read:
(PCTL) Write:
PLLIE
$001D
PLL Bandwidth Control Read:
Register (PBWC) Write:
AUTO
$001E
PLL Programming Register Read:
(PPG) Write:
MUL7
$001F
PLLF
1
1
1
1
0
0
0
0
MUL4
VRS7
VRS6
VRS5
VRS4
LVIPWR
SSREC
COPRS
STOP
COPD
0
0
PS2
PS1
PS0
TRST
R
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
PLLON
BCS
ACQ
XLD
MUL6
MUL5
R
LVIRST
TOIE
TSTOP
LOCK
Configuration Write-Once Read:
LVISTOP
Register (CONFIG-1) Write:
Timer A Status and Control Read:
Register (TASC) Write:
TOF
Keyboard Interrupt Enable Read:
Register (KBIER) Write:
0
$0021
Timer A Counter Register Read:
High (TACNTH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0022
R
R
R
R
R
R
R
R
Timer A Counter Register Read:
Low (TACNTL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
R
R
R
R
R
R
R
R
$0020
$0023
0
0
0
$0024
Timer A Modulo Register Read:
High (TAMODH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0025
Timer A Modulo Register Read:
Low (TAMODL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
= Unimplemented
R
= Reserved
Figure 2-2. I/O Data, Status and Control Registers (Sheet 3 of 6)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
33
Memory Map
Addr.
$0026
Register Name
Timer A Channel 0 Status and Read:
Control Register (TASC0) Write:
Bit 7
6
5
4
3
2
1
Bit 0
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
CH0F
0
$0027
Timer A Channel 0 Register Read:
High (TACH0H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0028
Timer A Channel 0 Register Read:
Low (TACH0L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$0029
Timer A Channel 1 Status and Read:
Control Register (TASC1) Write:
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
CH1F
0
CH1IE
0
R
$002A
Timer A Channel 1 Register Read:
High (TACH1H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$002B
Timer A Channel 1 Register Read:
Low (TACH1L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$002C
Timer A Channel 2 Status and Read:
Control Register (TASC2) Write:
CH2IE
MS2B
MS2A
ELS2B
ELS2A
TOV2
CH2MAX
CH2F
0
$002D
Timer A Channel 2 Register Read:
High (TACH2H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$002E
Timer A Channel 2 Register Read:
Low (TACH2L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$002F
Timer A Channel 3 Status and Read:
Control Register (TASC3) Write:
MS3A
ELS3B
ELS3A
TOV3
CH3MAX
CH3F
0
CH3IE
0
R
$0030
Timer A Channel 3 Register Read:
High (TACH3H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0031
Timer A Channel 3 Register Read:
Low (TACH3L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$0032
Timer A Channel 4 Status and Read:
Control Register (TASC4) Write:
CH4IE
MS4B
MS4A
ELS4B
ELS4A
TOV4
CH4MAX
CH4F
0
$0033
Timer A Channel 4 Register Read:
High (TACH4H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0034
Timer A Channel 4 Register Read:
Low (TACH4L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$0035
Timer A Channel 5 Status and Read:
Control Register (TASC5) Write:
MS5A
ELS5B
ELS5A
TOV5
CH5MAX
0
CH5F
CH5IE
0
R
= Unimplemented
R
= Reserved
Figure 2-2. I/O Data, Status and Control Registers (Sheet 4 of 6)
MC68HC908AZ32A Data Sheet, Rev. 2
34
Freescale Semiconductor
I/O Section
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
$0036
Timer A Channel 5 Register Read:
High (TACH5H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0037
Timer A Channel 5 Register Read:
Low (TACH5L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$0038
Analog-to-Digital Status and Read:
Control Register (ADSCR) Write:
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
R
R
R
R
R
R
R
R
0
0
0
0
ADIV2
ADIV1
ADIV0
ADICLK
R
R
R
R
PS2
PS1
PS0
$0039
$003A
$0040
$0041
$0042
Analog-to-Digital Data Read:
Register (ADR) Write:
Analog-to-Digital Input Read:
Clock Register (ADICLK) Write:
COCO
R
Timer B Status and Control Read:
Register (TBSCR) Write:
TOF
0
0
TRST
R
Timer B Counter Register Read:
High (TBCNTH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
R
R
R
R
R
R
R
R
Timer B Counter Register Read:
Low (TBCNTL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
R
R
R
R
R
R
R
R
TOIE
TSTOP
0
$0043
Timer B Modulo Register Read:
High (TBMODH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0044
Timer B Modulo Register Read:
Low (TBMODL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$0045
Timer B CH0 Status and Control Read:
Register (TBSC0) Write:
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
CH0F
0
$0046
Timer B CH0 Register High Read:
(TBCH0H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$0047
Timer B CH0 Register Low Read:
(TBCH0L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
$0048
Timer B CH1 Status and Control Read:
Register (TBSC1) Write:
CH1F
0
CH1IE
0
R
$0049
Timer B CH1 Register High Read:
(TBCH1H) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$004A
Timer B CH1 Register Low Read:
(TBCH1L) Write:
Bit 7
6
5
4
3
2
1
Bit 0
= Unimplemented
R
= Reserved
Figure 2-2. I/O Data, Status and Control Registers (Sheet 5 of 6)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
35
Memory Map
Addr.
Register Name
Bit 7
6
5
POIE
PSTOP
4
3
0
0
2
1
Bit 0
PPS2
PPS1
PPS0
PIT Status and Control Register Read:
(PSC) Write:
POF
PIT Counter Register High Read:
(PCNTH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$004C
PIT Counter Register Low Read:
(PCNTL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$004D
$004E
PIT Modulo Register High Read:
(PMODH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$004F
PIT Modulo Register Low Read:
(PMODL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
$004B
0
PRST
= Unimplemented
R
= Reserved
Figure 2-2. I/O Data, Status and Control Registers (Sheet 6 of 6)
2.3 Additional Status and Control Registers
Selected addresses in the range $FE00 to $FFCB contain additional Status and Control registers as
shown in Figure 2-3. A noted exception is the COP Control Register (COPCTL) at address $FFFF.
Addr.
$FE00
Register Name
SIM Break Status Register Read:
(SBSR) Write:
$FE01
SIM Reset Status Register Read:
(SRSR) Write:
$FE03
$FE09
Bit 7
6
5
4
3
2
R
R
R
R
R
R
1
Bit 0
BW
R
0
POR
PIN
COP
ILOP
ILAD
0
LVI
0
SIM Break Flag Control Register Read:
(SBFCR) Write:
BCFE
R
R
R
R
R
R
R
Configuration Write-Once Read:
Register (CONFIG-2) Write:
EEDIVCLK
R
EEMONSEC
AZ32A
R
R
R
R
R
$FE0C
Break Address Register High Read:
(BRKH) Write:
Bit 15
14
13
12
11
10
9
Bit 8
$FE0D
Break Address Register Low Read:
(BRKL) Write:
Bit 7
6
5
4
3
2
1
Bit 0
Break Status and Control Read:
Register (BRKSCR) Write:
0
0
0
0
0
0
$FE0E
BRKE
BRKA
= Unimplemented
R
= Reserved
Figure 2-3. Additional Status and Control Registers
MC68HC908AZ32A Data Sheet, Rev. 2
36
Freescale Semiconductor
Additional Status and Control Registers
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
LVI Status Register Read:
(LVISR) Write:
LVIOUT
0
0
0
0
0
0
0
$FE0F
$FE10
EEDIV Hi Non-volatile Register Read: EEDIVS(EEDIVHNVR) Write:
ECD
R
R
R
R
EEDIV10
EEDIV9
EEDIV8
$FE11
EEDIV Lo Non-volatile Register Read:
(EEDIVLNVR) Write:
EEDIV6
EEDIV5
EEDIV4
EEDIV3
EEDIV2
EEDIV1
EEDIV0
0
0
0
0
EEDIV10
EEDIV9
EEDIV8
EEDIV3
EEDIV2
EEDIV1
EEDIV0
EEBP3
EEBP2
EEBP1
EEBP0
EERAS1
EERAS0
EELAT
AUTO
EEPGM
UNUSED EEPRTCT
EEBP3
EEBP2
EEBP1
EEBP0
BPR3
BPR2
BPR1
BPR0
HVEN
VERF
ERASE
PGM
EEDIV7
$FE1A
EEDIV Divider High Register Read: EEDIVS(EEDIVH) Write:
ECD
$FE1B
EEDIV Divider Low Register Read:
(EEDIVL) Write:
EEDIV7
EEDIV6
EEDIV5
EEDIV4
$FE1C
EEPROM Nonvolatile Register Read:
UNUSED
(EENVR) Write:
UNUSED
UNUSED EEPRTCT
$FE1D
EEPROM Control Register Read:
UNUSED
(EECR) Write:
$FE1F
EEPROM Array Configuration Read: UNUSED
Register (EEACR) Write:
$FF80
FLASH Block Protect Register Read:
(FLBPR) Write:
$FF88
FLASH Control Register Read:
(FLCR) Write:
$FFFF
COP Control Register Read:
(COPCTL) Write:
0
EEOFF
UNUSED
BPR7
BPR6
BPR5
BPR4
0
0
0
0
LOW BYTE OF RESET VECTOR
WRITING TO $FFFF CLEARS COP COUNTER
= Unimplemented
R
= Reserved
Figure 2-3. Additional Status and Control Registers (Continued)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
37
Memory Map
2.4 Vector Addresses and Priority
Addresses in the range $FFCC to $FFFF contain the user-specified vector locations. The vector
addresses are shown in Table 2-1. It is recommended that all vector addresses are defined.
Table 2-1. Vector Addresses
Lowest Priority
Address
Vector Description
$FFCC
TIMA Channel 5 Vector (High)
$FFCD
TIMA Channel 5 Vector (Low)
$FFCE
TIMA Channel 4 Vector (High)
$FFCF
TIMA Channel 4 Vector (Low)
$FFD0
ADC Vector (High)
$FFD1
ADC Vector (Low)
$FFD2
Keyboard Vector (High)
$FFD3
Keyboard Vector (Low)
$FFD4
SCI Transmit Vector (High)
$FFD5
SCI Transmit Vector (Low)
$FFD6
SCI Receive Vector (High)
$FFD7
SCI Receive Vector (Low)
$FFD8
SCI Error Vector (High)
$FFD9
SCI Error Vector (Low)
$FFDA
CAN Transmit Vector (High)
$FFDB
CAN Transmit Vector (Low)
$FFDC
CAN Receive Vector (High)
$FFDD
CAN Receive Vector (Low)
$FFDE
CAN Error Vector (High)
$FFDF
CAN Error Vector (Low)
$FFE0
CAN Wakeup Vector (High)
$FFE1
CAN Wakeup Vector (Low)
$FFE2
SPI Transmit Vector (High)
$FFE3
SPI Transmit Vector (Low)
$FFE4
SPI Receive Vector (High)
$FFE5
SPI Receive Vector (Low)
$FFE6
TIMB Overflow Vector (High)
$FFE7
TIMB Overflow Vector (Low)
$FFE8
TIMB CH1 Vector (High)
$FFE9
TIMB CH1 Vector (Low)
— Continued on next page
MC68HC908AZ32A Data Sheet, Rev. 2
38
Freescale Semiconductor
Vector Addresses and Priority
Table 2-1. Vector Addresses (Continued)
Highest Priority
Address
Vector Description
$FFEA
TIMB CH0 Vector (High)
$FFEB
TIMB CH0 Vector (Low)
$FFEC
TIMA Overflow Vector (High)
$FFED
TIMA Overflow Vector (Low)
$FFEE
TIMA CH3 Vector (High)
$FFEF
TIMA CH3 Vector (Low)
$FFF0
TIMA CH2 Vector (High)
$FFF1
TIMA CH2 Vector (Low)
$FFF2
TIMA CH1 Vector (High)
$FFF3
TIMA CH1 Vector (Low)
$FFF4
TIMA CH0 Vector (High)
$FFF5
TIMA CH0 Vector (Low)
$FFF6
PIT Vector (High)
$FFF7
PIT Vector (Low)
$FFF8
PLL Vector (High)
$FFF9
PLL Vector (Low)
$FFFA
IRQ1 Vector (High)
$FFFB
IRQ1 Vector (Low)
$FFFC
SWI Vector (High)
$FFFD
SWI Vector (Low)
$FFFE
Reset Vector (High)
$FFFF
Reset Vector (Low)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
39
Memory Map
MC68HC908AZ32A Data Sheet, Rev. 2
40
Freescale Semiconductor
Chapter 3
RAM
3.1 Introduction
This section describes the 1024 bytes of random-access memory (RAM).
3.2 Functional Description
Addresses $0050 through $044F are RAM locations. The location of the stack RAM is programmable with
the reset stack pointer instruction (RSP). The 16-bit stack pointer allows the stack RAM to be anywhere
in the 64K-byte memory space.
NOTE
For correct operation, the stack pointer must point only to RAM locations.
Within page zero are 176 bytes of RAM. Because the location of the stack RAM is programmable, all page
zero RAM locations can be used for input/output (I/O) control and user data or code. When the stack
pointer is moved from its reset location at $00FF, direct addressing mode instructions can access all page
zero RAM locations efficiently. Page zero RAM, therefore, provides ideal locations for frequently
accessed global variables.
Before processing an interrupt, the CPU uses five bytes of the stack to save the contents of the CPU
registers.
NOTE
For M68HC05, M6805, and M146805 compatibility, the H register is not
stacked.
During a subroutine call, the CPU uses two bytes of the stack to store the return address. The stack
pointer decrements during pushes and increments during pulls.
NOTE
Be careful when using nested subroutines. The CPU could overwrite data
in the RAM during a subroutine or during the interrupt stacking operation.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
41
RAM
MC68HC908AZ32A Data Sheet, Rev. 2
42
Freescale Semiconductor
Chapter 4
Flash Memory
4.1 Introduction
This section describes the operation of the embedded FLASH memory. This memory can be read,
programmed and erased from a single external supply. The program and erase operations are enabled
through the use of an internal charge pump.
4.2 Functional Description
The FLASH memory is an array of 32,256 bytes with one byte of block protection and an additional
52 bytes of user vectors. An erased bit reads as a logic 1 and a programmed bit reads as a logic 0.
Memory in the FLASH array is organized into rows within pages. There are two rows of memory per page
with 64 bytes per row. The minimum erase block size is a single page,128 bytes. Programming is
performed on a per-row basis, 64 bytes at a time. Program and erase operations are facilitated through
control bits in the FLASH Control Register (FLCR). Details for these operations appear later in this
section.
The FLASH memory map consists of:
• $8000–$FDFF: User Memory (32,256 bytes)
• $FF80: FLASH Block Protect Register (FLBPR)
• $FF88: FLASH Control Register (FLCR)
• $FFCC–$FFFF: these locations are reserved for user-defined interrupt and reset vectors (Please
see 2.4 Vector Addresses and Priority for details)
Programming tools are available from Freescale. Contact your local Freescale representative for more
information.
NOTE
A security feature prevents viewing of the FLASH contents.(1)
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
43
Flash Memory
4.3 FLASH Control and Block Protect Registers
The FLASH array has two registers that control its operation, the FLASH Control Register (FLCR) and the
FLASH Block Protect Register (FLBPR).
4.3.1 FLASH Control Register
The FLASH Control Register (FLCR) controls FLASH program and erase operations.
Address:
Read:
$FF88
Bit 7
6
5
4
0
0
0
0
0
0
0
0
Write:
Reset:
3
2
1
Bit 0
HVEN
MASS
ERASE
PGM
0
0
0
0
= Unimplemented
Figure 4-1. FLASH Control Register (FLCR)
HVEN — High-Voltage Enable Bit
This read/write bit enables the charge pump to drive high voltages for program and erase operations
in the array. HVEN can only be set if either PGM = 1 or ERASE = 1 and the proper sequence for
program or erase is followed.
1 = High voltage enabled to array and charge pump on
0 = High voltage disabled to array and charge pump off
MASS — Mass Erase Control Bit
Setting this read/write bit configures the FLASH array for mass or page erase operation.
1 = Mass erase operation selected
0 = Page erase operation selected
ERASE — Erase Control Bit
This read/write bit configures the memory for erase operation. ERASE is interlocked with the PGM bit
such that both bits cannot be set at the same time.
1 = Erase operation selected
0 = Erase operation unselected
PGM — Program Control Bit
This read/write bit configures the memory for program operation. PGM is interlocked with the ERASE
bit such that both bits cannot be equal to 1 or set to 1 at the same time.
1 = Program operation selected
0 = Program operation unselected
MC68HC908AZ32A Data Sheet, Rev. 2
44
Freescale Semiconductor
FLASH Control and Block Protect Registers
4.3.2 FLASH Block Protect Register
The FLASH Block Protect Register (FLBPR) is implemented as a byte within the FLASH memory and
therefore can only be written during a FLASH programming sequence. The value in this register
determines the starting location of the protected range within the FLASH memory.
Address:
Read:
Write:
$FF80
Bit 7
6
5
4
3
2
1
Bit 0
BPR7
BPR6
BPR5
BPR4
BPR3
BPR2
BPR1
BPR0
Figure 4-2. FLASH Block Protect Register (FLBPR)
FLBPR[7:0] — Block Protect Register Bit7 to Bit0
These eight bits represent bits [14:7] of a 16-bit memory address. Bit-15 is logic 1 and bits [6:0] are
logic 0s.
The resultant 16-bit address is used for specifying the start address of the FLASH memory for block
protection. FLASH is protected from this start address to the end of FLASH memory at $FFFF. With
this mechanism, the protect start address can be $XX00 and $XX80 (128 byte page boundaries) within
the FLASH array.
16-bit memory address
Start address of FLASH block protect
1
FLBPR value
0
0
0
0
0
0
0
Figure 4-3. FLASH Block Protect Start Address
FLASH Protected Ranges:
FLBPR[7:0]
Protected Range
$FF
No Protection
$FE
$FF00 – $FFFF
$FD
$FE80 – $FFFF
$0B
$8580 – $FFFF
$0A
$8500 – $FFFF
$09
$8480 – $FFFF
$08
$8400 – $FFFF
$04
$8200 – $FFFF
$03
$8180 – $FFFF
$02
$8100 – $FFFF
$01
$8080 – $FFFF
$00
$8000 – $FFFF
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
45
Flash Memory
Decreasing the value in FLBPR by one increases the protected range by one page (128 bytes). However,
programming the block protect register with $FE protects a range twice that size, 256 bytes, in the
corresponding array. $FE means that locations $FF00–$FFFF are protected in FLASH.
The FLASH memory does not exist at some locations. The block protection range configuration is
unaffected if FLASH memory does not exist in that range. Refer to the memory map and make sure that
the desired locations are protected.
4.4 FLASH Block Protection
Due to the ability of the on-board charge pump to erase and program the FLASH memory in the target
application, provision is made for protecting blocks of memory from unintentional erase or program
operations due to system malfunction. This protection is done by using the FLASH Block Protection
Register (FLBPR). FLBPR determines the range of the FLASH memory which is to be protected. The
range of the protected area starts from a location defined by FLBPR and ends at the bottom of the FLASH
memory ($FFFF). When the memory is protected, the HVEN bit can not be set in either ERASE or
PROGRAM operations.
NOTE
In performing a program or erase operation, the FLASH Block Protect
Register must be read after setting the PGM or ERASE bit and before
asserting the HVEN bit.
When the FLASH Block Protect Register is programmed with all 0’s, the entire memory is protected from
being programmed and erased. When all the bits are erased (all 1’s), the entire memory is accessible for
program and erase.
When bits within FLBPR are programmed (logic 0), they lock a block of memory address ranges as shown
in 4.3.2 FLASH Block Protect Register. If FLBPR is programmed with any value other than $FF, the
protected block of FLASH memory can not be erased or programmed.
NOTE
The vector locations and the FLASH Block Protect Registers are located in
the same page. FLBPR is not protected with special hardware or software;
therefore, if this page is not protected by FLBPR and the vector locations
are erased by either a page or a mass erase operation, FLBPR will also get
erased.
MC68HC908AZ32A Data Sheet, Rev. 2
46
Freescale Semiconductor
FLASH Mass Erase Operation
4.5 FLASH Mass Erase Operation
Use this step-by-step procedure to erase the entire FLASH memory to read as logic 1:
1. Set both the ERASE bit and the MASS bit in the FLASH Control Register (FLCR).
2. Read the FLASH Block Protect Register (FLBPR).
3. Write to any FLASH address within the FLASH array with any data.
4.
5.
6.
7.
8.
9.
10.
NOTE
If the address written to in Step 3 is within address space protected by the
FLASH Block Protect Register (FLBPR), no erase will occur.
Wait for a time, tNVS.
Set the HVEN bit.
Wait for a time, tMERASE.
Clear the ERASE bit.
Wait for a time, t NVHL.
Clear the HVEN bit.
Wait for a time, tRCV, after which the memory can be accessed in normal read mode.
NOTE
A. Programming and erasing of FLASH locations can not be performed by
code being executed from the same FLASH array.
B. While these operations must be performed in the order shown, other
unrelated operations may occur between the steps. Care must be taken
however to ensure that these operations do not access any address within
the FLASH array memory space such as the COP Control Register
(COPCTL) at $FFFF.
C. It is highly recommended that interrupts be disabled during
program/erase operations.
4.6 FLASH Page Erase Operation
Use this step-by-step procedure to erase a page (128 bytes) of FLASH memory to read as logic 1:
1. Set the ERASE bit and clear the MASS bit in the FLASH Control Register (FLCR).
2. Read the FLASH Block Protect Register (FLBPR).
3. Write any data to any FLASH address within the address range of the page (128 byte block) to be
erased.
4. Wait for time, tNVS.
5. Set the HVEN bit.
6. Wait for time, tERASE.
7. Clear the ERASE bit.
8. Wait for time, t NVH.
9. Clear the HVEN bit.
10. Wait for a time, tRCV, after which the memory can be accessed in normal read mode.
NOTE
A. Programming and erasing of FLASH locations can not be performed by
code being executed from the same FLASH array.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
47
Flash Memory
B. While these operations must be performed in the order shown, other
unrelated operations may occur between the steps. Care must be taken
however to ensure that these operations do not access any address within
the FLASH array memory space such as the COP Control Register
(COPCTL) at $FFFF.
C. It is highly recommended that interrupts be disabled during
program/erase operations.
4.7 FLASH Program Operation
Programming of the FLASH memory is done on a row basis. A row consists of 64 consecutive bytes with
address ranges as follows:
• $XX00 to $XX3F
• $XX40 to $XX7F
• $XX80 to $XXBF
• $XXC0 to $XXFF
During the programming cycle, make sure that all addresses being written to fit within one of the ranges
specified above. Attempts to program addresses in different row ranges in one programming cycle will
fail. Use this step-by-step procedure to program a row of FLASH memory.
NOTE
In order to avoid program disturbs, the row must be erased before any byte on that row is programmed.
1. Set the PGM bit in the FLASH Control Register (FLCR). This configures the memory for program
operation and enables the latching of address and data programming.
2. Read the FLASH Block Protect Register (FLBPR).
3. Write to any FLASH address within the row address range desired with any data.
4. Wait for time, tNVS.
5. Set the HVEN bit.
6. Wait for time, tPGS.
7. Write data byte to the FLASH address to be programmed.
8. Wait for time, t PROG.
9. Repeat step 7 and 8 until all the bytes within the row are programmed.
10. Clear the PGM bit.
11. Wait for time, tNVH.
12. Clear the HVEN bit.
13. Wait for a time, tRCV, after which the memory can be accessed in normal read mode.
The FLASH Programming Algorithm Flowchart is shown in Figure 4-4.
NOTE
A. Programming and erasing of FLASH locations can not be performed by
code being executed from the same FLASH array.
B. While these operations must be performed in the order shown, other
unrelated operations may occur between the steps. Care must be taken
however to ensure that these operations do not access any address within
the FLASH array memory space such as the COP Control Register
(COPCTL) at $FFFF.
MC68HC908AZ32A Data Sheet, Rev. 2
48
Freescale Semiconductor
Low-Power Modes
•
C. It is highly recommended that interrupts be disabled during
program/erase operations.
D. Do not exceed t PROG maximum or tHV maximum. tHV is defined as the
cumulative high voltage programming time to the same row before next
erase. tHV must satisfy this condition: tNVS+ tNVH + tPGS + (tPROGX 64) ð tHV
max. Please also see 25.1.14 FLASH Memory Characteristics.
E. The time between each FLASH address change (step 7 to step 7), or the
time between the last FLASH address programmed to clearing the PGM bit
(step 7 to step 10) must not exceed the maximum programming time, tPROG
max.
F. Be cautious when programming the FLASH array to ensure that
non-FLASH locations are not used as the address that is written to when
selecting either the desired row address range in step 3 of the algorithm or
the byte to be programmed in step 7 of the algorithm. This applies
particularly to:
$FFCC-$FFFF: User Vector Area
4.8 Low-Power Modes
The WAIT and STOP instructions will place the MCU in low power consumption standby modes.
4.8.1 WAIT Mode
Putting the MCU into wait mode while the FLASH is in read mode does not affect the operation of the
FLASH memory directly; however, no memory activity will take place since the CPU is inactive.
The WAIT instruction should not be executed while performing a program or erase operation on the
FLASH. Wait mode will suspend any FLASH program/erase operations and leave the memory in a
Standby Mode.
4.8.2 STOP Mode
Putting the MCU into stop mode while the FLASH is in read mode does not affect the operation of the
FLASH memory directly; however, no memory activity will take place since the CPU is inactive.
The STOP instruction should not be executed while performing a program or erase operation on the
FLASH. Stop mode will suspend any FLASH program/erase operations and leave the memory in a
Standby Mode.
NOTE
Standby Mode is the power saving mode of the FLASH module, in which all
internal control signals to the FLASH are inactive and the current
consumption of the FLASH is minimum.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
49
Flash Memory
1
Algorithm for programming
a row (64 bytes) of FLASH memory
2
3
4
5
6
7
8
Set PGM bit
Read the FLASH block protect register
Write any data to any FLASH address
within the row address range desired
Wait for a time, tnvs
Set HVEN bit
Wait for a time, tpgs
Write data to the FLASH address
to be programmed
Wait for a time, tPROG
Completed
programming
this row?
Y
N
NOTE:
The time between each FLASH address change (step 7 to step 7), or
the time between the last FLASH address programmed
to clearing PGM bit (step 7 to step 10)
must not exceed the maximum programming
time, tPROG max.
10
Clear PGM bit
11
Wait for a time, tnvh
12
Clear HVEN bit
13
Wait for a time, trcv
This row program algorithm assumes the row/s
to be programmed are initially erased.
End of programming
Figure 4-4. FLASH Programming Algorithm Flowchart
MC68HC908AZ32A Data Sheet, Rev. 2
50
Freescale Semiconductor
Chapter 5
EEPROM
5.1 Introduction
This section describes the 512 bytes of electrically erasable programmable read-only memory (EEPROM)
residing at address range $0800 to $09FF.
5.2 Features
Features of the EEPROM include the following:
• 512 bytes Nonvolatile Memory
• Byte, Block, or Bulk Erasable
• Nonvolatile EEPROM Configuration and Block Protection Options
• On-chip Charge Pump for Programming/Erasing
• Security Option
• AUTO Bit Driven Programming/Erasing Time Feature
5.3 EEPROM Register Summary
The EEPROM Register Summary is shown in Figure 5-1.
5.4 Functional Description
The 512 bytes of EEPROM are located at $0800-$09FF and can be programmed or erased without an
additional external high voltage supply. The program and erase operations are enabled through the use
of an internal charge pump. For each byte of EEPROM, the write/erase endurance is 10,000 cycles.
5.4.1 EEPROM Configuration
The 8-bit EEPROM Nonvolatile Register (EENVR) and the 16-bit EEPROM Timebase Divider Nonvolatile
Register (EEDIVNVR) contain the default settings for the following EEPROM configurations:
• EEPROM Timebase Reference
• EEPROM Security Option
• EEPROM Block Protection
EENVR and EEDIVNVR are nonvolatile EEPROM registers. They are programmed and erased in the
same way as EEPROM bytes. The contents of these registers are loaded into their respective volatile
registers during a MCU reset. The values in these read/write volatile registers define the EEPROM
configurations.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
51
EEPROM
Addr.
$FE10
$FE11
$FE1A
$FE1B
$FE1C
$FE1D
$FE1F
Register Name
EEDIV Nonvolatile Read:
Register High Write:
(EEDIVHNVR)(1) Reset:
EEDIV Nonvolatile Read:
Register Low Write:
(EEDIVLNVR)(1) Reset:
EE Divider Register Read:
High Write:
(EEDIVH) Reset:
EE Divider Register Read:
Low Write:
(EEDIVL) Reset:
Bit 7
6
5
4
3
2
1
Bit 0
EEDIVSECD
R
R
R
R
EEDIV10
EEDIV9
EEDIV8
EEDIV1
EEDIV0
EEDIV9
EEDIV8
EEDIV1
EEDIV0
EEBP1
EEBP0
Unaffected by reset; $FF when blank
EEDIV7
EEDIV6
EEDIV5
EEDIV4
EEDIV3
EEDIV2
Unaffected by reset; $FF when blank
EEDIVSECD
0
0
0
0
EEDIV10
Contents of EEDIVHNVR ($FE10), Bits [6:3] = 0
EEDIV7
EEDIV6
EEDIV5
EEDIV4
EEDIV3
EEDIV2
Contents of EEDIVLNVR ($FE11)
EEPROM Nonvolatile Read: UNUSED
Register Write:
(EENVR)(1) Reset:
Read:
UNUSED
EEPROM Control
Write:
Register (EECR)
Reset:
0
EEPROM Array Read: UNUSED
Configuration Register Write:
(EEACR) Reset:
UNUSED
UNUSED
EEPRTCT
EEBP3
EEBP2
Unaffected by reset; $FF when blank; factory programmed $F0
0
EEOFF
EERAS1
EERAS0
EELAT
AUTO
EEPGM
0
0
0
0
0
0
0
UNUSED
UNUSED
EEPRTCT
EEBP3
EEBP2
EEBP1
EEBP0
UNUSED
= Unused
Contents of EENVR ($FE1C)
1. Nonvolatile EEPROM register; write by programming.
= Unimplemented
R
= Reserved
Figure 5-1. EEPROM Register Summary
For EENVR, the corresponding volatile register is the EEPROM Array Configuration Register (EEACR).
For the EEDIVNCR (two 8-bit registers: EEDIVHNVR and EEDIVLNVR), the corresponding volatile
register is the EEPROM Divider Register (EEDIV: EEDIVH and EE DIVL).
5.4.2 EEPROM Timebase Requirements
A 35μs timebase is required by the EEPROM control circuit for program and erase of EEPROM content.
This timebase is derived from dividing the CGMXCLK or bus clock (selected by EEDIVCLK bit in
CONFIG-2 Register) using a timebase divider circuit controlled by the 16-bit EEPROM Timebase Divider
EEDIV Register (EEDIVH and EEDIVL).
As the CGMXCLK or bus clock is user selected, the EEPROM Timebase Divider Register must be
configured with the appropriate value to obtain the 35 μs. The timebase divider value is calculated by
using the following formula:
EEDIV= INT[Reference Frequency(Hz) x 35 x10-6 +0.5]
This value is written to the EEPROM Timebase Divider Register (EEDIVH and EEDIVL) or programmed
into the EEPROM Timebase Divider Nonvolatile Register prior to any EEPROM program or erase
operations (see 5.4.1 EEPROM Configuration and 5.4.2 EEPROM Timebase Requirements).
MC68HC908AZ32A Data Sheet, Rev. 2
52
Freescale Semiconductor
Functional Description
5.4.3 EEPROM Program/Erase Protection
The EEPROM has a special feature that designates the 16 bytes of addresses from $08F0 to $08FF to
be permanently secured. This program/erase protect option is enabled by programming the EEPRTCT
bit in the EEPROM Nonvolatile Register (EENVR) to a logic zero.
Once the EEPRTCT bit is programmed to 0 for the first time:
• Programming and erasing of secured locations $08F0 to $08FF is permanently disabled.
• Secured locations $08F0 to $08FF can be read as normal.
• Programming and erasing of EENVR is permanently disabled.
• Bulk and Block Erase operations are disabled for the unprotected locations $0800-$08EF,
$0900-$09FF.
• Single byte program and erase operations are still available for locations $0800-$08EF and
$0900-$09FF for all bytes that are not protected by the EEPROM Block Protect EEBPx bits (see
5.4.4 EEPROM Block Protection and 5.5.2 EEPROM Array Configuration Register)
NOTE
Once armed, the protect option is permanently enabled. As a consequence,
all functions in the EENVR will remain in the state they were in immediately
before the security was enabled.
5.4.4 EEPROM Block Protection
The 512 bytes of EEPROM are divided into four 128-byte blocks. Each of these blocks can be protected
from erase/program operations by setting the EEBPx bit in the EENVR. Table 5-1 shows the address
ranges for the blocks.
Table 5-1. EEPROM Array Address Blocks
Block Number (EEBPx)
Address Range
EEBP0
$0800–$087F
EEBP1
$0880–$08FF
EEBP2
$0900–$097F
EEBP3
$0980–$09FF
These bits are effective after a reset or a upon read of the EENVR register. The block protect configuration
can be modified by erasing/programming the corresponding bits in the EENVR register and then reading
the EENVR register. Please see 5.5.2 EEPROM Array Configuration Register for more information.
NOTE
Once EEDIVSECD in the EEDIVHNVR is programmed to 0 and after a
system reset, the EEDIV security feature is permanently enabled because
the EEDIVSECD bit in the EEDIVH is always loaded with 0 thereafter. Once
this security feature is armed, erase and program mode are disabled for
EEDIVHNVR and EEDIVLNVR. Modifications to the EEDIVH and EEDIVL
registers are also disabled. Therefore, be cautious on programming a value
into the EEDIVHNVR.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
53
EEPROM
5.4.5 EEPROM Programming and Erasing
The unprogrammed or erase state of an EEPROM bit is a logic 1. The factory default for all bytes within
the EEPROM array is $FF.
The programming operation changes an EEPROM bit from logic 1 to logic 0 (programming cannot change
a bit from logic 0 to a logic 1). In a single programming operation, the minimum EEPROM programming
size is one bit; the maximum is eight bits (one byte).
The erase operation changes an EEPROM bit from logic 0 to logic 1. In a single erase operation, the
minimum EEPROM erase size is one byte; the maximum is the entire EEPROM array.
The EEPROM can be programmed such that one or multiple bits are programmed (written to a logic 0) at
a time. However, the user may never program the same bit location more than once before erasing the
entire byte. In other words, the user is not allowed to program a logic 0 to a bit that is already programmed
(bit state is already logic 0).
For some applications it might be advantageous to track more than 10K events with a single byte of
EEPROM by programming one bit at a time. For that purpose, a special selective bit programming
technique is available. An example of this technique is illustrated in Table 5-2.
Table 5-2. Example Selective Bit Programming Description
Program Data
in Binary
Result
in Binary
n/a
1111:1111
First event is recorded by programming bit position 0
1111:1110
1111:1110
Second event is recorded by programming bit position 1
1111:1101
1111:1100
Third event is recorded by programming bit position 2
1111:1011
1111:1000
Fourth event is recorded by programming bit position 3
1111:0111
1111:0000
Description
Original state of byte (erased)
Events five through eight are recorded in a similar fashion
Note that none of the bit locations are actually programmed more than once although the byte was
programmed eight times.
When this technique is utilized, a program/erase cycle is defined as multiple program sequences (up to
eight) to a unique location followed by a single erase operation.
5.4.5.1 Program/Erase Using AUTO Bit
An additional feature available for EEPROM program and erase operations is the AUTO mode.
When enabled, AUTO mode will activate an internal timer that will automatically terminate the
program/erase cycle and clear the EEPGM bit. Please see 5.4.5 EEPROM Programming and Erasing and
5.5.1 EEPROM Control Register for more information.
MC68HC908AZ32A Data Sheet, Rev. 2
54
Freescale Semiconductor
Functional Description
5.4.5.2 EEPROM Programming
The unprogrammed or erase state of an EEPROM bit is a logic 1. Programming changes the state to a
logic 0. Only EEPROM bytes in the non-protected blocks and the EENVR register can be programmed.
Use the following procedure to program a byte of EEPROM:
1. Clear EERAS1 and EERAS0 and set EELAT in the EECR.(A)
2.
3.
4.
5.
6.
7.
8.
NOTE
If using the AUTO mode, also set the AUTO bit during Step 1.
Write the desired data to the desired EEPROM address.(B)
Set the EEPGM bit.(C) Go to Step 7 if AUTO is set.
Wait for time, tEEPGM, to program the byte.
Clear EEPGM bit.
Wait for time, tEEFPV, for the programming voltage to fall. Go to Step 8.
Poll the EEPGM bit until it is cleared by the internal timer.(D)
Clear EELAT bits.(E)
NOTE
A. EERAS1 and EERAS0 must be cleared for programming. Setting the
EELAT bit configures the address and data buses to latch data for
programming the array. Only data with a valid EEPROM address will be
latched. If EELAT is set, other writes to the EECR will be allowed after a
valid EEPROM write.
B. If more than one valid EEPROM write occurs, the last address and data
will be latched overriding the previous address and data. Once data is
written to the desired address, do not read EEPROM locations other than
the written location. (Reading an EEPROM location returns the latched data
and causes the read address to be latched).
C. The EEPGM bit cannot be set if the EELAT bit is cleared or a non-valid
EEPROM address is latched. This is to ensure proper programming
sequence. Once EEPGM is set, do not read any EEPROM locations;
otherwise, the current program cycle will be unsuccessful. When EEPGM
is set, the on-board programming sequence will be activated.
D. The delay time for the EEPGM bit to be cleared in AUTO mode is less
than tEEPGM. However, on other MCUs, this delay time may be different.
For forward compatibility, software should not make any dependency on
this delay time.
E. Any attempt to clear both EEPGM and EELAT bits with a single
instruction will only clear EEPGM. This is to allow time for removal of high
voltage from the EEPROM array.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
55
EEPROM
5.4.5.3 EEPROM Erasing
The programmed state of an EEPROM bit is logic 0. Erasing changes the state to a logic 1. Only EEPROM
bytes in the non-protected blocks and the EENVR register can be erased.
Use the following procedure to erase a byte, block or the entire EEPROM array:
1. Configure EERAS1 and EERAS0 for byte, block or bulk erase; set EELAT in EECR.(A)
2.
3.
4.
5.
6.
7.
8.
NOTE
If using the AUTO mode, also set the AUTO bit in Step 1.
Byte erase: write any data to the desired address.(B)
Block erase: write any data to an address within the desired block.(B)
Bulk erase: write any data to an address within the array.(B)
Set the EEPGM bit.(C) Go to Step 7 if AUTO is set.
Wait for a time: tEEBYTE for byte erase; tEEBLOCK for block erase; tEEBULK. for bulk erase.
Clear EEPGM bit.
Wait for a time, tEEFPV, for the erasing voltage to fall. Go to Step 8.
Poll the EEPGM bit until it is cleared by the internal timer.(D)
Clear EELAT bits.(E)
NOTE
A. Setting the EELAT bit configures the address and data buses to latch
data for erasing the array. Only valid EEPROM addresses will be latched.
If EELAT is set, other writes to the EECR will be allowed after a valid
EEPROM write.
B. If more than one valid EEPROM write occurs, the last address and data
will be latched overriding the previous address and data. Once data is
written to the desired address, do not read EEPROM locations other than
the written location. (Reading an EEPROM location returns the latched data
and causes the read address to be latched).
C. The EEPGM bit cannot be set if the EELAT bit is cleared or a non-valid
EEPROM address is latched. This is to ensure proper programming
sequence. Once EEPGM is set, do not read any EEPROM locations;
otherwise, the current program cycle will be unsuccessful. When EEPGM
is set, the on-board programming sequence will be activated.
D. The delay time for the EEPGM bit to be cleared in AUTO mode is less
than tEEBYTE /tEEBLOCK/tEEBULK. However, on other MCUs, this delay time
may be different. For forward compatibility, software should not make any
dependency on this delay time.
E. Any attempt to clear both EEPGM and EELAT bits with a single
instruction will only clear EEPGM. This is to allow time for removal of high
voltage from the EEPROM array.
MC68HC908AZ32A Data Sheet, Rev. 2
56
Freescale Semiconductor
EEPROM Register Descriptions
5.5 EEPROM Register Descriptions
Four I/O registers and three nonvolatile registers control program, erase and options of the EEPROM
array.
5.5.1 EEPROM Control Register
This read/write register controls programming/erasing of the array.
Address:
$FE1D
Bit 7
Read:
Write:
Reset:
6
0
UNUSED
0
5
4
3
2
1
Bit 0
EEOFF
EERAS1
EERAS0
EELAT
AUTO
EEPGM
0
0
0
0
0
0
0
= Unimplemented
Figure 5-2. EEPROM Control Register (EECR)
Bit 7— Unused bit
This read/write bit is software programmable but has no functionality.
EEOFF — EEPROM power down
This read/write bit disables the EEPROM module for lower power consumption. Any attempts to
access the array will give unpredictable results. Reset clears this bit.
1 = Disable EEPROM array
0 = Enable EEPROM array
EERAS1 and EERAS0 — Erase/Program Mode Select Bits
These read/write bits set the erase modes. Reset clears these bits.
Table 5-3. EEPROM Program/Erase Mode Select
EEBPx
EERAS1
EERAS0
MODE
0
0
0
Byte Program
0
0
1
Byte Erase
0
1
0
Block Erase
0
1
1
Bulk Erase
1
X
X
No Erase/Program
X = don’t care
EELAT — EEPROM Latch Control
This read/write bit latches the address and data buses for programming the EEPROM array. EELAT
cannot be cleared if EEPGM is still set. Reset clears this bit.
1 = Buses configured for EEPROM programming or erase operation
0 = Buses configured for normal operation
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
57
EEPROM
AUTO — Automatic termination of program/erase cycle
When AUTO is set, EEPGM is cleared automatically after the program/erase cycle is terminated by
the internal timer.
(See note D for 5.4.5.25.4.5.25.4.5.2 EEPROM Programming, 5.4.5.3 EEPROM Erasing and 25.1.13
EEPROM Memory Characteristics)
1 = Automatic clear of EEPGM is enabled
0 = Automatic clear of EEPGM is disabled
EEPGM — EEPROM Program/Erase Enable
This read/write bit enables the internal charge pump and applies the programming/erasing voltage to
the EEPROM array if the EELAT bit is set and a write to a valid EEPROM location has occurred. Reset
clears the EEPGM bit.
1 = EEPROM programming/erasing power switched on
0 = EEPROM programming/erasing power switched off
NOTE
Writing logic 0s to both the EELAT and EEPGM bits with a single instruction
will clear EEPGM only to allow time for the removal of high voltage.
5.5.2 EEPROM Array Configuration Register
The EEPROM array configuration register configures EEPROM security and EEPROM block protection.
This read-only register is loaded with the contents of the EEPROM nonvolatile register (EENVR) after a
reset.
Address:
Read:
$FE1F
Bit 7
6
5
4
3
2
1
Bit 0
UNUSED
UNUSED
UNUSED
EEPRTCT
EEBP3
EEBP2
EEBP1
EEBP0
Write:
Reset:
Contents of EENVR ($FE1C)
= Unimplemented
Figure 5-3. EEPROM Array Configuration Register (EEACR)
Bit 7:5 — Unused Bits
These read/write bits are software programmable but have no functionality.
EEPRTCT — EEPROM Protection Bit
The EEPRTCT bit is used to enable the security feature in the EEPROM (see 5.4.3 EEPROM
Program/Erase Protection).
1 = EEPROM security disabled
0 = EEPROM security enabled
This feature is a write-once feature. Once the protection is enabled it may not be disabled.
EEBP[3:0] — EEPROM Block Protection Bits
These bits prevent blocks of EEPROM array from being programmed or erased.
1 = EEPROM array block is protected
0 = EEPROM array block is unprotected
See Table 5-4.
MC68HC908AZ32A Data Sheet, Rev. 2
58
Freescale Semiconductor
EEPROM Register Descriptions
Table 5-4. EEPROM Block Protection Bits
Block Number (EEBPx)
Address Range
EEBP0
$0800–$087F
EEBP1
$0880–$08FF
EEBP2
$0900–$097F
EEBP3
$0980–$09FF
Table 5-5. EEPROM Block Protect and Security Summary
Address Range
$0800 - $087F
$0880 - $08EF
$08F0 - $08FF
$0900 - $097F
$0980 - $09FF
EEBPx
EEPRTCT = 1
EEPRTCT = 0
EEBP0 = 0
Byte Programming Available
Bulk, Block and Byte Erasing Available
Byte Programming Available
Only Byte Erasing Available
EEBP0 = 1
Protected
Protected
EEBP1 = 0
Byte Programming Available
Bulk, Block and Byte Erasing Available
Byte Programming Available
Only Byte Erasing Available
EEBP1 = 1
Protected
Protected
EEBP1 = 0
Byte Programming Available
Bulk, Block and Byte Erasing Available
EEBP1 = 1
Protected
EEBP2 = 0
Byte Programming Available
Bulk, Block and Byte Erasing Available
Byte Programming Available
Only Byte Erasing Available
EEBP2 = 1
Protected
Protected
EEBP3 = 0
Byte Programming Available
Bulk, Block and Byte Available
Byte Programming Available
Only Byte Erasing Available
EEBP3 = 1
Protected
Protected
Secured
(No Programming or Erasing)
5.5.3 EEPROM Nonvolatile Register
The contents of this register is loaded into the EEPROM array configuration register (EEACR) after a
reset.
This register is erased and programmed in the same way as an EEPROM byte. (See 5.5.1 EEPROM
Control Register for individual bit descriptions).
Address:
Read:
Write:
$FE1C
Bit 7
6
5
4
3
2
1
Bit 0
UNUSED
UNUSED
UNUSED
EEPRTCT
EEBP3
EEBP2
EEBP1
EEBP0
Reset:
PV
PV = Programmed value or 1 in the erased state.
Figure 5-4. EEPROM Nonvolatile Register (EENVR)
NOTE
The EENVR will leave the factory programmed with $F0 such that the full
array is available and unprotected.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
59
EEPROM
5.5.4 EEPROM Timebase Divider Register
The 16-bit EEPROM timebase divider register consists of two 8-bit registers: EEDIVH and EEDIVL. The
11-bit value in this register is used to configure the timebase divider circuit to obtain the 35 μs timebase
for EEPROM control.
These two read/write registers are respectively loaded with the contents of the EEPROM timebase divider
onvolatile registers (EEDIVHNVR and EEDIVLNVR) after a reset.
Address:
Read:
Write:
$FE1A
Bit 7
6
5
4
3
EEDIVSECD
0
0
0
0
Reset:
2
1
Bit 0
EEDIV10
EEDIV9
EEDIV8
Contents of EEDIVHNVR ($FE10), Bits [6:3] = 0
= Unimplemented
Figure 5-5. EEDIV Divider High Register (EEDIVH)
Address:
Read:
Write:
Reset:
$FE1B
Bit 7
6
5
4
3
2
1
Bit 0
EEDIV7
EEDIV6
EEDIV5
EEDIV4
EEDIV3
EEDIV2
EEDIV1
EEDIV0
Contents of EEDIVLNVR ($FE11)
Figure 5-6. EEDIV Divider Low Register (EEDIVL)
EEDIVSECD — EEPROM Divider Security Disable
This bit enables/disables the security feature of the EEDIV registers. When EEDIV security feature is
enabled, the state of the registers EEDIVH and EEDIVL are locked (including EEDIVSECD bit). The
EEDIVHNVR and EEDIVLNVR nonvolatile memory registers are also protected from being
erased/programmed.
1 = EEDIV security feature disabled
0 = EEDIV security feature enabled
EEDIV[10:0] — EEPROM timebase prescaler
These prescaler bits store the value of EEDIV which is used as the divisor to derive a timebase of 35μs
from the selected reference clock source (CGMXCLK or bus block in the CONFIG-2 register) for the
EEPROM related internal timer and circuits. EEDIV[10:0] bits are readable at any time. They are
writable when EELAT = 0 and EEDIVSECD = 1.
The EEDIV value is calculated by the following formula:
EEDIV= INT[Reference Frequency(Hz) x 35 x10-6 +0.5]
Where the result inside the bracket is rounded down to the nearest integer value
For example, if the reference frequency is 4.9152MHz, the EEDIV value is 172
NOTE
Programming/erasing the EEPROM with an improper EEDIV value may
result in data lost and reduce endurance of the EEPROM device.
MC68HC908AZ32A Data Sheet, Rev. 2
60
Freescale Semiconductor
Low-Power Modes
5.5.5 EEPROM Timebase Divider Nonvolatile Register
The 16-bit EEPROM timebase divider nonvolatile register consists of two 8-bit registers: EEDIVHNVR
and EEDIVLNVR. The contents of these two registers are respectively loaded into the EEPROM timebase
divider registers, EEDIVH and EEDIVL, after a reset.
These two registers are erased and programmed in the same way as an EEPROM byte.
Address:
Read:
Write:
$FE10
Bit 7
6
5
4
3
2
1
Bit 0
EEDIVSECD
R
R
R
R
EEDIV10
EEDIV9
EEDIV8
R
= Reserved
Reset:
Unaffected by reset; $FF when blank
Figure 5-7. EEPROM Divider Nonvolatile Register High (EEDIVHNVR))
Address:
Read:
Write:
$FE11
Bit 7
6
5
4
3
2
1
Bit 0
EEDIV7
EEDIV6
EEDIV5
EEDIV4
EEDIV3
EEDIV2
EEDIV1
EEDIV0
Reset:
Unaffected by reset; $FF when blank
Figure 5-8. EEPROM Divider Nonvolatile Register Low (EEDIVLNVR)
These two registers are protected from erase and program operations if the EEDIVSECD is set to logic 1
in the EEDIVH (see EEPROM Timebase Divider Register) or programmed to a logic 1 in the
EEDIVHNVR.
NOTE
Once EEDIVSECD in the EEDIVHNVR is programmed to 0 and after a
system reset, the EEDIV security feature is permanently enabled because
the EEDIVSECD bit in the EEDIVH is always loaded with 0 thereafter. Once
this security feature is armed, erase and program mode are disabled for
EEDIVHNVR and EEDIVLNVR. Modifications to the EEDIVH and EEDIVL
registers are also disabled. Therefore, care should be taken before
programming a value into the EEDIVHNVR.
5.6 Low-Power Modes
The WAIT and STOP instructions can put the MCU in low power-consumption standby modes.
5.6.1 Wait Mode
The WAIT instruction does not affect the EEPROM. It is possible to start the program or erase sequence
on the EEPROM and put the MCU in wait mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
61
EEPROM
5.6.2 Stop Mode
The STOP instruction reduces the EEPROM power consumption to a minimum. The STOP instruction
should not be executed while a programming or erasing sequence is in progress.
If stop mode is entered while EELAT and EEPGM are set, the programming sequence will be stopped
and the programming voltage to the EEPROM array removed. The programming sequence will be
restarted after leaving stop mode; access to the EEPROM is only possible after the programming
sequence has completed.
If stop mode is entered while EELAT and EEPGM is cleared, the programming sequence will be
terminated abruptly.
In either case, the data integrity of the EEPROM is not guaranteed.
MC68HC908AZ32A Data Sheet, Rev. 2
62
Freescale Semiconductor
Chapter 6
Central Processor Unit (CPU)
6.1 Introduction
The M68HC08 CPU (central processor unit) is an enhanced and fully object-code-compatible version of
the M68HC05 CPU. The CPU08 Reference Manual (document order number CPU08RM/AD) contains a
description of the CPU instruction set, addressing modes, and architecture.
6.2 Features
Features of the CPU include:
• Object code fully upward-compatible with M68HC05 Family
• 16-bit stack pointer with stack manipulation instructions
• 16-bit index register with x-register manipulation instructions
• 8-MHz CPU internal bus frequency
• 64-Kbyte program/data memory space
• 16 addressing modes
• Memory-to-memory data moves without using accumulator
• Fast 8-bit by 8-bit multiply and 16-bit by 8-bit divide instructions
• Enhanced binary-coded decimal (BCD) data handling
• Modular architecture with expandable internal bus definition for extension of addressing range
beyond 64 Kbytes
• Low-power stop and wait modes
6.3 CPU Registers
Figure 6-1 shows the five CPU registers. CPU registers are not part of the memory map.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
63
Central Processor Unit (CPU)
0
7
ACCUMULATOR (A)
0
15
H
X
INDEX REGISTER (H:X)
15
0
STACK POINTER (SP)
15
0
PROGRAM COUNTER (PC)
7
0
V 1 1 H I N Z C
CONDITION CODE REGISTER (CCR)
CARRY/BORROW FLAG
ZERO FLAG
NEGATIVE FLAG
INTERRUPT MASK
HALF-CARRY FLAG
TWO’S COMPLEMENT OVERFLOW FLAG
Figure 6-1. CPU Registers
6.3.1 Accumulator
The accumulator is a general-purpose 8-bit register. The CPU uses the accumulator to hold operands and
the results of arithmetic/logic operations.
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
Unaffected by reset
Figure 6-2. Accumulator (A)
6.3.2 Index Register
The 16-bit index register allows indexed addressing of a 64-Kbyte memory space. H is the upper byte of
the index register, and X is the lower byte. H:X is the concatenated 16-bit index register.
In the indexed addressing modes, the CPU uses the contents of the index register to determine the
conditional address of the operand.
The index register can serve also as a temporary data storage location.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
0
0
0
0
0
0
0
0
X
X
X
X
X
X
X
X
Read:
Write:
Reset:
X = Indeterminate
Figure 6-3. Index Register (H:X)
MC68HC908AZ32A Data Sheet, Rev. 2
64
Freescale Semiconductor
CPU Registers
6.3.3 Stack Pointer
The stack pointer is a 16-bit register that contains the address of the next location on the stack. During a
reset, the stack pointer is preset to $00FF. The reset stack pointer (RSP) instruction sets the least
significant byte to $FF and does not affect the most significant byte. The stack pointer decrements as data
is pushed onto the stack and increments as data is pulled from the stack.
In the stack pointer 8-bit offset and 16-bit offset addressing modes, the stack pointer can function as an
index register to access data on the stack. The CPU uses the contents of the stack pointer to determine
the conditional address of the operand.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Read:
Write:
Reset:
Figure 6-4. Stack Pointer (SP)
NOTE
The location of the stack is arbitrary and may be relocated anywhere in
random-access memory (RAM). Moving the SP out of page 0 ($0000 to
$00FF) frees direct address (page 0) space. For correct operation, the
stack pointer must point only to RAM locations.
6.3.4 Program Counter
The program counter is a 16-bit register that contains the address of the next instruction or operand to be
fetched.
Normally, the program counter automatically increments to the next sequential memory location every
time an instruction or operand is fetched. Jump, branch, and interrupt operations load the program
counter with an address other than that of the next sequential location.
During reset, the program counter is loaded with the reset vector address located at $FFFE and $FFFF.
The vector address is the address of the first instruction to be executed after exiting the reset state.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
Read:
Write:
Reset:
Loaded with vector from $FFFE and $FFFF
Figure 6-5. Program Counter (PC)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
65
Central Processor Unit (CPU)
6.3.5 Condition Code Register
The 8-bit condition code register contains the interrupt mask and five flags that indicate the results of the
instruction just executed. Bits 6 and 5 are set permanently to 1. The following paragraphs describe the
functions of the condition code register.
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
V
1
1
H
I
N
Z
C
X
1
1
X
1
X
X
X
X = Indeterminate
Figure 6-6. Condition Code Register (CCR)
V — Overflow Flag
The CPU sets the overflow flag when a two's complement overflow occurs. The signed branch
instructions BGT, BGE, BLE, and BLT use the overflow flag.
1 = Overflow
0 = No overflow
H — Half-Carry Flag
The CPU sets the half-carry flag when a carry occurs between accumulator bits 3 and 4 during an
add-without-carry (ADD) or add-with-carry (ADC) operation. The half-carry flag is required for
binary-coded decimal (BCD) arithmetic operations. The DAA instruction uses the states of the H and
C flags to determine the appropriate correction factor.
1 = Carry between bits 3 and 4
0 = No carry between bits 3 and 4
I — Interrupt Mask
When the interrupt mask is set, all maskable CPU interrupts are disabled. CPU interrupts are enabled
when the interrupt mask is cleared. When a CPU interrupt occurs, the interrupt mask is set
automatically after the CPU registers are saved on the stack, but before the interrupt vector is fetched.
1 = Interrupts disabled
0 = Interrupts enabled
NOTE
To maintain M6805 Family compatibility, the upper byte of the index
register (H) is not stacked automatically. If the interrupt service routine
modifies H, then the user must stack and unstack H using the PSHH and
PULH instructions.
After the I bit is cleared, the highest-priority interrupt request is serviced first.
A return-from-interrupt (RTI) instruction pulls the CPU registers from the stack and restores the
interrupt mask from the stack. After any reset, the interrupt mask is set and can be cleared only by the
clear interrupt mask software instruction (CLI).
N — Negative Flag
The CPU sets the negative flag when an arithmetic operation, logic operation, or data manipulation
produces a negative result, setting bit 7 of the result.
1 = Negative result
0 = Non-negative result
MC68HC908AZ32A Data Sheet, Rev. 2
66
Freescale Semiconductor
Arithmetic/Logic Unit (ALU)
Z — Zero Flag
The CPU sets the zero flag when an arithmetic operation, logic operation, or data manipulation
produces a result of $00.
1 = Zero result
0 = Non-zero result
C — Carry/Borrow Flag
The CPU sets the carry/borrow flag when an addition operation produces a carry out of bit 7 of the
accumulator or when a subtraction operation requires a borrow. Some instructions — such as bit test
and branch, shift, and rotate — also clear or set the carry/borrow flag.
1 = Carry out of bit 7
0 = No carry out of bit 7
6.4 Arithmetic/Logic Unit (ALU)
The ALU performs the arithmetic and logic operations defined by the instruction set.
Refer to the CPU08 Reference Manual (document order number CPU08RM/AD) for a description of the
instructions and addressing modes and more detail about the architecture of the CPU.
6.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
6.5.1 Wait Mode
The WAIT instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling interrupts. After exit from
wait mode by interrupt, the I bit remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
6.5.2 Stop Mode
The STOP instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling external interrupts. After
exit from stop mode by external interrupt, the I bit remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
After exiting stop mode, the CPU clock begins running after the oscillator stabilization delay.
6.6 CPU During Break Interrupts
If a break module is present on the MCU, the CPU starts a break interrupt by:
• Loading the instruction register with the SWI instruction
• Loading the program counter with $FFFC:$FFFD or with $FEFC:$FEFD in monitor mode
The break interrupt begins after completion of the CPU instruction in progress. If the break address
register match occurs on the last cycle of a CPU instruction, the break interrupt begins immediately.
A return-from-interrupt instruction (RTI) in the break routine ends the break interrupt and returns the MCU
to normal operation if the break interrupt has been deasserted.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
67
Central Processor Unit (CPU)
6.7 Instruction Set Summary
Table 6-1 provides a summary of the M68HC08 instruction set.
ADC #opr
ADC opr
ADC opr
ADC opr,X
ADC opr,X
ADC ,X
ADC opr,SP
ADC opr,SP
ADD #opr
ADD opr
ADD opr
ADD opr,X
ADD opr,X
ADD ,X
ADD opr,SP
ADD opr,SP
V H I N Z C
A ← (A) + (M) + (C)
Add with Carry
A ← (A) + (M)
Add without Carry
IMM
DIR
EXT
IX2
– IX1
IX
SP1
SP2
A9
B9
C9
D9
E9
F9
9EE9
9ED9
ii
dd
hh ll
ee ff
ff
IMM
DIR
EXT
– IX2
IX1
IX
SP1
SP2
AB
BB
CB
DB
EB
FB
9EEB
9EDB
ii
dd
hh ll
ee ff
ff
ff
ee ff
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 1 of 6)
2
3
4
4
3
2
4
5
ff
ee ff
2
3
4
4
3
2
4
5
AIS #opr
Add Immediate Value (Signed) to SP
SP ← (SP) + (16 « M)
– – – – – – IMM
A7
ii
2
AIX #opr
Add Immediate Value (Signed) to H:X
H:X ← (H:X) + (16 « M)
– – – – – – IMM
AF
ii
2
A ← (A) & (M)
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
A4
B4
C4
D4
E4
F4
9EE4
9ED4
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
0
DIR
INH
INH
– – IX1
IX
SP1
38 dd
48
58
68 ff
78
9E68 ff
4
1
1
4
3
5
C
DIR
INH
– – INH
IX1
IX
SP1
37 dd
47
57
67 ff
77
9E67 ff
4
1
1
4
3
5
AND #opr
AND opr
AND opr
AND opr,X
AND opr,X
AND ,X
AND opr,SP
AND opr,SP
ASL opr
ASLA
ASLX
ASL opr,X
ASL ,X
ASL opr,SP
Logical AND
Arithmetic Shift Left
(Same as LSL)
C
b7
ASR opr
ASRA
ASRX
ASR opr,X
ASR opr,X
ASR opr,SP
Arithmetic Shift Right
BCC rel
Branch if Carry Bit Clear
b0
b7
BCLR n, opr
Clear Bit n in M
b0
PC ← (PC) + 2 + rel ? (C) = 0
Mn ← 0
ff
ee ff
– – – – – – REL
24
rr
3
DIR (b0)
DIR (b1)
DIR (b2)
– – – – – – DIR (b3)
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
11
13
15
17
19
1B
1D
1F
dd
dd
dd
dd
dd
dd
dd
dd
4
4
4
4
4
4
4
4
BCS rel
Branch if Carry Bit Set (Same as BLO)
PC ← (PC) + 2 + rel ? (C) = 1
– – – – – – REL
25
rr
3
BEQ rel
Branch if Equal
PC ← (PC) + 2 + rel ? (Z) = 1
– – – – – – REL
27
rr
3
BGE opr
Branch if Greater Than or Equal To
(Signed Operands)
PC ← (PC) + 2 + rel ? (N ⊕ V) = 0
– – – – – – REL
90
rr
3
BGT opr
Branch if Greater Than (Signed
Operands)
PC ← (PC) + 2 + rel ? (Z) | (N ⊕ V) = 0 – – – – – – REL
92
rr
3
BHCC rel
Branch if Half Carry Bit Clear
PC ← (PC) + 2 + rel ? (H) = 0
– – – – – – REL
28
rr
BHCS rel
Branch if Half Carry Bit Set
PC ← (PC) + 2 + rel ? (H) = 1
– – – – – – REL
29
rr
BHI rel
Branch if Higher
PC ← (PC) + 2 + rel ? (C) | (Z) = 0
– – – – – – REL
22
rr
3
3
3
MC68HC908AZ32A Data Sheet, Rev. 2
68
Freescale Semiconductor
Instruction Set Summary
Effect
on CCR
V H I N Z C
BHS rel
Branch if Higher or Same
(Same as BCC)
BIH rel
BIL rel
PC ← (PC) + 2 + rel ? (C) = 0
– – – – – – REL
Branch if IRQ Pin High
PC ← (PC) + 2 + rel ? IRQ = 1
Branch if IRQ Pin Low
PC ← (PC) + 2 + rel ? IRQ = 0
(A) & (M)
BIT #opr
BIT opr
BIT opr
BIT opr,X
BIT opr,X
BIT ,X
BIT opr,SP
BIT opr,SP
Bit Test
BLE opr
Branch if Less Than or Equal To
(Signed Operands)
Cycles
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 2 of 6)
24
rr
3
– – – – – – REL
2F
rr
3
– – – – – – REL
2E
rr
3
IMM
DIR
EXT
0 – – – IX2
IX1
IX
SP1
SP2
A5
B5
C5
D5
E5
F5
9EE5
9ED5
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
rr
3
PC ← (PC) + 2 + rel ? (Z) | (N ⊕ V) = 1 – – – – – – REL
93
BLO rel
Branch if Lower (Same as BCS)
PC ← (PC) + 2 + rel ? (C) = 1
– – – – – – REL
25
rr
3
BLS rel
Branch if Lower or Same
PC ← (PC) + 2 + rel ? (C) | (Z) = 1
– – – – – – REL
23
rr
3
BLT opr
Branch if Less Than (Signed Operands)
PC ← (PC) + 2 + rel ? (N ⊕ V) =1
– – – – – – REL
91
rr
3
BMC rel
Branch if Interrupt Mask Clear
PC ← (PC) + 2 + rel ? (I) = 0
– – – – – – REL
2C
rr
3
BMI rel
Branch if Minus
PC ← (PC) + 2 + rel ? (N) = 1
– – – – – – REL
2B
rr
3
BMS rel
Branch if Interrupt Mask Set
PC ← (PC) + 2 + rel ? (I) = 1
– – – – – – REL
2D
rr
3
3
BNE rel
Branch if Not Equal
PC ← (PC) + 2 + rel ? (Z) = 0
– – – – – – REL
26
rr
BPL rel
Branch if Plus
PC ← (PC) + 2 + rel ? (N) = 0
– – – – – – REL
2A
rr
3
BRA rel
Branch Always
PC ← (PC) + 2 + rel
– – – – – – REL
20
rr
3
DIR (b0)
DIR (b1)
DIR (b2)
DIR (b3)
– – – – – DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
01
03
05
07
09
0B
0D
0F
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
5
5
5
5
5
5
5
5
BRCLR n,opr,rel Branch if Bit n in M Clear
BRN rel
Branch Never
BRSET n,opr,rel Branch if Bit n in M Set
BSET n,opr
Set Bit n in M
BSR rel
Branch to Subroutine
CBEQ opr,rel
CBEQA #opr,rel
CBEQX #opr,rel Compare and Branch if Equal
CBEQ opr,X+,rel
CBEQ X+,rel
CBEQ opr,SP,rel
PC ← (PC) + 3 + rel ? (Mn) = 0
PC ← (PC) + 2
– – – – – – REL
21
rr
3
PC ← (PC) + 3 + rel ? (Mn) = 1
DIR (b0)
DIR (b1)
DIR (b2)
DIR (b3)
– – – – – DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
00
02
04
06
08
0A
0C
0E
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
5
5
5
5
5
5
5
5
Mn ← 1
DIR (b0)
DIR (b1)
DIR (b2)
– – – – – – DIR (b3)
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
10
12
14
16
18
1A
1C
1E
dd
dd
dd
dd
dd
dd
dd
dd
4
4
4
4
4
4
4
4
PC ← (PC) + 2; push (PCL)
SP ← (SP) – 1; push (PCH)
SP ← (SP) – 1
PC ← (PC) + rel
– – – – – – REL
AD
rr
4
PC ← (PC) + 3 + rel ? (A) – (M) = $00
PC ← (PC) + 3 + rel ? (A) – (M) = $00
PC ← (PC) + 3 + rel ? (X) – (M) = $00
PC ← (PC) + 3 + rel ? (A) – (M) = $00
PC ← (PC) + 2 + rel ? (A) – (M) = $00
PC ← (PC) + 4 + rel ? (A) – (M) = $00
DIR
IMM
– – – – – – IMM
IX1+
IX+
SP1
31
41
51
61
71
9E61
dd rr
ii rr
ii rr
ff rr
rr
ff rr
5
4
4
5
4
6
CLC
Clear Carry Bit
C←0
– – – – – 0 INH
98
1
CLI
Clear Interrupt Mask
I←0
– – 0 – – – INH
9A
2
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
69
Central Processor Unit (CPU)
CLR opr
CLRA
CLRX
CLRH
CLR opr,X
CLR ,X
CLR opr,SP
CMP #opr
CMP opr
CMP opr
CMP opr,X
CMP opr,X
CMP ,X
CMP opr,SP
CMP opr,SP
V H I N Z C
Clear
Compare A with M
COM opr
COMA
COMX
COM opr,X
COM ,X
COM opr,SP
Complement (One’s Complement)
CPHX #opr
CPHX opr
Compare H:X with M
CPX #opr
CPX opr
CPX opr
CPX ,X
CPX opr,X
CPX opr,X
CPX opr,SP
CPX opr,SP
Compare X with M
DAA
Decimal Adjust A
DEC opr
DECA
DECX
DEC opr,X
DEC ,X
DEC opr,SP
Decrement
DIV
Divide
INC opr
INCA
INCX
INC opr,X
INC ,X
INC opr,SP
Exclusive OR M with A
Increment
M ← $00
A ← $00
X ← $00
H ← $00
M ← $00
M ← $00
M ← $00
DIR
INH
INH
0 – – 0 1 – INH
IX1
IX
SP1
3F dd
4F
5F
8C
6F ff
7F
9E6F ff
(A) – (M)
IMM
DIR
EXT
IX2
– – IX1
IX
SP1
SP2
A1
B1
C1
D1
E1
F1
9EE1
9ED1
DIR
INH
INH
0 – – 1
IX1
IX
SP1
33 dd
43
53
63 ff
73
9E63 ff
M ← (M) = $FF – (M)
A ← (A) = $FF – (M)
X ← (X) = $FF – (M)
M ← (M) = $FF – (M)
M ← (M) = $FF – (M)
M ← (M) = $FF – (M)
(H:X) – (M:M + 1)
(X) – (M)
(A)10
DBNZ opr,rel
DBNZA rel
DBNZX rel
Decrement and Branch if Not Zero
DBNZ opr,X,rel
DBNZ X,rel
DBNZ opr,SP,rel
EOR #opr
EOR opr
EOR opr
EOR opr,X
EOR opr,X
EOR ,X
EOR opr,SP
EOR opr,SP
Effect
on CCR
ff
ee ff
2
3
4
4
3
2
4
5
4
1
1
4
3
5
ii ii+1
dd
3
4
IMM
DIR
EXT
IX2
– – IX1
IX
SP1
SP2
A3
B3
C3
D3
E3
F3
9EE3
9ED3
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
U – – INH
72
A ← (A) – 1 or M ← (M) – 1 or X ← (X) – 1
PC ← (PC) + 3 + rel ? (result) ≠ 0
DIR
PC ← (PC) + 2 + rel ? (result) ≠ 0
INH
PC ← (PC) + 2 + rel ? (result) ≠ 0
– – – – – – INH
PC ← (PC) + 3 + rel ? (result) ≠ 0
IX1
PC ← (PC) + 2 + rel ? (result) ≠ 0
IX
PC ← (PC) + 4 + rel ? (result) ≠ 0
SP1
3B
4B
5B
6B
7B
9E6B
ff
ee ff
2
dd rr
rr
rr
ff rr
rr
ff rr
M ← (M) – 1
A ← (A) – 1
X ← (X) – 1
M ← (M) – 1
M ← (M) – 1
M ← (M) – 1
DIR
INH
INH
– – –
IX1
IX
SP1
A ← (H:A)/(X)
H ← Remainder
– – – – INH
52
A ← (A ⊕ M)
IMM
DIR
EXT
0 – – – IX2
IX1
IX
SP1
SP2
A8
B8
C8
D8
E8
F8
9EE8
9ED8
DIR
INH
– – – INH
IX1
IX
SP1
3C dd
4C
5C
6C ff
7C
9E6C ff
M ← (M) + 1
A ← (A) + 1
X ← (X) + 1
M ← (M) + 1
M ← (M) + 1
M ← (M) + 1
3
1
1
1
3
2
4
65
75
– – IMM
DIR
ii
dd
hh ll
ee ff
ff
Cycles
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 3 of 6)
3A dd
4A
5A
6A ff
7A
9E6A ff
5
3
3
5
4
6
4
1
1
4
3
5
7
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
4
1
1
4
3
5
MC68HC908AZ32A Data Sheet, Rev. 2
70
Freescale Semiconductor
Instruction Set Summary
JSR opr
JSR opr
JSR opr,X
JSR opr,X
JSR ,X
Jump to Subroutine
LDHX #opr
LDHX opr
Load H:X from M
2
3
4
3
2
PC ← (PC) + n (n = 1, 2, or 3)
Push (PCL); SP ← (SP) – 1
Push (PCH); SP ← (SP) – 1
PC ← Unconditional Address
DIR
EXT
– – – – – – IX2
IX1
IX
BD
CD
DD
ED
FD
dd
hh ll
ee ff
ff
4
5
6
5
4
A ← (M)
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
A6
B6
C6
D6
E6
F6
9EE6
9ED6
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
ii jj
dd
3
4
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
H:X ← (M:M + 1)
Logical Shift Left
(Same as ASL)
Logical Shift Right
MOV opr,opr
MOV opr,X+
MOV #opr,opr
MOV X+,opr
Move
MUL
Unsigned multiply
C
b7
45
55
AE
BE
CE
DE
EE
FE
9EEE
9EDE
0
DIR
INH
INH
– – IX1
IX
SP1
38 dd
48
58
68 ff
78
9E68 ff
4
1
1
4
3
5
C
DIR
INH
– – 0 INH
IX1
IX
SP1
34 dd
44
54
64 ff
74
9E64 ff
4
1
1
4
3
5
b0
0
IMM
DIR
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
X ← (M)
b7
Negate (Two’s Complement)
0 – – –
b0
H:X ← (H:X) + 1 (IX+D, DIX+)
DD
DIX+
0 – – – IMD
IX+D
X:A ← (X) × (A)
– 0 – – – 0 INH
M ← –(M) = $00 – (M)
A ← –(A) = $00 – (A)
X ← –(X) = $00 – (X)
M ← –(M) = $00 – (M)
M ← –(M) = $00 – (M)
DIR
INH
INH
– – IX1
IX
SP1
(M)Destination ← (M)Source
4E
5E
6E
7E
dd dd
dd
ii dd
dd
42
No Operation
None
– – – – – – INH
9D
NSA
Nibble Swap A
A ← (A[3:0]:A[7:4])
– – – – – – INH
62
A ← (A) | (M)
IMM
DIR
EXT
IX2
0 – – –
IX1
IX
SP1
SP2
AA
BA
CA
DA
EA
FA
9EEA
9EDA
Inclusive OR A and M
ff
ee ff
5
4
4
4
5
30 dd
40
50
60 ff
70
9E60 ff
NOP
ORA #opr
ORA opr
ORA opr
ORA opr,X
ORA opr,X
ORA ,X
ORA opr,SP
ORA opr,SP
Cycles
dd
hh ll
ee ff
ff
Load X from M
LSR opr
LSRA
LSRX
LSR opr,X
LSR ,X
LSR opr,SP
NEG opr
NEGA
NEGX
NEG opr,X
NEG ,X
NEG opr,SP
BC
CC
DC
EC
FC
Jump
Load A from M
LSL opr
LSLA
LSLX
LSL opr,X
LSL ,X
LSL opr,SP
PC ← Jump Address
DIR
EXT
– – – – – – IX2
IX1
IX
Effect
on CCR
Description
V H I N Z C
LDA #opr
LDA opr
LDA opr
LDA opr,X
LDA opr,X
LDA ,X
LDA opr,SP
LDA opr,SP
LDX #opr
LDX opr
LDX opr
LDX opr,X
LDX opr,X
LDX ,X
LDX opr,SP
LDX opr,SP
Operand
JMP opr
JMP opr
JMP opr,X
JMP opr,X
JMP ,X
Operation
Address
Mode
Source
Form
Opcode
Table 6-1. Instruction Set Summary (Sheet 4 of 6)
4
1
1
4
3
5
1
3
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
PSHA
Push A onto Stack
Push (A); SP ← (SP) – 1
– – – – – – INH
87
2
PSHH
Push H onto Stack
Push (H); SP ← (SP) – 1
– – – – – – INH
8B
2
PSHX
Push X onto Stack
Push (X); SP ← (SP) – 1
– – – – – – INH
89
2
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
71
Central Processor Unit (CPU)
V H I N Z C
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 5 of 6)
PULA
Pull A from Stack
SP ← (SP + 1); Pull (A)
– – – – – – INH
86
2
PULH
Pull H from Stack
SP ← (SP + 1); Pull (H)
– – – – – – INH
8A
2
PULX
Pull X from Stack
SP ← (SP + 1); Pull (X)
– – – – – – INH
C
DIR
INH
INH
– – IX1
IX
SP1
39 dd
49
59
69 ff
79
9E69 ff
4
1
1
4
3
5
DIR
INH
– – INH
IX1
IX
SP1
36 dd
46
56
66 ff
76
9E66 ff
4
1
1
4
3
5
ROL opr
ROLA
ROLX
ROL opr,X
ROL ,X
ROL opr,SP
Rotate Left through Carry
b7
b0
88
2
ROR opr
RORA
RORX
ROR opr,X
ROR ,X
ROR opr,SP
Rotate Right through Carry
RSP
Reset Stack Pointer
SP ← $FF
– – – – – – INH
9C
1
RTI
Return from Interrupt
SP ← (SP) + 1; Pull (CCR)
SP ← (SP) + 1; Pull (A)
SP ← (SP) + 1; Pull (X)
SP ← (SP) + 1; Pull (PCH)
SP ← (SP) + 1; Pull (PCL)
INH
80
7
RTS
Return from Subroutine
SP ← SP + 1; Pull (PCH)
SP ← SP + 1; Pull (PCL)
– – – – – – INH
81
4
A ← (A) – (M) – (C)
IMM
DIR
EXT
– – IX2
IX1
IX
SP1
SP2
A2
B2
C2
D2
E2
F2
9EE2
9ED2
SBC #opr
SBC opr
SBC opr
SBC opr,X
SBC opr,X
SBC ,X
SBC opr,SP
SBC opr,SP
C
b7
Subtract with Carry
b0
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
SEC
Set Carry Bit
C←1
– – – – – 1 INH
99
1
SEI
Set Interrupt Mask
I←1
– – 1 – – – INH
9B
2
M ← (A)
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
B7
C7
D7
E7
F7
9EE7
9ED7
(M:M + 1) ← (H:X)
0 – – – DIR
35
I ← 0; Stop Processing
– – 0 – – – INH
8E
M ← (X)
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
BF
CF
DF
EF
FF
9EEF
9EDF
dd
hh ll
ee ff
ff
IMM
DIR
EXT
– – IX2
IX1
IX
SP1
SP2
A0
B0
C0
D0
E0
F0
9EE0
9ED0
ii
dd
hh ll
ee ff
ff
STA opr
STA opr
STA opr,X
STA opr,X
STA ,X
STA opr,SP
STA opr,SP
Store A in M
STHX opr
Store H:X in M
STOP
Enable Interrupts, Stop Processing,
Refer to MCU Documentation
STX opr
STX opr
STX opr,X
STX opr,X
STX ,X
STX opr,SP
STX opr,SP
SUB #opr
SUB opr
SUB opr
SUB opr,X
SUB opr,X
SUB ,X
SUB opr,SP
SUB opr,SP
Store X in M
Subtract
A ← (A) – (M)
dd
hh ll
ee ff
ff
ff
ee ff
3
4
4
3
2
4
5
dd
4
1
ff
ee ff
ff
ee ff
3
4
4
3
2
4
5
2
3
4
4
3
2
4
5
MC68HC908AZ32A Data Sheet, Rev. 2
72
Freescale Semiconductor
Opcode Map
SWI
Software Interrupt
PC ← (PC) + 1; Push (PCL)
SP ← (SP) – 1; Push (PCH)
SP ← (SP) – 1; Push (X)
SP ← (SP) – 1; Push (A)
SP ← (SP) – 1; Push (CCR)
SP ← (SP) – 1; I ← 1
PCH ← Interrupt Vector High Byte
PCL ← Interrupt Vector Low Byte
– – 1 – – – INH
83
9
CCR ← (A)
INH
84
2
X ← (A)
– – – – – – INH
97
1
A ← (CCR)
– – – – – – INH
85
(A) – $00 or (X) – $00 or (M) – $00
DIR
INH
INH
0 – – –
IX1
IX
SP1
H:X ← (SP) + 1
– – – – – – INH
95
2
A ← (X)
– – – – – – INH
9F
1
(SP) ← (H:X) – 1
– – – – – – INH
94
2
I bit ← 0; Inhibit CPU clocking
until interrupted
– – 0 – – – INH
8F
1
TAP
Transfer A to CCR
Transfer A to X
TPA
Transfer CCR to A
Test for Negative or Zero
TSX
Transfer SP to H:X
TXA
Transfer X to A
TXS
Transfer H:X to SP
WAIT
A
C
CCR
dd
dd rr
DD
DIR
DIX+
ee ff
EXT
ff
H
H
hh ll
I
ii
IMD
IMM
INH
IX
IX+
IX+D
IX1
IX1+
IX2
M
N
Cycles
V H I N Z C
TAX
TST opr
TSTA
TSTX
TST opr,X
TST ,X
TST opr,SP
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 6 of 6)
Enable Interrupts; Wait for Interrupt
Accumulator
Carry/borrow bit
Condition code register
Direct address of operand
Direct address of operand and relative offset of branch instruction
Direct to direct addressing mode
Direct addressing mode
Direct to indexed with post increment addressing mode
High and low bytes of offset in indexed, 16-bit offset addressing
Extended addressing mode
Offset byte in indexed, 8-bit offset addressing
Half-carry bit
Index register high byte
High and low bytes of operand address in extended addressing
Interrupt mask
Immediate operand byte
Immediate source to direct destination addressing mode
Immediate addressing mode
Inherent addressing mode
Indexed, no offset addressing mode
Indexed, no offset, post increment addressing mode
Indexed with post increment to direct addressing mode
Indexed, 8-bit offset addressing mode
Indexed, 8-bit offset, post increment addressing mode
Indexed, 16-bit offset addressing mode
Memory location
Negative bit
n
opr
PC
PCH
PCL
REL
rel
rr
SP1
SP2
SP
U
V
X
Z
&
|
⊕
()
–( )
#
«
←
?
:
—
3D dd
4D
5D
6D ff
7D
9E6D ff
1
3
1
1
3
2
4
Any bit
Operand (one or two bytes)
Program counter
Program counter high byte
Program counter low byte
Relative addressing mode
Relative program counter offset byte
Relative program counter offset byte
Stack pointer, 8-bit offset addressing mode
Stack pointer 16-bit offset addressing mode
Stack pointer
Undefined
Overflow bit
Index register low byte
Zero bit
Logical AND
Logical OR
Logical EXCLUSIVE OR
Contents of
Negation (two’s complement)
Immediate value
Sign extend
Loaded with
If
Concatenated with
Set or cleared
Not affected
6.8 Opcode Map
See Table 6-2.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
73
MSB
Branch
REL
DIR
INH
3
4
0
1
2
5
BRSET0
3 DIR
5
BRCLR0
3 DIR
5
BRSET1
3 DIR
5
BRCLR1
3 DIR
5
BRSET2
3 DIR
5
BRCLR2
3 DIR
5
BRSET3
3 DIR
5
BRCLR3
3 DIR
5
BRSET4
3 DIR
5
BRCLR4
3 DIR
5
BRSET5
3 DIR
5
BRCLR5
3 DIR
5
BRSET6
3 DIR
5
BRCLR6
3 DIR
5
BRSET7
3 DIR
5
BRCLR7
3 DIR
4
BSET0
2 DIR
4
BCLR0
2 DIR
4
BSET1
2 DIR
4
BCLR1
2 DIR
4
BSET2
2 DIR
4
BCLR2
2 DIR
4
BSET3
2 DIR
4
BCLR3
2 DIR
4
BSET4
2 DIR
4
BCLR4
2 DIR
4
BSET5
2 DIR
4
BCLR5
2 DIR
4
BSET6
2 DIR
4
BCLR6
2 DIR
4
BSET7
2 DIR
4
BCLR7
2 DIR
3
BRA
2 REL
3
BRN
2 REL
3
BHI
2 REL
3
BLS
2 REL
3
BCC
2 REL
3
BCS
2 REL
3
BNE
2 REL
3
BEQ
2 REL
3
BHCC
2 REL
3
BHCS
2 REL
3
BPL
2 REL
3
BMI
2 REL
3
BMC
2 REL
3
BMS
2 REL
3
BIL
2 REL
3
BIH
2 REL
Read-Modify-Write
INH
IX1
5
6
1
NEGX
1 INH
4
CBEQX
3 IMM
7
DIV
1 INH
1
COMX
1 INH
1
LSRX
1 INH
4
LDHX
2 DIR
1
RORX
1 INH
1
ASRX
1 INH
1
LSLX
1 INH
1
ROLX
1 INH
1
DECX
1 INH
3
DBNZX
2 INH
1
INCX
1 INH
1
TSTX
1 INH
4
MOV
2 DIX+
1
CLRX
1 INH
4
NEG
2
IX1
5
CBEQ
3 IX1+
3
NSA
1 INH
4
COM
2 IX1
4
LSR
2 IX1
3
CPHX
3 IMM
4
ROR
2 IX1
4
ASR
2 IX1
4
LSL
2 IX1
4
ROL
2 IX1
4
DEC
2 IX1
5
DBNZ
3 IX1
4
INC
2 IX1
3
TST
2 IX1
4
MOV
3 IMD
3
CLR
2 IX1
SP1
IX
9E6
7
Control
INH
INH
8
9
Register/Memory
IX2
SP2
IMM
DIR
EXT
A
B
C
D
9ED
4
SUB
3 EXT
4
CMP
3 EXT
4
SBC
3 EXT
4
CPX
3 EXT
4
AND
3 EXT
4
BIT
3 EXT
4
LDA
3 EXT
4
STA
3 EXT
4
EOR
3 EXT
4
ADC
3 EXT
4
ORA
3 EXT
4
ADD
3 EXT
3
JMP
3 EXT
5
JSR
3 EXT
4
LDX
3 EXT
4
STX
3 EXT
4
SUB
3 IX2
4
CMP
3 IX2
4
SBC
3 IX2
4
CPX
3 IX2
4
AND
3 IX2
4
BIT
3 IX2
4
LDA
3 IX2
4
STA
3 IX2
4
EOR
3 IX2
4
ADC
3 IX2
4
ORA
3 IX2
4
ADD
3 IX2
4
JMP
3 IX2
6
JSR
3 IX2
4
LDX
3 IX2
4
STX
3 IX2
5
SUB
4 SP2
5
CMP
4 SP2
5
SBC
4 SP2
5
CPX
4 SP2
5
AND
4 SP2
5
BIT
4 SP2
5
LDA
4 SP2
5
STA
4 SP2
5
EOR
4 SP2
5
ADC
4 SP2
5
ORA
4 SP2
5
ADD
4 SP2
IX1
SP1
IX
E
9EE
F
LSB
0
1
2
3
4
MC68HC908AZ32A Data Sheet, Rev. 2
5
6
7
8
9
A
B
C
D
E
Freescale Semiconductor
F
4
1
NEG
NEGA
2 DIR 1 INH
5
4
CBEQ CBEQA
3 DIR 3 IMM
5
MUL
1 INH
4
1
COM
COMA
2 DIR 1 INH
4
1
LSR
LSRA
2 DIR 1 INH
4
3
STHX
LDHX
2 DIR 3 IMM
4
1
ROR
RORA
2 DIR 1 INH
4
1
ASR
ASRA
2 DIR 1 INH
4
1
LSL
LSLA
2 DIR 1 INH
4
1
ROL
ROLA
2 DIR 1 INH
4
1
DEC
DECA
2 DIR 1 INH
5
3
DBNZ DBNZA
3 DIR 2 INH
4
1
INC
INCA
2 DIR 1 INH
3
1
TST
TSTA
2 DIR 1 INH
5
MOV
3 DD
3
1
CLR
CLRA
2 DIR 1 INH
INH Inherent
REL Relative
IMM Immediate
IX
Indexed, No Offset
DIR Direct
IX1 Indexed, 8-Bit Offset
EXT Extended
IX2 Indexed, 16-Bit Offset
DD Direct-Direct
IMD Immediate-Direct
IX+D Indexed-Direct DIX+ Direct-Indexed
*Pre-byte for stack pointer indexed instructions
5
3
NEG
NEG
3 SP1 1 IX
6
4
CBEQ
CBEQ
4 SP1 2 IX+
2
DAA
1 INH
5
3
COM
COM
3 SP1 1 IX
5
3
LSR
LSR
3 SP1 1 IX
4
CPHX
2 DIR
5
3
ROR
ROR
3 SP1 1 IX
5
3
ASR
ASR
3 SP1 1 IX
5
3
LSL
LSL
3 SP1 1 IX
5
3
ROL
ROL
3 SP1 1 IX
5
3
DEC
DEC
3 SP1 1 IX
6
4
DBNZ
DBNZ
4 SP1 2 IX
5
3
INC
INC
3 SP1 1 IX
4
2
TST
TST
3 SP1 1 IX
4
MOV
2 IX+D
4
2
CLR
CLR
3 SP1 1 IX
SP1 Stack Pointer, 8-Bit Offset
SP2 Stack Pointer, 16-Bit Offset
IX+ Indexed, No Offset with
Post Increment
IX1+ Indexed, 1-Byte Offset with
Post Increment
7
3
RTI
BGE
1 INH 2 REL
4
3
RTS
BLT
1 INH 2 REL
3
BGT
2 REL
9
3
SWI
BLE
1 INH 2 REL
2
2
TAP
TXS
1 INH 1 INH
1
2
TPA
TSX
1 INH 1 INH
2
PULA
1 INH
2
1
PSHA
TAX
1 INH 1 INH
2
1
PULX
CLC
1 INH 1 INH
2
1
PSHX
SEC
1 INH 1 INH
2
2
PULH
CLI
1 INH 1 INH
2
2
PSHH
SEI
1 INH 1 INH
1
1
CLRH
RSP
1 INH 1 INH
1
NOP
1 INH
1
STOP
*
1 INH
1
1
WAIT
TXA
1 INH 1 INH
2
SUB
2 IMM
2
CMP
2 IMM
2
SBC
2 IMM
2
CPX
2 IMM
2
AND
2 IMM
2
BIT
2 IMM
2
LDA
2 IMM
2
AIS
2 IMM
2
EOR
2 IMM
2
ADC
2 IMM
2
ORA
2 IMM
2
ADD
2 IMM
3
SUB
2 DIR
3
CMP
2 DIR
3
SBC
2 DIR
3
CPX
2 DIR
3
AND
2 DIR
3
BIT
2 DIR
3
LDA
2 DIR
3
STA
2 DIR
3
EOR
2 DIR
3
ADC
2 DIR
3
ORA
2 DIR
3
ADD
2 DIR
2
JMP
2 DIR
4
4
BSR
JSR
2 REL 2 DIR
2
3
LDX
LDX
2 IMM 2 DIR
2
3
AIX
STX
2 IMM 2 DIR
MSB
0
3
SUB
2 IX1
3
CMP
2 IX1
3
SBC
2 IX1
3
CPX
2 IX1
3
AND
2 IX1
3
BIT
2 IX1
3
LDA
2 IX1
3
STA
2 IX1
3
EOR
2 IX1
3
ADC
2 IX1
3
ORA
2 IX1
3
ADD
2 IX1
3
JMP
2 IX1
5
JSR
2 IX1
5
3
LDX
LDX
4 SP2 2 IX1
5
3
STX
STX
4 SP2 2 IX1
4
SUB
3 SP1
4
CMP
3 SP1
4
SBC
3 SP1
4
CPX
3 SP1
4
AND
3 SP1
4
BIT
3 SP1
4
LDA
3 SP1
4
STA
3 SP1
4
EOR
3 SP1
4
ADC
3 SP1
4
ORA
3 SP1
4
ADD
3 SP1
2
SUB
1 IX
2
CMP
1 IX
2
SBC
1 IX
2
CPX
1 IX
2
AND
1 IX
2
BIT
1 IX
2
LDA
1 IX
2
STA
1 IX
2
EOR
1 IX
2
ADC
1 IX
2
ORA
1 IX
2
ADD
1 IX
2
JMP
1 IX
4
JSR
1 IX
4
2
LDX
LDX
3 SP1 1 IX
4
2
STX
STX
3 SP1 1 IX
High Byte of Opcode in Hexadecimal
LSB
Low Byte of Opcode in Hexadecimal
0
5
Cycles
BRSET0 Opcode Mnemonic
3 DIR Number of Bytes / Addressing Mode
Central Processor Unit (CPU)
74
Table 6-2. Opcode Map
Bit Manipulation
DIR
DIR
Chapter 7
System Integration Module (SIM)
7.1 Introduction
This section describes the system integration module (SIM), which supports up to 32 external and/or
internal interrupts. Together with the central processor unit (CPU), the SIM controls all MCU activities. A
block diagram of the SIM is shown in Figure 7-2. Figure 7-1 is a summary of the SIM input/output (I/O)
registers. The SIM is a system state controller that coordinates CPU and exception timing. The SIM is
responsible for:
• Bus clock generation and control for CPU and peripherals
– Stop/wait/reset/break entry and recovery
– Internal clock control
• Master reset control, including power-on reset (POR) and computer operating properly (COP)
timeout
• Interrupt control:
– Acknowledge timing
– Arbitration control timing
– Vector address generation
• CPU enable/disable timing
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
SIM Break Status Register (SBSR)
R
R
R
R
R
R
BW
R
SIM Reset Status Register (SRSR)
POR
PIN
COP
ILOP
ILAD
0
LVI
0
SIM Break Flag Control Register (SBFCR)
BCFE
R
R
R
R
R
R
R
R
= Reserved
Figure 7-1. SIM I/O Register Summary
Table 7-1. I/O Register Address Summary
Register
SBSR
SRSR
SBFCR
Address
$FE00
$FE01
$FE03
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
75
System Integration Module (SIM)
MODULE STOP
MODULE WAIT
CPU STOP (FROM CPU)
CPU WAIT (FROM CPU)
STOP/WAIT
CONTROL
SIMOSCEN (TO CGM)
SIM
COUNTER
COP CLOCK
CGMXCLK (FROM CGM)
CGMOUT (FROM CGM)
÷2
CLOCK
CONTROL
RESET
PIN LOGIC
CLOCK GENERATORS
INTERNAL CLOCKS
LVI (FROM LVI MODULE)
POR CONTROL
MASTER
RESET
CONTROL
RESET PIN CONTROL
SIM RESET STATUS REGISTER
ILLEGAL OPCODE (FROM CPU)
ILLEGAL ADDRESS (FROM ADDRESS
MAP DECODERS)
COP (FROM COP MODULE)
RESET
INTERRUPT SOURCES
INTERRUPT CONTROL
AND PRIORITY DECODE
CPU INTERFACE
Figure 7-2. SIM Block Diagram
Table 7-2 shows the internal signal names used in this section.
Table 7-2. Signal Name Conventions
Signal Name
Description
CGMXCLK
Buffered Version of OSC1 from Clock Generator Module (CGM)
CGMVCLK
PLL Output
CGMOUT
PLL-Based or OSC1-Based Clock Output from CGM Module (Bus Clock = CGMOUT Divided by Two)
IAB
Internal Address Bus
IDB
Internal Data Bus
PORRST
Signal from the Power-On Reset Module to the SIM
IRST
Internal Reset Signal
R/W
Read/Write Signal
MC68HC908AZ32A Data Sheet, Rev. 2
76
Freescale Semiconductor
SIM Bus Clock Control and Generation
7.2 SIM Bus Clock Control and Generation
The bus clock generator provides system clock signals for the CPU and peripherals on the MCU. The
system clocks are generated from an incoming clock, CGMOUT, as shown in Figure 7-3. This clock can
come from either an external oscillator or from the on-chip PLL. (See Chapter 8 Clock Generator Module
(CGM)).
7.2.1 Bus Timing
In user mode, the internal bus frequency is either the crystal oscillator output (CGMXCLK) divided by four
or the PLL output (CGMVCLK) divided by four. (See Chapter 8 Clock Generator Module (CGM)).
7.2.2 Clock Startup from POR or LVI Reset
When the power-on reset module or the low-voltage inhibit module generates a reset, the clocks to the
CPU and peripherals are inactive and held in an inactive phase until after 4096 CGMXCLK cycles. The
RST pin is driven low by the SIM during this entire period. The bus clocks start upon completion of the
timeout.
CGMXCLK
OSC1
CGMVCLK
PLL
CLOCK
SELECT
CIRCUIT
÷2
A
CGMOUT
B S*
*When S = 1,
CGMOUT = B
SIM COUNTER
÷2
BUS CLOCK
GENERATORS
SIM
BCS
PTC3
MONITOR MODE
USER MODE
CGM
Figure 7-3. CGM Clock Signals
7.2.3 Clocks in Stop Mode and Wait Mode
Upon exit from stop mode by an interrupt, break, or reset, the SIM allows CGMXCLK to clock the SIM
counter. The CPU and peripheral clocks do not become active until after the stop delay timeout. This
timeout is selectable as 4096 or 32 CGMXCLK cycles. See 7.6.2 Stop Mode.
In wait mode, the CPU clocks are inactive. Refer to the wait mode subsection of each module to see if the
module is active or inactive in wait mode. Some modules can be programmed to be active in wait mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
77
System Integration Module (SIM)
7.3 Reset and System Initialization
The MCU has these reset sources:
• Power-on reset module (POR)
• External reset pin (RST)
• Computer operating properly module (COP)
• Low-voltage inhibit module (LVI)
• Illegal opcode
• Illegal address
All of these resets produce the vector $FFFE–FFFF ($FEFE–FEFF in monitor mode) and assert the
internal reset signal (IRST). IRST causes all registers to be returned to their default values and all
modules to be returned to their reset states.
An internal reset clears the SIM counter (see 7.4 SIM Counter), but an external reset does not. Each of
the resets sets a corresponding bit in the SIM reset status register (SRSR) (see 7.7 SIM Registers).
7.3.1 External Pin Reset
Pulling the asynchronous RST pin low halts all processing. The PIN bit of the SIM reset status register
(SRSR) is set as long as RST is held low for a minimum of 67 CGMXCLK cycles, assuming that neither
the POR nor the LVI was the source of the reset. See Table 7-3 for details. Figure 7-4 shows the relative
timing.
Table 7-3. PIN Bit Set Timing
Reset Type
Number of Cycles Required to Set PIN
POR/LVI
4163 (4096 + 64 + 3)
All others
67 (64 + 3)
CGMOUT
RST
IAB
PC
VECT H
VECT L
Figure 7-4. External Reset Timing
MC68HC908AZ32A Data Sheet, Rev. 2
78
Freescale Semiconductor
Reset and System Initialization
7.3.2 Active Resets from Internal Sources
All internal reset sources actively pull the RST pin low for 32 CGMXCLK cycles to allow resetting of
external peripherals. The internal reset signal IRST continues to be asserted for an additional 32 cycles
(see Figure 7-5). An internal reset can be caused by an illegal address, illegal opcode, COP timeout, LVI,
or POR (see Figure 7-6). Note that for LVI or POR resets, the SIM cycles through 4096 CGMXCLK cycles
during which the SIM forces the RST pin low. The internal reset signal then follows the sequence from the
falling edge of RST shown in Figure 7-5.
The COP reset is asynchronous to the bus clock.
The active reset feature allows the part to issue a reset to peripherals and other chips within a system
built around the MCU.
IRST
RST
RST PULLED LOW BY MCU
32 CYCLES
32 CYCLES
CGMXCLK
IAB
VECTOR HIGH
Figure 7-5. Internal Reset Timing
ILLEGAL ADDRESS RST
ILLEGAL OPCODE RST
COPRST
LVI
POR
INTERNAL RESET
Figure 7-6. Sources of Internal Reset
7.3.2.1 Power-On Reset
When power is first applied to the MCU, the power-on reset module (POR) generates a pulse to indicate
that power-on has occurred. The external reset pin (RST) is held low while the SIM counter counts out
4096 CGMXCLK cycles. Another sixty-four CGMXCLK cycles later, the CPU and memories are released
from reset to allow the reset vector sequence to occur. See Figure 7-7.
At power-on, the following events occur:
• A POR pulse is generated.
• The internal reset signal is asserted.
• The SIM enables CGMOUT.
• Internal clocks to the CPU and modules are held inactive for 4096 CGMXCLK cycles to allow
stabilization of the oscillator.
• The RST pin is driven low during the oscillator stabilization time.
• The POR bit of the SIM reset status register (SRSR) is set and all other bits in the register are
cleared.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
79
System Integration Module (SIM)
OSC1
PORRST
4096
CYCLES
32
CYCLES
32
CYCLES
CGMXCLK
CGMOUT
RST
IAB
$FFFE
$FFFF
Figure 7-7. POR Recovery
7.3.2.2 Computer Operating Properly (COP) Reset
The overflow of the COP counter causes an internal reset and sets the COP bit in the SIM reset status
register (SRSR) if the COPD bit in the CONFIG-1 register is at logic zero. See Chapter 13 Computer
Operating Properly (COP.
7.3.2.3 Illegal Opcode Reset
The SIM decodes signals from the CPU to detect illegal instructions. An illegal instruction sets the ILOP
bit in the SIM reset status register (SRSR) and causes a reset.
If the stop enable bit, STOP, in the CONFIG-1 register is logic zero, the SIM treats the STOP instruction
as an illegal opcode and causes an illegal opcode reset.
7.3.2.4 Illegal Address Reset
An opcode fetch from an unmapped address generates an illegal address reset. The SIM verifies that the
CPU is fetching an opcode prior to asserting the ILAD bit in the SIM reset status register SRSR) and
resetting the MCU. A data fetch from an unmapped address does not generate a reset. The SIM actively
pulls down the RST pin for all internal reset sources.
NOTE
Extra care should be exercised if code in this part has been migrated from
older HC08 devices since the illegal address reset specification may be
different. Also, extra care should be exercised when using this emulation
part for development of code to be run in ROM AZ, AB or AS family parts
with a smaller memory size since some legal addresses will become illegal
addresses on the smaller ROM memory map device and may as a result
generate unwanted resets.
MC68HC908AZ32A Data Sheet, Rev. 2
80
Freescale Semiconductor
SIM Counter
7.3.2.5 Low-Voltage Inhibit (LVI) Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when the VDD voltage falls to the VLVII
voltage. The LVI bit in the SIM reset status register (SRSR) is set and a chip reset is asserted if the
LVIPWRD and LVIRSTD bits in the CONFIG-1 register are at logic zero. The RST pin will be held low until
the SIM counts 4096 CGMXCLK cycles after VDD rises above VLVIR. Another sixty-four CGMXCLK cycles
later, the CPU is released from reset to allow the reset vector sequence to occur. See Chapter 14 Low
Voltage Inhibit (LVI).
7.4 SIM Counter
The SIM counter is used by the power-on reset module (POR) and in stop mode recovery to allow the
oscillator time to stabilize before enabling the internal bus (IBUS) clocks. The SIM counter also serves as
a prescaler for the computer operating properly module (COP). The SIM counter overflow supplies the
clock for the COP module. The SIM counter is 12 bits long and is clocked by the falling edge of
CGMXCLK.
7.4.1 SIM Counter During Power-On Reset
The power-on reset module (POR) detects power applied to the MCU. At power-on, the POR circuit
asserts the signal PORRST. Once the SIM is initialized, it enables the clock generation module (CGM) to
drive the bus clock state machine.
7.4.2 SIM Counter During Stop Mode Recovery
The SIM counter also is used for stop mode recovery. The STOP instruction clears the SIM counter. After
an interrupt or reset, the SIM senses the state of the short stop recovery bit, SSREC, in the CONFIG-1
register. If the SSREC bit is a logic one, then the stop recovery is reduced from the normal delay of 4096
CGMXCLK cycles down to 32 CGMXCLK cycles. This is ideal for applications using canned oscillators
that do not require long start-up times from stop mode. External crystal applications should use the full
stop recovery time, that is, with SSREC cleared.
7.4.3 SIM Counter and Reset States
External reset has no effect on the SIM counter. See 7.6.2 Stop Mode for details. The SIM counter is
free-running after all reset states. See 7.3.2 Active Resets from Internal Sources for counter control and
internal reset recovery sequences.
7.5 Program Exception Control
Normal, sequential program execution can be changed in three different ways:
• Interrupts
– Maskable hardware CPU interrupts
– Non-maskable software interrupt instruction (SWI)
• Reset
• Break interrupts
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
81
System Integration Module (SIM)
7.5.1 Interrupts
At the beginning of an interrupt, the CPU saves the CPU register contents on the stack and sets the
interrupt mask (I bit) to prevent additional interrupts. At the end of an interrupt, the RTI instruction recovers
the CPU register contents from the stack so that normal processing can resume. Figure 7-8 shows
interrupt entry timing. Figure 7-9 shows interrupt recovery timing.
Interrupts are latched, and arbitration is performed in the SIM at the start of interrupt processing. The
arbitration result is a constant that the CPU uses to determine which vector to fetch. Once an interrupt is
latched by the SIM, no other interrupt can take precedence, regardless of priority, until the latched
interrupt is serviced (or the I bit is cleared), see Figure 7-10.
MODULE
INTERRUPT
I BIT
IAB
IDB
SP
DUMMY
DUMMY
SP – 1
PC – 1[7:0]
SP – 2
SP – 3
PC–1[15:8]
X
SP – 4
A
VECT H
CCR
VECT L
V DATA H
START ADDR
V DATA L
OPCODE
R/W
Figure 7-8. Interrupt Entry
MODULE
INTERRUPT
I BIT
IAB
IDB
SP – 4
SP – 3
CCR
SP – 2
A
SP – 1
X
PC – 1 [7:0]
SP
PC
PC–1[15:8]
PC + 1
OPCODE
OPERAND
R/W
Figure 7-9. Interrupt Recovery
MC68HC908AZ32A Data Sheet, Rev. 2
82
Freescale Semiconductor
Program Exception Control
FROM RESET
YES
BREAK
INTERRUPT?
I BIT
SET?
NO
YES
I BIT SET?
NO
IRQ1
INTERRUPT?
YES
NO
STACK CPU REGISTERS.
SET I BIT.
LOAD PC WITH INTERRUPT VECTOR.
(AS MANY INTERRUPTS
AS EXIST ON CHIP)
FETCH NEXT
INSTRUCTION.
SWI
INSTRUCTION?
YES
NO
RTI
INSTRUCTION?
YES
UNSTACK CPU REGISTERS.
NO
EXECUTE INSTRUCTION.
Figure 7-10. Interrupt Processing
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
83
System Integration Module (SIM)
7.5.1.1 Hardware Interrupts
A hardware interrupt does not stop the current instruction. Processing of a hardware interrupt begins after
completion of the current instruction. When the current instruction is complete, the SIM checks all pending
hardware interrupts. If interrupts are not masked (I bit clear in the condition code register), and if the
corresponding interrupt enable bit is set, the SIM proceeds with interrupt processing; otherwise, the next
instruction is fetched and executed.
If more than one interrupt is pending at the end of an instruction execution, the highest priority interrupt is
serviced first. Figure 7-11 demonstrates what happens when two interrupts are pending. If an interrupt is
pending upon exit from the original interrupt service routine, the pending interrupt is serviced before the
LDA instruction is executed.
The LDA opcode is prefetched by both the INT1 and INT2 RTI instructions. However, in the case of the
INT1 RTI prefetch, this is a redundant operation.
NOTE
To maintain compatibility with the M68HC05, M6805 and M146805
Families the H register is not pushed on the stack during interrupt entry. If
the interrupt service routine modifies the H register or uses the indexed
addressing mode, software should save the H register and then restore it
prior to exiting the routine.
CLI
BACKGROUND
ROUTINE
LDA #$FF
INT1
PSHH
INT1 INTERRUPT SERVICE ROUTINE
PULH
RTI
INT2
PSHH
INT2 INTERRUPT SERVICE ROUTINE
PULH
RTI
Figure 7-11. Interrupt Recognition Example
7.5.1.2 SWI Instruction
The SWI instruction is a non-maskable instruction that causes an interrupt regardless of the state of the
interrupt mask (I bit) in the condition code register.
NOTE
A software interrupt pushes PC onto the stack. A software interrupt does
not push PC – 1, as a hardware interrupt does.
MC68HC908AZ32A Data Sheet, Rev. 2
84
Freescale Semiconductor
Low-Power Modes
7.5.2 Reset
All reset sources always have higher priority than interrupts and cannot be arbitrated.
7.5.3 Break Interrupts
The break module can stop normal program flow at a software-programmable break point by asserting its
break interrupt output. See Chapter 11 Brake Module. The SIM puts the CPU into the break state by
forcing it to the SWI vector location. Refer to the break interrupt subsection of each module to see how
each module is affected by the break state.
7.5.4 Status Flag Protection in Break Mode
The SIM controls whether status flags contained in other modules can be cleared during break mode. The
user can select whether flags are protected from being cleared by properly initializing the break clear flag
enable bit (BCFE) in the SIM break flag control register (SBFCR).
Protecting flags in break mode ensures that set flags will not be cleared while in break mode. This
protection allows registers to be freely read and written during break mode without losing status flag
information.
Setting the BCFE bit enables the clearing mechanisms. Once cleared in break mode, a flag remains
cleared even when break mode is exited. Status flags with a two-step clearing mechanism — for example,
a read of one register followed by the read or write of another — are protected, even when the first step
is accomplished prior to entering break mode. Upon leaving break mode, execution of the second step
will clear the flag as normal.
7.6 Low-Power Modes
Executing the WAIT or STOP instruction puts the MCU in a low power- consumption mode for standby
situations. The SIM holds the CPU in a non-clocked state. The operation of each of these modes is
described below. Both STOP and WAIT clear the interrupt mask (I) in the condition code register, allowing
interrupts to occur.
7.6.1 Wait Mode
In wait mode, the CPU clocks are inactive while one set of peripheral clocks continue to run. Figure 7-12
shows the timing for wait mode entry.
A module that is active during wait mode can wake up the CPU with an interrupt if the interrupt is enabled.
Stacking for the interrupt begins one cycle after the WAIT instruction during which the interrupt occurred.
Refer to the wait mode subsection of each module to see if the module is active or inactive in wait mode.
Some modules can be programmed to be active in wait mode.
Wait mode can also be exited by a reset or break. A break interrupt during wait mode sets the SIM break
wait bit, BW, in the SIM break status register (SBSR). If the COP disable bit, COPD, in the configuration
register is logic 0, then the computer operating properly module (COP) is enabled and remains active in
wait mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
85
System Integration Module (SIM)
IAB
WAIT ADDR + 1
WAIT ADDR
IDB
PREVIOUS DATA
SAME
SAME
NEXT OPCODE
SAME
SAME
R/W
NOTE: Previous data can be operand data or the WAIT opcode, depending on the last instruction.
Figure 7-12. Wait Mode Entry Timing
IAB
$6E0B
IDB
$A6
$A6
$6E0C
$A6
$01
$00FF
$00FE
$0B
$00FD
$00FC
$6E
EXITSTOPWAIT
NOTE: EXITSTOPWAIT = RST pin OR CPU interrupt OR break interrupt
Figure 7-13. Wait Recovery from Interrupt or Break
32
Cycles
$6E0B
IAB
IDB
$A6
$A6
32
Cycles
RSTVCTH
RST VCTL
$A6
RST
CGMXCLK
Figure 7-14. Wait Recovery from Internal Reset
7.6.2 Stop Mode
In stop mode, the SIM counter is reset and the system clocks are disabled. An interrupt request from a
module can cause an exit from stop mode. Stacking for interrupts begins after the selected stop recovery
time has elapsed. Reset also causes an exit from stop mode.
The SIM disables the clock generator module outputs (CGMOUT and CGMXCLK) in stop mode, stopping
the CPU and peripherals. Stop recovery time is selectable using the SSREC bit in the configuration
register (CONFIG-1). If SSREC is set, stop recovery is reduced from the normal delay of 4096 CGMXCLK
cycles down to 32. This is ideal for applications using canned oscillators that do not require long startup
times from stop mode.
NOTE
External crystal applications should use the full stop recovery time by
clearing the SSREC bit.
The break module is inactive in Stop mode. The STOP instruction does not affect break module register
states.
MC68HC908AZ32A Data Sheet, Rev. 2
86
Freescale Semiconductor
SIM Registers
The SIM counter is held in reset from the execution of the STOP instruction until the beginning of stop
recovery. It is then used to time the recovery period. Figure 7-15 shows stop mode entry timing.
CPUSTOP
IAB
STOP ADDR
IDB
STOP ADDR + 1
PREVIOUS DATA
SAME
NEXT OPCODE
SAME
SAME
SAME
R/W
NOTE: Previous data can be operand data or the STOP opcode, depending on the last
instruction.
Figure 7-15. Stop Mode Entry Timing
STOP RECOVERY PERIOD
CGMXCLK
INT/BREAK
IAB
STOP + 2
STOP +1
STOP + 2
SP
SP – 1
SP – 2
SP – 3
Figure 7-16. Stop Mode Recovery from Interrupt or Break
7.7 SIM Registers
The SIM has three memory mapped registers.
7.7.1 SIM Break Status Register
The SIM break status register contains a flag to indicate that a break caused an exit from wait mode.
Address:
Read:
Write:
$FE00
Bit 7
6
5
4
3
2
R
R
R
R
R
R
R
= Reserved
1
BW
See Note
Reset:
Bit 0
R
0
NOTE: Writing a 0 clears BW
Figure 7-17. SIM Break Status Register (SBSR)
BW — SIM Break Wait
This status bit is useful in applications requiring a return to wait mode after exiting from a break
interrupt. Clear BW by writing a 0 to it. Reset clears BW.
1 = Wait mode was exited by break interrupt
0 = Wait mode was not exited by break interrupt
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
87
System Integration Module (SIM)
7.7.2 SIM Reset Status Register
This register contains six flags that show the source of the last reset. The status register will automatically
clear after reading it. A power-on reset sets the POR bit and clears all other bits in the register.
Address:
Read:
$FE01
Bit 7
6
5
4
3
2
1
Bit 0
POR
PIN
COP
ILOP
ILAD
0
LVI
0
1
0
0
0
0
0
0
0
Write:
POR:
= Unimplemented
Figure 7-18. SIM Reset Status Register (SRSR)
POR — Power-On Reset Bit
1 = Last reset caused by POR circuit
0 = Read of SRSR
PIN — External Reset Bit
1 = Last reset caused by external reset pin (RST)
0 = POR or read of SRSR
COP — Computer Operating Properly Reset Bit
1 = Last reset caused by COP counter
0 = POR or read of SRSR
ILOP — Illegal Opcode Reset Bit
1 = Last reset caused by an illegal opcode
0 = POR or read of SRSR
ILAD — Illegal Address Reset Bit (opcode fetches only)
1 = Last reset caused by an opcode fetch from an illegal address
0 = POR or read of SRSR
LVI — Low-Voltage Inhibit Reset Bit
1 = Last reset was caused by the LVI circuit
0 = POR or read of SRSR
MC68HC908AZ32A Data Sheet, Rev. 2
88
Freescale Semiconductor
SIM Registers
7.7.3 SIM Break Flag Control Register
The SIM break control register contains a bit that enables software to clear status bits while the MCU is
in a break state.
Address:
Read:
Write:
Reset:
$FE03
Bit 7
6
5
4
3
2
1
Bit 0
BCFE
R
R
R
R
R
R
R
0
R
0
= Reserved
Figure 7-19. SIM Break Flag Control Register (SBFCR)
BCFE — Break Clear Flag Enable Bit
This read/write bit enables software to clear status bits by accessing status registers while the MCU is
in a break state. To clear status bits during the break state, the BCFE bit must be set.
1 = Status bits clearable during break
0 = Status bits not clearable during break
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
89
System Integration Module (SIM)
MC68HC908AZ32A Data Sheet, Rev. 2
90
Freescale Semiconductor
Chapter 8
Clock Generator Module (CGM)
8.1 Introduction
The CGM generates the crystal clock signal, CGMXCLK, which operates at the frequency of the crystal.
The CGM also generates the base clock signal, CGMOUT, from which the system clocks are derived.
CGMOUT is based on either the crystal clock divided by two or the phase-locked loop (PLL) clock,
CGMVCLK, divided by two. The PLL is a frequency generator designed for use with 1-MHz to 16-MHz
crystals or ceramic resonators. The PLL can generate an 8-MHz bus frequency without using high
frequency crystals.
8.2 Features
Features of the CGM include:
• Phase-Locked Loop with Output Frequency in Integer Multiples of the Crystal Reference
• Programmable Hardware Voltage-Controlled Oscillator (VCO) for Low-Jitter Operation
• Automatic Bandwidth Control Mode for Low-Jitter Operation
• Automatic Frequency Lock Detector
• CPU Interrupt on Entry or Exit from Locked Condition
8.3 Functional Description
The CGM consists of three major submodules:
• Crystal oscillator circuit — The crystal oscillator circuit generates the constant crystal frequency
clock, CGMXCLK.
• Phase-locked loop (PLL) — The PLL generates the programmable VCO frequency clock
CGMVCLK.
• Base clock selector circuit — This software-controlled circuit selects either CGMXCLK divided by
two or the VCO clock, CGMVCLK, divided by two as the base clock, CGMOUT. The system clocks
are derived from CGMOUT.
Figure 8-1 shows the structure of the CGM.
8.3.1 Crystal Oscillator Circuit
The crystal oscillator circuit consists of an inverting amplifier and an external crystal. The OSC1 pin is the
input to the amplifier and the OSC2 pin is the output. The SIMOSCEN signal enables the crystal oscillator
circuit.
The CGMXCLK signal is the output of the crystal oscillator circuit and runs at a rate equal to the crystal
frequency. CGMXCLK is then buffered to produce CGMRCLK, the PLL reference clock.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
91
Clock Generator Module (CGM)
CGMXCLK can be used by other modules which require precise timing for operation. The duty cycle of
CGMXCLK is not guaranteed to be 50% and depends on external factors, including the crystal and related
external components.
An externally generated clock also can feed the OSC1 pin of the crystal oscillator circuit. Connect the
external clock to the OSC1 pin and let the OSC2 pin float.
CGMXCLK
OSC1
CLOCK
SELECT
CIRCUIT
CGMRDV
÷2
CGMRCLK
A
CGMOUT
B S*
*When S = 1,
CGMOUT = B
BCS
PTC3
VDDA
CGMXFC
VSS
MONITOR MODE
VRS7–VRS4
USER MODE
PHASE
DETECTOR
VOLTAGE
CONTROLLED
OSCILLATOR
LOOP
FILTER
PLL ANALOG
LOCK
DETECTOR
LOCK
BANDWIDTH
CONTROL
AUTO
ACQ
INTERRUPT
CONTROL
PLLIE
CGMINT
PLLF
MUL7–MUL4
CGMVDV
FREQUENCY
DIVIDER
CGMVCLK
Figure 8-1. CGM Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
92
Freescale Semiconductor
Functional Description
Register Name
Bit 7
Read:
PLL Control Register
(PCTL)
Write:
Reset:
Read:
PLL Bandwidth Control Register
(PBWC)
Write:
Reset:
Read:
PLL Programming Register
(PPG)
Write:
Reset:
6
PLLF
PLLIE
0
5
PLLON
BCS
1
0
ACQ
XLD
0
AUTO
LOCK
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
MUL7
MUL6
MUL5
MUL4
VRS7
VRS6
VRS5
VRS4
0
1
1
0
0
1
1
0
= Unimplemented
Figure 8-2. I/O Register Summary
Table 8-1. I/O Register Address Summary
Register
PCTL
PBWC
PPG
Address
$001C
$001D
$001E
8.3.2 Phase-Locked Loop Circuit (PLL)
The PLL is a frequency generator that can operate in either acquisition mode or tracking mode, depending
on the accuracy of the output frequency. The PLL can change between acquisition and tracking modes
either automatically or manually.
8.3.2.1 Circuits
The PLL consists of these circuits:
• Voltage-controlled oscillator (VCO)
• Modulo VCO frequency divider
• Phase detector
• Loop filter
• Lock detector
The operating range of the VCO is programmable for a wide range of frequencies and for maximum
immunity to external noise, including supply and CGMXFC noise. The VCO frequency is bound to a range
from roughly one-half to twice the center-of-range frequency, fCGMVRS. Modulating the voltage on the
CGMXFC pin changes the frequency within this range. By design, fCGMVRS is equal to the nominal
center-of-range frequency, fNOM, (4.9152 MHz) times a linear factor L or (L)fNOM.
CGMRCLK is the PLL reference clock, a buffered version of CGMXCLK. CGMRCLK runs at a frequency,
fCGMRCLK, and is fed to the PLL through a buffer. The buffer output is the final reference clock, CGMRDV,
running at a frequency fCGMRDV = fCGMRCLK.
The VCO’s output clock, CGMVCLK, running at a frequency fCGMVCLK, is fed back through a
programmable modulo divider. The modulo divider reduces the VCO clock by a factor, N. The divider’s
output is the VCO feedback clock, CGMVDV, running at a frequency fCGMVDV = fCGMVCLK/N. See 8.3.2.4
Programming the PLL for more information.
The phase detector then compares the VCO feedback clock, CGMVDV, with the final reference clock,
CGMRDV. A correction pulse is generated based on the phase difference between the two signals. The
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
93
Clock Generator Module (CGM)
loop filter then slightly alters the dc voltage on the external capacitor connected to CGMXFC based on
the width and direction of the correction pulse. The filter can make fast or slow corrections depending on
its mode, as described in 8.3.2.2 Acquisition and Tracking Modes. The value of the external capacitor and
the reference frequency determines the speed of the corrections and the stability of the PLL.
The lock detector compares the frequencies of the VCO feedback clock, CGMVDV, and the final
reference clock, CGMRDV. Therefore, the speed of the lock detector is directly proportional to the final
reference frequency, fCGMRDV. The circuit determines the mode of the PLL and the lock condition based
on this comparison.
8.3.2.2 Acquisition and Tracking Modes
The PLL filter is manually or automatically configurable into one of two operating modes:
• Acquisition mode — In acquisition mode, the filter can make large frequency corrections to the
VCO. This mode is used at PLL startup or when the PLL has suffered a severe noise hit and the
VCO frequency is far off the desired frequency. When in acquisition mode, the ACQ bit is clear in
the PLL bandwidth control register. See 8.5.2 PLL Bandwidth Control Register.
• Tracking mode — In tracking mode, the filter makes only small corrections to the frequency of the
VCO. PLL jitter is much lower in tracking mode, but the response to noise is also slower. The PLL
enters tracking mode when the VCO frequency is nearly correct, such as when the PLL is selected
as the base clock source. See 8.3.3 Base Clock Selector Circuit. The PLL is automatically in
tracking mode when it’s not in acquisition mode or when the ACQ bit is set.
8.3.2.3 Manual and Automatic PLL Bandwidth Modes
The PLL can change the bandwidth or operational mode of the loop filter manually or automatically.
In automatic bandwidth control mode (AUTO = 1), the lock detector automatically switches between
acquisition and tracking modes. Automatic bandwidth control mode also is used to determine when the
VCO clock, CGMVCLK, is safe to use as the source for the base clock, CGMOUT. See 8.5.2 PLL
Bandwidth Control Register. If PLL CPU interrupt requests are enabled, the software can wait for a PLL
CPU interrupt request and then check the LOCK bit. If CPU interrupts are disabled, software can poll the
LOCK bit continuously (during PLL startup, usually) or at periodic intervals. In either case, when the LOCK
bit is set, the VCO clock is safe to use as the source for the base clock. See 8.3.3 Base Clock Selector
Circuit. If the VCO is selected as the source for the base clock and the LOCK bit is clear, the PLL has
suffered a severe noise hit and the software must take appropriate action, depending on the application.
See 8.6 Interrupts.
These conditions apply when the PLL is in automatic bandwidth control mode:
• The ACQ bit (see 8.5.2 PLL Bandwidth Control Register) is a read-only indicator of the mode of the
filter. See 8.3.2.2 Acquisition and Tracking Modes.
• The ACQ bit is set when the VCO frequency is within a certain tolerance, Δtrk, and is cleared when
the VCO frequency is out of a certain tolerance, Δunt. See Chapter 25 Electrical Specifications.
• The LOCK bit is a read-only indicator of the locked state of the PLL.
• The LOCK bit is set when the VCO frequency is within a certain tolerance, ΔLock, and is cleared
when the VCO frequency is out of a certain tolerance, Δunl. See Chapter 25 Electrical
Specifications.
• CPU interrupts can occur if enabled (PLLIE = 1) when the PLL’s lock condition changes, toggling
the LOCK bit. See 8.5.1 PLL Control Register.
MC68HC908AZ32A Data Sheet, Rev. 2
94
Freescale Semiconductor
Functional Description
The PLL also can operate in manual mode (AUTO = 0). Manual mode is used by systems that do not
require an indicator of the lock condition for proper operation. Such systems typically operate well below
fbusmax and require fast startup. The following conditions apply when in manual mode:
• ACQ is a writable control bit that controls the mode of the filter. Before turning on the PLL in manual
mode, the ACQ bit must be clear.
• Before entering tracking mode (ACQ = 1), software must wait a given time, tacq (see Chapter 25
Electrical Specifications), after turning on the PLL by setting PLLON in the PLL control register
(PCTL).
• Software must wait a given time, tal, after entering tracking mode before selecting the PLL as the
clock source to CGMOUT (BCS = 1).
• The LOCK bit is disabled.
• CPU interrupts from the CGM are disabled.
8.3.2.4 Programming the PLL
Use this 9-step procedure to program the PLL. The table below lists the variables used and their meaning
(Please also reference Figure 8-1).
Table 8-2. Variable Definitions
Variable
Definition
fBUSDES
Desired Bus Clock Frequency
fVCLKDES
Desired VCO Clock Frequency
fCGMRCLK
Chosen Reference Crystal Frequency
fCGMVCLK
Calculated VCO Clock Frequency
fBUS
Calculated Bus Clock Frequency
fNOM
Nominal VCO Center Frequency
fCGMVRS
Shifted VCO Center Frequency
1. Choose the desired bus frequency, fBUSDES.
Example: fBUSDES = 8 MHz
2. Calculate the desired VCO frequency, fVCLKDES.
fVCLKDES = 4 × fBUSDES
Example: fVCLKDES = 4 × 8 MHz = 32 MHz
3. Using a reference frequency, fRCLK, equal to the crystal frequency, calculate the VCO frequency
multiplier, N. Round the result to the nearest integer.
f VCLKDES
N = ------------------------fCGMRCLK
32 MHz
4 MHz
Example: N = -------------------- = 8
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
95
Clock Generator Module (CGM)
4. Calculate the VCO frequency, fCGMVCLK.
f CGMVCLK = N × f CGMRCLK
Example: fCGMVCLK = 8 × 4 MHz = 32 MHz
5. Calculate the bus frequency, fBUS, and compare fBUS with fBUSDES.
f CGMVCLK
f BUS = -----------------------4
32 MHz
4
Example: f BUS = -------------------- = 8 MHz
6. If the calculated fbus is not within the tolerance limits of your application, select another fBUSDES or
another fRCLK.
7. Using the value 4.9152 MHz for fNOM, calculate the VCO linear range multiplier, L. The linear range
multiplier controls the frequency range of the PLL.
f CGMVCLK
L = round ⎛ ------------------------⎞
⎝ f NOM ⎠
32 MHz
4.9152 MHz
Example: L = -------------------------------- = 7
8. Calculate the VCO center-of-range frequency, fCGMVRS. The center-of-range frequency is the
midpoint between the minimum and maximum frequencies attainable by the PLL.
fCGMVRS = L × fNOM
Example: fCGMVRS = 7 × 4.9152 MHz = 34.4 MHz
NOTE
f NOM
For proper operation, f CGMVRS – f CGMVCLK ≤ ---------------.
2
Exceeding the recommended maximum bus frequency or VCO frequency
can crash the MCU.
9. Program the PLL registers accordingly:
a. In the upper four bits of the PLL programming register (PPG), program the binary equivalent
of N.
b. In the lower four bits of the PLL programming register (PPG), program the binary equivalent
of L.
8.3.2.5 Special Programming Exceptions
The programming method described in 8.3.2.4 Programming the PLL, does not account for two possible
exceptions. A value of 0 for N or L is meaningless when used in the equations given. To account for these
exceptions:
• A 0 value for N is interpreted the same as a value of 1.
• A 0 value for L disables the PLL and prevents its selection as the source for the base clock. See
8.3.3 Base Clock Selector Circuit.
MC68HC908AZ32A Data Sheet, Rev. 2
96
Freescale Semiconductor
Functional Description
8.3.3 Base Clock Selector Circuit
This circuit is used to select either the crystal clock, CGMXCLK, or the VCO clock, CGMVCLK, as the
source of the base clock, CGMOUT. The two input clocks go through a transition control circuit that waits
up to three CGMXCLK cycles and three CGMVCLK cycles to change from one clock source to the other.
During this time, CGMOUT is held in stasis. The output of the transition control circuit is then divided by
two to correct the duty cycle. Therefore, the bus clock frequency, which is one-half of the base clock
frequency, is one-fourth the frequency of the selected clock (CGMXCLK or CGMVCLK).
The BCS bit in the PLL control register (PCTL) selects which clock drives CGMOUT. The VCO clock
cannot be selected as the base clock source if the PLL is not turned on. The PLL cannot be turned off if
the VCO clock is selected. The PLL cannot be turned on or off simultaneously with the selection or
deselection of the VCO clock. The VCO clock also cannot be selected as the base clock source if the
factor L is programmed to a 0. This value would set up a condition inconsistent with the operation of the
PLL, so that the PLL would be disabled and the crystal clock would be forced as the source of the base
clock.
8.3.4 CGM External Connections
In its typical configuration, the CGM requires seven external components. Five of these are for the crystal
oscillator and two are for the PLL.
The crystal oscillator is normally connected in a Pierce oscillator configuration, as shown in Figure 8-3.
Figure 8-3 shows only the logical representation of the internal components and may not represent actual
circuitry. The oscillator configuration uses five components:
• Crystal, X1
• Fixed capacitor, C1
• Tuning capacitor, C2 (can also be a fixed capacitor)
• Feedback resistor, RB
• Series resistor, RS (optional)
SIMOSCEN
VDDA
CGMXFC
VSS
OSC2
OSC1
CGMXCLK
RS*
VDD
CF
RB
CBYP
X1
C1
C2
*RS can be 0 (shorted) when used with higher-frequency crystals. Refer to manufacturer’s data.
Figure 8-3. CGM External Connections
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
97
Clock Generator Module (CGM)
The series resistor (RS) may not be required for all ranges of operation, especially with high-frequency
crystals. Refer to the crystal manufacturer’s data for more information.
Figure 8-3 also shows the external components for the PLL:
• Bypass capacitor, CBYP
• Filter capacitor, CF
Routing should be done with great care to minimize signal cross talk and noise. (See 8.9 Acquisition/Lock
Time Specifications for routing information and more information on the filter capacitor’s value and its
effects on PLL performance).
8.4 I/O Signals
The following paragraphs describe the CGM input/output (I/O) signals.
8.4.1 Crystal Amplifier Input Pin (OSC1)
The OSC1 pin is an input to the crystal oscillator amplifier.
8.4.2 Crystal Amplifier Output Pin (OSC2)
The OSC2 pin is the output of the crystal oscillator inverting amplifier.
8.4.3 External Filter Capacitor Pin (CGMXFC)
The CGMXFC pin is required by the loop filter to filter out phase corrections. A small external capacitor is
connected to this pin.
NOTE
To prevent noise problems, CF should be placed as close to the CGMXFC
pin as possible with minimum routing distances and no routing of other
signals across the CF connection.
8.4.4 Analog Power Pin (VDDA)
VDDA is a power pin used by the analog portions of the PLL. Connect the VDDA pin to the same voltage
potential as the VDD pin.
NOTE
Route VDDA carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
8.4.5 Oscillator Enable Signal (SIMOSCEN)
The SIMOSCEN signal enables the oscillator and PLL.
8.4.6 Crystal Output Frequency Signal (CGMXCLK)
CGMXCLK is the crystal oscillator output signal. It runs at the full speed of the crystal (fCGMXCLK) and
comes directly from the crystal oscillator circuit. Figure 8-3 shows only the logical relation of CGMXCLK
to OSC1 and OSC2 and may not represent the actual circuitry. The duty cycle of CGMXCLK is unknown
and may depend on the crystal and other external factors. Also, the frequency and amplitude of
CGMXCLK can be unstable at startup.
MC68HC908AZ32A Data Sheet, Rev. 2
98
Freescale Semiconductor
CGM Registers
8.4.7 CGM Base Clock Output (CGMOUT)
CGMOUT is the clock output of the CGM. This signal is used to generate the MCU clocks. CGMOUT is
a 50% duty cycle clock running at twice the bus frequency. CGMOUT is software programmable to be
either the oscillator output, CGMXCLK, divided by two or the VCO clock, CGMVCLK, divided by two.
8.4.8 CGM CPU Interrupt (CGMINT)
CGMINT is the CPU interrupt signal generated by the PLL lock detector.
8.5 CGM Registers
Three registers control and monitor operation of the CGM:
• PLL control register (PCTL)
• PLL bandwidth control register (PBWC)
• PLL programming register (PPG)
8.5.1 PLL Control Register
The PLL control register contains the interrupt enable and flag bits, the on/off switch, and the base clock
selector bit.
Address:
$001C
Bit 7
Read:
Write:
Reset:
PLLIE
0
6
5
PLLF
0
4
PLLON
BCS
1
0
3
2
1
Bit 0
1
1
1
1
1
1
1
1
= Unimplemented
Figure 8-4. PLL Control Register (PCTL)
PLLIE — PLL Interrupt Enable Bit
This read/write bit enables the PLL to generate a CPU interrupt request when the LOCK bit toggles,
setting the PLL flag, PLLF. When the AUTO bit in the PLL bandwidth control register (PBWC) is clear,
PLLIE cannot be written and reads as logic 0. Reset clears the PLLIE bit.
1 = PLL CPU interrupt requests enabled
0 = PLL CPU interrupt requests disabled
PLLF — PLL Flag Bit
This read-only bit is set whenever the LOCK bit toggles. PLLF generates a CPU interrupt request if the
PLLIE bit also is set. PLLF always reads as logic 0 when the AUTO bit in the PLL bandwidth control
register (PBWC) is clear. Clear the PLLF bit by reading the PLL control register. Reset clears the PLLF
bit.
1 = Change in lock condition
0 = No change in lock condition
NOTE
Do not inadvertently clear the PLLF bit. Be aware that any read or
read-modify-write operation on the PLL control register clears the PLLF bit.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
99
Clock Generator Module (CGM)
PLLON — PLL On Bit
This read/write bit activates the PLL and enables the VCO clock, CGMVCLK. PLLON cannot be
cleared if the VCO clock is driving the base clock, CGMOUT (BCS = 1). See 8.3.3 Base Clock Selector
Circuit. Reset sets this bit so that the loop can stabilize as the MCU is powering up.
1 = PLL on
0 = PLL off
BCS — Base Clock Select Bit
This read/write bit selects either the crystal oscillator output, CGMXCLK, or the VCO clock,
CGMVCLK, as the source of the CGM output, CGMOUT. CGMOUT frequency is one-half the
frequency of the selected clock. BCS cannot be set while the PLLON bit is clear. After toggling BCS,
it may take up to three CGMXCLK and three CGMVCLK cycles to complete the transition from one
source clock to the other. During the transition, CGMOUT is held in stasis. See 8.3.3 Base Clock
Selector Circuit. Reset and the STOP instruction clear the BCS bit.
1 = CGMVCLK divided by two drives CGMOUT
0 = CGMXCLK divided by two drives CGMOUT
NOTE
PLLON and BCS have built-in protection that prevents the base clock
selector circuit from selecting the VCO clock as the source of the base clock
if the PLL is off. Therefore, PLLON cannot be cleared when BCS is set, and
BCS cannot be set when PLLON is clear. If the PLL is off (PLLON = 0),
selecting CGMVCLK requires two writes to the PLL control register. See
8.3.3 Base Clock Selector Circuit.
PCTL3–PCTL0 — Unimplemented
These bits provide no function and always read as logic 1s.
8.5.2 PLL Bandwidth Control Register
The PLL bandwidth control register:
• Selects automatic or manual (software-controlled) bandwidth control mode
• Indicates when the PLL is locked
• In automatic bandwidth control mode, indicates when the PLL is in acquisition or tracking mode
• In manual operation, forces the PLL into acquisition or tracking mode
Address:
$001D
Bit 7
Read:
Write:
Reset:
AUTO
0
6
LOCK
0
5
4
ACQ
XLD
0
0
3
2
1
Bit 0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 8-5. PLL Bandwidth Control Register (PBWC)
AUTO — Automatic Bandwidth Control Bit
This read/write bit selects automatic or manual bandwidth control. When initializing the PLL for manual
operation (AUTO = 0), clear the ACQ bit before turning on the PLL. Reset clears the AUTO bit.
1 = Automatic bandwidth control
0 = Manual bandwidth control
MC68HC908AZ32A Data Sheet, Rev. 2
100
Freescale Semiconductor
CGM Registers
LOCK — Lock Indicator Bit
When the AUTO bit is set, LOCK is a read-only bit that becomes set when the VCO clock, CGMVCLK,
is locked (running at the programmed frequency). When the AUTO bit is clear, LOCK reads as logic 0
and has no meaning. Reset clears the LOCK bit.
1 = VCO frequency correct or locked
0 = VCO frequency incorrect or unlocked
ACQ — Acquisition Mode Bit
When the AUTO bit is set, ACQ is a read-only bit that indicates whether the PLL is in acquisition mode
or tracking mode. When the AUTO bit is clear, ACQ is a read/write bit that controls whether the PLL is
in acquisition or tracking mode.
In automatic bandwidth control mode (AUTO = 1), the last-written value from manual operation is
stored in a temporary location and is recovered when manual operation resumes. Reset clears this bit,
enabling acquisition mode.
1 = Tracking mode
0 = Acquisition mode
XLD — Crystal Loss Detect Bit
When the VCO output, CGMVCLK, is driving CGMOUT, this read/write bit can indicate whether the
crystal reference frequency is active or not.
1 = Crystal reference not active
0 = Crystal reference active
To check the status of the crystal reference, do the following:
1. Write a logic 1 to XLD.
2. Wait N × 4 cycles. N is the VCO frequency multiplier.
3. Read XLD.
The crystal loss detect function works only when the BCS bit is set, selecting CGMVCLK to drive
CGMOUT. When BCS is clear, XLD always reads as logic 0.
Bits 3–0 — Reserved for Test
These bits enable test functions not available in user mode. To ensure software portability from
development systems to user applications, software should write 0s to bits 3–0 when writing to PBWC.
8.5.3 PLL Programming Register
The PLL programming register contains the programming information for the modulo feedback divider
and the programming information for the hardware configuration of the VCO.
Address:
Read:
Write:
Reset:
$001E
Bit 7
6
5
4
3
2
1
Bit 0
MUL7
MUL6
MUL5
MUL4
VRS7
VRS6
VRS5
VRS4
0
1
1
0
0
1
1
0
Figure 8-6. PLL Programming Register (PPG)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
101
Clock Generator Module (CGM)
MUL7–MUL4 — Multiplier Select Bits
These read/write bits control the modulo feedback divider that selects the VCO frequency multiplier, N.
(See 8.3.2.1 Circuits and 8.3.2.4 Programming the PLL). A value of $0 in the multiplier select bits
configures the modulo feedback divider the same as a value of $1. Reset initializes these bits to $6 to
give a default multiply value of 6.
See Table 8-3.
NOTE
The multiplier select bits have built-in protection that prevents them from
being written when the PLL is on (PLLON = 1).
Table 8-3. VCO Frequency Multiplier (N) Selection
MUL7:MUL6:MUL5:MUL4
VCO Frequency Multiplier (N)
0000
1
0001
1
0010
2
0011
3
1101
13
1110
14
1111
15
VRS7–VRS4 — VCO Range Select Bits
These read/write bits control the hardware center-of-range linear multiplier L, which controls the
hardware center-of-range frequency, fVRS. (See 8.3.2.1 Circuits, 8.3.2.4 Programming the PLL, and
8.5.1 PLL Control Register.) VRS7–VRS4 cannot be written when the PLLON bit in the PLL control
register (PCTL) is set. See 8.3.2.5 Special Programming Exceptions. A value of $0 in the VCO range
select bits disables the PLL and clears the BCS bit in the PCTL. (See 8.3.3 Base Clock Selector Circuit
and 8.3.2.5 Special Programming Exceptions for more information.) Reset initializes the bits to $6 to
give a default range multiply value of 6.
NOTE
The VCO range select bits have built-in protection that prevents them from
being written when the PLL is on (PLLON = 1) and prevents selection of the
VCO clock as the source of the base clock (BCS = 1) if the VCO range
select bits are all clear. The VCO range select bits must be programmed
correctly. Incorrect programming can result in failure of the PLL to achieve
lock.
MC68HC908AZ32A Data Sheet, Rev. 2
102
Freescale Semiconductor
Interrupts
8.6 Interrupts
When the AUTO bit is set in the PLL bandwidth control register (PBWC), the PLL can generate a CPU
interrupt request every time the LOCK bit changes state. The PLLIE bit in the PLL control register (PCTL)
enables CPU interrupt requests from the PLL. PLLF, the interrupt flag in the PCTL, becomes set whether
CPU interrupt requests are enabled or not. When the AUTO bit is clear, CPU interrupt requests from the
PLL are disabled and PLLF reads as logic 0.
Software should read the LOCK bit after a PLL CPU interrupt request to see if the request was due to an
entry into lock or an exit from lock. When the PLL enters lock, the VCO clock, CGMVCLK, divided by two
can be selected as the CGMOUT source by setting BCS in the PCTL. When the PLL exits lock, the VCO
clock frequency is corrupt, and appropriate precautions should be taken. If the application is not frequency
sensitive, CPU interrupt requests should be disabled to prevent PLL interrupt service routines from
impeding software performance or from exceeding stack limitations.
NOTE
Software can select the CGMVCLK divided by two as the CGMOUT source
even if the PLL is not locked (LOCK = 0). Therefore, software should make
sure the PLL is locked before setting the BCS bit.
8.7 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
8.7.1 Wait Mode
The CGM remains active in wait mode. Before entering wait mode, software can disengage and turn off
the PLL by clearing the BCS and PLLON bits in the PLL control register (PCTL). Less power-sensitive
applications can disengage the PLL without turning it off. Applications that require the PLL to wake the
MCU from wait mode also can deselect the PLL output without turning off the PLL.
8.7.2 Stop Mode
The STOP instruction disables the CGM and holds low all CGM outputs (CGMXCLK, CGMOUT, and
CGMINT).
If CGMOUT is being driven by CGMVCLK and a STOP instruction is executed; the PLL will clear the BCS
bit in the PLL control register, causing CGMOUT to be driven by CGMXCLK. When the MCU recovers
from STOP, the crystal clock divided by two drives CGMOUT and BCS remains clear.
8.8 CGM During Break Interrupts
The BCFE bit in the break flag control register (BFCR) enables software to clear status bits during the
break state. See Chapter 11 Brake Module.
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect the PLLF bit during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write the PLL control register during the break state without affecting
the PLLF bit.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
103
Clock Generator Module (CGM)
8.9 Acquisition/Lock Time Specifications
The acquisition and lock times of the PLL are, in many applications, the most critical PLL design
parameters. Proper design and use of the PLL ensures the highest stability and lowest acquisition/lock
times.
8.9.1 Acquisition/Lock Time Definitions
Typical control systems refer to the acquisition time or lock time as the reaction time, within specified
tolerances, of the system to a step input. In a PLL, the step input occurs when the PLL is turned on or
when it suffers a noise hit. The tolerance is usually specified as a percent of the step input or when the
output settles to the desired value plus or minus a percent of the frequency change. Therefore, the
reaction time is constant in this definition, regardless of the size of the step input. For example, consider
a system with a 5% acquisition time tolerance. If a command instructs the system to change from 0 Hz to
1 MHz, the acquisition time is the time taken for the frequency to reach 1 MHz ±50 kHz. Fifty kHz = 5%
of the 1-MHz step input. If the system is operating at 1 MHz and suffers a –100 kHz noise hit, the
acquisition time is the time taken to return from 900 kHz to 1 MHz ±5 kHz. Five kHz = 5% of the 100-kHz
step input.
Other systems refer to acquisition and lock times as the time the system takes to reduce the error between
the actual output and the desired output to within specified tolerances. Therefore, the acquisition or lock
time varies according to the original error in the output. Minor errors may not even be registered. Typical
PLL applications prefer to use this definition because the system requires the output frequency to be
within a certain tolerance of the desired frequency regardless of the size of the initial error.
The discrepancy in these definitions makes it difficult to specify an acquisition or lock time for a typical
PLL. Therefore, the definitions for acquisition and lock times for this module are:
• Acquisition time, tacq, is the time the PLL takes to reduce the error between the actual output
frequency and the desired output frequency to less than the tracking mode entry tolerance, Δtrk.
Acquisition time is based on an initial frequency error, (fdes – forig)/fdes, of not more than ±100%. In
automatic bandwidth control mode (see 8.3.2.3 Manual and Automatic PLL Bandwidth Modes),
acquisition time expires when the ACQ bit becomes set in the PLL bandwidth control register
(PBWC).
• Lock time, tLock, is the time the PLL takes to reduce the error between the actual output frequency
and the desired output frequency to less than the lock mode entry tolerance, ΔLock. Lock time is
based on an initial frequency error, (fdes – forig)/fdes, of not more than ±100%. In automatic
bandwidth control mode, lock time expires when the LOCK bit becomes set in the PLL bandwidth
control register (PBWC). (See 8.3.2.3 Manual and Automatic PLL Bandwidth Modes).
Obviously, the acquisition and lock times can vary according to how large the frequency error is and may
be shorter or longer in many cases.
MC68HC908AZ32A Data Sheet, Rev. 2
104
Freescale Semiconductor
Acquisition/Lock Time Specifications
8.9.2 Parametric Influences on Reaction Time
Acquisition and lock times are designed to be as short as possible while still providing the highest possible
stability. These reaction times are not constant, however. Many factors directly and indirectly affect the
acquisition time.
The most critical parameter which affects the reaction times of the PLL is the reference frequency,
fCGMRDV (please reference Figure 8-1). This frequency is the input to the phase detector and controls how
often the PLL makes corrections. For stability, the corrections must be small compared to the desired
frequency, so several corrections are required to reduce the frequency error. Therefore, the slower the
reference the longer it takes to make these corrections. This parameter is also under user control via the
choice of crystal frequency fCGMXCLK.
Another critical parameter is the external filter capacitor. The PLL modifies the voltage on the VCO by
adding or subtracting charge from this capacitor. Therefore, the rate at which the voltage changes for a
given frequency error (thus a change in charge) is proportional to the capacitor size. The size of the
capacitor also is related to the stability of the PLL. If the capacitor is too small, the PLL cannot make small
enough adjustments to the voltage and the system cannot lock. If the capacitor is too large, the PLL may
not be able to adjust the voltage in a reasonable time. See 8.9.3 Choosing a Filter Capacitor.
Also important is the operating voltage potential applied to VDDA. The power supply potential alters the
characteristics of the PLL. A fixed value is best. Variable supplies, such as batteries, are acceptable if
they vary within a known range at very slow speeds. Noise on the power supply is not acceptable,
because it causes small frequency errors which continually change the acquisition time of the PLL.
Temperature and processing also can affect acquisition time because the electrical characteristics of the
PLL change. The part operates as specified as long as these influences stay within the specified limits.
External factors, however, can cause drastic changes in the operation of the PLL. These factors include
noise injected into the PLL through the filter capacitor, filter capacitor leakage, stray impedances on the
circuit board, and even humidity or circuit board contamination.
8.9.3 Choosing a Filter Capacitor
As described in 8.9.2 Parametric Influences on Reaction Time, the external filter capacitor, CF, is critical
to the stability and reaction time of the PLL. The PLL is also dependent on reference frequency and supply
voltage. The value of the capacitor must, therefore, be chosen with supply potential and reference
frequency in mind. For proper operation, the external filter capacitor must be chosen according to this
equation:
V DDA ⎞
C F = C fact ⎛ -----------------⎝ f C G M R D V⎠
For acceptable values of Cfact, (see Chapter 25 Electrical Specifications). For the value of VDDA, choose
the voltage potential at which the MCU is operating. If the power supply is variable, choose a value near
the middle of the range of possible supply values.
This equation does not always yield a commonly available capacitor size, so round to the nearest
available size. If the value is between two different sizes, choose the higher value for better stability.
Choosing the lower size may seem attractive for acquisition time improvement, but the PLL may become
unstable. Also, always choose a capacitor with a tight tolerance (±20% or better) and low dissipation.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
105
Clock Generator Module (CGM)
8.9.4 Reaction Time Calculation
The actual acquisition and lock times can be calculated using the equations below. These equations yield
nominal values under the following conditions:
• Correct selection of filter capacitor, CF (see 8.9.3 Choosing a Filter Capacitor).
• Room temperature operation
• Negligible external leakage on CGMXFC
• Negligible noise
The K factor in the equations is derived from internal PLL parameters. Kacq is the K factor when the PLL
is configured in acquisition mode, and Ktrk is the K factor when the PLL is configured in tracking mode.
(See 8.3.2.2 Acquisition and Tracking Modes).
V DDA ⎞ ⎛ 8 ⎞
- ------------t acq = ⎛ ------------------⎝ f CGMRDV⎠ ⎝ K ACQ⎠
V DDA ⎞ ⎛ 4 ⎞
- -----------t al = ⎛ ------------------⎝ f CGMRDV⎠ ⎝ K TRK⎠
t Lock = t ACQ + t AL
Note the inverse proportionality between the lock time and the reference frequency.
In automatic bandwidth control mode, the acquisition and lock times are quantized into units based on the
reference frequency. (See 8.3.2.3 Manual and Automatic PLL Bandwidth Modes). A certain number of
clock cycles, nACQ, is required to ascertain that the PLL is within the tracking mode entry tolerance, ΔTRK,
before exiting acquisition mode. A certain number of clock cycles, nTRK, is required to ascertain that the
PLL is within the lock mode entry tolerance, ΔLock. Therefore, the acquisition time, tACQ, is an integer
multiple of nACQ/fCGMRDV, and the acquisition to lock time, tAL, is an integer multiple of nTRK/fCGMRDV.
Also, since the average frequency over the entire measurement period must be within the specified
tolerance, the total time usually is longer than tLock as calculated above.
In manual mode, it is usually necessary to wait considerably longer than tLock before selecting the PLL
clock (see 8.3.3 Base Clock Selector Circuit), because the factors described in 8.9.2 Parametric
Influences on Reaction Time, may slow the lock time considerably.
When defining a limit in software for the maximum lock time, the value must allow for variation due to all
of the factors mentioned in this section, especially due to the CF capacitor and application specific
influences.
The calculated lock time is only an indication and it is the customer’s responsibility to allow enough of a
guard band for their application. Prior to finalizing any software and while determining the maximum lock
time, take into account all device to device differences. Typically, applications set the maximum lock time
as an order of magnitude higher than the measured value. This is considered sufficient for all such device
to device variation.
Freescale recommends measuring the lock time of the application system by utilizing dedicated software,
running in FLASH, EEPROM or RAM. This should toggle a port pin when the PLL is first configured and
switched on, then again when it goes from acquisition to lock mode and finally again when the PLL lock
MC68HC908AZ32A Data Sheet, Rev. 2
106
Freescale Semiconductor
Acquisition/Lock Time Specifications
bit is set. The resultant waveform can be captured on an oscilloscope and used to determine the typical
lock time for the microcontroller and the associated external application circuit.
e.g.
tLOCK
tACQ
Init. low
tAL
Signal on port pin
tTRK Complete and Lock Set
tACQ Complete
PLL Configured and switched on
NOTE
The filter capacitor should be fully discharged prior to making any
measurements.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
107
Clock Generator Module (CGM)
MC68HC908AZ32A Data Sheet, Rev. 2
108
Freescale Semiconductor
Chapter 9
Configuration Register (CONFIG-1)
9.1 Introduction
This section describes the configuration register (CONFIG-1), which contains bits that configure these
options:
• Resets caused by the LVI module
• Power to the LVI module
• LVI enabled during stop mode
• Stop mode recovery time (32 CGMXCLK cycles or 4096 CGMXCLK cycles)
• Computer operating properly module (COP)
• STOP instruction enable/disable.
9.2 Functional Description
The configuration register is a write-once register. Out of reset, the configuration register will read the
default value. Once the register is written, further writes will have no effect until a reset occurs.
NOTE
If the LVI module and the LVI reset signal are enabled, a reset occurs when
VDD falls to a voltage, LVITRIPF, and remains at or below that level for at
least nine consecutive CPU cycles. Once an LVI reset occurs, the MCU
remains in reset until VDD rises to a voltage, LVITRIPR.
Address:
Read:
Write:
Reset:
$001F
Bit 7
6
5
4
3
2
1
Bit 0
LVISTOP
R
LVIRST
LVIPWR
SSREC
COPRS
STOP
COPD
0
1
1
1
0
0
0
0
R
= Reserved
Figure 9-1. Configuration Register (CONFIG-1)
LVISTOP — LVI Stop Mode Enable Bit
LVISTOP enables the LVI module in stop mode. (See Chapter 14 Low Voltage Inhibit (LVI)).
1 = LVI enabled during stop mode
0 = LVI disabled during stop mode
NOTE
To have the LVI enabled in stop mode, the LVIPWR must be at a logic 1
and the LVISTOP bit must be at a logic 1. Take note that by enabling the
LVI in stop mode, the stop IDD current will be higher.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
109
Configuration Register (CONFIG-1)
LVIRST — LVI Reset Enable Bit
LVIRST enables the reset signal from the LVI module. (See Chapter 14 Low Voltage Inhibit (LVI)).
1 = LVI module resets enabled
0 = LVI module resets disabled
LVIPWR — LVI Power Enable Bit
LVIPWR enables the LVI module. (See Chapter 14 Low Voltage Inhibit (LVI)).
1 = LVI module power enabled
0 = LVI module power disabled
SSREC — Short Stop Recovery Bit
SSREC enables the CPU to exit stop mode with a delay of 32 CGMXCLK cycles instead of a
4096-CGMXCLK cycle delay. (See 7.6.2 Stop Mode).
1 = Stop mode recovery after 32 CGMXCLK cycles
0 = Stop mode recovery after 4096 CGMXCLK cycles
NOTE
If using an external crystal oscillator, do not set the SSREC bit.
COPRS — COP Rate Select Bit
COPRS enables the shorter COP timeout period. (See Chapter 13 Computer Operating Properly
(COP).
1 = COP timeout period is 8176 CGMXCLK cycles
0 = COP timeout period is 262,128 CGMXCLK cycles
STOP — STOP Instruction Enable Bit
STOP enables the STOP instruction.
1 = STOP instruction enabled
0 = STOP instruction treated as illegal opcode
COPD — COP Disable Bit
COPD disables the COP module. (See Chapter 13 Computer Operating Properly (COP).
1 = COP module disabled
0 = COP module enabled
CAUTION
Extra care should be exercised when using this emulation part for
development of code to be run in ROM AZ or AB parts that the options
selected by setting the CONFIG-1 register match exactly the options
selected on any ROM code request submitted. The enable/disable logic is
not necessarily identical in all parts of the AZ and AB families. If in doubt,
check with your local field applications representative.
MC68HC908AZ32A Data Sheet, Rev. 2
110
Freescale Semiconductor
Chapter 10
Configuration Register (CONFIG-2)
10.1 Introduction
This section describes the configuration register (CONFIG-2). This register contains bits that configure
these options:
• EEPROM Reference Clock Source
• EEPROM Read Protection
10.2 Functional Description
The configuration register is a write-once register. Out of reset, the configuration register will read the
default. Once the register is written, further writes will have no effect until a reset occurs.
Address:
$FE09
Bit 7
6
5
4
3
R
R
EEMONSEC
AZ32A
Write:
EEDIV
CLK
Reset:
0
0
0
1
1
R
= Reserved
Read:
R
2
1
Bit 0
R
R
R
0
0
0
Figure 10-1. Configuration Register (CONFIG-2)
EEDIVCLK — EEPROM Timebase Divider Clock select bit
This bit selects the reference clock source for the EEPROM-1 and EEPROM-2 timebase divider
modules.
1 = EExDIV clock input is driven by internal bus clock
0 = EExDIV clock input is driven by CGMXCLK
EEMONSEC — EEPROM Read Protection in Monitor Mode Bit
When EEMONSEC is set the entire EEPROM array cannot be accessed in monitor mode unless a
valid security code is entered.
1 = EEPROM read protection in monitor mode enabled
0 = EEPROM read protection in monitor mode disabled
AZ32A — Device indicator
This read-only bit is used to indicate that the MC68HC908AZ32A is an ‘A’ suffix version HC08 rather
than a non-’A’.
1 = ‘A’ version
0 = Non-’A’ version
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
111
Configuration Register (CONFIG-2)
MC68HC908AZ32A Data Sheet, Rev. 2
112
Freescale Semiconductor
Chapter 11
Brake Module
11.1 Introduction
The break module can generate a break interrupt that stops normal program flow at a defined address to
enter a background program.
11.2 Features
•
•
•
•
Accessible I/O Registers during Break Interrupts
CPU-Generated Break Interrupts
Software-Generated Break Interrupts
COP Disabling during Break Interrupts
11.3 Functional Description
When the internal address bus matches the value written in the break address registers, the break module
issues a breakpoint signal to the CPU. The CPU then loads the instruction register with a software
interrupt instruction (SWI) after completion of the current CPU instruction. The program counter vectors
to $FFFC and $FFFD ($FEFC and $FEFD in monitor mode).
The following events can cause a break interrupt to occur:
• A CPU-generated address (the address in the program counter) matches the contents of the break
address registers.
• Software writes a logic 1 to the BRKA bit in the break status and control register.
When a CPU-generated address matches the contents of the break address registers, the break interrupt
begins after the CPU completes its current instruction. A return-from-interrupt instruction (RTI) in the
break routine ends the break interrupt and returns the MCU to normal operation. Figure 11-1 shows the
structure of the break module.
IAB[15:8]
BREAK ADDRESS REGISTER HIGH
8-BIT COMPARATOR
IAB[15:0]
CONTROL
BREAK
8-BIT COMPARATOR
BREAK ADDRESS REGISTER LOW
IAB[7:0]
Figure 11-1. Break Module Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
113
Brake Module
Register Name
Read:
Break Address Register High
Write:
(BRKH)
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
BRKE
BRKA
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Read:
Break Address Register Low
Write:
(BRKL)
Reset:
Read:
Break Status and Control
Write:
Register (BSCR)
Reset:
= Unimplemented
Figure 11-2. I/O Register Summary
Table 11-1. I/O Register Address Summary
Register
BRKH
BRKL
BSCR
Address
$FE0C
$FE0D
$FE0B
11.3.1 Flag Protection During Break Interrupts
The BCFE bit in the break flag control register (BFCR) enables software to clear status bits during the
break state.
11.3.2 CPU During Break Interrupts
The CPU starts a break interrupt by:
• Loading the instruction register with the SWI instruction
• Loading the program counter with $FFFC:$FFFD ($FEFC:$FEFD in monitor mode)
The break interrupt begins after completion of the CPU instruction in progress. If the break address
register match occurs on the last cycle of a CPU instruction, the break interrupt begins immediately.
11.3.3 TIM During Break Interrupts
A break interrupt stops the timer counter.
11.3.4 COP During Break Interrupts
The COP is disabled during a break interrupt when VHi is present on the RST pin.
11.4 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
MC68HC908AZ32A Data Sheet, Rev. 2
114
Freescale Semiconductor
Break Module Registers
11.4.1 Wait Mode
If enabled, the break module is active in wait mode. The SIM break wait bit (BW) in the SIM break status
register indicates whether wait was exited by a break interrupt. If so, the user can modify the return
address on the stack by subtracting one from it. See 7.7.1 SIM Break Status Register.
11.4.2 Stop Mode
The break module is inactive in stop mode. The STOP instruction does not affect break module register
states.
11.5 Break Module Registers
These registers control and monitor operation of the break module:
• Break address register high (BRKH)
• Break address register low (BRKL)
• Break status and control register (BSCR)
11.5.1 Break Status and Control Register
The break status and control register contains break module enable and status bits.
Address:
$FE0B
Bit 7
Read:
Write:
Reset:
6
BRKE
BRKA
0
0
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 11-3. Break Status and Control Register (BSCR)
BRKE — Break Enable Bit
This read/write bit enables breaks on break address register matches. Clear BRKE by writing a logic
0 to bit 7. Reset clears the BRKE bit.
1 = Breaks enabled on 16-bit address match
0 = Breaks disabled on 16-bit address match
BRKA — Break Active Bit
This read/write status and control bit is set when a break address match occurs. Writing a logic 1 to
BRKA generates a break interrupt. Clear BRKA by writing a logic 0 to it before exiting the break routine.
Reset clears the BRKA bit.
1 = (When read) Break address match
0 = (When read) No break address match
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
115
Brake Module
11.5.2 Break Address Registers
The break address registers contain the high and low bytes of the desired breakpoint address. Reset
clears the break address registers.
Register:
BRKH
BRKL
Address:
$FE0C
$FE0D
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
Read:
Write:
Reset:
Read:
Write:
Reset:
Figure 11-4. Break Address Registers (BRKH and BRKL)
MC68HC908AZ32A Data Sheet, Rev. 2
116
Freescale Semiconductor
Chapter 12
Monitor ROM (MON)
12.1 Introduction
This section describes the monitor ROM (MON). The monitor ROM allows complete testing of the MCU
through a single-wire interface with a host computer.
12.2 Features
Features of the monitor ROM include:
• Normal User-Mode Pin Functionality
• One Pin Dedicated to Serial Communication between Monitor ROM and Host Computer
• Standard Mark/Space Non-Return-to-Zero (NRZ) Communication with Host Computer
• Up to 28.8 kBaud Communication with Host Computer
• Execution of Code in RAM or FLASH
• FLASH Security
• FLASH Programming
12.3 Functional Description
Monitor ROM receives and executes commands from a host computer. Figure 12-1 shows a sample
circuit used to enter monitor mode and communicate with a host computer via a standard RS-232
interface.
While simple monitor commands can access any memory address, the MC68HC908AZ32A has a FLASH
security feature to prevent external viewing of the contents of FLASH. Proper procedures must be
followed to verify FLASH content. Access to the FLASH is denied to unauthorized users of customer
specified software (see 12.3.7 Security).
In monitor mode, the MCU can execute host-computer code in RAM while all MCU pins except PTA0
retain normal operating mode functions. All communication between the host computer and the MCU is
through the PTA0 pin. A level-shifting and multiplexing interface is required between PTA0 and the host
computer. PTA0 is used in a wired-OR configuration and requires a pullup resistor.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
117
Monitor ROM (MON)
VDD
68HC08
10 kΩ
RST
0.1 μF
VHI
1 KΩ
IRQ
9.1V
CGMXFC
1
10 μF
+
20
MC145407
+
OSC1
20 pF
17
4
+
+
10 μF
18
3
10 μF
0.022 μF
10 μF
10 MΩ
OSC2
VDD
VDDA
20 pF
19
2
*
X1
4.9152 MHz
0.1 μF
VDDA/VDDAREF
VSSA
VSS
DB-25
2
5
16
3
6
15
0.1 μF
VDD
7
VDD
VDD
1
2
3
6
5
4
7
NOTE: Position A — Bus clock = CGMXCLK ÷ 4 or CGMVCLK ÷ 4
Position B — Bus clock = CGMXCLK ÷ 2
MC74HC125
VDD
14
10 kΩ
PTA0
PTC3
VDD
VDD
10 kΩ
A
(SEE
NOTE.)
10 kΩ
B
PTC0
PTC1
* = Refer to Table 12-9 for correct value.
Figure 12-1. Monitor Mode Circuit
MC68HC908AZ32A Data Sheet, Rev. 2
118
Freescale Semiconductor
Functional Description
12.3.1 Entering Monitor Mode
Table 12-1 shows the pin conditions for entering monitor mode.
Table 12-1. Mode Selection
IRQ1
Pin
PTC0
Pin
PTC1
Pin
PTA0
Pin
PTC3
Pin
Mode
CGMOUT
Bus
Frequency
VHI(1)
1
0
1
1
Monitor
CGMXCLK
CGMVCLK
----------------------------- or ----------------------------2
2
CGMOUT
-------------------------2
VHI(1)
1
0
1
0
Monitor
CGMXCLK
CGMOUT
-------------------------2
1. For VHI, 25.1.4 5.0 Volt DC Electrical Characteristics, and 25.1.1 Maximum Ratings.
Enter monitor mode by either
• Executing a software interrupt instruction (SWI) or
• Applying a logic 0 and then a logic 1 to the RST pin.
Once out of reset, the MCU waits for the host to send eight security bytes (see 12.3.7 Security). After the
security bytes, the MCU sends a break signal (10 consecutive logic 0s) to the host computer, indicating
that it is ready to receive a command.
Monitor mode uses alternate vectors for reset, SWI and break interrupt. The alternate vectors are in the
$FE page instead of the $FF page and allow code execution from the internal monitor firmware instead
of user code. The COP module is disabled in monitor mode as long as VHI (see 25.1.4 5.0 Volt DC
Electrical Characteristics), is applied to either the IRQ1 pin or the RESET pin. (See Chapter 7 System
Integration Module (SIM) for more information on modes of operation).
NOTE
Holding the PTC3 pin low when entering monitor mode causes a bypass of
a divide-by-two stage at the oscillator. The CGMOUT frequency is equal to
the CGMXCLK frequency, and the OSC1 input directly generates internal
bus clocks. In this case, the OSC1 signal must have a 50% duty cycle at
maximum bus frequency.
Table 12-2 is a summary of the differences between user mode and monitor mode.
Table 12-2. Mode Differences
Functions
COP
Reset
Vector
High
Reset
Vector
Low
Break
Vector
High
Break
Vector
Low
SWI
Vector
High
SWI
Vector
Low
User
Enabled
$FFFE
$FFFF
$FFFC
$FFFD
$FFFC
$FFFD
Monitor
Disabled(1)
$FEFE
$FEFF
$FEFC
$FEFD
$FEFC
$FEFD
Modes
1. If the high voltage (VHI) is removed from the IRQ and/or RESET pin while in monitor mode, the SIM asserts its COP enable output. The COP is enabled or disabled by the COPD bit in the configuration register. (see 25.1.4 5.0 Volt DC Electrical Characteristics).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
119
Monitor ROM (MON)
12.3.2 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.
(See Figure 12-2 and Figure 12-3.)
The data transmit and receive rate can be anywhere up to 28.8 kBaud. Transmit and receive baud rates
must be identical.
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
STOP
BIT
BIT 7
NEXT
START
BIT
Figure 12-2. Monitor Data Format
$A5
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BREAK
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
NEXT
START
BIT
STOP
BIT
STOP
BIT
NEXT
START
BIT
Figure 12-3. Sample Monitor Waveforms
12.3.3 Echoing
As shown in Figure 12-4, the monitor ROM immediately echoes each received byte back to the PTA0 pin
for error checking.
Any result of a command appears after the echo of the last byte of the command.
SENT TO
MONITOR
READ
READ
ADDR. HIGH
ADDR. HIGH
ADDR. LOW
ADDR. LOW
DATA
ECHO
RESULT
Figure 12-4. Read Transaction
12.3.4 Break Signal
A start bit followed by nine low bits is a break signal. (See Figure 12-5). When the monitor receives a break
signal, it drives the PTA0 pin high for the duration of two bits before echoing the break signal.
MISSING STOP BIT
TWO-STOP-BIT DELAY BEFORE ZERO ECHO
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Figure 12-5. Break Transaction
MC68HC908AZ32A Data Sheet, Rev. 2
120
Freescale Semiconductor
Functional Description
12.3.5 Commands
The monitor ROM uses these commands:
• READ, read memory
• WRITE, write memory
• IREAD, indexed read
• IWRITE, indexed write
• READSP, read stack pointer
• RUN, run user program
A sequence of IREAD or IWRITE commands can access a block of memory sequentially over the full
64-Kbyte memory map.
Table 12-3. READ (Read Memory) Command
Description
Read byte from memory
Operand
Specifies 2-byte address in high byte:low byte order
Data Returned
Returns contents of specified address
Opcode
$4A
Command Sequence
SENT TO
MONITOR
READ
READ
ADDR. HIGH
ADDR. HIGH
ADDR. LOW
ADDR. LOW
ECHO
DATA
RESULT
Table 12-4. WRITE (Write Memory) Command
Description
Write byte to memory
Operand
Specifies 2-byte address in high byte:low byte order; low byte followed by data byte
Data Returned
None
Opcode
$49
Command Sequence
SENT TO
MONITOR
WRITE
WRITE
ADDR. HIGH
ADDR. HIGH
ADDR. LOW
ADDR. LOW
DATA
DATA
ECHO
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
121
Monitor ROM (MON)
Table 12-5. IREAD (Indexed Read) Command
Description
Read next 2 bytes in memory from last address accessed
Operand
Specifies 2-byte address in high byte:low byte order
Data Returned
Returns contents of next two addresses
Opcode
$1A
Command Sequence
SENT TO
MONITOR
IREAD
IREAD
DATA
DATA
RESULT
ECHO
Table 12-6. IWRITE (Indexed Write) Command
Description
Write to last address accessed + 1
Operand
Specifies single data byte
Data Returned
None
Opcode
$19
Command Sequence
SENT TO
MONITOR
IWRITE
IWRITE
DATA
DATA
ECHO
Table 12-7. READSP (Read Stack Pointer) Command
Description
Reads stack pointer
Operand
None
Data Returned
Returns stack pointer in high byte:low byte order
Opcode
$0C
Command Sequence
SENT TO
MONITOR
READSP
READSP
SP HIGH
SP LOW
RESULT
ECHO
MC68HC908AZ32A Data Sheet, Rev. 2
122
Freescale Semiconductor
Functional Description
Table 12-8. RUN (Run User Program) Command
Description
Executes RTI instruction
Operand
None
Data Returned
None
Opcode
$28
Command Sequence
SENT TO
MONITOR
RUN
RUN
ECHO
12.3.6 Baud Rate
The MC68HC908AZ32A features a monitor mode which is optimised to operate with either a 4.9152 MHz
crystal clock source (or multiples of 4.9152 MHz) or a 4 MHz crystal (or multiples of 4 MHz). This supports
designs which use the MSCAN module, which is generally clocked from a 4 MHz, 8 MHz or 16 MHZ
internal reference clock. The table below outlines the available baud rates for a range of crystals and how
they can match to a PC baud rate.
Table 12-9 MC68HC908AZ32A Monitor Baud Rate Selection
Baud rate
Closest PC baud PC
Error %
Clock freq
PTC3=0
PTC3=1
PTC3=0
PTC3=1
PTC3=0
PTC3=1
32kHz
57.97
28.98
57.6
28.8
0.64
0.63
1MHz
1811.59
905.80
1800
900
0.64
0.64
2MHz
3623.19
1811.59
3600
1800
0.64
0.64
4MHz
7246.37
3623.19
7200
3600
0.64
0.64
4.194MHz
7597.83
3798.91
7680
3840
1.08
1.08
4.9152MHz
8904.35
4452.17
8861
4430
0.49
0.50
8MHz
14492.72
7246.37
14400
7200
0.64
0.64
16MHz
28985.51
14492.75
28800
14400
0.64
0.64
CAUTION
Care should be taken when setting the baud rate since incorrect baud
rate setting can result in communications failure.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
123
Monitor ROM (MON)
12.3.7 Security
A security feature discourages unauthorized reading of FLASH locations while in monitor mode. The host
can bypass the security feature at monitor mode entry by sending eight security bytes that match the
bytes at locations $FFF6–$FFFD. Locations $FFF6–$FFFD contain user-defined data.
NOTE
Do not leave locations $FFF6–$FFFD blank. For security reasons, program
locations $FFF6–$FFFD even if they are not used for vectors. If FLASH is
unprogrammed, the eight security byte values to be sent are $FF, the
unprogrammed state of FLASH.
During monitor mode entry, the MCU waits after the power-on reset for the host to send the eight security
bytes on pin PA0.
VDD
4096 + 32 CGMXCLK CYCLES
RST
Command
Byte 8
Byte 2
Byte 1
24 BUS CYCLES (MINIMUM)
FROM HOST
PA0
4
Break
2
1
Command Echo
NOTE: 1 = Echo delay (2 bit times)
2 = Data return delay (2 bit times)
4 = Wait 1 bit time before sending next byte.
1
Byte 8 Echo
Byte 1 Echo
FROM MCU
1
Byte 2 Echo
4
1
Figure 12-6. Monitor Mode Entry Timing
If the received bytes match those at locations $FFF6–$FFFD, the host bypasses the security feature and
can read all FLASH locations and execute code from FLASH. Security remains bypassed until a power-on
reset occurs. After the host bypasses security, any reset other than a power-on reset requires the host to
send another eight bytes. If the reset was not a power-on reset, the security remains bypassed regardless
of the data that the host sends.
If the received bytes do not match the data at locations $FFF6–$FFFD, the host fails to bypass the
security feature. The MCU remains in monitor mode, but reading FLASH locations returns undefined data,
and trying to execute code from FLASH causes an illegal address reset. After the host fails to bypass
security, any reset other than a power-on reset causes an endless loop of illegal address resets.
After receiving the eight security bytes from the host, the MCU transmits a break character signalling that
it is ready to receive a command.
NOTE
The MCU does not transmit a break character until after the host sends the
eight security bytes.
MC68HC908AZ32A Data Sheet, Rev. 2
124
Freescale Semiconductor
Chapter 13
Computer Operating Properly (COP
13.1 Introduction
The COP module contains a free-running counter that generates a reset if allowed to overflow. The COP
module helps software recover from runaway code. Prevent a COP reset by periodically clearing the COP
counter.
13.2 Functional Description
The COP counter is a free-running 6-bit counter preceded by a 12-bit prescaler. If not cleared by software,
the COP counter overflows and generates an asynchronous reset after 8176 or 262,128 CGMXCLK
cycles, depending on the state of the COP rate select bit, COPRS, in the CONFIG-1 register. When
COPRS = 0, a 4.9152-MHz crystal gives a COP timeout period of 53.3 ms. Writing any value to location
$FFFF before an overflow occurs prevents a COP reset by clearing the COP counter and stages 4–12 of
the SIM counter.
NOTE
Service the COP immediately after reset and before entering or after exiting
stop mode to guarantee the maximum time before the first COP counter
overflow.
A COP reset pulls the RST pin low for 32 CGMXCLK cycles and sets the COP bit in the reset status
register (RSR).
In monitor mode, the COP is disabled if the RST pin or the IRQ pin is held at VHi. During the break
state, VHi on the RST pin disables the COP.
NOTE
Place COP clearing instructions in the main program and not in an interrupt
subroutine. Such an interrupt subroutine could keep the COP from
generating a reset even while the main program is not working properly.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
125
Computer Operating Properly (COP
13.3 I/O Signals
The following paragraphs describe the signals shown in Figure 13-1.
12-BIT COP PRESCALER
CLEAR STAGES 4–12
STOP INSTRUCTION
INTERNAL RESET SOURCES
RESET VECTOR FETCH
CLEAR ALL STAGES
CGMXCLK
COPCTL WRITE
RESET
RESET STATUS
REGISTER
6-BIT COP COUNTER
COPD FROM CONFIG-1
RESET
COPCTL WRITE
CLEAR COP
COUNTER
COPRS FROM CONFIG-1
Figure 13-1. COP Block Diagram
13.3.1 CGMXCLK
CGMXCLK is the crystal oscillator output signal. CGMXCLK frequency is equal to the crystal frequency.
13.3.2 STOP Instruction
The STOP instruction clears the COP prescaler.
13.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) (see 13.4 COP Control Register), clears the COP
counter and clears stages 12 through 4 of the COP prescaler. Reading the COP control register returns
the reset vector.
13.3.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK cycles after power-up.
MC68HC908AZ32A Data Sheet, Rev. 2
126
Freescale Semiconductor
COP Control Register
13.3.5 Internal Reset
An internal reset clears the COP prescaler and the COP counter.
13.3.6 Reset Vector Fetch
A reset vector fetch occurs when the vector address appears on the data bus. A reset vector fetch clears
the COP prescaler.
13.3.7 COPD
The COPD signal reflects the state of the COP disable bit (COPD) in the configuration register. (See
Chapter 9 Configuration Register (CONFIG-1)).
13.3.8 COPRS
The COPRS signal reflects the state of the COP rate select bit. (COPRS) in the configuration register.
(See Chapter 9 Configuration Register (CONFIG-1)).
13.4 COP Control Register
The COP control register is located at address $FFFF and overlaps the reset vector. Writing any value to
$FFFF clears the COP counter and starts a new timeout period. Reading location $FFFF returns the low
byte of the reset vector.
Address:
$FFFF
Bit 7
6
5
4
3
Read:
Low Byte of Reset Vector
Write:
Clear COP Counter
Reset:
Unaffected by Reset
2
1
Bit 0
Figure 13-2. COP Control Register (COPCTL)
13.5 Interrupts
The COP does not generate CPU interrupt requests.
13.6 Monitor Mode
The COP is disabled in monitor mode when VHi is present on the IRQ1 pin or on the RST pin.
13.7 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
13.7.1 Wait Mode
The COP remains active in wait mode. To prevent a COP reset during wait mode, periodically clear the
COP counter in a CPU interrupt routine.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
127
Computer Operating Properly (COP
13.7.2 Stop Mode
Stop mode turns off the CGMXCLK input to the COP and clears the COP prescaler. Service the COP
immediately before entering or after exiting stop mode to ensure a full COP timeout period after entering
or exiting stop mode.
The STOP bit in the configuration register (CONFIG-1) enables the STOP instruction. To prevent
inadvertently turning off the COP with a STOP instruction, disable the STOP instruction by clearing the
STOP bit.
13.8 COP Module During Break Interrupts
The COP is disabled during a break interrupt when VHi is present on the RST pin.
MC68HC908AZ32A Data Sheet, Rev. 2
128
Freescale Semiconductor
Chapter 14
Low Voltage Inhibit (LVI)
14.1 Introduction
This section describes the low-voltage inhibit module (LVI47, Version A), which monitors the voltage on
the VDD pin and can force a reset when the VDD voltage falls to the LVI trip voltage.
14.2 Features
Features of the LVI module include:
• Programmable LVI Reset
• Programmable Power Consumption
• Digital Filtering of VDD Pin Level
NOTE
If a low voltage interrupt (LVI) occurs during programming of EEPROM or
Flash memory, then adequate programming time may not have been
allowed to ensure the integrity and retention of the data. It is the
responsibility of the user to ensure that in the event of an LVI any addresses
being programmed receive specification programming conditions.
14.3 Functional Description
Figure 14-1 shows the structure of the LVI module. The LVI is enabled out of reset. The LVI module
contains a bandgap reference circuit and comparator. The LVI power bit, LVIPWR, enables the LVI to
monitor VDD voltage. The LVI reset bit, LVIRST, enables the LVI module to generate a reset when VDD
falls below a voltage, LVITRIPF, and remains at or below that level for nine or more consecutive CPU
cycles.
Note that short VDD spikes may not trip the LVI. It is the user’s responsibility to ensure a clean VDD signal
within the specified operating voltage range if normal microcontroller operation is to be guaranteed.
LVISTOP, enables the LVI module during stop mode. This will ensure when the STOP instruction is
implemented, the LVI will continue to monitor the voltage level on VDD. LVIPWR, LVISTOP, and LVIRST
are in the configuration register, CONFIG-1 (see Chapter 9 Configuration Register (CONFIG-1)).
Once an LVI reset occurs, the MCU remains in reset until VDD rises above a voltage, LVITRIPR. VDD must
be above LVITRIPR for only one CPU cycle to bring the MCU out of reset (see 14.3.2 Forced Reset
Operation). The output of the comparator controls the state of the LVIOUT flag in the LVI status register
(LVISR).
An LVI reset also drives the RST pin low to provide low-voltage protection to external peripheral devices.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
129
Low Voltage Inhibit (LVI)
VDD
LVIPWR
FROM CONFIG-1
FROM CONFIG-1
CPU CLOCK
LOW VDD
DETECTOR
LVIRST
VDD
DIGITAL FILTER
VDD > LVITRIP = 0
LVI RESET
VDD < LVITRIP = 1
Stop Mode
Filter Bypass
ANLGTRIP
LVIOUT
LVISTOP
FROM CONFIG-1
Figure 14-1. LVI Module Block Diagram
Addr.
$FE0F
Register Name
Bit 7
Read: LVIOUT
LVI Status Register
(LVISR)
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
Write:
= Unimplemented
Figure 14-2. LVI I/O Register Summary
14.3.1 Polled LVI Operation
In applications that can operate at VDD levels below the LVITRIPF level, software can monitor VDD by
polling the LVIOUT bit. In the configuration register, the LVIPWR bit must be at logic 1 to enable the LVI
module, and the LVIRST bit must be at logic 0 to disable LVI resets.
14.3.2 Forced Reset Operation
In applications that require VDD to remain above the LVITRIPF level, enabling LVI resets allows the LVI
module to reset the MCU when VDD falls to the LVITRIPF level and remains at or below that level for nine
or more consecutive CPU cycles. In the configuration register, the LVIPWR and LVIRST bits must be at
logic 1 to enable the LVI module and to enable LVI resets.
14.3.3 False Reset Protection
The VDD pin level is digitally filtered to reduce false resets due to power supply noise. In order for the LVI
module to reset the MCU,VDD must remain at or below the LVITRIPF level for nine or more consecutive
CPU cycles. VDD must be above LVITRIPR for only one CPU cycle to bring the MCU out of reset.
MC68HC908AZ32A Data Sheet, Rev. 2
130
Freescale Semiconductor
LVI Status Register
14.4 LVI Status Register
The LVI status register flags VDD voltages below the LVITRIPF level.
Address:
Read:
$FE0F
Bit 7
6
5
4
3
2
1
Bit 0
LVIOUT
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 14-3. LVI Status Register (LVISR)
LVIOUT — LVI Output Bit
This read-only flag becomes set when the VDD voltage falls below the LVITRIPF voltage for 32 to 40
CGMXCLK cycles. (See Table 14-1). Reset clears the LVIOUT bit.
Table 14-1. LVIOUT Bit Indication
VDD
For Number of
CGMXCLK Cycles:
LVIOUT
At Level:
VDD > LVITRIPR
Any
0
VDD < LVITRIPF
< 32 CGMXCLK Cycles
0
VDD < LVITRIPF
Between 32 and 40
CGMXCLK Cycles
0 or 1
VDD < LVITRIPF
> 40 CGMXCLK Cycles
1
LVITRIPF < VDD < LVITRIPR
Any
Previous Value
14.5 LVI Interrupts
The LVI module does not generate interrupt requests.
14.6 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
14.6.1 Wait Mode
With the LVIPWR bit in the configuration register programmed to logic 1, the LVI module is active after a
WAIT instruction.
With the LVIRST bit in the configuration register programmed to logic 1, the LVI module can generate a
reset and bring the MCU out of wait mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
131
Low Voltage Inhibit (LVI)
14.6.2 Stop Mode
With the LVISTOP and LVIPWR bits in the configuration register programmed to a logic 1, the LVI module
will be active after a STOP instruction. Because CPU clocks are disabled during stop mode, the LVI trip
must bypass the digital filter to generate a reset and bring the MCU out of stop.
With the LVIPWR bit in the configuration register programmed to logic 1 and the LVISTOP bit at a logic
0, the LVI module will be inactive after a STOP instruction.
Note that the LVI feature is intended to provide the safe shutdown of the microcontroller and thus
protection of related circuitry prior to any application VDD voltage collapsing completely to an unsafe level.
It is not intended that users operate the microcontroller at lower than specified operating voltage VDD.
MC68HC908AZ32A Data Sheet, Rev. 2
132
Freescale Semiconductor
Chapter 15
External Interrupt Module (IRQ1)
15.1 Introduction
This section describes the nonmaskable external interrupt (IRQ) input.
15.2 Features
Features include:
• Dedicated External Interrupt Pin (IRQ1)
• Hysteresis Buffer
• Programmable Edge-Only or Edge- and Level-Interrupt Sensitivity
• Automatic Interrupt Acknowledge
15.3 Functional Description
A logic 0 applied to the external interrupt pin can latch a CPU interrupt request. Figure 15-1 shows the
structure of the IRQ module.
Interrupt signals on the IRQ1 pin are latched into the IRQ latch. An interrupt latch remains set until one of
the following actions occurs:
• Vector fetch — A vector fetch automatically generates an interrupt acknowledge signal that clears
the latch that caused the vector fetch.
• Software clear — Software can clear an interrupt latch by writing to the appropriate acknowledge
bit in the interrupt status and control register (ISCR). Writing a logic 1 to the ACK bit clears the IRQ
latch.
• Reset — A reset automatically clears both interrupt latches.
The external interrupt pin is falling-edge triggered and is software- configurable to be both falling-edge
and low-level triggered. The MODE bit in the ISCR controls the triggering sensitivity of the IRQ1 pin.
When an interrupt pin is edge-triggered only, the interrupt latch remains set until a vector fetch, software
clear, or reset occurs.
When an interrupt pin is both falling-edge and low-level-triggered, the interrupt latch remains set until both
of the following occur:
• Vector fetch or software clear
• Return of the interrupt pin to logic 1
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
133
External Interrupt Module (IRQ1)
INTERNAL ADDRESS BUS
ACK
TO CPU FOR
BIL/BIH
INSTRUCTIONS
VECTOR
FETCH
DECODER
VDD
IRQF
D
CLR
Q
SYNCHRONIZER
CK
IRQ1
IRQ
INTERRUPT
REQUEST
IRQ
LATCH
IMASK
MODE
HIGH
VOLTAGE
DETECT
TO MODE
SELECT
LOGIC
Figure 15-1. IRQ Block Diagram
Addr.
$001A
Register Name
IRQ Status/Control Register Read:
(ISCR) Write:
Bit 7
6
5
4
3
2
0
0
0
0
IRQF
0
R
R
R
R
R
ACK
R
= Reserved
1
Bit 0
IMASK
MODE
Figure 15-2. IRQ I/O Register Summary
The vector fetch or software clear may occur before or after the interrupt pin returns to logic 1. As long as
the pin is low, the interrupt request remains pending. A reset will clear the latch and the MODE1 control
bit, thereby clearing the interrupt even if the pin stays low.
When set, the IMASK bit in the ISCR masks all external interrupt requests. A latched interrupt request is
not presented to the interrupt priority logic unless the corresponding IMASK bit is clear.
NOTE
The interrupt mask (I) in the condition code register (CCR) masks all
interrupt requests, including external interrupt requests.
(See Figure 15-3).
MC68HC908AZ32A Data Sheet, Rev. 2
134
Freescale Semiconductor
Functional Description
FROM RESET
YES
I BIT SET?
NO
INTERRUPT?
YES
NO
STACK CPU REGISTERS.
SET I BIT.
LOAD PC WITH INTERRUPT VECTOR.
FETCH NEXT
INSTRUCTION.
SWI
INSTRUCTION?
YES
NO
RTI
INSTRUCTION?
YES
UNSTACK CPU REGISTERS.
NO
EXECUTE INSTRUCTION.
Figure 15-3. IRQ Interrupt Flowchart
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
135
External Interrupt Module (IRQ1)
15.4 IRQ Pin
A logic 0 on the IRQ1 pin can latch an interrupt request into the IRQ latch. A vector fetch, software clear,
or reset clears the IRQ latch.
If the MODE bit is set, the IRQ1 pin is both falling-edge sensitive and low-level sensitive. With MODE set,
both of the following actions must occur to clear the IRQ latch:
• Vector fetch or software clear — A vector fetch generates an interrupt acknowledge signal to clear
the latch. Software may generate the interrupt acknowledge signal by writing a logic 1 to the ACK
bit in the interrupt status and control register (ISCR). The ACK bit is useful in applications that poll
the IRQ1 pin and require software to clear the IRQ latch. Writing to the ACK bit can also prevent
spurious interrupts due to noise. Setting ACK does not affect subsequent transitions on the IRQ1
pin. A falling edge on IRQ that occurs after writing to the ACK bit latches another interrupt request.
If the IRQ mask bit, IMASK, is clear, the CPU loads the program counter with the vector address
at locations $FFFA and $FFFB.
• Return of the IRQ1 pin to logic 1 — As long as the IRQ1 pin is at logic 0, the IRQ1 latch remains set.
The vector fetch or software clear and the return of the IRQ1 pin to logic 1 can occur in any order. The
interrupt request remains pending as long as the IRQ1 pin is at logic 0. A reset will clear the latch and the
MODE control bit, thereby clearing the interrupt even if the pin stays low.
If the MODE bit is clear, the IRQ1 pin is falling-edge sensitive only. With MODE clear, a vector fetch or
software clear immediately clears the IRQ latch.
The IRQF bit in the ISCR register can be used to check for pending interrupts. The IRQF bit is not affected
by the IMASK bit, which makes it useful in applications where polling is preferred.
Use the BIH or BIL instruction to read the logic level on the IRQ1 pin.
NOTE
When using the level-sensitive interrupt trigger, avoid false interrupts by
masking interrupt requests in the interrupt routine.
15.5 IRQ Module During Break Interrupts
The system integration module (SIM) controls whether the IRQ interrupt latch can be cleared during the
break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear the
latches during the break state. (See 7.7.3 SIM Break Flag Control Register
To allow software to clear the IRQ latch during a break interrupt, write a logic 1 to the BCFE bit. If a latch
is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect the latch during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its default
state), writing to the ACK bit in the IRQ status and control register during the break state has no effect on
the IRQ latch.
MC68HC908AZ32A Data Sheet, Rev. 2
136
Freescale Semiconductor
IRQ Status and Control Register
15.6 IRQ Status and Control Register
The IRQ status and control register (ISCR) controls and monitors operation of the IRQ module. The ISCR
has these functions:
• Shows the state of the IRQ interrupt flag
• Clears the IRQ interrupt latch
• Masks IRQ interrupt request
• Controls triggering sensitivity of the IRQ1 interrupt pin
Address:
$001A
Bit 7
6
5
4
3
2
Read:
0
0
0
0
IRQF
0
Write:
R
R
R
R
R
ACK
Reset:
0
0
0
0
0
0
R
= Reserved
1
Bit 0
IMASK
MODE
0
0
Figure 15-4. IRQ Status and Control Register (ISCR)
IRQF — IRQ Flag Bit
This read-only status bit is high when the IRQ interrupt is pending.
1 = IRQ interrupt pending
0 = IRQ interrupt not pending
ACK — IRQ Interrupt Request Acknowledge Bit
Writing a logic 1 to this write-only bit clears the IRQ latch. ACK always reads as logic 0. Reset clears
ACK.
IMASK — IRQ Interrupt Mask Bit
Writing a logic 1 to this read/write bit disables IRQ interrupt requests. Reset clears IMASK.
1 = IRQ interrupt requests disabled
0 = IRQ interrupt requests enabled
MODE — IRQ Edge/Level Select Bit
This read/write bit controls the triggering sensitivity of the IRQ1 pin. Reset clears MODE.
1 = IRQ1 interrupt requests on falling edges and low levels
0 = IRQ1 interrupt requests on falling edges only
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
137
External Interrupt Module (IRQ1)
MC68HC908AZ32A Data Sheet, Rev. 2
138
Freescale Semiconductor
Chapter 16
Serial Communications Interface (SCI)
16.1 Introduction
The SCI allows asynchronous communications with peripheral devices and other MCUs.
16.2 Features
The SCI module’s features include:
• Full Duplex Operation
• Standard Mark/Space Non-Return-to-Zero (NRZ) Format
• 32 Programmable Baud Rates
• Programmable 8-Bit or 9-Bit Character Length
• Separately Enabled Transmitter and Receiver
• Separate Receiver and Transmitter CPU Interrupt Requests
• Programmable Transmitter Output Polarity
• Two Receiver Wakeup Methods:
– Idle Line Wakeup
– Address Mark Wakeup
• Interrupt-Driven Operation with Eight Interrupt Flags:
– Transmitter Empty
– Transmission Complete
– Receiver Full
– Idle Receiver Input
– Receiver Overrun
– Noise Error
– Framing Error
– Parity Error
• Receiver Framing Error Detection
• Hardware Parity Checking
• 1/16 Bit-Time Noise Detection
16.3 Pin Name Conventions
The generic names of the SCI input/output (I/O) pins are:
• RxD (receive data)
• TxD (transmit data)
SCI I/O lines are implemented by sharing parallel I/O port pins. The full name of an SCI input or output
reflects the name of the shared port pin. Table 16-1 shows the full names and the generic names of the
SCI I/O pins.The generic pin names appear in the text of this section.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
139
Serial Communications Interface (SCI)
Table 16-1. Pin Name Conventions
Generic Pin Names
RxD
TxD
Full Pin Names
PTE1/SCRxD
PTE0/SCTxD
16.4 Functional Description
Figure 16-1 shows the structure of the SCI module. The SCI allows full-duplex, asynchronous, NRZ serial
communication between the MCU and remote devices, including other MCUs. The transmitter and
receiver of the SCI operate independently, although they use the same baud rate generator. During
normal operation, the CPU monitors the status of the SCI, writes the data to be transmitted, and
processes received data.
INTERNAL BUS
ERROR
INTERRUPT
CONTROL
RECEIVE
SHIFT REGISTER
RxD
SCI DATA
REGISTER
RECEIVER
INTERRUPT
CONTROL
TRANSMITTER
INTERRUPT
CONTROL
SCI DATA
REGISTER
TRANSMIT
SHIFT REGISTER
TxD
TXINV
SCTIE
R8
TCIE
T8
SCRIE
ILIE
TE
SCTE
RE
TC
RWU
SBK
SCRF
OR
ORIE
IDLE
NF
NEIE
FE
FEIE
PE
PEIE
LOOPS
LOOPS
RECEIVE
CONTROL
WAKEUP
CONTROL
ENSCI
ENSCI
TRANSMIT
CONTROL
FLAG
CONTROL
BKF
M
RPF
WAKE
ILTY
CGMXCLK
÷4
PRESCALER
BAUD RATE
GENERATOR
÷ 16
PEN
PTY
DATA SELECTION
CONTROL
Figure 16-1. SCI Module Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
140
Freescale Semiconductor
Functional Description
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
Reset:
0
0
0
0
0
0
0
0
Read:
R8
T8
R
R
ORIE
NEIE
FEIE
PEIE
Read:
SCI Control Register 1 (SCC1) Write:
Reset:
Read:
SCI Control Register 2 (SCC2) Write:
SCI Control Register 3 (SCC3) Write:
Reset:
U
U
0
0
0
0
0
0
Read:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
Reset:
1
1
0
0
0
0
0
0
Read:
0
0
0
0
0
0
BKF
RPF
Reset:
0
0
0
0
0
0
0
0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
SCI Data Register (SCDR) Write:
T7
T6
T5
T4
T3
T2
T1
T0
SCI Status Register 1 (SCS1) Write:
SCI Status Register 2 (SCS2) Write:
Reset:
Read:
Unaffected by Reset
0
0
0
0
SCI Baud Rate Register (SCBR) Write:
Reset:
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
= Unimplemented
U = Unaffected
R = Reserved
Figure 16-2. SCI I/O Register Summary
Table 16-2. SCI I/O Register Address Summary
Register
SCC1
SCC2
SCC3
SCS1
SCS2
SCDR
SCBR
Address
$0013
$0014
$0015
$0016
$0017
$0018
$0019
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
141
Serial Communications Interface (SCI)
16.4.1 Data Format
The SCI uses the standard non-return-to-zero mark/space data format illustrated in Figure 16-3.
8-BIT DATA FORMAT
(BIT M IN SCC1 CLEAR)
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
PARITY
OR DATA
BIT
BIT 6
9-BIT DATA FORMAT
(BIT M IN SCC1 SET)
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
NEXT
START
BIT
STOP
BIT
BIT 7
PARITY
OR DATA
BIT
BIT 7
BIT 8 STOP
BIT
BIT 6
NEXT
START
BIT
Figure 16-3. SCI Data Formats
16.4.2 Transmitter
Figure 16-4 shows the structure of the SCI transmitter.
INTERNAL BUS
÷ 16
SCI DATA REGISTER
SCP1
11-BIT
TRANSMIT
SHIFT REGISTER
STOP
CGMXCLK
BAUD
DIVIDER
SCP0
SCR1
H
SCR2
8
7
6
5
4
3
2
START
PRESCALER
÷4
1
0
L
TxD
MSB
TXINV
PARITY
GENERATION
T8
BREAK
(ALL ZEROS)
PTY
PREAMBLE
(ALL ONES)
PEN
SHIFT ENABLE
M
LOAD FROM SCDR
TRANSMITTER CPU INTERRUPT REQUEST
SCR0
TRANSMITTER
CONTROL LOGIC
SCTE
SCTE
SCTIE
TC
TCIE
SBK
LOOPS
SCTIE
ENSCI
TC
TE
TCIE
Figure 16-4. SCI Transmitter
MC68HC908AZ32A Data Sheet, Rev. 2
142
Freescale Semiconductor
Functional Description
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
Reset:
0
0
0
0
0
0
0
0
Read:
R8
T8
R
R
ORIE
NEIE
FEIE
PEIE
Read:
SCI Control Register 1 (SCC1) Write:
Reset:
Read:
SCI Control Register 2 (SCC2) Write:
SCI Control Register 3 (SCC3) Write:
Reset:
U
U
0
0
0
0
0
0
Read:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
Reset:
1
1
0
0
0
0
0
0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
SCI Data Register (SCDR) Write:
T7
T6
T5
T4
T3
T2
T1
T0
SCI Status Register 1 (SCS1) Write:
Reset:
Read:
Unaffected by Reset
0
0
0
0
SCI Baud Rate Register (SCBR) Write:
Reset:
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
= Unimplemented
U = Unaffected
R = Reserved
Figure 16-5. SCI Transmitter I/O Register Summary
Table 16-3. SCI Transmitter I/O Address Summary
Register
SCC1
SCC2
SCC3
SCS1
SCDR
SCBR
Address
$0013
$0014
$0015
$0016
$0018
$0019
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
143
Serial Communications Interface (SCI)
16.4.2.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI control register 1
(SCC1) determines character length. When transmitting 9-bit data, bit T8 in SCI control register 3 (SCC3)
is the ninth bit (bit 8).
16.4.2.2 Character Transmission
During an SCI transmission, the transmit shift register shifts a character out to the TxD pin. The SCI data
register (SCDR) is the write-only buffer between the internal data bus and the transmit shift register. To
initiate an SCI transmission:
1. Enable the SCI by writing a logic 1 to the enable SCI bit (ENSCI) in SCI control register 1 (SCC1).
2. Enable the transmitter by writing a logic 1 to the transmitter enable bit (TE) in SCI control register 2
(SCC2).
3. Clear the SCI transmitter empty bit (SCTE) by first reading SCI status register 1 (SCS1) and then
writing to the SCDR.
4. Repeat step 3 for each subsequent transmission.
At the start of a transmission, transmitter control logic automatically loads the transmit shift register with
a preamble of logic 1s. After the preamble shifts out, control logic transfers the SCDR data into the
transmit shift register. A logic 0 start bit automatically goes into the least significant bit position of the
transmit shift register. A logic 1 stop bit goes into the most significant bit position.
The SCI transmitter empty bit, SCTE, in SCS1 becomes set when the SCDR transfers a byte to the
transmit shift register. The SCTE bit indicates that the SCDR can accept new data from the internal data
bus. If the SCI transmit interrupt enable bit, SCTIE, in SCC2 is also set, the SCTE bit generates a
transmitter CPU interrupt request.
When the transmit shift register is not transmitting a character, the TxD pin goes to the idle condition, logic
1. If at any time software clears the ENSCI bit in SCI control register 1 (SCC1), the transmitter and
receiver relinquish control of the port E pins.
16.4.2.3 Break Characters
Writing a logic 1 to the send break bit, SBK, in SCC2 loads the transmit shift register with a break
character. A break character contains all logic 0s and has no start, stop, or parity bit. Break character
length depends on the M bit in SCC1. As long as SBK is at logic 1, transmitter logic continuously loads
break characters into the transmit shift register. After software clears the SBK bit, the shift register finishes
transmitting the last break character and then transmits at least one logic 1. The automatic logic 1 at the
end of a break character guarantees the recognition of the start bit of the next character.
The SCI recognizes a break character when a start bit is followed by eight or nine logic 0 data bits and a
logic 0 where the stop bit should be. Receiving a break character has the following effects on SCI
registers:
• Sets the framing error bit (FE) in SCS1
• Sets the SCI receiver full bit (SCRF) in SCS1
• Clears the SCI data register (SCDR)
• Clears the R8 bit in SCC3
• Sets the break flag bit (BKF) in SCS2
• May set the overrun (OR), noise flag (NF), parity error (PE), or reception in progress flag (RPF) bits
MC68HC908AZ32A Data Sheet, Rev. 2
144
Freescale Semiconductor
Functional Description
16.4.2.4 Idle Characters
An idle character contains all logic 1s and has no start, stop, or parity bit. Idle character length depends
on the M bit in SCC1. The preamble is a synchronizing idle character that begins every transmission.
If the TE bit is cleared during a transmission, the TxD pin becomes idle after completion of the
transmission in progress. Clearing and then setting the TE bit during a transmission queues an idle
character to be sent after the character currently being transmitted.
NOTE
When a break sequence is followed immediately by an idle character, this
SCI design exhibits a condition in which the break character length is
reduced by one half bit time. In this instance, the break sequence will
consist of a valid start bit, eight or nine data bits (as defined by the M bit in
SCC1) of logic 0 and one half data bit length of logic 0 in the stop bit position
followed immediately by the idle character. To ensure a break character of
the proper length is transmitted, always queue up a byte of data to be
transmitted while the final break sequence is in progress.
NOTE
When queueing an idle character, return the TE bit to logic 1 before the stop
bit of the current character shifts out to the TxD pin. Setting TE after the stop
bit appears on TxD causes data previously written to the SCDR to be lost.
A good time to toggle the TE bit for a queued idle character is when the
SCTE bit becomes set and just before writing the next byte to the SCDR.
16.4.2.5 Inversion of Transmitted Output
The transmit inversion bit (TXINV) in SCI control register 1 (SCC1) reverses the polarity of transmitted
data. All transmitted values, including idle, break, start, and stop bits, are inverted when TXINV is at logic
1. (See 16.8.1 SCI Control Register 1.)
16.4.2.6 Transmitter Interrupts
The following conditions can generate CPU interrupt requests from the SCI transmitter:
• SCI transmitter empty (SCTE) — The SCTE bit in SCS1 indicates that the SCDR has transferred
a character to the transmit shift register. SCTE can generate a transmitter CPU interrupt request.
Setting the SCI transmit interrupt enable bit, SCTIE, in SCC2 enables the SCTE bit to generate
transmitter CPU interrupt requests.
• Transmission complete (TC) — The TC bit in SCS1 indicates that the transmit shift register and the
SCDR are empty and that no break or idle character has been generated. The transmission
complete interrupt enable bit, TCIE, in SCC2 enables the TC bit to generate transmitter CPU
interrupt requests.
16.4.3 Receiver
Figure 16-6 shows the structure of the SCI receiver.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
145
Serial Communications Interface (SCI)
INTERNAL BUS
SCR1
SCP0
SCR0
BAUD
DIVIDER
÷ 16
CGMXCLK
DATA
RECOVERY
RxD
BKF
ALL ZEROS
CPU INTERRUPT REQUEST
RPF
ERROR CPU INTERRUPT REQUEST
STOP
PRESCALER
H
ALL ONES
÷4
SCI DATA REGISTER
11-BIT
RECEIVE SHIFT REGISTER
8
7
M
WAKE
ILTY
PEN
PTY
START
SCR2
6
5
4
3
2
1
0
L
MSB
SCP1
SCRF
WAKEUP
LOGIC
IDLE
R8
PARITY
CHECKING
IDLE
ILIE
SCRF
SCRIE
RWU
ILIE
SCRIE
OR
ORIE
NF
NEIE
FE
FEIE
PE
PEIE
OR
ORIE
NF
NEIE
FE
FEIE
PE
PEIE
Figure 16-6. SCI Receiver Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
146
Freescale Semiconductor
Functional Description
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
Reset:
0
0
0
0
0
0
0
0
Read:
R8
T8
R
R
ORIE
NEIE
FEIE
PEIE
Read:
SCI Control Register 1 (SCC1) Write:
Reset:
Read:
SCI Control Register 2 (SCC2) Write:
SCI Control Register 3 (SCC3) Write:
Reset:
U
U
0
0
0
0
0
0
Read:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
Reset:
1
1
0
0
0
0
0
0
Read:
0
0
0
0
0
0
BKF
RPF
Reset:
0
0
0
0
0
0
0
0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
SCI Data Register (SCDR) Write:
T7
T6
T5
T4
T3
T2
T1
T0
SCI Status Register 1 (SCS1) Write:
SCI Status Register 2 (SCS2) Write:
Reset:
Read:
Unaffected by Reset
0
0
0
0
SCI Baud Rate Register (SCBR) Write:
Reset:
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
R
= Reserved
= Unimplemented
U = Unaffected
Figure 16-7. SCI I/O Receiver Register Summary
Table 16-4. SCI Receiver I/O Address Summary
Register
SCC1
SCC2
SCC3
SCS1
SCS2
SCDR
SCBR
Address
$0013
$0014
$0015
$0016
$0017
$0018
$0019
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
147
Serial Communications Interface (SCI)
16.4.3.1 Character Length
The receiver can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI control register 1
(SCC1) determines character length. When receiving 9-bit data, bit R8 in SCI control register 2 (SCC2)
is the ninth bit (bit 8). When receiving 8-bit data, bit R8 is a copy of the eighth bit (bit 7).
16.4.3.2 Character Reception
During an SCI reception, the receive shift register shifts characters in from the RxD pin. The SCI data
register (SCDR) is the read-only buffer between the internal data bus and the receive shift register.
After a complete character shifts into the receive shift register, the data portion of the character transfers
to the SCDR. The SCI receiver full bit, SCRF, in SCI status register 1 (SCS1) becomes set, indicating that
the received byte can be read. If the SCI receive interrupt enable bit, SCRIE, in SCC2 is also set, the
SCRF bit generates a receiver CPU interrupt request.
16.4.3.3 Data Sampling
The receiver samples the RxD pin at the RT clock rate. The RT clock is an internal signal with a frequency
16 times the baud rate. To adjust for baud rate mismatch, the RT clock is resynchronized at the following
times (see Figure 16-8):
• After every start bit
• After the receiver detects a data bit change from logic 1 to logic 0 (after the majority of data bit
samples at RT8, RT9, and RT10 returns a valid logic 1 and the majority of the next RT8, RT9, and
RT10 samples returns a valid logic 0)
To locate the start bit, data recovery logic does an asynchronous search for a logic 0 preceded by three
logic 1s. When the falling edge of a possible start bit occurs, the RT clock begins to count to 16.
START BIT
RxD
SAMPLES
START BIT
QUALIFICATION
LSB
START BIT
DATA
VERIFICATION SAMPLING
RT CLOCK
STATE
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT2
RT3
RT4
RT5
RT6
RT7
RT8
RT9
RT10
RT11
RT12
RT13
RT14
RT15
RT16
RT1
RT2
RT3
RT4
RT
CLOCK
RT CLOCK
RESET
Figure 16-8. Receiver Data Sampling
MC68HC908AZ32A Data Sheet, Rev. 2
148
Freescale Semiconductor
Functional Description
To verify the start bit and to detect noise, data recovery logic takes samples at RT3, RT5, and RT7. Table
16-5 summarizes the results of the start bit verification samples.
Table 16-5. Start Bit Verification
RT3, RT5, and RT7 Samples
Start Bit Verification
Noise Flag
000
Yes
0
001
Yes
1
010
Yes
1
011
No
0
100
Yes
1
101
No
0
110
No
0
111
No
0
If start bit verification is not successful, the RT clock is reset and a new search for a start bit begins.
To determine the value of a data bit and to detect noise, recovery logic takes samples at RT8, RT9, and
RT10. Table 16-6 summarizes the results of the data bit samples.
Table 16-6. Data Bit Recovery
RT8, RT9, and RT10 Samples
Data Bit Determination
Noise Flag
000
0
0
001
0
1
010
0
1
011
1
1
100
0
1
101
1
1
110
1
1
111
1
0
NOTE
The RT8, RT9, and RT10 samples do not affect start bit verification. If any
or all of the RT8, RT9, and RT10 start bit samples are logic 1s following a
successful start bit verification, the noise flag (NF) is set and the receiver
assumes that the bit is a start bit.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
149
Serial Communications Interface (SCI)
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and RT10. Table 16-7
summarizes the results of the stop bit samples.
Table 16-7. Stop Bit Recovery
RT8, RT9, and RT10 Samples
Framing Error Flag
Noise Flag
000
1
0
001
1
1
010
1
1
011
0
1
100
1
1
101
0
1
110
0
1
111
0
0
16.4.3.4 Framing Errors
If the data recovery logic does not detect a logic 1 where the stop bit should be in an incoming character,
it sets the framing error bit, FE, in SCS1. A break character also sets the FE bit because a break character
has no stop bit. The FE bit is set at the same time that the SCRF bit is set.
16.4.3.5 Baud Rate Tolerance
A transmitting device may be operating at a baud rate below or above the receiver baud rate.
Accumulated bit time misalignment can cause one of the three stop bit data samples to fall outside the
actual stop bit. Then a noise error occurs. If more than one of the samples is outside the stop bit, a framing
error occurs. In most applications, the baud rate tolerance is much more than the degree of misalignment
that is likely to occur.
As the receiver samples an incoming character, it resynchronizes the RT clock on any valid falling edge
within the character. Resynchronization within characters corrects misalignments between transmitter bit
times and receiver bit times.
Slow Data Tolerance
Figure 16-9 shows how much a slow received character can be misaligned without causing a noise
error or a framing error. The slow stop bit begins at RT8 instead of RT1 but arrives in time for the stop
bit data samples at RT8, RT9, and RT10.
MSB
STOP
RT16
RT15
RT14
RT13
RT12
RT11
RT10
RT9
RT8
RT7
RT6
RT5
RT4
RT3
RT2
RT1
RECEIVER
RT CLOCK
DATA
SAMPLES
Figure 16-9. Slow Data
MC68HC908AZ32A Data Sheet, Rev. 2
150
Freescale Semiconductor
Functional Description
For an 8-bit character, data sampling of the stop bit takes the receiver
9 bit times × 16 RT cycles + 10 RT cycles = 154 RT cycles.
With the misaligned character shown in Figure 16-9, the receiver counts 154 RT cycles at the point
when the count of the transmitting device is 9 bit times × 16 RT cycles + 3 RT cycles = 147 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a slow 8-bit
character with no errors is
154 – 147
-------------------------- × 100 = 4.54%
154
For a 9-bit character, data sampling of the stop bit takes the receiver
10 bit times × 16 RT cycles + 10 RT cycles = 170 RT cycles.
With the misaligned character shown in Figure 16-9, the receiver counts 170 RT cycles at the point
when the count of the transmitting device is 10 bit
times × 16 RT cycles + 3 RT cycles = 163 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a slow 9-bit
character with no errors is
170 – 163
-------------------------- × 100 = 4.12%
170
Fast Data Tolerance
Figure 16-10 shows how much a fast received character can be misaligned without causing a noise
error or a framing error. The fast stop bit ends at RT10 instead of RT16 but is still there for the stop bit
data samples at RT8, RT9, and RT10.
STOP
IDLE OR NEXT CHARACTER
RT16
RT15
RT14
RT13
RT12
RT11
RT10
RT9
RT8
RT7
RT6
RT5
RT4
RT3
RT2
RT1
RECEIVER
RT CLOCK
DATA
SAMPLES
Figure 16-10. Fast Data
For an 8-bit character, data sampling of the stop bit takes the receiver
9 bit times × 16 RT cycles + 10 RT cycles = 154 RT cycles.
With the misaligned character shown in Figure 16-10, the receiver counts 154 RT cycles at the point
when the count of the transmitting device is 10 bit times × 16 RT cycles = 160 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a fast 8-bit
character with no errors is
154 – 160
-------------------------- × 100 = 3.90%.
154
For a 9-bit character, data sampling of the stop bit takes the receiver
10 bit times × 16 RT cycles + 10 RT cycles = 170 RT cycles.
With the misaligned character shown in Figure 16-10, the receiver counts 170 RT cycles at the point
when the count of the transmitting device is 11 bit times × 16 RT cycles = 176 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a fast 9-bit
character with no errors is
170 – 176
-------------------------- × 100 = 3.53%.
170
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
151
Serial Communications Interface (SCI)
16.4.3.6 Receiver Wakeup
So that the MCU can ignore transmissions intended only for other receivers in multiple-receiver systems,
the receiver can be put into a standby state. Setting the receiver wakeup bit, RWU, in SCC2 puts the
receiver into a standby state during which receiver interrupts are disabled.
Depending on the state of the WAKE bit in SCC1, either of two conditions on the RxD pin can bring the
receiver out of the standby state:
• Address mark — An address mark is a logic 1 in the most significant bit position of a received
character. When the WAKE bit is set, an address mark wakes the receiver from the standby state
by clearing the RWU bit. The address mark also sets the SCI receiver full bit, SCRF. Software can
then compare the character containing the address mark to the user-defined address of the
receiver. If they are the same, the receiver remains awake and processes the characters that
follow. If they are not the same, software can set the RWU bit and put the receiver back into the
standby state.
• Idle input line condition — When the WAKE bit is clear, an idle character on the RxD pin wakes the
receiver from the standby state by clearing the RWU bit. The idle character that wakes the receiver
does not set the receiver idle bit, IDLE, or the SCI receiver full bit, SCRF. The idle line type bit,
ILTY, determines whether the receiver begins counting logic 1s as idle character bits after the start
bit or after the stop bit.
NOTE
With the WAKE bit clear, setting the RWU bit after the RxD pin has been
idle may cause the receiver to wake up immediately.
16.4.3.7 Receiver Interrupts
• The following sources can generate CPU interrupt requests from the SCI receiver:
• SCI receiver full (SCRF) — The SCRF bit in SCS1 indicates that the receive shift register has
transferred a character to the SCDR. SCRF can generate a receiver CPU interrupt request. Setting
the SCI receive interrupt enable bit, SCRIE, in SCC2 enables the SCRF bit to generate receiver
CPU interrupts.
• Idle input (IDLE) — The IDLE bit in SCS1 indicates that 10 or 11 consecutive logic 1s shifted in
from the RxD pin. The idle line interrupt enable bit, ILIE, in SCC2 enables the IDLE bit to generate
CPU interrupt requests.
16.4.3.8 Error Interrupts
The following receiver error flags in SCS1 can generate CPU interrupt requests:
• Receiver overrun (OR) — The OR bit indicates that the receive shift register shifted in a new
character before the previous character was read from the SCDR. The previous character remains
in the SCDR, and the new character is lost. The overrun interrupt enable bit, ORIE, in SCC3
enables OR to generate SCI error CPU interrupt requests.
• Noise flag (NF) — The NF bit is set when the SCI detects noise on incoming data or break
characters, including start, data, and stop bits. The noise error interrupt enable bit, NEIE, in SCC3
enables NF to generate SCI error CPU interrupt requests.
• Framing error (FE) — The FE bit in SCS1 is set when a logic 0 occurs where the receiver expects
a stop bit. The framing error interrupt enable bit, FEIE, in SCC3 enables FE to generate SCI error
CPU interrupt requests.
MC68HC908AZ32A Data Sheet, Rev. 2
152
Freescale Semiconductor
Low-Power Modes
•
Parity error (PE) — The PE bit in SCS1 is set when the SCI detects a parity error in incoming data.
The parity error interrupt enable bit, PEIE, in SCC3 enables PE to generate SCI error CPU interrupt
requests.
16.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
16.5.1 Wait Mode
The SCI module remains active in wait mode. Any enabled CPU interrupt request from the SCI module
can bring the MCU out of wait mode.
If SCI module functions are not required during wait mode, reduce power consumption by disabling the
module before executing the WAIT instruction.
16.5.2 Stop Mode
The SCI module is inactive in stop mode. The STOP instruction does not affect SCI register states. Any
enabled CPU interrupt request from the SCI module does not bring the MCU out of Stop mode. SCI
module operation resumes after the MCU exits stop mode.
Because the internal clock is inactive during stop mode, entering stop mode during an SCI transmission
or reception results in invalid data.
16.6 SCI During Break Module Interrupts
The BCFE bit in the break flag control register (BFCR) enables software to clear status bits during the
break state. (See Chapter 11 Brake Module).
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a two-step read/write clearing procedure. If software does the first step on such a
bit before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
16.7 I/O Signals
Port E shares two of its pins with the SCI module. The two SCI I/O pins are:
• PTE0/SCTxD — Transmit data
• PTE1/SCRxD — Receive data
16.7.1 PTE0/SCTxD (Transmit Data)
The PTE0/SCTxD pin is the serial data output from the SCI transmitter. The SCI shares the PTE0/SCTxD
pin with port E. When the SCI is enabled, the PTE0/SCTxD pin is an output regardless of the state of the
DDRE2 bit in data direction register E (DDRE).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
153
Serial Communications Interface (SCI)
16.7.2 PTE1/SCRxD (Receive Data)
The PTE1/SCRxD pin is the serial data input to the SCI receiver. The SCI shares the PTE1/SCRxD pin
with port E. When the SCI is enabled, the PTE1/SCRxD pin is an input regardless of the state of the
DDRE1 bit in data direction register E (DDRE).
16.8 I/O Registers
The following I/O registers control and monitor SCI operation:
• SCI control register 1 (SCC1)
• SCI control register 2 (SCC2)
• SCI control register 3 (SCC3)
• SCI status register 1 (SCS1)
• SCI status register 2 (SCS2)
• SCI data register (SCDR)
• SCI baud rate register (SCBR)
16.8.1 SCI Control Register 1
SCI control register 1:
• Enables loop mode operation
• Enables the SCI
• Controls output polarity
• Controls character length
• Controls SCI wakeup method
• Controls idle character detection
• Enables parity function
• Controls parity type
Address:
Read:
Write:
Reset:
$0013
Bit 7
6
5
4
3
2
1
Bit 0
LOOPS
ENSCI
TXINV
M
WAKE
ILLTY
PEN
PTY
0
0
0
0
0
0
0
0
Figure 16-11. SCI Control Register 1 (SCC1)
LOOPS — Loop Mode Select Bit
This read/write bit enables loop mode operation. In loop mode the RxD pin is disconnected from the
SCI, and the transmitter output goes into the receiver input. Both the transmitter and the receiver must
be enabled to use loop mode. Reset clears the LOOPS bit.
1 = Loop mode enabled
0 = Normal operation enabled
MC68HC908AZ32A Data Sheet, Rev. 2
154
Freescale Semiconductor
I/O Registers
ENSCI — Enable SCI Bit
This read/write bit enables the SCI and the SCI baud rate generator. Clearing ENSCI sets the SCTE
and TC bits in SCI status register 1 and disables transmitter interrupts. Reset clears the ENSCI bit.
1 = SCI enabled
0 = SCI disabled
TXINV — Transmit Inversion Bit
This read/write bit reverses the polarity of transmitted data. Reset clears the TXINV bit.
1 = Transmitter output inverted
0 = Transmitter output not inverted
NOTE
Setting the TXINV bit inverts all transmitted values, including idle, break,
start, and stop bits.
M — Mode (Character Length) Bit
This read/write bit determines whether SCI characters are eight or nine bits long. (See Table 16-8).The
ninth bit can serve as an extra stop bit, as a receiver wakeup signal, or as a parity bit. Reset clears the
M bit.
1 = 9-bit SCI characters
0 = 8-bit SCI characters
WAKE — Wakeup Condition Bit
This read/write bit determines which condition wakes up the SCI: a logic 1 (address mark) in the most
significant bit position of a received character or an idle condition on the RxD pin. Reset clears the
WAKE bit.
1 = Address mark wakeup
0 = Idle line wakeup
ILTY — Idle Line Type Bit
This read/write bit determines when the SCI starts counting logic 1s as idle character bits. The counting
begins either after the start bit or after the stop bit. If the count begins after the start bit, then a string
of logic 1s preceding the stop bit may cause false recognition of an idle character. Beginning the count
after the stop bit avoids false idle character recognition, but requires properly synchronized
transmissions. Reset clears the ILTY bit.
1 = Idle character bit count begins after stop bit
0 = Idle character bit count begins after start bit
PEN — Parity Enable Bit
This read/write bit enables the SCI parity function. (See Table 16-8). When enabled, the parity function
inserts a parity bit in the most significant bit position. (See Table 16-7). Reset clears the PEN bit.
1 = Parity function enabled
0 = Parity function disabled
PTY — Parity Bit
This read/write bit determines whether the SCI generates and checks for odd parity or even parity.
(See Table 16-8). Reset clears the PTY bit.
1 = Odd parity
0 = Even parity
NOTE
Changing the PTY bit in the middle of a transmission or reception can
generate a parity error.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
155
Serial Communications Interface (SCI)
Table 16-8. Character Format Selection
Control Bits
Character Format
M
PEN:PTY
Start
Bits
Data
Bits
Parity
Stop
Bits
Character
Length
0
0X
1
8
None
1
10 Bits
1
0X
1
9
None
1
11 Bits
0
10
1
7
Even
1
10 Bits
0
11
1
7
Odd
1
10 Bits
1
10
1
8
Even
1
11 Bits
1
11
1
8
Odd
1
11 Bits
16.8.2 SCI Control Register 2
SCI control register 2:
• Enables the following CPU interrupt requests:
– Enables the SCTE bit to generate transmitter CPU interrupt requests
– Enables the TC bit to generate transmitter CPU interrupt requests
– Enables the SCRF bit to generate receiver CPU interrupt requests
– Enables the IDLE bit to generate receiver CPU interrupt requests
• Enables the transmitter
• Enables the receiver
• Enables SCI wakeup
• Transmits SCI break characters
Address:
Read:
Write:
Reset:
$0014
Bit 7
6
5
4
3
2
1
Bit 0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
0
0
0
0
0
0
0
0
Figure 16-12. SCI Control Register 2 (SCC2)
SCTIE — SCI Transmit Interrupt Enable Bit
This read/write bit enables the SCTE bit to generate SCI transmitter CPU interrupt requests. Setting
the SCTIE bit in SCC3 enables the SCTE bit to generate CPU interrupt requests. Reset clears the
SCTIE bit.
1 = SCTE enabled to generate CPU interrupt
0 = SCTE not enabled to generate CPU interrupt
TCIE — Transmission Complete Interrupt Enable Bit
This read/write bit enables the TC bit to generate SCI transmitter CPU interrupt requests. Reset clears
the TCIE bit.
1 = TC enabled to generate CPU interrupt requests
0 = TC not enabled to generate CPU interrupt requests
MC68HC908AZ32A Data Sheet, Rev. 2
156
Freescale Semiconductor
I/O Registers
SCRIE — SCI Receive Interrupt Enable Bit
This read/write bit enables the SCRF bit to generate SCI receiver CPU interrupt requests. Setting the
SCRIE bit in SCC3 enables the SCRF bit to generate CPU interrupt requests. Reset clears the SCRIE
bit.
1 = SCRF enabled to generate CPU interrupt
0 = SCRF not enabled to generate CPU interrupt
ILIE — Idle Line Interrupt Enable Bit
This read/write bit enables the IDLE bit to generate SCI receiver CPU interrupt requests. Reset clears
the ILIE bit.
1 = IDLE enabled to generate CPU interrupt requests
0 = IDLE not enabled to generate CPU interrupt requests
TE — Transmitter Enable Bit
Setting this read/write bit begins the transmission by sending a preamble of 10 or 11 logic 1s from the
transmit shift register to the TxD pin. If software clears the TE bit, the transmitter completes any
transmission in progress before the TxD returns to the idle condition (logic 1). Clearing and then setting
TE during a transmission queues an idle character to be sent after the character currently being
transmitted. Reset clears the TE bit.
1 = Transmitter enabled
0 = Transmitter disabled
NOTE
Writing to the TE bit is not allowed when the enable SCI bit (ENSCI) is clear.
ENSCI is in SCI control register 1.
RE — Receiver Enable Bit
Setting this read/write bit enables the receiver. Clearing the RE bit disables the receiver but does not
affect receiver interrupt flag bits. Reset clears the RE bit.
1 = Receiver enabled
0 = Receiver disabled
NOTE
Writing to the RE bit is not allowed when the enable SCI bit (ENSCI) is
clear. ENSCI is in SCI control register 1.
RWU — Receiver Wakeup Bit
This read/write bit puts the receiver in a standby state during which receiver interrupts are disabled.
The WAKE bit in SCC1 determines whether an idle input or an address mark brings the receiver out
of the standby state and clears the RWU bit. Reset clears the RWU bit.
1 = Standby state
0 = Normal operation
SBK — Send Break Bit
Setting and then clearing this read/write bit transmits a break character followed by a logic 1. The logic
1 after the break character guarantees recognition of a valid start bit. If SBK remains set, the
transmitter continuously transmits break characters with no logic 1s between them. Reset clears the
SBK bit.
1 = Transmit break characters
0 = No break characters being transmitted
NOTE
Do not toggle the SBK bit immediately after setting the SCTE bit. Toggling
SBK before the preamble begins causes the SCI to send a break character
instead of a preamble.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
157
Serial Communications Interface (SCI)
16.8.3 SCI Control Register 3
SCI control register 3:
• Stores the ninth SCI data bit received and the ninth SCI data bit to be transmitted.
• Enables the following interrupts:
– Receiver overrun interrupts
– Noise error interrupts
– Framing error interrupts
– Parity error interrupts
Address:
$0015
Bit 7
Read:
R8
Write:
Reset:
U
6
5
4
3
2
1
Bit 0
T8
R
R
ORIE
NEIE
FEIE
PEIE
U
0
0
0
0
0
0
R
= Reserved
= Unimplemented
U = Unaffected
Figure 16-13. SCI Control Register 3 (SCC3)
R8 — Received Bit 8
When the SCI is receiving 9-bit characters, R8 is the read-only ninth bit (bit 8) of the received character.
R8 is received at the same time that the SCDR receives the other 8 bits.
When the SCI is receiving 8-bit characters, R8 is a copy of the eighth bit (bit 7). Reset has no effect on
the R8 bit.
T8 — Transmitted Bit 8
When the SCI is transmitting 9-bit characters, T8 is the read/write ninth bit (bit 8) of the transmitted
character. T8 is loaded into the transmit shift register at the same time that the SCDR is loaded into
the transmit shift register. Reset has no effect on the T8 bit.
ORIE — Receiver Overrun Interrupt Enable Bit
This read/write bit enables SCI error CPU interrupt requests generated by the receiver overrun bit, OR.
1 = SCI error CPU interrupt requests from OR bit enabled
0 = SCI error CPU interrupt requests from OR bit disabled
NEIE — Receiver Noise Error Interrupt Enable Bit
This read/write bit enables SCI error CPU interrupt requests generated by the noise error bit, NE.
Reset clears NEIE.
1 = SCI error CPU interrupt requests from NE bit enabled
0 = SCI error CPU interrupt requests from NE bit disabled
FEIE — Receiver Framing Error Interrupt Enable Bit
This read/write bit enables SCI error CPU interrupt requests generated by the framing error bit, FE.
Reset clears FEIE.
1 = SCI error CPU interrupt requests from FE bit enabled
0 = SCI error CPU interrupt requests from FE bit disabled
PEIE — Receiver Parity Error Interrupt Enable Bit
This read/write bit enables SCI receiver CPU interrupt requests generated by the parity error bit, PE.
Reset clears PEIE.
1 = SCI error CPU interrupt requests from PE bit enabled
0 = SCI error CPU interrupt requests from PE bit disabled
MC68HC908AZ32A Data Sheet, Rev. 2
158
Freescale Semiconductor
I/O Registers
16.8.4 SCI Status Register 1
SCI status register 1 contains flags to signal the following conditions:
• Transfer of SCDR data to transmit shift register complete
• Transmission complete
• Transfer of receive shift register data to SCDR complete
• Receiver input idle
• Receiver overrun
• Noisy data
• Framing error
• Parity error
Address:
$0016
Bit 7
6
5
4
3
2
1
Bit 0
Read:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
1
1
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 16-14. SCI Status Register 1 (SCS1)
SCTE — SCI Transmitter Empty Bit
This clearable, read-only bit is set when the SCDR transfers a character to the transmit shift register.
SCTE can generate an SCI transmitter CPU interrupt request. When the SCTIE bit in SCC2 is set,
SCTE generates an SCI transmitter CPU interrupt request. In normal operation, clear the SCTE bit by
reading SCS1 with SCTE set and then writing to SCDR. Reset sets the SCTE bit.
1 = SCDR data transferred to transmit shift register
0 = SCDR data not transferred to transmit shift register
TC — Transmission Complete Bit
This read-only bit is set when the SCTE bit is set, and no data, preamble, or break character is being
transmitted. TC generates an SCI transmitter CPU interrupt request if the TCIE bit in SCC2 is also set.
TC is cleared automatically when data, preamble, or break is queued and ready to be sent. There may
be up to 1.5 transmitter clocks of latency between queueing data, preamble, and break and the
transmission actually starting. Reset sets the TC bit.
1 = No transmission in progress
0 = Transmission in progress
SCRF — SCI Receiver Full Bit
This clearable, read-only bit is set when the data in the receive shift register transfers to the SCI data
register. SCRF can generate an SCI receiver CPU interrupt request. When the SCRIE bit in SCC2 is
set the SCRF generates a CPU interrupt request. In normal operation, clear the SCRF bit by reading
SCS1 with SCRF set and then reading the SCDR. Reset clears SCRF.
1 = Received data available in SCDR
0 = Data not available in SCDR
IDLE — Receiver Idle Bit
This clearable, read-only bit is set when 10 or 11 consecutive logic 1s appear on the receiver input.
IDLE generates an SCI error CPU interrupt request if the ILIE bit in SCC2 is also set. Clear the IDLE
bit by reading SCS1 with IDLE set and then reading the SCDR. After the receiver is enabled, it must
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
159
Serial Communications Interface (SCI)
receive a valid character that sets the SCRF bit before an idle condition can set the IDLE bit. Also, after
the IDLE bit has been cleared, a valid character must again set the SCRF bit before an idle condition
can set the IDLE bit. Reset clears the IDLE bit.
1 = Receiver input idle
0 = Receiver input active (or idle since the IDLE bit was cleared)
OR — Receiver Overrun Bit
This clearable, read-only bit is set when software fails to read the SCDR before the receive shift
register receives the next character. The OR bit generates an SCI error CPU interrupt request if the
ORIE bit in SCC3 is also set. The data in the shift register is lost, but the data already in the SCDR is
not affected. Clear the OR bit by reading SCS1 with OR set and then reading the SCDR. Reset clears
the OR bit.
1 = Receive shift register full and SCRF = 1
0 = No receiver overrun
Software latency may allow an overrun to occur between reads of SCS1 and SCDR in the flag-clearing
sequence. Figure 16-15 shows the normal flag-clearing sequence and an example of an overrun caused
by a delayed flag-clearing sequence. The delayed read of SCDR does not clear the OR bit because OR
was not set when SCS1 was read. Byte 2 caused the overrun and is lost. The next flag-clearing sequence
reads byte 3 in the SCDR instead of byte 2.
In applications that are subject to software latency or in which it is important to know which byte is lost
due to an overrun, the flag-clearing routine can check the OR bit in a second read of SCS1 after reading
the data register.
BYTE 1
BYTE 2
BYTE 3
SCRF = 0
SCRF = 1
SCRF = 0
SCRF = 1
SCRF = 0
SCRF = 1
NORMAL FLAG CLEARING SEQUENCE
BYTE 4
READ SCS1
SCRF = 1
OR = 0
READ SCS1
SCRF = 1
OR = 0
READ SCS1
SCRF = 1
OR = 0
READ SCDR
BYTE 1
READ SCDR
BYTE 2
READ SCDR
BYTE 3
BYTE 1
BYTE 2
BYTE 3
SCRF = 0
OR = 0
SCRF = 1
OR = 1
SCRF = 0
OR = 1
SCRF = 1
SCRF = 1
OR = 1
DELAYED FLAG CLEARING SEQUENCE
BYTE 4
READ SCS1
SCRF = 1
OR = 0
READ SCS1
SCRF = 1
OR = 1
READ SCDR
BYTE 1
READ SCDR
BYTE 3
Figure 16-15. Flag Clearing Sequence
NF — Receiver Noise Flag Bit
This clearable, read-only bit is set when the SCI detects noise on the RxD pin. NF generates an NF
CPU interrupt request if the NEIE bit in SCC3 is also set. Clear the NF bit by reading SCS1 and then
reading the SCDR. Reset clears the NF bit.
1 = Noise detected
0 = No noise detected
MC68HC908AZ32A Data Sheet, Rev. 2
160
Freescale Semiconductor
I/O Registers
FE — Receiver Framing Error Bit
This clearable, read-only bit is set when a logic 0 is accepted as the stop bit. FE generates an SCI error
CPU interrupt request if the FEIE bit in SCC3 also is set. Clear the FE bit by reading SCS1 with FE set
and then reading the SCDR. Reset clears the FE bit.
1 = Framing error detected
0 = No framing error detected
PE — Receiver Parity Error Bit
This clearable, read-only bit is set when the SCI detects a parity error in incoming data. PE generates
a PE CPU interrupt request if the PEIE bit in SCC3 is also set. Clear the PE bit by reading SCS1 with
PE set and then reading the SCDR. Reset clears the PE bit.
1 = Parity error detected
0 = No parity error detected
16.8.5 SCI Status Register 2
SCI status register 2 contains flags to signal the following conditions:
• Break character detected
• Incoming data
Address:
Read:
$0017
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
BKF
RPF
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 16-16. SCI Status Register 2 (SCS2)
BKF — Break Flag Bit
This clearable, read-only bit is set when the SCI detects a break character on the RxD pin. In SCS1,
the FE and SCRF bits are also set. In 9-bit character transmissions, the R8 bit in SCC3 is cleared. BKF
does not generate a CPU interrupt request. Clear BKF by reading SCS2 with BKF set and then reading
the SCDR. Once cleared, BKF can become set again only after logic 1s again appear on the RxD pin
followed by another break character. Reset clears the BKF bit.
1 = Break character detected
0 = No break character detected
RPF — Reception in Progress Flag Bit
This read-only bit is set when the receiver detects a logic 0 during the RT1 time period of the start bit
search. RPF does not generate an interrupt request. RPF is reset after the receiver detects false start
bits (usually from noise or a baud rate mismatch), or when the receiver detects an idle character.
Polling RPF before disabling the SCI module or entering stop mode can show whether a reception is
in progress.
1 = Reception in progress
0 = No reception in progress
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
161
Serial Communications Interface (SCI)
16.8.6 SCI Data Register
The SCI data register is the buffer between the internal data bus and the receive and transmit shift
registers. Reset has no effect on data in the SCI data register.
Address:
$0018
Bit 7
6
5
4
3
2
1
Bit 0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
Write:
T7
T6
T5
T4
T3
T2
T1
T0
Reset:
Unaffected by Reset
Figure 16-17. SCI Data Register (SCDR)
R7/T7:R0/T0 — Receive/Transmit Data Bits
Reading address $0018 accesses the read-only received data bits, R7:R0. Writing to address $0018
writes the data to be transmitted, T7:T0. Reset has no effect on the SCI data register.
NOTE
Do not use read-modify-write instructions on the SCI data register.
16.8.7 SCI Baud Rate Register
The baud rate register selects the baud rate for both the receiver and the transmitter.
Address:
Read:
$0019
Bit 7
6
0
0
0
0
Write:
Reset:
5
4
3
2
1
Bit 0
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
R
= Reserved
= Unimplemented
Figure 16-18. SCI Baud Rate Register (SCBR)
SCP1 and SCP0 — SCI Baud Rate Prescaler Bits
These read/write bits select the baud rate prescaler divisor as shown in Table 16-9. Reset clears SCP1
and SCP0.
Table 16-9. SCI Baud Rate Prescaling
SCP[1:0]
Prescaler Divisor (PD)
00
1
01
3
10
4
11
13
MC68HC908AZ32A Data Sheet, Rev. 2
162
Freescale Semiconductor
I/O Registers
SCR2 – SCR0 — SCI Baud Rate Select Bits
These read/write bits select the SCI baud rate divisor as shown in Table 16-10. Reset clears
SCR2–SCR0.
Table 16-10. SCI Baud Rate Selection
SCR[2:1:0]
Baud Rate Divisor (BD)
000
1
001
2
010
4
011
8
100
16
101
32
110
64
111
128
Use the following formula to calculate the SCI baud rate:
f Crystal
Baud rate = -----------------------------------64 × PD × BD
where:
fCrystal = crystal frequency
PD = prescaler divisor
BD = baud rate divisor
Table 16-11 shows the SCI baud rates that can be generated with a 4.9152-MHz crystal.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
163
Serial Communications Interface (SCI)
Table 16-11. SCI Baud Rate Selection Examples
SCP[1:0]
Prescaler
Divisor
(PD)
SCR[2:1:0]
Baud Rate
Divisor
(BD)
Baud Rate
(fCrystal = 4.9152 MHz)
00
1
000
1
76,800
00
1
001
2
38,400
00
1
010
4
19,200
00
1
011
8
9600
00
1
100
16
4800
00
1
101
32
2400
00
1
110
64
1200
00
1
111
128
600
01
3
000
1
25,600
01
3
001
2
12,800
01
3
010
4
6400
01
3
011
8
3200
01
3
100
16
1600
01
3
101
32
800
01
3
110
64
400
01
3
111
128
200
10
4
000
1
19,200
10
4
001
2
9600
10
4
010
4
4800
10
4
011
8
2400
10
4
100
16
1200
10
4
101
32
600
10
4
110
64
300
10
4
111
128
150
11
13
000
1
5908
11
13
001
2
2954
11
13
010
4
1477
11
13
011
8
739
11
13
100
16
369
11
13
101
32
185
11
13
110
64
92
11
13
111
128
46
MC68HC908AZ32A Data Sheet, Rev. 2
164
Freescale Semiconductor
Chapter 17
Serial Peirpheral Interface (SPI)
17.1 Introduction
This section describes the serial peripheral interface (SPI) module, which allows full-duplex, synchronous,
serial communications with peripheral devices.
17.2 Features
Features of the SPI module include:
• Full-Duplex Operation
• Master and Slave Modes
• Double-Buffered Operation with Separate Transmit and Receive Registers
• Four Master Mode Frequencies (Maximum = Bus Frequency ÷ 2)
• Maximum Slave Mode Frequency = Bus Frequency
• Serial Clock with Programmable Polarity and Phase
• Two Separately Enabled Interrupts with CPU Service:
– SPRF (SPI Receiver Full)
– SPTE (SPI Transmitter Empty)
• Mode Fault Error Flag with CPU Interrupt Capability
• Overflow Error Flag with CPU Interrupt Capability
• Programmable Wired-OR Mode
• I2C (Inter-Integrated Circuit) Compatibility
17.3 Pin Name and Register Name Conventions
The generic names of the SPI input/output (I/O) pins are:
• SS (slave select)
• SPSCK (SPI serial clock)
• MOSI (master out slave in)
• MISO (master in slave out)
The SPI shares four I/O pins with a parallel I/O port. The full name of an SPI pin reflects the name of the
shared port pin. Table 17-1 shows the full names of the SPI I/O pins. The generic pin names appear in
the text that follows.
Table 17-1. Pin Name Conventions
SPI Generic Pin Name
Full SPI Pin Name
MISO
MOSI
SS
SPSCK
PTE5/MISO
PTE6/MOSI
PTE4/SS
PTE7/SPSCK
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
165
Serial Peirpheral Interface (SPI)
The generic names of the SPI I/O registers are:
• SPI control register (SPCR)
• SPI status and control register (SPSCR)
• SPI data register (SPDR)
Table 17-2 shows the names and the addresses of the SPI I/O registers.
Table 17-2. I/O Register Addresses
Register Name
Address
SPI Control Register (SPCR)
$0010
SPI Status and Control Register (SPSCR)
$0011
SPI Data Register (SPDR)
$0012
17.4 Functional Description
Figure 17-1 summarizes the SPI I/O registers and Figure 17-2 shows the structure of the SPI module.
Addr
$0010
$0011
$0012
Register Name
SPI Control Register
(SPCR)
SPI Status and Control
Register (SPSCR)
SPI Data Register
(SPDR)
R/W
Bit 7
6
5
4
3
2
1
Bit 0
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
Reset:
0
0
1
0
1
0
0
0
Read:
SPRF
OVRF
MODF
SPTE
MODFEN
SPR1
SPR0
Read:
Write:
ERRIE
Write:
Reset:
0
0
0
0
1
0
0
0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
Write:
T7
T6
T5
T4
T3
T2
T1
T0
Reset:
Unaffected by Reset
R
= Reserved
= Unimplemented
Figure 17-1. SPI I/O Register Summary
The SPI module allows full-duplex, synchronous, serial communication between the MCU and peripheral
devices, including other MCUs. Software can poll the SPI status flags or SPI operation can be interrupt
driven. All SPI interrupts can be serviced by the CPU.
The following paragraphs describe the operation of the SPI module.
MC68HC908AZ32A Data Sheet, Rev. 2
166
Freescale Semiconductor
Functional Description
INTERNAL BUS
TRANSMIT DATA REGISTER
SHIFT REGISTER
BUS CLOCK
7
6
5
4
3
2
1
MISO
0
÷2
CLOCK
DIVIDER
MOSI
÷8
RECEIVE DATA REGISTER
÷ 32
PIN
CONTROL
LOGIC
÷ 128
SPMSTR
SPE
CLOCK
SELECT
SPR1
SPSCK
M
CLOCK
LOGIC
S
SS
SPR0
SPMSTR
TRANSMITTER CPU INTERRUPT REQUEST
CPHA
MODFEN
CPOL
SPWOM
ERRIE
SPI
CONTROL
SPTIE
RECEIVER/ERROR CPU INTERRUPT REQUEST
SPRIE
SPE
SPRF
SPTE
OVRF
MODF
Figure 17-2. SPI Module Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
167
Serial Peirpheral Interface (SPI)
17.4.1 Master Mode
The SPI operates in master mode when the SPI master bit, SPMSTR (SPCR $0010), is set.
NOTE
Configure the SPI modules as master and slave before enabling them.
Enable the master SPI before enabling the slave SPI. Disable the slave SPI
before disabling the master SPI. See 17.13.1 SPI Control Register.
Only a master SPI module can initiate transmissions. Software begins the transmission from a master SPI
module by writing to the SPI data register. If the shift register is empty, the byte immediately transfers to
the shift register, setting the SPI transmitter empty bit, SPTE (SPSCR $0011). The byte begins shifting
out on the MOSI pin under the control of the serial clock. (See Table 17-3).
The SPR1 and SPR0 bits control the baud rate generator and determine the speed of the shift register.
(See 17.13.2 SPI Status and Control Register). Through the SPSCK pin, the baud rate generator of the
master also controls the shift register of the slave peripheral.
MASTER MCU
SHIFT REGISTER
SLAVE MCU
MISO
MISO
MOSI
MOSI
SHIFT REGISTER
SPSCK
BAUD RATE
GENERATOR
SS
SPSCK
VDD
SS
Figure 17-3. Full-Duplex Master-Slave Connections
As the byte shifts out on the MOSI pin of the master, another byte shifts in from the slave on the master’s
MISO pin. The transmission ends when the receiver full bit, SPRF (SPSCR), becomes set. At the same
time that SPRF becomes set, the byte from the slave transfers to the receive data register. In normal
operation, SPRF signals the end of a transmission. Software clears SPRF by reading the SPI status and
control register and then reading the SPI data register. Writing to the SPI data register clears the SPTIE
bit.
17.4.2 Slave Mode
The SPI operates in slave mode when the SPMSTR bit (SPCR, $0010) is clear. In slave mode the SPSCK
pin is the input for the serial clock from the master MCU. Before a data transmission occurs, the SS pin
of the slave MCU must be at logic 0. SS must remain low until the transmission is complete. (See 17.6.2
Mode Fault Error).
In a slave SPI module, data enters the shift register under the control of the serial clock from the master
SPI module. After a byte enters the shift register of a slave SPI, it is transferred to the receive data
register, and the SPRF bit (SPSCR) is set. To prevent an overflow condition, slave software then must
read the SPI data register before another byte enters the shift register.
MC68HC908AZ32A Data Sheet, Rev. 2
168
Freescale Semiconductor
Transmission Formats
The maximum frequency of the SPSCK for an SPI configured as a slave is the bus clock speed, which is
twice as fast as the fastest master SPSCK clock that can be generated. The frequency of the SPSCK for
an SPI configured as a slave does not have to correspond to any SPI baud rate. The baud rate only
controls the speed of the SPSCK generated by an SPI configured as a master. Therefore, the frequency
of the SPSCK for an SPI configured as a slave can be any frequency less than or equal to the bus speed.
When the master SPI starts a transmission, the data in the slave shift register begins shifting out on the
MISO pin. The slave can load its shift register with a new byte for the next transmission by writing to its
transmit data register. The slave must write to its transmit data register at least one bus cycle before the
master starts the next transmission. Otherwise the byte already in the slave shift register shifts out on the
MISO pin. Data written to the slave shift register during a a transmission remains in a buffer until the end
of the transmission.
When the clock phase bit (CPHA) is set, the first edge of SPSCK starts a transmission. When CPHA is
clear, the falling edge of SS starts a transmission. (See 17.5 Transmission Formats).
If the write to the data register is late, the SPI transmits the data already in the shift register from the
previous transmission.
NOTE
To prevent SPSCK from appearing as a clock edge, SPSCK must be in the
proper idle state before the slave is enabled.
17.5 Transmission Formats
During an SPI transmission, data is simultaneously transmitted (shifted out serially) and received (shifted
in serially). A serial clock line synchronizes shifting and sampling on the two serial data lines. A slave
select line allows individual selection of a slave SPI device; slave devices that are not selected do not
interfere with SPI bus activities. On a master SPI device, the slave select line can be used optionally to
indicate a multiple-master bus contention.
17.5.1 Clock Phase and Polarity Controls
Software can select any of four combinations of serial clock (SCK) phase and polarity using two bits in
the SPI control register (SPCR). The clock polarity is specified by the CPOL control bit, which selects an
active high or low clock and has no significant effect on the transmission format.
The clock phase (CPHA) control bit (SPCR) selects one of two fundamentally different transmission
formats. The clock phase and polarity should be identical for the master SPI device and the
communicating slave device. In some cases, the phase and polarity are changed between transmissions
to allow a master device to communicate with peripheral slaves having different requirements.
NOTE
Before writing to the CPOL bit or the CPHA bit (SPCR), disable the SPI by
clearing the SPI enable bit (SPE).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
169
Serial Peirpheral Interface (SPI)
17.5.2 Transmission Format When CPHA = 0
Figure 17-4 shows an SPI transmission in which CPHA (SPCR) is logic 0. The figure should not be used
as a replacement for data sheet parametric information. Two waveforms are shown for SCK: one for
CPOL = 0 and another for CPOL = 1. The diagram may be interpreted as a master or slave timing
diagram since the serial clock (SCK), master in/slave out (MISO), and master out/slave in (MOSI) pins
are directly connected between the master and the slave. The MISO signal is the output from the slave,
and the MOSI signal is the output from the master. The SS line is the slave select input to the slave. The
slave SPI drives its MISO output only when its slave select input (SS) is at logic 0, so that only the selected
slave drives to the master. The SS pin of the master is not shown but is assumed to be inactive. The SS
pin of the master must be high or must be reconfigured as general-purpose I/O not affecting the SPI (see
17.6.2 Mode Fault Error). When CPHA = 0, the first SPSCK edge is the MSB capture strobe. Therefore,
the slave must begin driving its data before the first SPSCK edge, and a falling edge on the SS pin is used
to start the transmission. The SS pin must be toggled high and then low again between each byte
transmitted.
SCK CYCLE #
FOR REFERENCE
1
2
3
4
5
6
7
8
MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
SCK CPOL = 0
SCK CPOL = 1
MOSI
FROM MASTER
MISO
FROM SLAVE
MSB
SS TO SLAVE
CAPTURE STROBE
Figure 17-4. Transmission Format (CPHA = 0)
17.5.3 Transmission Format When CPHA = 1
Figure 17-5 shows an SPI transmission in which CPHA (SPCR) is logic 1. The figure should not be used
as a replacement for data sheet parametric information. Two waveforms are shown for SCK: one for
CPOL = 0 and another for CPOL = 1. The diagram may be interpreted as a master or slave timing
diagram since the serial clock (SCK), master in/slave out (MISO), and master out/slave in (MOSI) pins
are directly connected between the master and the slave. The MISO signal is the output from the slave,
and the MOSI signal is the output from the master. The SS line is the slave select input to the slave. The
slave SPI drives its MISO output only when its slave select input (SS) is at logic 0, so that only the selected
slave drives to the master. The SS pin of the master is not shown but is assumed to be inactive. The SS
pin of the master must be high or must be reconfigured as general-purpose I/O not affecting the SPI. (See
17.6.2 Mode Fault Error). When CPHA = 1, the master begins driving its MOSI pin on the first SPSCK
edge. Therefore, the slave uses the first SPSCK edge as a start transmission signal. The SS pin can
remain low between transmissions. This format may be preferable in systems having only one master and
only one slave driving the MISO data line.
MC68HC908AZ32A Data Sheet, Rev. 2
170
Freescale Semiconductor
Transmission Formats
SCK CYCLE #
FOR REFERENCE
1
2
3
4
5
6
7
8
MOSI
FROM MASTER
MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
MISO
FROM SLAVE
MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
SCK CPOL = 0
SCK CPOL =1
LSB
SS TO SLAVE
CAPTURE STROBE
Figure 17-5. Transmission Format (CPHA = 1)
17.5.4 Transmission Initiation Latency
When the SPI is configured as a master (SPMSTR = 1), transmissions are started by a software write to
the SPDR ($0012). CPHA has no effect on the delay to the start of the transmission, but it does affect the
initial state of the SCK signal. When CPHA = 0, the SCK signal remains inactive for the first half of the
first SCK cycle. When CPHA = 1, the first SCK cycle begins with an edge on the SCK line from its inactive
to its active level. The SPI clock rate (selected by SPR1–SPR0) affects the delay from the write to SPDR
and the start of the SPI transmission. (See Figure 17-6). The internal SPI clock in the master is a
free-running derivative of the internal MCU clock. It is only enabled when both the SPE and SPMSTR bits
(SPCR) are set to conserve power. SCK edges occur half way through the low time of the internal MCU
clock. Since the SPI clock is free-running, it is uncertain where the write to the SPDR will occur relative
to the slower SCK. This uncertainty causes the variation in the initiation delay shown in Figure 17-6. This
delay will be no longer than a single SPI bit time. That is, the maximum delay between the write to SPDR
and the start of the SPI transmission is two MCU bus cycles for DIV2, eight MCU bus cycles for DIV8, 32
MCU bus cycles for DIV32, and 128 MCU bus cycles for DIV128.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
171
Serial Peirpheral Interface (SPI)
WRITE
TO SPDR
INITIATION DELAY
BUS
CLOCK
MOSI
MSB
BIT 6
BIT 5
SCK
CPHA = 1
SCK
CPHA = 0
SCK CYCLE
NUMBER
1
2
3
INITIATION DELAY FROM WRITE SPDR TO TRANSFER BEGIN
⎧
⎨
⎮
⎮
⎩
⎮
⎮
⎮
WRITE
TO SPDR
BUS
CLOCK
EARLIEST LATEST
SCK = INTERNAL CLOCK ÷ 2;
2 POSSIBLE START POINTS
WRITE
TO SPDR
BUS
CLOCK
EARLIEST
WRITE
TO SPDR
SCK = INTERNAL CLOCK ÷ 8;
8 POSSIBLE START POINTS
LATEST
SCK = INTERNAL CLOCK ÷ 32;
32 POSSIBLE START POINTS
LATEST
SCK = INTERNAL CLOCK ÷ 128;
128 POSSIBLE START POINTS
LATEST
BUS
CLOCK
EARLIEST
WRITE
TO SPDR
BUS
CLOCK
EARLIEST
Figure 17-6. Transmission Start Delay (Master)
MC68HC908AZ32A Data Sheet, Rev. 2
172
Freescale Semiconductor
Error Conditions
17.6 Error Conditions
Two flags signal SPI error conditions:
1. Overflow (OVRF in SPSCR) — Failing to read the SPI data register before the next byte enters the
shift register sets the OVRF bit. The new byte does not transfer to the receive data register, and
the unread byte still can be read by accessing the SPI data register. OVRF is in the SPI status and
control register.
2. Mode fault error (MODF in SPSCR) — The MODF bit indicates that the voltage on the slave select
pin (SS) is inconsistent with the mode of the SPI. MODF is in the SPI status and control register.
17.6.1 Overflow Error
The overflow flag (OVRF in SPSCR) becomes set if the SPI receive data register still has unread data
from a previous transmission when the capture strobe of bit 1 of the next transmission occurs. (See Figure
17-4 and Figure 17-5.) If an overflow occurs, the data being received is not transferred to the receive data
register so that the unread data can still be read. Therefore, an overflow error always indicates the loss
of data.
OVRF generates a receiver/error CPU interrupt request if the error interrupt enable bit (ERRIE in SPSCR)
is also set. MODF and OVRF can generate a receiver/error CPU interrupt request. (See Figure 17-9). It
is not possible to enable only MODF or OVRF to generate a receiver/error CPU interrupt request.
However, leaving MODFEN low prevents MODF from being set.
If an end-of-block transmission interrupt was meant to pull the MCU out of wait, having an overflow
condition without overflow interrupts enabled causes the MCU to hang in wait mode. If the OVRF is
enabled to generate an interrupt, it can pull the MCU out of wait mode instead.
If the CPU SPRF interrupt is enabled and the OVRF interrupt is not, watch for an overflow condition.
Figure 17-7 shows how it is possible to miss an overflow.
BYTE 1
1
BYTE 2
4
BYTE 3
6
BYTE 4
8
SPRF
OVRF
READ SPSCR
READ SPDR
2
5
3
1
BYTE 1 SETS SPRF BIT.
2
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
BYTE 2 SETS SPRF BIT.
3
4
7
5
6
7
8
CPU READS SPSCRW WITH SPRF BIT SET
AND OVRF BIT CLEAR.
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
CPU READS BYTE 2 IN SPDR, CLEARING SPRF BIT,
BUT NOT OVRF BIT.
BYTE 4 FAILS TO SET SPRF BIT BECAUSE
OVRF BIT IS SET. BYTE 4 IS LOST.
Figure 17-7. Missed Read of Overflow Condition
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
173
Serial Peirpheral Interface (SPI)
The first part of Figure 17-7 shows how to read the SPSCR and SPDR to clear the SPRF without
problems. However, as illustrated by the second transmission example, the OVRF flag can be set in
between the time that SPSCR and SPDR are read.
In this case, an overflow can be easily missed. Since no more SPRF interrupts can be generated until this
OVRF is serviced, it will not be obvious that bytes are being lost as more transmissions are completed.
To prevent this, either enable the OVRF interrupt or do another read of the SPSCR after the read of the
SPDR. This ensures that the OVRF was not set before the SPRF was cleared and that future
transmissions will complete with an SPRF interrupt. Figure 17-8 illustrates this process. Generally, to
avoid this second SPSCR read, enable the OVRF to the CPU by setting the ERRIE bit (SPSCR).
BYTE 1
BYTE 2
BYTE 3
BYTE 4
1
5
7
11
SPI RECEIVE
COMPLETE
SPRF
OVRF
2
READ SPSCR
4
6
9
3
READ SPDR
1
BYTE 1 SETS SPRF BIT.
2
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
3
8
12
10
8
CPU READS BYTE 2 IN SPDR,
CLEARING SPRF BIT.
9
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
14
13
10 CPU READS BYTE 2 SPDR,
CLEARING OVRF BIT.
4
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
11 BYTE 4 SETS SPRF BIT.
5
BYTE 2 SETS SPRF BIT.
12 CPU READS SPSCR.
6
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
13 CPU READS BYTE 4 IN SPDR,
CLEARING SPRF BIT.
7
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
14 CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
Figure 17-8. Clearing SPRF When OVRF Interrupt Is Not Enabled
17.6.2 Mode Fault Error
For the MODF flag (in SPSCR) to be set, the mode fault error enable bit (MODFEN in SPSCR) must be
set. Clearing the MODFEN bit does not clear the MODF flag but does prevent MODF from being set again
after MODF is cleared.
MODF generates a receiver/error CPU interrupt request if the error interrupt enable bit (ERRIE in SPSCR)
is also set. The SPRF, MODF, and OVRF interrupts share the same CPU interrupt vector. MODF and
OVRF can generate a receiver/error CPU interrupt request. (See Figure 17-9). It is not possible to enable
only MODF or OVRF to generate a receiver/error CPU interrupt request. However, leaving MODFEN low
prevents MODF from being set.
MC68HC908AZ32A Data Sheet, Rev. 2
174
Freescale Semiconductor
Error Conditions
In a master SPI with the mode fault enable bit (MODFEN) set, the mode fault flag (MODF) is set if SS
goes to logic 0. A mode fault in a master SPI causes the following events to occur:
• If ERRIE = 1, the SPI generates an SPI receiver/error CPU interrupt request.
• The SPE bit is cleared.
• The SPTE bit is set.
• The SPI state counter is cleared.
• The data direction register of the shared I/O port regains control of port drivers.
NOTE
To prevent bus contention with another master SPI after a mode fault error,
clear all data direction register (DDR) bits associated with the SPI shared
port pins.
NOTE
Setting the MODF flag (SPSCR) does not clear the SPMSTR bit. Reading
SPMSTR when MODF = 1 will indicate a MODE fault error occurred in
either master mode or slave mode.
When configured as a slave (SPMSTR = 0), the MODF flag is set if SS goes high during a transmission.
When CPHA = 0, a transmission begins when SS goes low and ends once the incoming SPSCK returns
to its idle level after the shift of the eighth data bit. When CPHA = 1, the transmission begins when the
SPSCK leaves its idle level and SS is already low. The transmission continues until the SPSCK returns
to its IDLE level after the shift of the last data bit. (See 17.5 Transmission Formats).
NOTE
When CPHA = 0, a MODF occurs if a slave is selected (SS is at logic 0) and
later deselected (SS is at logic 1) even if no SPSCK is sent to that slave.
This happens because SS at logic 0 indicates the start of the transmission
(MISO driven out with the value of MSB) for CPHA = 0. When CPHA = 1, a
slave can be selected and then later deselected with no transmission
occurring. Therefore, MODF does not occur since a transmission was
never begun.
In a slave SPI (MSTR = 0), the MODF bit generates an SPI receiver/error CPU interrupt request if the
ERRIE bit is set. The MODF bit does not clear the SPE bit or reset the SPI in any way. Software can abort
the SPI transmission by toggling the SPE bit of the slave.
NOTE
A logic 1 voltage on the SS pin of a slave SPI puts the MISO pin in a high
impedance state. Also, the slave SPI ignores all incoming SPSCK clocks,
even if a transmission has begun.
To clear the MODF flag, read the SPSCR and then write to the SPCR register. This entire clearing
procedure must occur with no MODF condition existing or else the flag will not be cleared.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
175
Serial Peirpheral Interface (SPI)
17.7 Interrupts
Four SPI status flags can be enabled to generate CPU interrupt requests:
Table 17-3. SPI Interrupts
Flag
Request
SPTE (Transmitter Empty)
SPI Transmitter CPU Interrupt Request (SPTIE = 1)
SPRF (Receiver Full)
SPI Receiver CPU Interrupt Request (SPRIE = 1)
OVRF (Overflow)
SPI Receiver/Error Interrupt Request
(SPRIE = 1, ERRIE = 1)
MODF (Mode Fault)
SPI Receiver/Error Interrupt Request
(SPRIE = 1, ERRIE = 1, MODFEN = 1)
The SPI transmitter interrupt enable bit (SPTIE) enables the SPTE flag to generate transmitter CPU
interrupt requests.
The SPI receiver interrupt enable bit (SPRIE) enables the SPRF bit to generate receiver CPU interrupt,
provided that the SPI is enabled (SPE = 1).
The error interrupt enable bit (ERRIE) enables both the MODF and OVRF flags to generate a
receiver/error CPU interrupt request.
The mode fault enable bit (MODFEN) can prevent the MODF flag from being set so that only the OVRF
flag is enabled to generate receiver/error CPU interrupt requests.
SPTE
SPTIE
SPE
SPI TRANSMITTER
CPU INTERRUPT REQUEST
SPRIE
ERRIE
SPRF
SPI RECEIVER/ERROR
CPU INTERRUPT REQUEST
MODF
OVRF
Figure 17-9. SPI Interrupt Request Generation
Two sources in the SPI status and control register can generate CPU interrupt requests:
1. SPI receiver full bit (SPRF) — The SPRF bit becomes set every time a byte transfers from the shift
register to the receive data register. If the SPI receiver interrupt enable bit, SPRIE, is also set,
SPRF can generate an SPI receiver/error CPU interrupt request.
2. SPI transmitter empty (SPTE) — The SPTE bit becomes set every time a byte transfers from the
transmit data register to the shift register. If the SPI transmit interrupt enable bit, SPTIE, is also set,
SPTE can generate an SPTE CPU interrupt request.
MC68HC908AZ32A Data Sheet, Rev. 2
176
Freescale Semiconductor
Queuing Transmission Data
17.8 Queuing Transmission Data
The double-buffered transmit data register allows a data byte to be queued and transmitted. For an SPI
configured as a master, a queued data byte is transmitted immediately after the previous transmission
has completed. The SPI transmitter empty flag (SPTE in SPSCR) indicates when the transmit data buffer
is ready to accept new data. Write to the SPI data register only when the SPTE bit is high. Figure 17-10
shows the timing associated with doing back-to-back transmissions with the SPI (SPSCK has
CPHA:CPOL = 1:0).
WRITE TO SPDR
SPTE
1
3
8
5
2
10
SPSCK (CPHA:CPOL = 1:0)
MOSI
MSB BIT BIT BIT BIT BIT BIT LSB MSB BIT BIT BIT BIT BIT BIT LSB MSB BIT BIT BIT
6 5 4 3 2 1
6 5 4 3 2 1
6 5 4
BYTE 1
BYTE 2
BYTE 3
9
4
SPRF
6
READ SPSCR
11
7
READ SPDR
1
CPU WRITES BYTE 1 TO SPDR, CLEARING
SPTE BIT.
2
BYTE 1 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
3
CPU WRITES BYTE 2 TO SPDR, QUEUEING
BYTE 2 AND CLEARING SPTE BIT.
4
FIRST INCOMING BYTE TRANSFERS FROM SHIFT
REGISTER TO RECEIVE DATA REGISTER, SETTING
SPRF BIT.
5
BYTE 2 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
6
CPU READS SPSCR WITH SPRF BIT SET.
12
7
CPU READS SPDR, CLEARING SPRF BIT.
8
CPU WRITES BYTE 3 TO SPDR, QUEUEING
BYTE 3 AND CLEARING SPTE BIT.
9
SECOND INCOMING BYTE TRANSFERS FROM SHIFT
REGISTER TO RECEIVE DATA REGISTER, SETTING
SPRF BIT.
10 BYTE 3 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
11 CPU READS SPSCR WITH SPRF BIT SET.
12 CPU READS SPDR, CLEARING SPRF BIT.
Figure 17-10. SPRF/SPTE CPU Interrupt Timing
For a slave, the transmit data buffer allows back-to-back transmissions to occur without the slave having
to time the write of its data between the transmissions. Also, if no new data is written to the data buffer,
the last value contained in the shift register will be the next data word transmitted.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
177
Serial Peirpheral Interface (SPI)
17.9 Resetting the SPI
Any system reset completely resets the SPI. Partial reset occurs whenever the SPI enable bit (SPE) is
low. Whenever SPE is low, the following occurs:
• The SPTE flag is set.
• Any transmission currently in progress is aborted.
• The shift register is cleared.
• The SPI state counter is cleared, making it ready for a new complete transmission.
• All the SPI port logic is defaulted back to being general-purpose I/O.
The following additional items are reset only by a system reset:
• All control bits in the SPCR register
• All control bits in the SPSCR register (MODFEN, ERRIE, SPR1, and SPR0)
• The status flags SPRF, OVRF, and MODF
By not resetting the control bits when SPE is low, the user can clear SPE between transmissions without
having to reset all control bits when SPE is set back to high for the next transmission.
By not resetting the SPRF, OVRF, and MODF flags, the user can still service these interrupts after the
SPI has been disabled. The user can disable the SPI by writing 0 to the SPE bit. The SPI also can be
disabled by a mode fault occurring in an SPI that was configured as a master with the MODFEN bit set.
17.10 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power- consumption standby modes.
17.10.1 Wait Mode
The SPI module remains active after the execution of a WAIT instruction. In wait mode, the SPI module
registers are not accessible by the CPU. Any enabled CPU interrupt request from the SPI module can
bring the MCU out of wait mode.
If SPI module functions are not required during wait mode, reduce power consumption by disabling the
SPI module before executing the WAIT instruction.
To exit wait mode when an overflow condition occurs, enable the OVRF bit to generate CPU interrupt
requests by setting the error interrupt enable bit (ERRIE). (See 17.7 Interrupts).
17.10.2 Stop Mode
The SPI module is inactive after the execution of a STOP instruction. The STOP instruction does not
affect register conditions. SPI operation resumes after the MCU exits stop mode. If stop mode is exited
by reset, any transfer in progress is aborted and the SPI is reset.
17.11 SPI During Break Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR, $FE03) enables software to
clear status bits during the break state. (See 7.7.3 SIM Break Flag Control Register).
MC68HC908AZ32A Data Sheet, Rev. 2
178
Freescale Semiconductor
I/O Signals
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a two-step read/write clearing procedure. If software does the first step on such a
bit before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
Since the SPTE bit cannot be cleared during a break with the BCFE bit cleared, a write to the data register
in break mode will not initiate a transmission nor will this data be transferred into the shift register.
Therefore, a write to the SPDR in break mode with the BCFE bit cleared has no effect.
17.12 I/O Signals
The SPI module has four I/O pins and shares three of them with a parallel I/O port.
• MISO — Data received
• MOSI — Data transmitted
• SPSCK — Serial clock
• SS — Slave select
• VSS — Clock ground
The SPI has limited inter-integrated circuit (I2C) capability (requiring software support) as a master in a
single-master environment. To communicate with I2C peripherals, MOSI becomes an open-drain output
when the SPWOM bit in the SPI control register is set. In I2C communication, the MOSI and MISO pins
are connected to a bidirectional pin from the I2C peripheral and through a pullup resistor to VDD.
17.12.1 MISO (Master In/Slave Out)
MISO is one of the two SPI module pins that transmit serial data. In full duplex operation, the MISO pin
of the master SPI module is connected to the MISO pin of the slave SPI module. The master SPI
simultaneously receives data on its MISO pin and transmits data from its MOSI pin.
Slave output data on the MISO pin is enabled only when the SPI is configured as a slave. The SPI is
configured as a slave when its SPMSTR bit is logic 0 and its SS pin is at logic 0. To support a
multiple-slave system, a logic 1 on the SS pin puts the MISO pin in a high-impedance state.
When enabled, the SPI controls data direction of the MISO pin regardless of the state of the data direction
register of the shared I/O port.
17.12.2 MOSI (Master Out/Slave In)
MOSI is one of the two SPI module pins that transmit serial data. In full duplex operation, the MOSI pin
of the master SPI module is connected to the MOSI pin of the slave SPI module. The master SPI
simultaneously transmits data from its MOSI pin and receives data on its MISO pin.
When enabled, the SPI controls data direction of the MOSI pin regardless of the state of the data direction
register of the shared I/O port.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
179
Serial Peirpheral Interface (SPI)
17.12.3 SPSCK (Serial Clock)
The serial clock synchronizes data transmission between master and slave devices. In a master MCU,
the SPSCK pin is the clock output. In a slave MCU, the SPSCK pin is the clock input. In full duplex
operation, the master and slave MCUs exchange a byte of data in eight serial clock cycles.
When enabled, the SPI controls data direction of the SPSCK pin regardless of the state of the data
direction register of the shared I/O port.
17.12.4 SS (Slave Select)
The SS pin has various functions depending on the current state of the SPI. For an SPI configured as a
slave, the SS is used to select a slave. For CPHA = 0, the SS is used to define the start of a transmission.
17.5 Transmission Formats Since it is used to indicate the start of a transmission, the SS must be toggled
high and low between each byte transmitted for the CPHA = 0 format. However, it can remain low
throughout the transmission for the CPHA = 1 format. See Figure 17-11.
MISO/MOSI
BYTE 1
BYTE 2
BYTE 3
MASTER SS
SLAVE SS
CPHA = 0
SLAVE SS
CPHA = 1
Figure 17-11. CPHA/SS Timing
When an SPI is configured as a slave, the SS pin is always configured as an input. It cannot be used as
a general-purpose I/O regardless of the state of the MODFEN control bit. However, the MODFEN bit can
still prevent the state of the SS from creating a MODF error. (See 17.13.2 SPI Status and Control
Register).
NOTE
A logic 1 voltage on the SS pin of a slave SPI puts the MISO pin in a
high-impedance state. The slave SPI ignores all incoming SPSCK clocks,
even if a transmission already has begun.
When an SPI is configured as a master, the SS input can be used in conjunction with the MODF flag to
prevent multiple masters from driving MOSI and SPSCK. (See 17.6.2 Mode Fault Error). For the state of
the SS pin to set the MODF flag, the MODFEN bit in the SPSCK register must be set. If the MODFEN bit
is low for an SPI master, the SS pin can be used as a general-purpose I/O under the control of the data
direction register of the shared I/O port. With MODFEN high, it is an input-only pin to the SPI regardless
of the state of the data direction register of the shared I/O port.
The CPU can always read the state of the SS pin by configuring the appropriate pin as an input and
reading the data register. (See Table 17-4.)
Table 17-4. SPI Configuration
SPE
SPMSTR
MODFEN
SPI Configuration
State of SS Logic
0
X
X
Not Enabled
General-Purpose I/O; SS Ignored by SPI
1
0
X
Slave
Input-Only to SPI
1
1
0
Master without MODF
General-Purpose I/O; SS Ignored by SPI
1
1
1
Master with MODF
Input-Only to SPI
X = don’t care
MC68HC908AZ32A Data Sheet, Rev. 2
180
Freescale Semiconductor
I/O Registers
17.12.5 VSS (Clock Ground)
VSS is the ground return for the serial clock pin, SPSCK, and the ground for the port output buffers. To
reduce the ground return path loop and minimize radio frequency (RF) emissions, connect the ground pin
of the slave to the VSS pin.
17.13 I/O Registers
Three registers control and monitor SPI operation:
• SPI control register (SPCR $0010)
• SPI status and control register (SPSCR $0011)
• SPI data register (SPDR $0012)
17.13.1 SPI Control Register
The SPI control register:
• Enables SPI module interrupt requests
• Selects CPU interrupt requests
• Configures the SPI module as master or slave
• Selects serial clock polarity and phase
• Configures the SPSCK, MOSI, and MISO pins as open-drain outputs
• Enables the SPI module
Address:
Read:
Write:
Reset:
$0010
Bit 7
6
5
4
3
2
1
Bit 0
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
0
0
1
0
1
0
0
0
R
= Reserved
Figure 17-12. SPI Control Register (SPCR)
SPRIE — SPI Receiver Interrupt Enable Bit
This read/write bit enables CPU interrupt requests generated by the SPRF bit. The SPRF bit is set
when a byte transfers from the shift register to the receive data register. Reset clears the SPRIE bit.
1 = SPRF CPU interrupt requests enabled
0 = SPRF CPU interrupt requests disabled
SPMSTR — SPI Master Bit
This read/write bit selects master mode operation or slave mode operation. Reset sets the SPMSTR
bit.
1 = Master mode
0 = Slave mode
CPOL — Clock Polarity Bit
This read/write bit determines the logic state of the SPSCK pin between transmissions. (See Figure
17-4 and Figure 17-5.) To transmit data between SPI modules, the SPI modules must have identical
CPOL bits. Reset clears the CPOL bit.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
181
Serial Peirpheral Interface (SPI)
CPHA — Clock Phase Bit
This read/write bit controls the timing relationship between the serial clock and SPI data. (See Figure
17-4 and Figure 17-5.) To transmit data between SPI modules, the SPI modules must have identical
CPHA bits. When CPHA = 0, the SS pin of the slave SPI module must be set to logic 1 between bytes.
(See Figure 17-11). Reset sets the CPHA bit.
When CPHA = 0 for a slave, the falling edge of SS indicates the beginning of the transmission. This
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data. Once
the transmission begins, no new data is allowed into the shift register from the data register. Therefore,
the slave data register must be loaded with the desired transmit data before the falling edge of SS. Any
data written after the falling edge is stored in the data register and transferred to the shift register at
the current transmission.
When CPHA = 1 for a slave, the first edge of the SPSCK indicates the beginning of the transmission.
The same applies when SS is high for a slave. The MISO pin is held in a high-impedance state, and
the incoming SPSCK is ignored. In certain cases, it may also cause the MODF flag to be set. (See
17.6.2 Mode Fault Error). A logic 1 on the SS pin does not in any way affect the state of the SPI state
machine.
SPWOM — SPI Wired-OR Mode Bit
This read/write bit disables the pullup devices on pins SPSCK, MOSI, and MISO so that those pins
become open-drain outputs.
1 = Wired-OR SPSCK, MOSI, and MISO pins
0 = Normal push-pull SPSCK, MOSI, and MISO pins
SPE — SPI Enable Bit
This read/write bit enables the SPI module. Clearing SPE causes a partial reset of the SPI (see 17.9
Resetting the SPI). Reset clears the SPE bit.
1 = SPI module enabled
0 = SPI module disabled
SPTIE — SPI Transmit Interrupt Enable Bit
This read/write bit enables CPU interrupt requests generated by the SPTE bit. SPTE is set when a byte
transfers from the transmit data register to the shift register. Reset clears the SPTIE bit.
1 = SPTE CPU interrupt requests enabled
0 = SPTE CPU interrupt requests disabled
17.13.2 SPI Status and Control Register
The SPI status and control register contains flags to signal the following conditions:
• Receive data register full
• Failure to clear SPRF bit before next byte is received (overflow error)
• Inconsistent logic level on SS pin (mode fault error)
• Transmit data register empty
The SPI status and control register also contains bits that perform these functions:
• Enable error interrupts
• Enable mode fault error detection
• Select master SPI baud rate
MC68HC908AZ32A Data Sheet, Rev. 2
182
Freescale Semiconductor
I/O Registers
Address:
$0011
Bit 7
Read:
SPRF
Write:
Reset:
6
ERRIE
0
0
R
= Reserved
5
4
3
OVRF
MODF
SPTE
0
0
1
2
1
Bit 0
MODFEN
SPR1
SPR0
0
0
0
= Unimplemented
Figure 17-13. SPI Status and Control Register (SPSCR)
SPRF — SPI Receiver Full Bit
This clearable, read-only flag is set each time a byte transfers from the shift register to the receive data
register. SPRF generates a CPU interrupt request if the SPRIE bit in the SPI control register is set also.
During an SPRF CPU interrupt, the CPU clears SPRF by reading the SPI status and control register
with SPRF set and then reading the SPI data register. Any read of the SPI data register clears the
SPRF bit.
Reset clears the SPRF bit.
1 = Receive data register full
0 = Receive data register not full
ERRIE — Error Interrupt Enable Bit
This read-only bit enables the MODF and OVRF flags to generate CPU interrupt requests. Reset
clears the ERRIE bit.
1 = MODF and OVRF can generate CPU interrupt requests
0 = MODF and OVRF cannot generate CPU interrupt requests
OVRF — Overflow Bit
This clearable, read-only flag is set if software does not read the byte in the receive data register before
the next byte enters the shift register. In an overflow condition, the byte already in the receive data
register is unaffected, and the byte that shifted in last is lost. Clear the OVRF bit by reading the SPI
status and control register with OVRF set and then reading the SPI data register. Reset clears the
OVRF flag.
1 = Overflow
0 = No overflow
MODF — Mode Fault Bit
This clearable, read-only flag is set in a slave SPI if the SS pin goes high during a transmission. In a
master SPI, the MODF flag is set if the SS pin goes low at any time. Clear the MODF bit by reading
the SPI status and control register with MODF set and then writing to the SPI data register. Reset
clears the MODF bit.
1 = SS pin at inappropriate logic level
0 = SS pin at appropriate logic level
SPTE — SPI Transmitter Empty Bit
This clearable, read-only flag is set each time the transmit data register transfers a byte into the shift
register. SPTE generates an SPTE CPU interrupt request if the SPTIE bit in the SPI control register is
set also.
NOTE
Do not write to the SPI data register unless the SPTE bit is high.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
183
Serial Peirpheral Interface (SPI)
For an idle master or idle slave that has no data loaded into its transmit buffer, the SPTE will be set
again within two bus cycles since the transmit buffer empties into the shift register. This allows the user
to queue up a 16-bit value to send. For an already active slave, the load of the shift register cannot
occur until the transmission is completed. This implies that a back-to-back write to the transmit data
register is not possible. The SPTE indicates when the next write can occur.
Reset sets the SPTE bit.
1 = Transmit data register empty
0 = Transmit data register not empty
MODFEN — Mode Fault Enable Bit
This read/write bit, when set to 1, allows the MODF flag to be set. If the MODF flag is set, clearing the
MODFEN does not clear the MODF flag. If the SPI is enabled as a master and the MODFEN bit is low,
then the SS pin is available as a general-purpose I/O.
If the MODFEN bit is set, then this pin is not available as a general purpose I/O. When the SPI is
enabled as a slave, the SS pin is not available as a general-purpose I/O regardless of the value of
MODFEN. (See 17.12.4 SS (Slave Select)).
If the MODFEN bit is low, the level of the SS pin does not affect the operation of an enabled SPI
configured as a master. For an enabled SPI configured as a slave, having MODFEN low only prevents
the MODF flag from being set. It does not affect any other part of SPI operation. (See 17.6.2 Mode
Fault Error).
SPR1 and SPR0 — SPI Baud Rate Select Bits
In master mode, these read/write bits select one of four baud rates as shown in Table 17-5. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Table 17-5. SPI Master Baud Rate Selection
SPR1:SPR0
Baud Rate Divisor (BD)
00
2
01
8
10
32
11
128
Use this formula to calculate the SPI baud rate:
CGMOUT
Baud rate = -------------------------2 × BD
where:
CGMOUT = base clock output of the clock generator module (CGM),
see Chapter 8 Clock Generator Module (CGM).
BD = baud rate divisor
MC68HC908AZ32A Data Sheet, Rev. 2
184
Freescale Semiconductor
I/O Registers
17.13.3 SPI Data Register
The SPI data register is the read/write buffer for the receive data register and the transmit data register.
Writing to the SPI data register writes data into the transmit data register. Reading the SPI data register
reads data from the receive data register. The transmit data and receive data registers are separate
buffers that can contain different values. See Figure 17-2.
Address:
$0012
Bit 7
6
5
4
3
2
1
Bit 0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
Write:
T7
T6
T5
T4
T3
T2
T1
T0
Reset:
Indeterminate after Reset
Figure 17-14. SPI Data Register (SPDR)
R7–R0/T7–T0 — Receive/Transmit Data Bits
NOTE
Do not use read-modify-write instructions on the SPI data register since the
buffer read is not the same as the buffer written.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
185
Serial Peirpheral Interface (SPI)
MC68HC908AZ32A Data Sheet, Rev. 2
186
Freescale Semiconductor
Chapter 18
Timer Interface Module A (TIMA)
18.1 Introduction
This section describes the timer interface module (TIMA). The TIMA is a 6-channel timer that provides a
timing reference with input capture, output compare and pulse-width-modulation functions. Figure 18-1 is
a block diagram of the TIMA.
18.2 Features
Features of the TIMA include:
• Six Input Capture/Output Compare Channels
– Rising-Edge, Falling-Edge or Any-Edge Input Capture Trigger
– Set, Clear or Toggle Output Compare Action
• Buffered and Unbuffered Pulse Width Modulation (PWM) Signal Generation
• Programmable TIMA Clock Input
– 7 Frequency Internal Bus Clock Prescaler Selection
– External TIMA Clock Input (4 MHz Maximum Frequency)
• Free-Running or Modulo Up-Count Operation
• Toggle Any Channel Pin on Overflow
• TIMA Counter Stop and Reset Bits
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
187
Timer Interface Module A (TIMA)
TCLK
PTD6/ATD14/TCLK
PRESCALER SELECT
INTERNAL
BUS CLOCK
PRESCALER
TSTOP
PS2
TRST
PS1
PS0
16-BIT COUNTER
TOF
TOIE
INTERRUPT
LOGIC
16-BIT COMPARATOR
TMODH:TMODL
CHANNEL 0
ELS0B
ELS0A
TOV0
CH0MAX
16-BIT COMPARATOR
TCH0H:TCH0L
CH0F
16-BIT LATCH
MS0A
CHANNEL 1
ELS1B
MS0B
ELS1A
TOV1
CH1MAX
16-BIT COMPARATOR
TCH1H:TCH1L
CH0IE
CH1F
16-BIT LATCH
CH1IE
MS1A
CHANNEL 2
ELS2B
ELS2A
TOV2
CH2MAX
16-BIT COMPARATOR
TCH2H:TCH2L
CH2F
16-BIT LATCH
MS2A
CHANNEL 3
ELS3B
MS2B
ELS3A
TOV3
CH3MAX
16-BIT COMPARATOR
TCH3H:TCH3L
CH2IE
CH3F
16-BIT LATCH
CH3IE
MS3A
CHANNEL 4
ELS4B
ELS4A
TOV4
CH5MAX
16-BIT COMPARATOR
TCH4H:TCH4L
CH4F
16-BIT LATCH
MS4A
CHANNEL 5
ELS5B
MS4B
ELS5A
TOV5
CH5MAX
16-BIT COMPARATOR
TCH5H:TCH5L
CH4IE
CH5F
16-BIT LATCH
MS5A
CH5IE
PTE2
LOGIC
PTE2/TCH0
INTERRUPT
LOGIC
PTE3
LOGIC
PTE3/TCH1
INTERRUPT
LOGIC
PTF0
LOGIC
PTF0/TCH2
INTERRUPT
LOGIC
PTF1
LOGIC
PTF1/TCH3
INTERRUPT
LOGIC
PTF2
LOGIC
PTF2/TCH4/TACH4
INTERRUPT
LOGIC
PTF3
LOGIC
PTF3/TCH5/TACH5
INTERRUPT
LOGIC
Figure 18-1. TIMA Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
188
Freescale Semiconductor
Functional Description
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
TOF
TOIE
TSTOP
TRST
0
PS2
PS1
PS0
R
R
R
R
R
R
R
R
$0020
TIMA Status/Control Register (TASC)
$0021
Reserved
$0022
TIMA Counter Register High (TACNTH)
Bit 15
14
13
12
11
10
9
Bit 8
$0023
TIMA Counter Register Low (TACNTL)
Bit 7
6
5
4
3
2
1
Bit 0
$0024
TIMA Counter Modulo Reg. High (TAMODH)
Bit 15
14
13
12
11
10
9
Bit 8
$0025
TIMA Counter Modulo Reg. Low (TAMODL)
Bit 7
6
5
4
3
2
1
Bit 0
$0026
TIMA Ch. 0 Status/Control Register (TASC0)
CH0F
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
$0027
TIMA Ch. 0 Register High (TACH0H)
Bit 15
14
13
12
11
10
9
Bit 8
$0028
TIMA Ch. 0 Register Low (TACH0L)
Bit 7
6
5
4
3
2
1
Bit 0
$0029
TIMA Ch. 1 Status/Control Register (TASC1)
CH1F
CH1IE
0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
$002A
TIMA Ch. 1 Register High (TACH1H)
Bit 15
14
13
12
11
10
9
Bit 8
$002B
TIMA Ch. 1 Register Low (TACH1L)
Bit 7
6
5
4
3
2
1
Bit 0
$002C
TIMA Ch. 2 Status/Control Register (TASC2)
CH2F
CH2IE
MS2B
MS2A
ELS2B
ELS2A
TOV2
CH2MAX
$002D
TIMA Ch. 2 Register High (TACH2H)
Bit 15
14
13
12
11
10
9
Bit 8
$002E
TIMA Ch. 2 Register Low (TACH2L)
Bit 7
6
5
4
3
2
1
Bit 0
$002F
TIMA Ch. 3 Status/Control Register (TASC3)
CH3F
CH3IE
0
MS3A
ELS3B
ELS3A
TOV3
CH3MAX
$0030
TIMA Ch. 3 Register High (TACH3H)
Bit 15
14
13
12
11
10
9
Bit 8
$0031
TIMA Ch. 3 Register Low (TACH3L)
Bit 7
6
5
4
3
2
1
Bit 0
$0032
TIMA Ch. 4 Status/Control Register (TASC4)
CH4F
CH4IE
MS4B
MS4A
ELS4B
ELS4A
TOV4
CH4MAX
$0033
TIMA Ch. 4 Register High (TACH4H)
Bit 15
14
13
12
11
10
9
Bit 8
$0034
TIMA Ch. 4 Register Low (TACH4L)
Bit 7
6
5
4
3
2
1
Bit 0
$0035
TIMA Ch. 5 Status/Control Register (TASC5)
CH5F
CH5IE
0
MS5A
ELS5B
ELS5A
TOV5
CH5MAX
$0036
TIMA Ch. 5 Register High (TACH5H)
Bit 15
14
13
12
11
10
9
Bit 8
$0037
TIMA Ch. 5 Register Low (TACH5L)
Bit 7
6
5
4
3
2
1
Bit 0
R
= Reserved
Figure 18-2. TIMA I/O Register Summary
18.3 Functional Description
Figure 18-1 shows the TIMA structure. The central component of the TIMA is the 16-bit TIMA counter that
can operate as a free-running counter or a modulo up-counter. The TIMA counter provides the timing
reference for the input capture and output compare functions. The TIMA counter modulo registers,
TAMODH–TAMODL, control the modulo value of the TIMA counter. Software can read the TIMA counter
value at any time without affecting the counting sequence.
The six TIMA channels are programmable independently as input capture or output compare channels.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
189
Timer Interface Module A (TIMA)
18.3.1 TIMA Counter Prescaler
The TIMA clock source can be one of the seven prescaler outputs or the TIMA clock pin,
PTD6/ATD14/TCLK. The prescaler generates seven clock rates from the internal bus clock. The
prescaler select bits, PS[2:0], in the TIMA status and control register select the TIMA clock source.
18.3.2 Input Capture
An input capture function has three basic parts: edge select logic, an input capture latch and a 16-bit
counter. Two 8-bit registers, which make up the 16-bit input capture register, are used to latch the value
of the free-running counter after the corresponding input capture edge detector senses a defined
transition. The polarity of the active edge is programmable. The level transition which triggers the counter
transfer is defined by the corresponding input edge bits (ELSxB and ELSxA in TASC0 through TASC5
control registers with x referring to the active channel number). When an active edge occurs on the pin of
an input capture channel, the TIMA latches the contents of the TIMA counter into the TIMA channel
registers, TACHxH–TACHxL. Input captures can generate TIMA CPU interrupt requests. Software can
determine that an input capture event has occurred by enabling input capture interrupts or by polling the
status flag bit.
The result obtained by an input capture will be two more than the value of the free-running counter on the
rising edge of the internal bus clock preceding the external transition. This delay is required for internal
synchronization.
The free-running counter contents are transferred to the TIMA channel register (TACHxH–TACHxL see
18.8.5 TIMA Channel Registers) on each proper signal transition regardless of whether the TIMA channel
flag (CH0F–CH5F in TASC0–TASC5 registers) is set or clear. When the status flag is set, a CPU interrupt
is generated if enabled. The value of the count latched or “captured” is the time of the event. Because this
value is stored in the input capture register 2 bus cycles after the actual event occurs, user software can
respond to this event at a later time and determine the actual time of the event. However, this must be
done prior to another input capture on the same pin; otherwise, the previous time value will be lost.
By recording the times for successive edges on an incoming signal, software can determine the period
and/or pulse width of the signal. To measure a period, two successive edges of the same polarity are
captured. To measure a pulse width, two alternate polarity edges are captured. Software should track the
overflows at the 16-bit module counter to extend its range.
Another use for the input capture function is to establish a time reference. In this case, an input capture
function is used in conjunction with an output compare function. For example, to activate an output signal
a specified number of clock cycles after detecting an input event (edge), use the input capture function to
record the time at which the edge occurred. A number corresponding to the desired delay is added to this
captured value and stored to an output compare register (see 18.8.5 TIMA Channel Registers). Because
both input captures and output compares are referenced to the same 16-bit modulo counter, the delay
can be controlled to the resolution of the counter independent of software latencies.
Reset does not affect the contents of the TIMA channel register (TACHxH–TACHxL).
18.3.3 Output Compare
With the output compare function, the TIMA can generate a periodic pulse with a programmable polarity,
duration and frequency. When the counter reaches the value in the registers of an output compare
channel, the TIMA can set, clear or toggle the channel pin. Output compares can generate TIMA CPU
interrupt requests.
MC68HC908AZ32A Data Sheet, Rev. 2
190
Freescale Semiconductor
Functional Description
18.3.3.1 Unbuffered Output Compare
Any output compare channel can generate unbuffered output compare pulses as described in 18.3.3
Output Compare. The pulses are unbuffered because changing the output compare value requires writing
the new value over the old value currently in the TIMA channel registers.
An unsynchronized write to the TIMA channel registers to change an output compare value could cause
incorrect operation for up to two counter overflow periods. For example, writing a new value before the
counter reaches the old value but after the counter reaches the new value prevents any compare during
that counter overflow period. Also, using a TIMA overflow interrupt routine to write a new, smaller output
compare value may cause the compare to be missed. The TIMA may pass the new value before it is
written.
Use the following methods to synchronize unbuffered changes in the output compare value on channel x:
• When changing to a smaller value, enable channel x output compare interrupts and write the new
value in the output compare interrupt routine. The output compare interrupt occurs at the end of
the current output compare pulse. The interrupt routine has until the end of the counter overflow
period to write the new value.
• When changing to a larger output compare value, enable TIMA overflow interrupts and write the
new value in the TIMA overflow interrupt routine. The TIMA overflow interrupt occurs at the end of
the current counter overflow period. Writing a larger value in an output compare interrupt routine
(at the end of the current pulse) could cause two output compares to occur in the same counter
overflow period.
18.3.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare channel whose output appears on the
PTE2/TCH0 pin. The TIMA channel registers of the linked pair alternately control the output.
Setting the MS0B bit in TIMA channel 0 status and control register (TASC0) links channel 0 and
channel 1. The output compare value in the TIMA channel 0 registers initially controls the output on the
PTE2/TCH0 pin. Writing to the TIMA channel 1 registers enables the TIMA channel 1 registers to
synchronously control the output after the TIMA overflows. At each subsequent overflow, the TIMA
channel registers (0 or 1) that control the output are the ones written to last. TASC0 controls and monitors
the buffered output compare function and TIMA channel 1 status and control register (TASC1) is unused.
While the MS0B bit is set, the channel 1 pin, PTE3/TACH1, is available as a general-purpose I/O pin.
Channels 2 and 3 can be linked to form a buffered output compare channel whose output appears on the
PTF0/TCH2 pin. The TIMA channel registers of the linked pair alternately control the output.
Setting the MS2B bit in TIMA channel 2 status and control register (TASC2) links channel 2 and
channel 3. The output compare value in the TIMA channel 2 registers initially controls the output on the
PTF0/TCH2 pin. Writing to the TIMA channel 3 registers enables the TIMA channel 3 registers to
synchronously control the output after the TIMA overflows. At each subsequent overflow, the TIMA
channel registers (2 or 3) that control the output are the ones written to last. TASC2 controls and monitors
the buffered output compare function, and TIMA channel 3 status and control register (TASC3) is unused.
While the MS2B bit is set, the channel 3 pin, PTF1/TCH3, is available as a general-purpose I/O pin.
Channels 4 and 5 can be linked to form a buffered output compare channel whose output appears on the
PTF2/TCH4 pin. The TIMA channel registers of the linked pair alternately control the output.
Setting the MS4B bit in TIMA channel 4 status and control register (TASC4) links channel 4 and
channel 5. The output compare value in the TIMA channel 4 registers initially controls the output on the
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
191
Timer Interface Module A (TIMA)
PTF2/TCH4 pin. Writing to the TIMA channel 5 registers enables the TIMA channel 5 registers to
synchronously control the output after the TIMA overflows. At each subsequent overflow, the TIMA
channel registers (4 or 5) that control the output are the ones written to last. TASC4 controls and monitors
the buffered output compare function and TIMA channel 5 status and control register (TASC5) is unused.
While the MS4B bit is set, the channel 5 pin, PTF3/TCH5, is available as a general-purpose I/O pin.
NOTE
In buffered output compare operation, do not write new output compare
values to the currently active channel registers. Writing to the active
channel registers is the same as generating unbuffered output compares.
18.3.4 Pulse Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare channel, the TIMA can generate a PWM
signal. The value in the TIMA counter modulo registers determines the period of the PWM signal. The
channel pin toggles when the counter reaches the value in the TIMA counter modulo registers. The time
between overflows is the period of the PWM signal.
As Figure 18-3 shows, the output compare value in the TIMA channel registers determines the pulse width
of the PWM signal. The time between overflow and output compare is the pulse width. Program the TIMA
to clear the channel pin on output compare if the state of the PWM pulse is logic 1. Program the TIMA to
set the pin if the state of the PWM pulse is logic 0.
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PULSE
WIDTH
PTEx/TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 18-3. PWM Period and Pulse Width
The value in the TIMA counter modulo registers and the selected prescaler output determines the
frequency of the PWM output. The frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIMA counter modulo registers produces a PWM period of 256 times the internal bus
clock period if the prescaler select value is $000 (see 18.8.1 TIMA Status and Control Register).
The value in the TIMA channel registers determines the pulse width of the PWM output. The pulse width
of an 8-bit PWM signal is variable in 256 increments. Writing $0080 (128) to the TIMA channel registers
produces a duty cycle of 128/256 or 50%.
18.3.4.1 Unbuffered PWM Signal Generation
Any output compare channel can generate unbuffered PWM pulses as described in 18.3.4 Pulse Width
Modulation (PWM). The pulses are unbuffered because changing the pulse width requires writing the new
pulse width value over the value currently in the TIMA channel registers.
MC68HC908AZ32A Data Sheet, Rev. 2
192
Freescale Semiconductor
Functional Description
An unsynchronized write to the TIMA channel registers to change a pulse width value could cause
incorrect operation for up to two PWM periods. For example, writing a new value before the counter
reaches the old value but after the counter reaches the new value prevents any compare during that PWM
period. Also, using a TIMA overflow interrupt routine to write a new, smaller pulse width value may cause
the compare to be missed. The TIMA may pass the new value before it is written to the TIMA channel
registers.
Use the following methods to synchronize unbuffered changes in the PWM pulse width on channel x:
• When changing to a shorter pulse width, enable channel x output compare interrupts and write the
new value in the output compare interrupt routine. The output compare interrupt occurs at the end
of the current pulse. The interrupt routine has until the end of the PWM period to write the new
value.
• When changing to a longer pulse width, enable TIMA overflow interrupts and write the new value
in the TIMA overflow interrupt routine. The TIMA overflow interrupt occurs at the end of the current
PWM period. Writing a larger value in an output compare interrupt routine (at the end of the current
pulse) could cause two output compares to occur in the same PWM period.
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
event of software error or noise. Toggling on output compare also can
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
18.3.4.2 Buffered PWM Signal Generation
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the
PTE2/TCH0 pin. The TIMA channel registers of the linked pair alternately control the pulse width of the
output.
Setting the MS0B bit in TIMA channel 0 status and control register (TASC0) links channel 0 and
channel 1. The TIMA channel 0 registers initially control the pulse width on the PTE2/TCH0 pin. Writing
to the TIMA channel 1 registers enables the TIMA channel 1 registers to synchronously control the pulse
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers
(0 or 1) that control the pulse width are the ones written to last. TASC0 controls and monitors the buffered
PWM function and TIMA channel 1 status and control register (TASC1) is unused. While the MS0B bit is
set, the channel 1 pin, PTE3/TCH1, is available as a general-purpose I/O pin.
Channels 2 and 3 can be linked to form a buffered PWM channel whose output appears on the
PTF0/TCH2 pin. The TIMA channel registers of the linked pair alternately control the pulse width of the
output.
Setting the MS2B bit in TIMA channel 2 status and control register (TASC2) links channel 2 and
channel 3. The TIMA channel 2 registers initially control the pulse width on the PTF0/TCH2 pin. Writing
to the TIMA channel 3 registers enables the TIMA channel 3 registers to synchronously control the pulse
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers
(2 or 3) that control the pulse width are the ones written to last. TASC2 controls and monitors the buffered
PWM function and TIMA channel 3 status and control register (TASC3) is unused. While the MS2B bit is
set, the channel 3 pin, PTF1/TCH3, is available as a general-purpose I/O pin.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
193
Timer Interface Module A (TIMA)
Channels 4 and 5 can be linked to form a buffered PWM channel whose output appears on the
PTF2/TCH4 pin. The TIMA channel registers of the linked pair alternately control the pulse width of the
output.
Setting the MS4B bit in TIMA channel 4 status and control register (TASC4) links channel 4 and
channel 5. The TIMA channel 4 registers initially control the pulse width on the PTF2/TCH4 pin. Writing
to the TIMA channel 5 registers enables the TIMA channel 5 registers to synchronously control the pulse
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers
(4 or 5) that control the pulse width are the ones written to last. TASC4 controls and monitors the buffered
PWM function and TIMA channel 5 status and control register (TASC5) is unused. While the MS4B bit is
set, the channel 5 pin, PTF3/TCH5, is available as a general-purpose I/O pin.
NOTE
In buffered PWM signal generation, do not write new pulse width values to
the currently active channel registers. Writing to the active channel
registers is the same as generating unbuffered PWM signals.
18.3.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use the following
initialization procedure:
1. In the TIMA status and control register (TASC):
a. Stop the TIMA counter by setting the TIMA stop bit, TSTOP.
b. Reset the TIMA counter and prescaler by setting the TIMA reset bit, TRST.
2. In the TIMA counter modulo registers (TAMODH–TAMODL) write the value for the required PWM
period.
3. In the TIMA channel x registers (TACHxH–TACHxL) write the value for the required pulse width.
4. In TIMA channel x status and control register (TASCx):
a. Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for buffered output compare
or PWM signals) to the mode select bits, MSxB–MSxA (see Table 18-2).
b. Write 1 to the toggle-on-overflow bit, TOVx.
c. Write 1:0 (to clear output on compare) or 1:1 (to set output on compare) to the edge/level
select bits, ELSxB–ELSxA. The output action on compare must force the output to the
complement of the pulse width level (see Table 18-2).
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
event of software error or noise. Toggling on output compare can also
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
5. In the TIMA status control register (TASC) clear the TIMA stop bit, TSTOP.
MC68HC908AZ32A Data Sheet, Rev. 2
194
Freescale Semiconductor
Interrupts
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIMA
channel 0 registers (TACH0H–TACH0L) initially control the buffered PWM output. TIMA status control
register 0 (TASC0) controls and monitors the PWM signal from the linked channels. MS0B takes priority
over MS0A.
Setting MS2B links channels 2 and 3 and configures them for buffered PWM operation. The TIMA channel
2 registers (TACH2H–TACH2L) initially control the buffered PWM output. TIMA status control register 2
(TASC2) controls and monitors the PWM signal from the linked channels. MS2B takes priority over MS2A.
Setting MS4B links channels 4 and 5 and configures them for buffered PWM operation. The TIMA channel
4 registers (TACH4H–TACH4L) initially control the buffered PWM output. TIMA status control register 4
(TASC4) controls and monitors the PWM signal from the linked channels. MS4B takes priority over MS4A.
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIMA overflows. Subsequent output
compares try to force the output to a state it is already in and have no effect. The result is a 0% duty cycle
output.
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100% duty
cycle output (see 18.8.4 TIMA Channel Status and Control Registers).
18.4 Interrupts
The following TIMA sources can generate interrupt requests:
• TIMA overflow flag (TOF) — The TOF bit is set when the TIMA counter reaches the modulo value
programmed in the TIMA counter modulo registers. The TIMA overflow interrupt enable bit, TOIE,
enables TIMA overflow CPU interrupt requests. TOF and TOIE are in the TIMA status and control
register.
• TIMA channel flags (CH5F–CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. Channel x TIMA CPU interrupt requests are controlled by the channel x
interrupt enable bit, CHxIE.
18.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
18.5.1 Wait Mode
The TIMA remains active after the execution of a WAIT instruction. In wait mode, the TIMA registers are
not accessible by the CPU. Any enabled CPU interrupt request from the TIMA can bring the MCU out of
wait mode.
If TIMA functions are not required during wait mode, reduce power consumption by stopping the TIMA
before executing the WAIT instruction.
18.5.2 Stop Mode
The TIMA is inactive after the execution of a STOP instruction. The STOP instruction does not affect
register conditions or the state of the TIMA counter. TIMA operation resumes when the MCU exits stop
mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
195
Timer Interface Module A (TIMA)
18.6 TIMA During Break Interrupts
A break interrupt stops the TIMA counter and inhibits input captures.
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state (see 7.7.3 SIM Break Flag Control Register).
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a 2-step read/write clearing procedure. If software does the first step on such a bit
before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
18.7 I/O Signals
Port D shares one of its pins with the TIMA. Port E shares two of its pins with the TIMA and port F shares
four of its pins with the TIMA. PTD6/ATD14/TCLK is an external clock input to the TIMA prescaler. The
six TIMA channel I/O pins are PTE2/TCH0, PTE3/TCH1, PTF0/TCH2, PTF1/TCH3, PTF2/TCH4, and
PTF3/TCH5.
18.7.1 TIMA Clock Pin (PTD6/ATD14/TACLK)
PTD6/ATD14/TCLK is an external clock input that can be the clock source for the TIMA counter instead
of the prescaled internal bus clock. Select the PTD6/ATD14/TCLK input by writing logic 1s to the three
prescaler select bits, PS[2:0] (see 18.8.1 TIMA Status and Control Register). The minimum TCLK pulse
width, TCLKLMIN or TCLKHMIN, is:
1
------------------------------------- + t
bus frequency SU
The maximum TCLK frequency is the least: 4 MHz or bus frequency ÷ 2.
PTD6/ATD14/TCLK is available as a general-purpose I/O pin or ADC channel when not used as the TIMA
clock input. When the PTD6/ATD14/TCLK pin is the TIMA clock input, it is an input regardless of the state
of the DDRD6 bit in data direction register D.
18.7.2 TIMA Channel I/O Pins (PTF3/TCH5–PTF0/TCH2 and PTE3/TCH1–PTE2/TCH0)
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.
PTE2/TCH0, PTF0/TACH2 and PTF2/TCH4 can be configured as buffered output compare or buffered
PWM pins.
MC68HC908AZ32A Data Sheet, Rev. 2
196
Freescale Semiconductor
I/O Registers
18.8 I/O Registers
These I/O registers control and monitor TIMA operation:
• TIMA status and control register (TASC)
• TIMA control registers (TACNTH–TACNTL)
• TIMA counter modulo registers (TAMODH–TAMODL)
• TIMA channel status and control registers (TASC0, TASC1, TASC2, TASC3, TASC4 and TASC5)
• TIMA channel registers (TACH0H–TACH0L, TACH1H–TACH1L, TACH2H–TACH2L,
TACH3H–TACH3L, TACH4H–TACH4L and TACH5H–TACH5L)
18.8.1 TIMA Status and Control Register
The TIMA status and control register:
• Enables TIMA overflow interrupts
• Flags TIMA overflows
• Stops the TIMA counter
• Resets the TIMA counter
• Prescales the TIMA counter clock
Address:
$0020
Bit 7
Read:
6
5
TOIE
TSTOP
TOF
Write:
0
Reset:
0
0
R
= Reserved
1
4
3
0
0
TRST
R
0
0
2
1
Bit 0
PS2
PS1
PS0
0
0
0
Figure 18-4. TIMA Status and Control Register (TASC)
TOF — TIMA Overflow Flag Bit
This read/write flag is set when the TIMA counter reaches the modulo value programmed in the TIMA
counter modulo registers. Clear TOF by reading the TIMA status and control register when TOF is set
and then writing a logic 0 to TOF. If another TIMA overflow occurs before the clearing sequence is
complete, then writing logic 0 to TOF has no effect. Therefore, a TOF interrupt request cannot be lost
due to inadvertent clearing of TOF. Reset clears the TOF bit. Writing a logic 1 to TOF has no effect.
1 = TIMA counter has reached modulo value.
0 = TIMA counter has not reached modulo value.
TOIE — TIMA Overflow Interrupt Enable Bit
This read/write bit enables TIMA overflow interrupts when the TOF bit becomes set. Reset clears the
TOIE bit.
1 = TIMA overflow interrupts enabled
0 = TIMA overflow interrupts disabled
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
197
Timer Interface Module A (TIMA)
TSTOP — TIMA Stop Bit
This read/write bit stops the TIMA counter. Counting resumes when TSTOP is cleared. Reset sets the
TSTOP bit, stopping the TIMA counter until software clears the TSTOP bit.
1 = TIMA counter stopped
0 = TIMA counter active
NOTE
Do not set the TSTOP bit before entering wait mode if the TIMA is required
to exit wait mode. Also, when the TSTOP bit is set and input capture mode
is enabled, input captures are inhibited until TSTOP is cleared.
When using TSTOP to stop the timer counter, see if any timer flags are set.
If a timer flag is set, it must be cleared by clearing TSTOP, then clearing the
flag, then setting TSTOP again.
TRST — TIMA Reset Bit
Setting this write-only bit resets the TIMA counter and the TIMA prescaler. Setting TRST has no effect
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMA
counter is reset and always reads as logic 0. Reset clears the TRST bit.
1 = Prescaler and TIMA counter cleared
0 = No effect
NOTE
Setting the TSTOP and TRST bits simultaneously stops the TIMA counter
at a value of $0000.
PS[2:0] — Prescaler Select Bits
These read/write bits select either the PTD6/ATD14/TCLK pin or one of the seven prescaler outputs
as the input to the TIMA counter as Table 18-1 shows. Reset clears the PS[2:0] bits.
Table 18-1. Prescaler Selection
PS[2:0]
TIMA Clock Source
000
Internal Bus Clock ÷1
001
Internal Bus Clock ÷ 2
010
Internal Bus Clock ÷ 4
011
Internal Bus Clock ÷ 8
100
Internal Bus Clock ÷ 16
101
Internal Bus Clock ÷ 32
110
Internal Bus Clock ÷ 64
111
PTD6/ATD14/TCLK
MC68HC908AZ32A Data Sheet, Rev. 2
198
Freescale Semiconductor
I/O Registers
18.8.2 TIMA Counter Registers
The two read-only TIMA counter registers contain the high and low bytes of the value in the TIMA counter.
Reading the high byte (TACNTH) latches the contents of the low byte (TACNTL) into a buffer. Subsequent
reads of TACNTH do not affect the latched TACNTL value until TACNTL is read. Reset clears the TIMA
counter registers. Setting the TIMA reset bit (TRST) also clears the TIMA counter registers.
NOTE
If TACNTH is read during a break interrupt, be sure to unlatch TACNTL by
reading TACNTL before exiting the break interrupt. Otherwise, TACNTL
retains the value latched during the break.
Register Name and Address
TACNTH — $0022
Bit 7
6
5
4
3
2
1
Bit 0
Read:
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
Register Name and Address
TACNTL — $0023
Bit 7
6
5
4
3
2
1
Bit 0
Read:
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 18-5. TIMA Counter Registers (TACNTH and TACNTL)
18.8.3 TIMA Counter Modulo Registers
The read/write TIMA modulo registers contain the modulo value for the TIMA counter. When the TIMA
counter reaches the modulo value, the overflow flag (TOF) becomes set and the TIMA counter resumes
counting from $0000 at the next clock. Writing to the high byte (TAMODH) inhibits the TOF bit and
overflow interrupts until the low byte (TAMODL) is written. Reset sets the TIMA counter modulo
registers.
Register Name and Address
Read:
Write:
Reset:
TAMODH — $0024
Bit 7
6
5
4
3
2
1
Bit 0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
1
1
1
1
1
1
1
1
Register Name and Address
Read:
Write:
Reset:
TAMODL — $0025
Bit 7
6
5
4
3
2
1
Bit 0
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1
1
1
1
1
1
1
1
Figure 18-6. TIMA Counter Modulo Registers (TAMODH and TAMODL)
NOTE
Reset the TIMA counter before writing to the TIMA counter modulo registers.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
199
Timer Interface Module A (TIMA)
18.8.4 TIMA Channel Status and Control Registers
Each of the TIMA channel status and control registers:
• Flags input captures and output compares
• Enables input capture and output compare interrupts
• Selects input capture, output compare or PWM operation
• Selects high, low or toggling output on output compare
• Selects rising edge, falling edge or any edge as the active input capture trigger
• Selects output toggling on TIMA overflow
• Selects 0% and 100% PWM duty cycle
• Selects buffered or unbuffered output compare/PWM operation
Register Name and Address
Bit 7
Read:
CH0F
Write:
0
Reset:
0
TASC0 — $0026
6
5
4
3
2
1
Bit 0
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
4
3
2
1
Bit 0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
Register Name and Address
Bit 7
TASC1 — $0029
6
5
Read:
CH1F
Write:
0
Reset:
0
0
R
= Reserved
CH1IE
Read:
CH2F
Write:
0
Reset:
0
TASC2 — $002C
6
5
4
3
2
1
Bit 0
CH2IE
MS2B
MS2A
ELS2B
ELS2A
TOV2
CH2MAX
0
0
0
0
0
0
0
4
3
2
1
Bit 0
MS3A
ELS3B
ELS3A
TOV3
CH3MAX
0
0
0
0
0
Register Name and Address
Bit 7
Read:
CH3F
Write:
0
Reset:
0
R
R
0
Register Name and Address
Bit 7
0
TASC3 — $002F
6
5
CH3IE
0
0
R
0
= Reserved
Figure 18-7. TIMA Channel Status
and Control Registers (TASC0–TASC5)
MC68HC908AZ32A Data Sheet, Rev. 2
200
Freescale Semiconductor
I/O Registers
Register Name and Address
Bit 7
Read:
CH4F
Write:
0
Reset:
0
TASC4 — $0032
6
5
4
3
2
1
Bit 0
CH4IE
MS4B
MS4A
ELS4B
ELS4A
TOV4
CH4MAX
0
0
0
0
0
0
0
4
3
2
1
Bit 0
MS5A
ELS5B
ELS5A
TOV5
CH5MAX
0
0
0
0
0
Register Name and Address
Bit 7
Read:
CH5F
Write:
0
Reset:
0
R
TASC5 — $0035
6
5
CH5IE
0
0
R
0
= Reserved
Figure 18-7. TIMA Channel Status
and Control Registers (TASC0–TASC5) (Continued)
CHxF — Channel x Flag Bit
When channel x is an input capture channel, this read/write bit is set when an active edge occurs on
the channel x pin. When channel x is an output compare channel, CHxF is set when the value in the
TIMA counter registers matches the value in the TIMA channel x registers.
When CHxIE = 1, clear CHxF by reading TIMA channel x status and control register with CHxF set and
then writing a logic 0 to CHxF. If another interrupt request occurs before the clearing sequence is
complete, then writing logic 0 to CHxF has no effect. Therefore, an interrupt request cannot be lost due
to inadvertent clearing of CHxF.
Reset clears the CHxF bit. Writing a logic 1 to CHxF has no effect.
1 = Input capture or output compare on channel x
0 = No input capture or output compare on channel x
CHxIE — Channel x Interrupt Enable Bit
This read/write bit enables TIMA CPU interrupts on channel x.
Reset clears the CHxIE bit.
1 = Channel x CPU interrupt requests enabled
0 = Channel x CPU interrupt requests disabled
MSxB — Mode Select Bit B
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIMA
channel 0, TIMA channel 2 and TIMA channel 4 status and control registers.
Setting MS0B disables the channel 1 status and control register and reverts TACH1 pin to
general-purpose I/O.
Setting MS2B disables the channel 3 status and control register and reverts TACH3 pin to
general-purpose I/O.
Setting MS4B disables the channel 5 status and control register and reverts TACH5 pin to
general-purpose I/O.
Reset clears the MSxB bit.
1 = Buffered output compare/PWM operation enabled
0 = Buffered output compare/PWM operation disabled
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
201
Timer Interface Module A (TIMA)
MSxA — Mode Select Bit A
When ELSxB:A ≠ 00, this read/write bit selects either input capture operation or unbuffered output
compare/PWM operation. See Table 18-2.
1 = Unbuffered output compare/PWM operation
0 = Input capture operation
When ELSxB:A = 00, this read/write bit selects the initial output level of the TACHx pin once PWM,
output compare mode or input capture mode is enabled. See Table 18-2. Reset clears the MSxA bit.
1 = Initial output level low
0 = Initial output level high
NOTE
Before changing a channel function by writing to the MSxB or MSxA bit, set
the TSTOP and TRST bits in the TIMA status and control register (TASC).
ELSxB and ELSxA — Edge/Level Select Bits
When channel x is an input capture channel, these read/write bits control the active edge-sensing logic
on channel x.
When channel x is an output compare channel, ELSxB and ELSxA control the channel x output
behavior when an output compare occurs.
When ELSxB and ELSxA are both clear, channel x is not connected to port E or port F and pin
PTEx/TACHx or pin PTFx/TACHx is available as a general-purpose I/O pin. However, channel x is at
a state determined by these bits and becomes transparent to the respective pin when PWM, input
capture mode or output compare operation mode is enabled. Table 18-2 shows how ELSxB and
ELSxA work. Reset clears the ELSxB and ELSxA bits.
Table 18-2. Mode, Edge, and Level Selection
MSxB:MSxA
ELSxB:ELSxA
X0
00
Mode
Output Preset
Configuration
Pin under Port Control;
Initialize Timer
Output Level High
X1
00
Pin under Port Control;
Initialize Timer
Output Level Low
00
01
Capture on Rising Edge Only
00
10
00
11
01
01
01
10
01
11
1X
01
1X
10
1X
11
Input Capture
Capture on Falling Edge Only
Capture on Rising or Falling Edge
Output
Compare
or PWM
Buffered Output
Compare or
Buffered PWM
Toggle Output on Compare
Clear Output on Compare
Set Output on Compare
Toggle Output on Compare
Clear Output on Compare
Set Output on Compare
NOTE
Before enabling a TIMA channel register for input capture operation, make
sure that the PTEx/TACHx pin or PTFx/TACHx pin is stable for at least two
bus clocks.
MC68HC908AZ32A Data Sheet, Rev. 2
202
Freescale Semiconductor
I/O Registers
TOVx — Toggle-On-Overflow Bit
When channel x is an output compare channel, this read/write bit controls the behavior of the channel
x output when the TIMA counter overflows. When channel x is an input capture channel, TOVx has no
effect. Reset clears the TOVx bit.
1 = Channel x pin toggles on TIMA counter overflow.
0 = Channel x pin does not toggle on TIMA counter overflow.
NOTE
When TOVx is set, a TIMA counter overflow takes precedence over a
channel x output compare if both occur at the same time.
CHxMAX — Channel x Maximum Duty Cycle Bit
When the TOVx bit is at logic 1, setting the CHxMAX bit forces the duty cycle of buffered and
unbuffered PWM signals to 100%. As Figure 18-8 shows, the CHxMAX bit takes effect in the cycle after
it is set or cleared. The output stays at the 100% duty cycle level until the cycle after CHxMAX is
cleared.
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PTEx/TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
Figure 18-8. CHxMAX Latency
18.8.5 TIMA Channel Registers
These read/write registers contain the captured TIMA counter value of the input capture function or the
output compare value of the output compare function. The state of the TIMA channel registers after reset
is unknown.
In input capture mode (MSxB–MSxA = 0:0) reading the high byte of the TIMA channel x registers
(TACHxH) inhibits input captures until the low byte (TACHxL) is read.
In output compare mode (MSxB–MSxA ≠ 0:0) writing to the high byte of the TIMA channel x registers
(TACHxH) inhibits output compares and the CHxF bit until the low byte (TACHxL) is written.
Register Name and Address
Read:
Write:
Reset:
TACH0H — $0027
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Indeterminate after Reset
Figure 18-9. TIMA Channel Registers
(TACH0H/L–TACH5H/L) (Sheet 1 of 3)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
203
Timer Interface Module A (TIMA)
Register Name and Address
Read:
Write:
TACH0L — $0028
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH1H — $002A
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH1L — $002B
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH2H — $002D
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH2L — $002E
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH3H — $0030
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH3L — $0031
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
Reset:
TACH4H — $0033
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Indeterminate after Reset
Figure 18-9. TIMA Channel Registers
(TACH0H/L–TACH5H/L) (Sheet 2 of 3)
MC68HC908AZ32A Data Sheet, Rev. 2
204
Freescale Semiconductor
I/O Registers
Register Name and Address
Read:
Write:
TACH4L — $0034
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TACH5H — $0036
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
Reset:
TACH5L — $0037
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Indeterminate after Reset
Figure 18-9. TIMA Channel Registers
(TACH0H/L–TACH5H/L) (Sheet 3 of 3)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
205
Timer Interface Module A (TIMA)
MC68HC908AZ32A Data Sheet, Rev. 2
206
Freescale Semiconductor
Chapter 19
Timer Interface Module B (TIMB)
19.1 Introduction
This section describes the timer interface module (TIMB). The TIMB is a 2-channel timer that provides a
timing reference with input capture, output compare and pulse width modulation functions. Figure 19-1 is
a block diagram of the TIMB.
19.2 Features
Features of the TIMB include:
• Two Input Capture/Output Compare Channels
– Rising-Edge, Falling-Edge or Any-Edge Input Capture Trigger
– Set, Clear or Toggle Output Compare Action
• Buffered and Unbuffered Pulse Width Modulation (PWM) Signal Generation
• Programmable TIMB Clock Input
– 7 Frequency Internal Bus Clock Prescaler Selection
– External TIMB Clock Input (4 MHz Maximum Frequency)
• Free-Running or Modulo Up-Count Operation
• Toggle Any Channel Pin on Overflow
• TIMB Counter Stop and Reset Bits
19.3 Functional Description
Figure 19-1 shows the TIMB structure. The central component of the TIMB is the 16-bit TIMB counter that
can operate as a free-running counter or a modulo up-counter. The TIMB counter provides the timing
reference for the input capture and output compare functions. The TIMB counter modulo registers,
TBMODH–TBMODL, control the modulo value of the TIMB counter. Software can read the TIMB counter
value at any time without affecting the counting sequence.
The two TIMB channels are programmable independently as input capture or output compare channels.
19.3.1 TIMB Counter Prescaler
The TIMB clock source can be one of the seven prescaler outputs or the TIMB clock pin, PTD4/ATD12.
The prescaler generates seven clock rates from the internal bus clock. The prescaler select bits, PS[2:0],
in the TIMB status and control register select the TIMB clock source.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
207
Timer Interface Module B (TIMB)
TCLK
PTD4/ATD12
PRESCALER SELECT
INTERNAL
BUS CLOCK
PRESCALER
TSTOP
PS2
TRST
PS1
PS0
16-BIT COUNTER
INTERRUPT
LOGIC
TOF
TOIE
16-BIT COMPARATOR
TMODH:TMODL
ELS0B
CHANNEL 0
ELS0A
TOV0
CH0MAX
16-BIT COMPARATOR
TCH0H:TCH0L
PTF4
LOGIC
CH0F
INTERRUPT
LOGIC
16-BIT LATCH
MS0A
ELS1B
CHANNEL 1
CH0IE
MS0B
ELS1A
TOV1
CH1MAX
16-BIT COMPARATOR
TCH1H:TCH1L
PTF5
LOGIC
CH1F
PTF5/TBCH1
INTERRUPT
LOGIC
16-BIT LATCH
CH1IE
MS1A
PTF4
Figure 19-1. TIMB Block Diagram
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
$0040
TIMB Status/Control Register (TBSC)
TOF
TOIE
TSTOP
TRST
0
PS2
PS1
PS0
$0041
TIMB Counter Register High (TBCNTH)
Bit 15
14
13
12
11
10
9
Bit 8
$0042
TIMB Counter Register Low (TBCNTL)
Bit 7
6
5
4
3
2
1
Bit 0
$0043
TIMB Counter Modulo Reg. High (TBMODH)
Bit 15
14
13
12
11
10
9
Bit 8
$0044
TIMB Counter Modulo Reg. Low (TBMODL)
Bit 7
6
5
4
3
2
1
Bit 0
$0045
TIMB Ch. 0 Status/Control Register (TBSC0)
CH0F
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
$0046
TIMB Ch. 0 Register High (TBCH0H)
Bit 15
14
13
12
11
10
9
Bit 8
$0047
TIMB Ch. 0 Register Low (TBCH0L)
Bit 7
6
5
4
3
2
1
Bit 0
$0048
TIMB Ch. 1 Status/Control Register (TBSC1)
CH1F
CH1IE
0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
$0049
TIMB Ch. 1 Register High (TBCH1H)
Bit 15
14
13
12
11
10
9
Bit 8
$004A
TIMB Ch. 1 Register Low (TBCH1L)
Bit 7
6
5
4
3
2
1
Bit 0
R
= Reserved
Figure 19-2. TIMB I/O Register Summary
MC68HC908AZ32A Data Sheet, Rev. 2
208
Freescale Semiconductor
Functional Description
19.3.2 Input Capture
An input capture function has three basic parts: edge select logic, an input capture latch and a 16-bit
counter. Two 8-bit registers, which make up the 16-bit input capture register, are used to latch the value
of the free-running counter after the corresponding input capture edge detector senses a defined
transition. The polarity of the active edge is programmable. The level transition which triggers the counter
transfer is defined by the corresponding input edge bits (ELSxB and ELSxA in TBSC0 through TBSC1
control registers with x referring to the active channel number). When an active edge occurs on the pin of
an input capture channel, the TIMB latches the contents of the TIMB counter into the TIMB channel
registers, TBCHxH–TBCHxL. Input captures can generate TIMB CPU interrupt requests. Software can
determine that an input capture event has occurred by enabling input capture interrupts or by polling the
status flag bit.
The result obtained by an input capture will be two more than the value of the free-running counter on the
rising edge of the internal bus clock preceding the external transition. This delay is required for internal
synchronization.
The free-running counter contents are transferred to the TIMB channel register (TBCHxH–TBCHxL, see
19.8.5 TIMB Channel Registers) on each proper signal transition regardless of whether the TIMB channel
flag (CH0F–CH1F in TBSC0–TBSC1 registers) is set or clear. When the status flag is set, a CPU interrupt
is generated if enabled. The value of the count latched or “captured” is the time of the event. Because this
value is stored in the input capture register 2 bus cycles after the actual event occurs, user software can
respond to this event at a later time and determine the actual time of the event. However, this must be
done prior to another input capture on the same pin; otherwise, the previous time value will be lost.
By recording the times for successive edges on an incoming signal, software can determine the period
and/or pulse width of the signal. To measure a period, two successive edges of the same polarity are
captured. To measure a pulse width, two alternate polarity edges are captured. Software should track the
overflows at the 16-bit module counter to extend its range.
Another use for the input capture function is to establish a time reference. In this case, an input capture
function is used in conjunction with an output compare function. For example, to activate an output signal
a specified number of clock cycles after detecting an input event (edge), use the input capture function to
record the time at which the edge occurred. A number corresponding to the desired delay is added to this
captured value and stored to an output compare register (see 19.8.5 TIMB Channel Registers). Because
both input captures and output compares are referenced to the same 16-bit modulo counter, the delay
can be controlled to the resolution of the counter independent of software latencies.
Reset does not affect the contents of the input capture channel register (TBCHxH–TBCHxL).
19.3.3 Output Compare
With the output compare function, the TIMB can generate a periodic pulse with a programmable polarity,
duration and frequency. When the counter reaches the value in the registers of an output compare
channel, the TIMB can set, clear or toggle the channel pin. Output compares can generate TIMB CPU
interrupt requests.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
209
Timer Interface Module B (TIMB)
19.3.3.1 Unbuffered Output Compare
Any output compare channel can generate unbuffered output compare pulses as described in 19.3.3
Output Compare. The pulses are unbuffered because changing the output compare value requires writing
the new value over the old value currently in the TIMB channel registers.
An unsynchronized write to the TIMB channel registers to change an output compare value could cause
incorrect operation for up to two counter overflow periods. For example, writing a new value before the
counter reaches the old value but after the counter reaches the new value prevents any compare during
that counter overflow period. Also, using a TIMB overflow interrupt routine to write a new, smaller output
compare value may cause the compare to be missed. The TIMB may pass the new value before it is
written.
Use the following methods to synchronize unbuffered changes in the output compare value on channel x:
• When changing to a smaller value, enable channel x output compare interrupts and write the new
value in the output compare interrupt routine. The output compare interrupt occurs at the end of
the current output compare pulse. The interrupt routine has until the end of the counter overflow
period to write the new value.
• When changing to a larger output compare value, enable TIMB overflow interrupts and write the
new value in the TIMB overflow interrupt routine. The TIMB overflow interrupt occurs at the end of
the current counter overflow period. Writing a larger value in an output compare interrupt routine
(at the end of the current pulse) could cause two output compares to occur in the same counter
overflow period.
19.3.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare channel whose output appears on the
PTF4 pin. The TIMB channel registers of the linked pair alternately control the output.
Setting the MS0B bit in TIMB channel 0 status and control register (TBSC0) links channel 0 and
channel 1. The output compare value in the TIMB channel 0 registers initially controls the output on the
PTF4 pin. Writing to the TIMB channel 1 registers enables the TIMB channel 1 registers to synchronously
control the output after the TIMB overflows. At each subsequent overflow, the TIMB channel registers (0
or 1) that control the output are the ones written to last. TBSC0 controls and monitors the buffered output
compare function and TIMB channel 1 status and control register (TBSC1) is unused. While the MS0B bit
is set, the channel 1 pin, PTF5/TBCH1, is available as a general-purpose I/O pin.
NOTE
In buffered output compare operation, do not write new output compare
values to the currently active channel registers. Writing to the active
channel registers is the same as generating unbuffered output compares.
19.3.4 Pulse Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare channel, the TIMB can generate a PWM
signal. The value in the TIMB counter modulo registers determines the period of the PWM signal. The
channel pin toggles when the counter reaches the value in the TIMB counter modulo registers. The time
between overflows is the period of the PWM signal.
As Figure 19-3 shows, the output compare value in the TIMB channel registers determines the pulse width
of the PWM signal. The time between overflow and output compare is the pulse width. Program the TIMB
MC68HC908AZ32A Data Sheet, Rev. 2
210
Freescale Semiconductor
Functional Description
to clear the channel pin on output compare if the state of the PWM pulse is logic 1. Program the TIMB to
set the pin if the state of the PWM pulse is logic 0.
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PULSE
WIDTH
PTEx/TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 19-3. PWM Period and Pulse Width
The value in the TIMB counter modulo registers and the selected prescaler output determines the
frequency of the PWM output. The frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIMB counter modulo registers produces a PWM period of 256 times the internal bus
clock period if the prescaler select value is $000 19.8.1 TIMB Status and Control Register.
The value in the TIMB channel registers determines the pulse width of the PWM output. The pulse width
of an 8-bit PWM signal is variable in 256 increments. Writing $0080 (128) to the TIMB channel registers
produces a duty cycle of 128/256 or 50%.
19.3.4.1 Unbuffered PWM Signal Generation
Any output compare channel can generate unbuffered PWM pulses as described in 19.3.4 Pulse Width
Modulation (PWM). The pulses are unbuffered because changing the pulse width requires writing the new
pulse width value over the value currently in the TIMB channel registers.
An unsynchronized write to the TIMB channel registers to change a pulse width value could cause
incorrect operation for up to two PWM periods. For example, writing a new value before the counter
reaches the old value but after the counter reaches the new value prevents any compare during that PWM
period. Also, using a TIMB overflow interrupt routine to write a new, smaller pulse width value may cause
the compare to be missed. The TIMB may pass the new value before it is written to the TIMB channel
registers.
Use the following methods to synchronize unbuffered changes in the PWM pulse width on channel x:
• When changing to a shorter pulse width, enable channel x output compare interrupts and write the
new value in the output compare interrupt routine. The output compare interrupt occurs at the end
of the current pulse. The interrupt routine has until the end of the PWM period to write the new
value.
• When changing to a longer pulse width, enable TIMB overflow interrupts and write the new value
in the TIMB overflow interrupt routine. The TIMB overflow interrupt occurs at the end of the current
PWM period. Writing a larger value in an output compare interrupt routine (at the end of the current
pulse) could cause two output compares to occur in the same PWM period.
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
211
Timer Interface Module B (TIMB)
event of software error or noise. Toggling on output compare also can
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
19.3.4.2 Buffered PWM Signal Generation
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the PTF4 pin.
The TIMB channel registers of the linked pair alternately control the pulse width of the output.
Setting the MS0B bit in TIMB channel 0 status and control register (TBSC0) links channel 0 and
channel 1. The TIMB channel 0 registers initially control the pulse width on the PTF4 pin. Writing to the
TIMB channel 1 registers enables the TIMB channel 1 registers to synchronously control the pulse width
at the beginning of the next PWM period. At each subsequent overflow, the TIMB channel registers (0
or 1) that control the pulse width are the ones written to last. TBSC0 controls and monitors the buffered
PWM function, and TIMB channel 1 status and control register (TBSC1) is unused. While the MS0B bit is
set, the channel 1 pin, PTF5/TBCH1, is available as a general-purpose I/O pin.
NOTE
In buffered PWM signal generation, do not write new pulse width values to
the currently active channel registers. Writing to the active channel
registers is the same as generating unbuffered PWM signals.
19.3.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use the following
initialization procedure:
1. In the TIMB status and control register (TBSC):
a. Stop the TIMB counter by setting the TIMB stop bit, TSTOP.
b. Reset the TIMB counter and prescaler by setting the TIMB reset bit, TRST.
2. In the TIMB counter modulo registers (TBMODH–TBMODL) write the value for the required PWM
period.
3. In the TIMB channel x registers (TBCHxH–TBCHxL) write the value for the required pulse width.
4. In TIMB channel x status and control register (TBSCx):
a. Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for buffered output compare
or PWM signals) to the mode select bits, MSxB–MSxA (see Table 19-2).
b. Write 1 to the toggle-on-overflow bit, TOVx.
c. Write 1:0 (to clear output on compare) or 1:1 (to set output on compare) to the edge/level
select bits, ELSxB–ELSxA. The output action on compare must force the output to the
complement of the pulse width level (see Table 19-2).
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
event of software error or noise. Toggling on output compare can also
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
5. In the TIMB status control register (TBSC) clear the TIMB stop bit, TSTOP.
MC68HC908AZ32A Data Sheet, Rev. 2
212
Freescale Semiconductor
Interrupts
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIMB channel
0 registers (TBCH0H–TBCH0L) initially control the buffered PWM output. TIMB status control register 0
(TBSC0) controls and monitors the PWM signal from the linked channels. MS0B takes priority over MS0A.
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIMB overflows. Subsequent output
compares try to force the output to a state it is already in and have no effect. The result is a 0% duty cycle
output.
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100% duty
cycle output (see 19.8.4 TIMB Channel Status and Control Registers).
19.4 Interrupts
The following TIMB sources can generate interrupt requests:
• TIMB overflow flag (TOF) — The TOF bit is set when the TIMB counter value rolls over to $0000
after matching the value in the TIMB counter modulo registers. The TIMB overflow interrupt enable
bit, TOIE, enables TIMB overflow CPU interrupt requests. TOF and TOIE are in the TIMB status
and control register.
• TIMB channel flags (CH1F–CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. Channel x TIMB CPU interrupt requests are controlled by the channel x
interrupt enable bit, CHxIE.
19.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power- consumption standby modes.
19.5.1 Wait Mode
The TIMB remains active after the execution of a WAIT instruction. In wait mode, the TIMB registers are
not accessible by the CPU. Any enabled CPU interrupt request from the TIMB can bring the MCU out of
wait mode.
If TIMB functions are not required during wait mode, reduce power consumption by stopping the TIMB
before executing the WAIT instruction.
19.5.2 Stop Mode
The TIMB is inactive after the execution of a STOP instruction. The STOP instruction does not affect
register conditions or the state of the TIMB counter. TIMB operation resumes when the MCU exits stop
mode.
19.6 TIMB During Break Interrupts
A break interrupt stops the TIMB counter and inhibits input captures.
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state (see 7.7.3 SIM Break Flag Control Register).
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
213
Timer Interface Module B (TIMB)
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a 2-step read/write clearing procedure. If software does the first step on such a bit
before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
19.7 I/O Signals
Port D shares one of its pins with the TIMB. Port F shares two of its pins with the TIMB. PTD4/ATD12 is
an external clock input to the TIMB prescaler. The two TIMB channel I/O pins are PTF4 and PTF5/TBCH1.
19.7.1 TIMB Clock Pin (PTD4/ATD12)
PTD4/ATD12 is an external clock input that can be the clock source for the TIMB counter instead of the
prescaled internal bus clock. Select the PTD4/ATD12 input by writing logic 1s to the three prescaler select
bits, PS[2:0] 19.8.1 TIMB Status and Control Register. The minimum TCLK pulse width, TCLKLMIN or
TCLKHMIN, is:
1
------------------------------------- + t
bus frequency SU
The maximum TCLK frequency is the least: 4 MHz or bus frequency ÷ 2.
PTD4/ATD12 is available as a general-purpose I/O pin or ADC channel when not used as the TIMB clock
input. When the PTD4/ATD12 pin is the TIMB clock input, it is an input regardless of the state of the
DDRD4 bit in data direction register D.
19.7.2 TIMB Channel I/O Pins (PTF5/TBCH1–PTF4)
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.
PTF4 and PTF5/TBCH1 can be configured as buffered output compare or buffered PWM pins.
19.8 I/O Registers
These I/O registers control and monitor TIMB operation:
• TIMB status and control register (TBSC)
• TIMB control registers (TBCNTH–TBCNTL)
• TIMB counter modulo registers (TBMODH–TBMODL)
• TIMB channel status and control registers (TBSC0 and TBSC1)
• TIMB channel registers (TBCH0H–TBCH0L, TBCH1H–TBCH1L)
19.8.1 TIMB Status and Control Register
The TIMB status and control register:
• Enables TIMB overflow interrupts
• Flags TIMB overflows
• Stops the TIMB counter
• Resets the TIMB counter
• Prescales the TIMB counter clock
MC68HC908AZ32A Data Sheet, Rev. 2
214
Freescale Semiconductor
I/O Registers
Address:
$0040
Bit 7
6
5
TOIE
TSTOP
1
Read:
TOF
Write:
0
Reset:
0
0
R
= Reserved
4
3
0
0
TRST
R
0
0
2
1
Bit 0
PS2
PS1
PS0
0
0
0
Figure 19-4. TIMB Status and Control Register (TBSC)
TOF — TIMB Overflow Flag Bit
This read/write flag is set when the TIMB counter resets to $0000 after reaching the modulo value
programmed in the TIMB counter modulo registers. Clear TOF by reading the TIMB status and control
register when TOF is set and then writing a logic 0 to TOF. If another TIMB overflow occurs before the
clearing sequence is complete, then writing logic 0 to TOF has no effect. Therefore, a TOF interrupt
request cannot be lost due to inadvertent clearing of TOF. Reset clears the TOF bit. Writing a logic 1
to TOF has no effect.
1 = TIMB counter has reached modulo value
0 = TIMB counter has not reached modulo value
TOIE — TIMB Overflow Interrupt Enable Bit
This read/write bit enables TIMB overflow interrupts when the TOF bit becomes set. Reset clears the
TOIE bit.
1 = TIMB overflow interrupts enabled
0 = TIMB overflow interrupts disabled
TSTOP — TIMB Stop Bit
This read/write bit stops the TIMB counter. Counting resumes when TSTOP is cleared. Reset sets the
TSTOP bit, stopping the TIMB counter until software clears the TSTOP bit.
1 = TIMB counter stopped
0 = TIMB counter active
NOTE
Do not set the TSTOP bit before entering wait mode if the TIMA is required
to exit wait mode. Also, when the TSTOP bit is set and input capture mode
is enabled, input captures are inhibited until TSTOP is cleared.
When using TSTOP to stop the timer counter, see if any timer flags are set.
If a timer flag is set, it must be cleared by clearing TSTOP, then clearing the
flag, then setting TSTOP again.
TRST — TIMB Reset Bit
Setting this write-only bit resets the TIMB counter and the TIMB prescaler. Setting TRST has no effect
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMB
counter is reset and always reads as logic 0. Reset clears the TRST bit.
1 = Prescaler and TIMB counter cleared
0 = No effect
NOTE
Setting the TSTOP and TRST bits simultaneously stops the TIMB counter
at a value of $0000.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
215
Timer Interface Module B (TIMB)
PS[2:0] — Prescaler Select Bits
These read/write bits select either the PTD4/ATD12 pin or one of the seven prescaler outputs as the
input to the TIMB counter as Table 19-1 shows. Reset clears the PS[2:0] bits.
Table 19-1. Prescaler Selection
PS[2:0]
TIMB Clock Source
000
Internal Bus Clock ÷1
001
Internal Bus Clock ÷ 2
010
Internal Bus Clock ÷ 4
011
Internal Bus Clock ÷ 8
100
Internal Bus Clock ÷ 16
101
Internal Bus Clock ÷ 32
110
Internal Bus Clock ÷ 64
111
PTD4/ATD12
19.8.2 TIMB Counter Registers
The two read-only TIMB counter registers contain the high and low bytes of the value in the TIMB counter.
Reading the high byte (TBCNTH) latches the contents of the low byte (TBCNTL) into a buffer. Subsequent
reads of TBCNTH do not affect the latched TBCNTL value until TBCNTL is read. Reset clears the TIMB
counter registers. Setting the TIMB reset bit (TRST) also clears the TIMB counter registers.
NOTE
If TBCNTH is read during a break interrupt, be sure to unlatch TBCNTL by
reading TBCNTL before exiting the break interrupt. Otherwise, TBCNTL
retains the value latched during the break.
Register Name and Address
TBCNTH — $0041
Bit 7
6
5
4
3
2
1
Bit 0
Read:
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
Register Name and Address
TBCNTL — $0042
Bit 7
6
5
4
3
2
1
Bit 0
Read:
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
Reserved
Figure 19-5. TIMB Counter Registers (TBCNTH and TBCNTL)
MC68HC908AZ32A Data Sheet, Rev. 2
216
Freescale Semiconductor
I/O Registers
19.8.3 TIMB Counter Modulo Registers
The read/write TIMB modulo registers contain the modulo value for the TIMB counter. When the TIMB
counter reaches the modulo value, the overflow flag (TOF) becomes set and the TIMB counter resumes
counting from $0000 at the next clock. Writing to the high byte (TBMODH) inhibits the TOF bit and
overflow interrupts until the low byte (TBMODL) is written. Reset sets the TIMB counter modulo registers.
Register Name and Address
Read:
Write:
Reset:
TBMODH — $0043
Bit 7
6
5
4
3
2
1
Bit 0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
1
1
1
1
1
1
1
1
Register Name and Address
Read:
Write:
Reset:
TBMODL — $0044
Bit 7
6
5
4
3
2
1
Bit 0
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1
1
1
1
1
1
1
1
Figure 19-6. TIMB Counter Modulo Registers (TBMODH and TBMODL)
NOTE
Reset the TIMB counter before writing to the TIMB counter modulo registers.
19.8.4 TIMB Channel Status and Control Registers
Each of the TIMB channel status and control registers:
• Flags input captures and output compares
• Enables input capture and output compare interrupts
• Selects input capture, output compare or PWM operation
• Selects high, low or toggling output on output compare
• Selects rising edge, falling edge or any edge as the active input capture trigger
• Selects output toggling on TIMB overflow
• Selects 0% and 100% PWM duty cycle
• Selects buffered or unbuffered output compare/PWM operation
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
217
Timer Interface Module B (TIMB)
Register Name and Address
Bit 7
Read:
CH0F
Write:
0
Reset:
0
TBSC0 — $0045
6
5
4
3
2
1
Bit 0
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
4
3
2
1
Bit 0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
Register Name and Address
Bit 7
TBSC1 — $0048
6
5
Read:
CH1F
Write:
0
Reset:
0
0
R
Reserved
CH1IE
0
R
0
Figure 19-7. TIMB Channel Status
and Control Registers (TBSC0–TBSC1)
CHxF — Channel x Flag Bit
When channel x is an input capture channel, this read/write bit is set when an active edge occurs on
the channel x pin. When channel x is an output compare channel, CHxF is set when the value in the
TIMB counter registers matches the value in the TIMB channel x registers.
When CHxIE = 1, clear CHxF by reading TIMB channel x status and control register with CHxF set,
and then writing a logic 0 to CHxF. If another interrupt request occurs before the clearing sequence is
complete, then writing logic 0 to CHxF has no effect. Therefore, an interrupt request cannot be lost due
to inadvertent clearing of CHxF.
Reset clears the CHxF bit. Writing a logic 1 to CHxF has no effect.
1 = Input capture or output compare on channel x
0 = No input capture or output compare on channel x
CHxIE — Channel x Interrupt Enable Bit
This read/write bit enables TIMB CPU interrupts on channel x.
Reset clears the CHxIE bit.
1 = Channel x CPU interrupt requests enabled
0 = Channel x CPU interrupt requests disabled
MSxB — Mode Select Bit B
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIMB
channel 0.
Setting MS0B disables the channel 1 status and control register and reverts TBCH1 to
general-purpose I/O.
Reset clears the MSxB bit.
1 = Buffered output compare/PWM operation enabled
0 = Buffered output compare/PWM operation disabled
MC68HC908AZ32A Data Sheet, Rev. 2
218
Freescale Semiconductor
I/O Registers
MSxA — Mode Select Bit A
When ELSxB:A ≠ 00, this read/write bit selects either input capture operation or unbuffered output
compare/PWM operation (see Table 19-2).
1 = Unbuffered output compare/PWM operation
0 = Input capture operation
When ELSxB:A = 00, this read/write bit selects the initial output level of the TBCHx pin once PWM,
input capture or output compare operation is enabled (see Table 19-2). Reset clears the MSxA bit.
1 = Initial output level low
0 = Initial output level high
NOTE
Before changing a channel function by writing to the MSxB or MSxA bit, set
the TSTOP and TRST bits in the TIMB status and control register (TBSC).
ELSxB and ELSxA — Edge/Level Select Bits
When channel x is an input capture channel, these read/write bits control the active edge-sensing logic
on channel x.
When channel x is an output compare channel, ELSxB and ELSxA control the channel x output
behavior when an output compare occurs.
When ELSxB and ELSxA are both clear, channel x is not connected to port F and pin PTFx/TBCHx is
available as a general-purpose I/O pin. However, channel x is at a state determined by these bits and
becomes transparent to the respective pin when PWM, input capture, or output compare mode is
enabled. Table 19-2 shows how ELSxB and ELSxA work. Reset clears the ELSxB and ELSxA bits.
Table 19-2. Mode, Edge, and Level Selection
MSxB:MSxA
ELSxB:ELSxA
X0
00
Mode
Output Preset
Configuration
Pin under Port Control;
Initialize Timer
Output Level High
X1
00
Pin under Port Control;
Initialize Timer
Output Level Low
00
01
Capture on Rising Edge Only
00
10
00
11
01
01
01
10
01
11
1X
01
1X
10
1X
11
Input Capture
Capture on Falling Edge Only
Capture on Rising or Falling Edge
Output
Compare
or PWM
Buffered
Output Compare
or Buffered PWM
Toggle Output on Compare
Clear Output on Compare
Set Output on Compare
Toggle Output on Compare
Clear Output on Compare
Set Output on Compare
NOTE
Before enabling a TIMB channel register for input capture operation, make
sure that the PTFx/TBCHx pin is stable for at least two bus clocks.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
219
Timer Interface Module B (TIMB)
TOVx — Toggle-On-Overflow Bit
When channel x is an output compare channel, this read/write bit controls the behavior of the channel
x output when the TIMB counter overflows. When channel x is an input capture channel, TOVx has no
effect. Reset clears the TOVx bit.
1 = Channel x pin toggles on TIMB counter overflow.
0 = Channel x pin does not toggle on TIMB counter overflow.
NOTE
When TOVx is set, a TIMB counter overflow takes precedence over a
channel x output compare if both occur at the same time.
CHxMAX — Channel x Maximum Duty Cycle Bit
When the TOVx bit is at logic 1, setting the CHxMAX bit forces the duty cycle of buffered and
unbuffered PWM signals to 100%. As Figure 19-8 shows, the CHxMAX bit takes effect in the cycle after
it is set or cleared. The output stays at the 100% duty cycle level until the cycle after CHxMAX is
cleared.
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PTEx/TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
Figure 19-8. CHxMAX Latency
19.8.5 TIMB Channel Registers
These read/write registers contain the captured TIMB counter value of the input capture function or the
output compare value of the output compare function. The state of the TIMB channel registers after reset
is unknown.
In input capture mode (MSxB–MSxA = 0:0) reading the high byte of the TIMB channel x registers
(TBCHxH) inhibits input captures until the low byte (TBCHxL) is read.
In output compare mode (MSxB–MSxA ≠ 0:0) writing to the high byte of the TIMB channel x registers
(TBCHxH) inhibits output compares and the CHxF bit until the low byte (TBCHxL) is written.
Register Name and Address
Read:
Write:
Reset:
TBCH0H — $0046
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Indeterminate after Reset
Figure 19-9. TIMB Channel Registers
(TBCH0H/L–TBCH1H/L)
MC68HC908AZ32A Data Sheet, Rev. 2
220
Freescale Semiconductor
I/O Registers
Register Name and Address
Read:
Write:
TBCH0L — $0047
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
TBCH1H — $0049
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Reset:
Indeterminate after Reset
Register Name and Address
Read:
Write:
Reset:
TBCH1L — $004A
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Indeterminate after Reset
Figure 19-9. TIMB Channel Registers
(TBCH0H/L–TBCH1H/L) (Continued)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
221
Timer Interface Module B (TIMB)
MC68HC908AZ32A Data Sheet, Rev. 2
222
Freescale Semiconductor
Chapter 20
Programmable Interrupt Timer (PIT)
20.1 Introduction
This section describes the Programmable Interrupt Timer (PIT) which is a periodic interrupt timer whose
counter is clocked internally via software programmable options. Figure 20-1 is a block diagram of the
PIT.
20.2 Features
Features of the PIT include:
• Programmable PIT Clock Input
• Free-Running or Modulo Up-Count Operation
• PIT Counter Stop and Reset Bits
20.3 Functional Description
Figure 20-1 shows the structure of the PIT. The central component of the PIT is the 16-bit PIT counter
that can operate as a free-running counter or a modulo up-counter. The counter provides the timing
reference for the interrupt. The PIT counter modulo registers, PMODH–PMODL, control the modulo value
of the counter. Software can read the counter value at any time without affecting the counting sequence.
PRESCALER SELECT
INTERNAL
BUS CLOCK
PRESCALER
CSTOP
PPS2
CRST
PPS1
PPS0
16-BIT COUNTER
POF
POIE
INTERRUPT
LOGIC
16-BIT COMPARATOR
TIMPMODH:TIMPMODL
Figure 20-1. PIT Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
223
Programmable Interrupt Timer (PIT)
Register Name
Bit 7
Read:
POF
6
5
4
3
0
0
2
1
Bit 0
PPS2
PPS1
PPS0
POIE
PSTOP
0
0
1
0
0
0
0
0
Read:
PIT Counter Register High
Write:
(PCNTH)
Reset:
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Read:
PIT Counter Register Low
Write:
(PCNTL)
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
PIT Status and Control Register
Write:
(PSC)
Reset:
Read:
PIT Counter Modulo Register High
Write:
(PMODH)
Reset:
Read:
PIT Counter Modulo Register Low
Write:
(PMODL)
Reset:
0
PRST
=Unimplemented
Figure 20-2. PIT I/O Register Summary
Table 20-1. PIT I/O Register Address Summary
Register
PSC
PCNTH
PCNTL
PMODH
PMODL
Address
$004B
$004C
$004D
$004E
$004F
20.4 PIT Counter Prescaler
The clock source can be one of the seven prescaler outputs. The prescaler generates seven clock rates
from the internal bus clock. The prescaler select bits, PPS[2:0], in the status and control register select
the PIT clock source.
The value in the PIT counter modulo registers and the selected prescaler output determines the frequency
of the periodic interrupt. The PIT overflow flag (POF) is set when the PIT counter value rolls over to $0000
after matching the value in the PIT counter modulo registers. The PIT interrupt enable bit, POIE, enables
PIT overflow CPU interrupt requests. POF and POIE are in the PIT status and control register.
20.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
20.5.1 Wait Mode
The PIT remains active after the execution of a WAIT instruction. In wait mode the PIT registers are not
accessible by the CPU. Any enabled CPU interrupt request from the PIT can bring the MCU out of wait
mode.
If PIT functions are not required during wait mode, reduce power consumption by stopping the PIT before
executing the WAIT instruction.
MC68HC908AZ32A Data Sheet, Rev. 2
224
Freescale Semiconductor
PIT During Break Interrupts
20.5.2 Stop Mode
The PIT is inactive after the execution of a STOP instruction. The STOP instruction does not affect
register conditions or the state of the PIT counter. PIT operation resumes when the MCU exits stop mode
after an external interrupt.
20.6 PIT During Break Interrupts
A break interrupt stops the PIT counter.
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state (see 7.7.3 SIM Break Flag Control Register).
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a 2-step read/write clearing procedure. If software does the first step on such a bit
before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
20.7 I/O Registers
The following I/O registers control and monitor operation of the PIT:
• PIT status and control register (PSC)
• PIT counter registers (PCNTH–PCNTL)
• PIT counter modulo registers (PMODH–PMODL)
20.7.1 TIM Status and Control Register
The PIT status and control register:
• Enables PIT interrupt
• Flags PIT overflows
• Stops the PIT counter
• Resets the PIT counter
• Prescales the PIT counter clock
Address:
$004B
Bit 7
Read:
POF
Write:
0
Reset:
0
6
5
POIE
PSTOP
0
1
4
3
0
0
PRST
0
2
1
Bit 0
PPS2
PPS1
PPS0
0
0
0
0
= Unimplemented
Figure 20-3. PIT Status and Control Register (PSC)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
225
Programmable Interrupt Timer (PIT)
POF — PIT Overflow Flag Bit
This read/write flag is set when the PIT counter resets to $0000 after reaching the modulo value
programmed in the PIT counter modulo registers. Clear POF by reading the PIT status and control
register when POF is set and then writing a logic 0 to POF. If another PIT overflow occurs before the
clearing sequence is complete, then writing logic 0 to POF has no effect. Therefore, a POF interrupt
request cannot be lost due to inadvertent clearing of POF. Reset clears the POF bit. Writing a logic 1
to POF has no effect.
1 = PIT counter has reached modulo value
0 = PIT counter has not reached modulo value
POIE — PIT Overflow Interrupt Enable Bit
This read/write bit enables PIT overflow interrupts when the POF bit becomes set. Reset clears the
POIE bit.
1 = PIT overflow interrupts enabled
0 = PIT overflow interrupts disabled
PSTOP — PIT Stop Bit
This read/write bit stops the PIT counter. Counting resumes when PSTOP is cleared. Reset sets the
PSTOP bit, stopping the PIT counter until software clears the PSTOP bit.
1 = PIT counter stopped
0 = PIT counter active
NOTE
Do not set the PSTOP bit before entering wait mode if the PIT is required
to exit wait mode.
PRST — PIT Reset Bit
Setting this write-only bit resets the PIT counter and the PIT prescaler. Setting PRST has no effect on
any other registers. Counting resumes from $0000. PRST is cleared automatically after the PIT
counter is reset and always reads as logic zero. Reset clears the PRST bit.
1 = Prescaler and PIT counter cleared
0 = No effect
NOTE
Setting the PSTOP and PRST bits simultaneously stops the PIT counter at
a value of $0000.
PPS[2:0] — Prescaler Select Bits
These read/write bits select one of the seven prescaler outputs as the input to the PIT counter as Table
20-2 shows. Reset clears the PPS[2:0] bits.
Table 20-2. Prescaler Selection
PPS[2:0]
PIT Clock Source
000
Internal Bus Clock ÷1
001
Internal Bus Clock ÷ 2
010
Internal Bus Clock ÷ 4
011
Internal Bus Clock ÷ 8
100
Internal Bus Clock ÷ 16
101
Internal Bus Clock ÷ 32
110
Internal Bus Clock ÷ 64
111
Internal Bus Clock ÷ 64
MC68HC908AZ32A Data Sheet, Rev. 2
226
Freescale Semiconductor
I/O Registers
20.7.2 TIM Counter Registers
The two read-only PIT counter registers contain the high and low bytes of the value in the PIT counter.
Reading the high byte (PCNTH) latches the contents of the low byte (PCNTL) into a buffer. Subsequent
reads of PCNTH do not affect the latched PCNTL value until PCNTL is read. Reset clears the PIT counter
registers. Setting the PIT reset bit (PRST) also clears the PIT counter registers.
NOTE
If you read PCNTH during a break interrupt, be sure to unlatch PCNTL by
reading PCNTL before exiting the break interrupt. Otherwise, PCNTL
retains the value latched during the break
Address: $004C
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
Write:
Reset:
Address: $004D
Read:
Write:
Reset:
0
= Unimplemented
Figure 20-4. PIT Counter Registers (PCNTH–PCNTL)
20.7.3 TIM Counter Modulo Registers
The read/write PIT modulo registers contain the modulo value for the PIT counter. When the PIT counter
reaches the modulo value the overflow flag (POF) becomes set and the PIT counter resumes counting
from $0000 at the next clock. Writing to the high byte (PMODH) inhibits the POF bit and overflow
interrupts until the low byte (PMODL) is written. Reset sets the PIT counter modulo registers.
Address: $004E:$004F
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
Address: $004E:$004F
Read:
Write:
Reset:
Figure 20-5. PIT Counter Modulo Registers (PMODH–PMODL)
NOTE
Reset the PIT counter before writing to the PIT counter modulo registers.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
227
Programmable Interrupt Timer (PIT)
MC68HC908AZ32A Data Sheet, Rev. 2
228
Freescale Semiconductor
Chapter 21
Analog-To-Digital Converter (ADC-15)
21.1 Introduction
This section describes the analog-to-digital converter (ADC-15). The ADC is an 8-bit analog-to-digital
converter.
21.2 Features
Features of the ADC module include:
• 15 Channels with Multiplexed Input
• Linear Successive Approximation
• 8-Bit Resolution
• Single or Continuous Conversion
• Conversion Complete Flag or Conversion Complete Interrupt
• Selectable ADC Clock
21.3 Functional Description
Fifteen ADC channels are available for sampling external sources at pins
PTD6/ATD14/TCLK–PTD0/ATD8 and PTB7–PTB0. An analog multiplexer allows the single ADC
converter to select one of 15 ADC channels as ADC voltage in (ADCVIN). ADCVIN is converted by the
successive approximation register-based counters. When the conversion is completed, ADC places the
result in the ADC data register and sets a flag or generates an interrupt. See Figure 21-1.
21.3.1 ADC Port I/O Pins
PTD6/ATD14/TCLK–PTD0/ATD8 and PTB7–PTB0 are general-purpose I/O pins that share with the ADC
channels.
The channel select bits define which ADC channel/port pin will be used as the input signal. The ADC
overrides the port I/O logic by forcing that pin as input to the ADC. The remaining ADC channels/port pins
are controlled by the port I/O logic and can be used as general-purpose I/O. Writes to the port register or
DDR will not have any affect on the port pin that is selected by the ADC. Read of a port pin which is in
use by the ADC will return a logic 0 if the corresponding DDR bit is at logic 0. If the DDR bit is at logic 1,
the value in the port data latch is read.
NOTE
Do not use ADC channels ATD14 or ATD12 when using the
PTD6/ATD14/TCLK or PTD4/ATD12 pins as the clock inputs for the 16-bit
Timers.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
229
Analog-To-Digital Converter (ADC-15)
INTERNAL
DATA BUS
READ DDRB/DDRB
WRITE DDRB/DDRD
RESET
WRITE PTB/PTD
DISABLE
DDRBx/DDRDx
PTBx/PTDx
PTBx/PTDx
ADC CHANNEL x
READ PTB/PTD
DISABLE
ADC DATA REGISTER
INTERRUPT
LOGIC
AIEN
CONVERSION
COMPLETE
ADC VOLTAGE IN
ADCVIN
ADC
CHANNEL
SELECT
ADCH[4:0]
COCO
ADC CLOCK
CGMXCLK
BUS CLOCK
CLOCK
GENERATOR
ADIV[2:0]
ADICLK
Figure 21-1. ADC Block Diagram
21.3.2 Voltage Conversion
When the input voltage to the ADC equals VREFH (see 25.1.6 ADC Characteristics), the ADC converts the
signal to $FF (full scale). If the input voltage equals VSSA, the ADC converts it to $00. Input voltages
between VREFH and VSSA are a straight-line linear conversion. Conversion accuracy of all other input
voltages is not guaranteed. Avoid current injection on unused ADC inputs to prevent potential conversion
error.
NOTE
Input voltage should not exceed the analog supply voltages.
21.3.3 Conversion Time
Conversion starts after a write to the ADSCR (ADC status control register, $0038), and requires between
16 and 17 ADC clock cycles to complete. Conversion time in terms of the number of bus cycles is a
function of ADICLK select, CGMXCLK frequency, bus frequency, and ADIV prescaler bits. For example,
with a CGMXCLK frequency of 4 MHz, bus frequency of 8 MHz, and fixed ADC clock frequency of 1 MHz,
MC68HC908AZ32A Data Sheet, Rev. 2
230
Freescale Semiconductor
Interrupts
one conversion will take between 16 and 17 μs and there will be between 128 bus cycles between each
conversion. Sample rate is approximately 60 kHz.
Refer to 25.1.6 ADC Characteristics.
16 to 17 ADC Clock Cycles
Conversion Time = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
ADC Clock Frequency
Number of Bus Cycles = Conversion Time x Bus Frequency
21.3.4 Continuous Conversion
In the continuous conversion mode, the ADC data register will be filled with new data after each
conversion. Data from the previous conversion will be overwritten whether that data has been read or not.
Conversions will continue until the ADCO bit (ADC status control register, $0038) is cleared. The COCO
bit is set after the first conversion and will stay set for the next several conversions until the next write of
the ADC status and control register or the next read of the ADC data register.
21.3.5 Accuracy and Precision
The conversion process is monotonic and has no missing codes. See 25.1.6 ADC Characteristics for
accuracy information.
21.4 Interrupts
When the AIEN bit is set, the ADC module is capable of generating a CPU interrupt after each ADC
conversion. A CPU interrupt is generated if the COCO bit (ADC status control register, $0038) is at logic
0. If the COCO bit is set, an interrupt is generated. The COCO bit is not used as a conversion complete
flag when interrupts are enabled.
21.5 Low-Power Modes
The following subsections describe the low-power modes.
21.5.1 Wait Mode
The ADC continues normal operation during wait mode. Any enabled CPU interrupt request from the ADC
can bring the MCU out of wait mode. If the ADC is not required to bring the MCU out of wait mode, power
down the ADC by setting the ADCH[4:0] bits in the ADC status and control register before executing the
WAIT instruction.
21.5.2 Stop Mode
The ADC module is inactive after the execution of a STOP instruction. Any pending conversion is aborted.
ADC conversions resume when the MCU exits stop mode. Allow one conversion cycle to stabilize the
analog circuitry before attempting a new ADC conversion after exiting stop mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
231
Analog-To-Digital Converter (ADC-15)
21.6 I/O Signals
The ADC module has 15 channels that are shared with I/O ports B and D. Refer to 25.1.6 ADC
Characteristics for voltages referenced below.
21.6.1 ADC Analog Power Pin (VDDAREF)/ADC Voltage Reference Pin (VREFH)
The ADC analog portion uses VDDAREF as its power pin. Connect the VDDA/VDDAREF pin to the same
voltage potential as VDD. External filtering may be necessary to ensure clean VDDAREF for good results.
VREFH is the high reference voltage for all analog-to-digital conversions.
NOTE
Route VDDAREF carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package. VDDAREF must be present
for operation of the ADC.
21.6.2 ADC Analog Ground Pin (VSSA)/ADC Voltage Reference Low Pin (VREFL)
The ADC analog portion uses VSSA as its ground pin. Connect the VSSA pin to the same voltage potential
as VSS.
VREFL is the lower reference supply for the ADC.
21.6.3 ADC Voltage In (ADCVIN)
ADCVIN is the input voltage signal from one of the 15 ADC channels to the ADC module.
21.7 I/O Registers
These I/O registers control and monitor ADC operation:
• ADC status and control register (ADSCR)
• ADC data register (ADR)
• ADC clock register (ADICLK)
21.7.1 ADC Status and Control Register
The following paragraphs describe the function of the ADC status and control register.
Address:
$0038
Bit 7
6
5
4
3
2
1
Bit 0
AIEN
ADCO
CH4
CH3
CH2
CH1
CH0
0
1
1
1
1
1
Read:
COCO
Write:
R
Reset:
0
0
R
= Reserved
Figure 21-2. ADC Status and Control Register (ADSCR)
MC68HC908AZ32A Data Sheet, Rev. 2
232
Freescale Semiconductor
I/O Registers
COCO — Conversions Complete Bit
When the AIEN bit is a logic 0, the COCO is a read-only bit which is set each time a conversion is
completed. This bit is cleared whenever the ADC status and control register is written or whenever the
ADC data register is read.
If the AIEN bit is a logic 1, the COCO is a read/write bit which selects the CPU to service the ADC
interrupt request. Reset clears this bit.
1 = conversion completed (AIEN = 0)
0 = conversion not completed (AIEN = 0)
or
CPU interrupt enabled (AIEN = 1)
AIEN — ADC Interrupt Enable Bit
When this bit is set, an interrupt is generated at the end of an ADC conversion. The interrupt signal is
cleared when the data register is read or the status/control register is written. Reset clears the AIEN bit.
1 = ADC interrupt enabled
0 = ADC interrupt disabled
ADCO — ADC Continuous Conversion Bit
When set, the ADC will convert samples continuously and update the ADR register at the end of each
conversion. Only one conversion is allowed when this bit is cleared. Reset clears the ADCO bit.
1 = Continuous ADC conversion
0 = One ADC conversion
ADCH[4:0] — ADC Channel Select Bits
ADCH4, ADCH3, ADCH2, ADCH1, and ADCH0 form a 5-bit field which is used to select one of 15 ADC
channels. Channel selection is detailed in the following table. Care should be taken when using a port
pin as both an analog and a digital input simultaneously to prevent switching noise from corrupting the
analog signal. See Table 21-1.
The ADC subsystem is turned off when the channel select bits are all set to one. This feature allows
for reduced power consumption for the MCU when the ADC is not used. Reset sets these bits.
NOTE
Recovery from the disabled state requires one conversion cycle to stabilize.
Table 21-1. Mux Channel Select
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
Input Select
0
0
0
0
0
PTB0
0
0
0
0
1
PTB1
0
0
0
1
0
PTB2
0
0
0
1
1
PTB3
0
0
1
0
0
PTB4
0
0
1
0
1
PTB5
0
0
1
1
0
PTB6
0
0
1
1
1
PTB7
0
1
0
0
0
PTD0/ATD8/ATD8
0
1
0
0
1
PTD1/ATD9/ATD9
0
1
0
1
0
PTD2/ATD10/ATD10
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
233
Analog-To-Digital Converter (ADC-15)
Table 21-1. Mux Channel Select (Continued)
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
Input Select
0
1
0
1
1
PTD3/ATD11/ATD11
0
1
1
0
0
PTD4/ATD12/ATD12
0
1
1
0
1
PTD5/ATD13/ATD13
0
1
1
1
0
PTD6/ATD14/TCLK/ATD14
Unused (see Note(1))
Range 01111 ($0F) to 11010 ($1A)
Unused (see Note(1))
1
1
0
1
1
Reserved
1
1
1
0
0
Unused (see Note (1))
1
1
1
0
1
VREFH (see Note(2))
1
1
1
1
0
VSSA/VREFL (see Note (2))
1
1
1
1
1
[ADC power off]
1. If any unused channels are selected, the resulting ADC conversion will be unknown.
2. The voltage levels supplied from internal reference nodes as specified in the table are used
to verify the operation of the ADC converter both in production test and for user applications.
21.7.2 ADC Data Register
One 8-bit result register is provided. This register is updated each time an ADC conversion completes.
Address:
$0039
Bit 7
6
5
4
3
2
1
Bit 0
Read:
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
Write:
R
R
R
R
R
R
R
R
Reset:
Indeterminate after Reset
R
= Reserved
Figure 21-3. ADC Data Register (ADR)
21.7.3 ADC Input Clock Register
This register selects the clock frequency for the ADC.
Address:
Read:
Write:
Reset:
$003A
Bit 7
6
5
4
ADIV2
ADIV1
ADIV0
ADICLK
0
0
0
0
R
= Reserved
3
2
1
Bit 0
0
0
0
0
R
R
R
R
0
0
0
0
Figure 21-4. ADC Input Clock Register (ADICLK)
MC68HC908AZ32A Data Sheet, Rev. 2
234
Freescale Semiconductor
I/O Registers
ADIV2–ADIV0 — ADC Clock Prescaler Bits
ADIV2, ADIV1, and ADIV0 form a 3-bit field which selects the divide ratio used by the ADC to generate
the internal ADC clock. Table 21-2 shows the available clock configurations. The ADC clock should be
set to approximately 1 MHz.
Table 21-2. ADC Clock Divide Ratio
ADIV2
ADIV1
ADIV0
ADC Clock Rate
0
0
0
ADC Input Clock /1
0
0
1
ADC Input Clock / 2
0
1
0
ADC Input Clock / 4
0
1
1
ADC Input Clock / 8
1
X
X
ADC Input Clock / 16
X = don’t care
ADICLK — ADC Input Clock Register Bit
ADICLK selects either bus clock or CGMXCLK as the input clock source to generate the internal ADC
clock. Reset selects CGMXCLK as the ADC clock source.
If the external clock (CGMXCLK) is equal to or greater than 1 MHz, CGMXCLK can be used as the
clock source for the ADC. If CGMXCLK is less than 1 MHz, use the PLL-generated bus clock as the
clock source. As long as the internal ADC clock is at approximately 1 MHz, correct operation can be
guaranteed. See 25.1.6 ADC Characteristics.
1 = Internal bus clock
0 = External clock (CGMXCLK)
fXCLK or Bus Frequency
1 MHz = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
ADIV[2:0]
NOTE
During the conversion process, changing the ADC clock will result in an
incorrect conversion.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
235
Analog-To-Digital Converter (ADC-15)
MC68HC908AZ32A Data Sheet, Rev. 2
236
Freescale Semiconductor
Chapter 22
Keyboard Module (KBD)
22.1 Introduction
The keyboard interrupt module (KBD) provides five independently maskable external interrupt pins.
This module is only available on 64-pin package options.
22.2 Features
KBD features include:
• Five Keyboard Interrupt Pins with Separate Keyboard Interrupt Enable Bits and One Keyboard
Interrupt Mask
• Hysteresis Buffers
• Programmable Edge-Only or Edge- and Level- Interrupt Sensitivity
• Automatic Interrupt Acknowledge
• Exit from Low-Power Modes
INTERNAL BUS
KBD0
VECTOR FETCH
DECODER
ACKK
VDD
KEYF
RESET
TO
PULLUP
ENABLE
.
D
CLR
Q
SYNCHRONIZER
.
CK
KB0IE
.
KEYBOARD
INTERRUPT FF
KBD4
TO
PULLUP
ENABLE
IMASKK
KEYBOARD
INTERRUPT
REQUEST
MODEK
KB4IE
Figure 22-1. Keyboard Module Block Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
237
Keyboard Module (KBD)
Register Name
Read:
Keyboard Status and Control Register
Write:
(KBSCR)
Reset:
Read:
Keyboard Interrupt Enable Register
Write:
(KBIER)
Reset:
Bit 7
6
5
4
3
2
0
0
0
0
KEYF
0
ACKK
0
0
0
0
0
0
0
0
0
1
Bit 0
IMASKK
MODEK
0
0
0
0
0
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
0
0
0
0
0
= Unimplemented
Figure 22-2. I/O Register Summary
Table 22-1. I/O Register Address Summary
Register
KBSCR
KBIER
Address
$001B
$0021
22.3 Functional Description
Writing to the KBIE4–KBIE0 bits in the keyboard interrupt enable register independently enables or
disables each port G or port H pin as a keyboard interrupt pin. Enabling a keyboard interrupt pin also
enables its internal pullup device. A logic 0 applied to an enabled keyboard interrupt pin latches a
keyboard interrupt request.
A keyboard interrupt is latched when one or more keyboard pins goes low after all were high. The MODEK
bit in the keyboard status and control register controls the triggering mode of the keyboard interrupt.
• If the keyboard interrupt is edge-sensitive only, a falling edge on a keyboard pin does not latch an
interrupt request if another keyboard pin is already low. To prevent losing an interrupt request on
one pin because another pin is still low, software can disable the latter pin while it is low.
• If the keyboard interrupt is falling edge- and low level-sensitive, an interrupt request is present as
long as any keyboard pin is low.
If the MODEK bit is set, the keyboard interrupt pins are both falling edge- and low level-sensitive, and both
of the following actions must occur to clear a keyboard interrupt request:
• Vector fetch or software clear — A vector fetch generates an interrupt acknowledge signal to clear
the interrupt request. Software may generate the interrupt acknowledge signal by writing a logic 1
to the ACKK bit in the keyboard status and control register (KBSCR). The ACKK bit is useful in
applications that poll the keyboard interrupt pins and require software to clear the keyboard
interrupt request. Writing to the ACKK bit prior to leaving an interrupt service routine also can
prevent spurious interrupts due to noise. Setting ACKK does not affect subsequent transitions on
the keyboard interrupt pins. A falling edge that occurs after writing to the ACKK bit latches another
interrupt request. If the keyboard interrupt mask bit, IMASKK, is clear, the CPU loads the program
counter with the vector address at locations $FFDE and $FFDF.
• Return of all enabled keyboard interrupt pins to logic 1. As long as any enabled keyboard interrupt
pin is at logic 0, the keyboard interrupt remains set.
The vector fetch or software clear and the return of all enabled keyboard interrupt pins to logic 1 may occur
in any order.
MC68HC908AZ32A Data Sheet, Rev. 2
238
Freescale Semiconductor
Keyboard Initialization
If the MODEK bit is clear, the keyboard interrupt pin is falling edge-sensitive only. With MODEK clear, a
vector fetch or software clear immediately clears the keyboard interrupt request.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a
keyboard interrupt pin stays at logic 0.
The keyboard flag bit (KEYF) in the keyboard status and control register can be used to see if a pending
interrupt exists. The KEYF bit is not affected by the keyboard interrupt mask bit (IMASKK) which makes
it useful in applications where polling is preferred.
To determine the logic level on a keyboard interrupt pin, use the data direction register to configure the
pin as an input and read the data register.
NOTE
Setting a keyboard interrupt enable bit (KBIEx) forces the corresponding
keyboard interrupt pin to be an input, overriding the data direction register.
However, the data direction register bit must be a logic 0 for software to
read the pin.
22.4 Keyboard Initialization
When a keyboard interrupt pin is enabled, it takes time for the internal pullup to reach a logic 1. Therefore,
a false interrupt can occur as soon as the pin is enabled.
To prevent a false interrupt on keyboard initialization:
1. Mask keyboard interrupts by setting the IMASKK bit in the keyboard status and control register
2. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard interrupt enable register
3. Write to the ACKK bit in the keyboard status and control register to clear any false interrupts
4. Clear the IMASKK bit.
An interrupt signal on an edge-triggered pin can be acknowledged immediately after enabling the pin. An
interrupt signal on an edge- and level-triggered interrupt pin must be acknowledged after a delay that
depends on the external load.
Another way to avoid a false interrupt:
1. Configure the keyboard pins as outputs by setting the appropriate DDRG bits in data direction
register G.
2. Configure the keyboard pins as outputs by setting the appropriate DDRH bits in data direction
register H.
3. Write logic 1s to the appropriate port G and port H data register bits.
4. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard interrupt enable register.
22.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low-power-consumption standby modes.
22.5.1 Wait Mode
The keyboard module remains active in wait mode. Clearing the IMASKK bit in the keyboard status and
control register enables keyboard interrupt requests to bring the MCU out of wait mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
239
Keyboard Module (KBD)
22.5.2 Stop Mode
The keyboard module remains active in stop mode. Clearing the IMASKK bit in the keyboard status and
control register enables keyboard interrupt requests to bring the MCU out of stop mode.
22.6 Keyboard Module During Break Interrupts
The BCFE bit in the break flag control register (BFCR) enables software to clear status bits during the
break state. See Chapter 11 Brake Module.
To allow software to clear the KEYF bit during a break interrupt, write a logic 1 to the BCFE bit. If KEYF
is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect the KEYF bit during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0, writing
to the keyboard acknowledge bit (ACKK) in the keyboard status and control register during the break state
has no effect. See 22.7.1 Keyboard Status and Control Register.
22.7 I/O Registers
The following registers control and monitor operation of the keyboard module:
• Keyboard status and control register (KBSCR)
• Keyboard interrupt enable register (KBIER)
22.7.1 Keyboard Status and Control Register
The keyboard status and control register:
• Flags keyboard interrupt requests
• Acknowledges keyboard interrupt requests
• Masks keyboard interrupt requests
• Controls keyboard interrupt triggering sensitivity
Address: $001B
Read:
Bit 7
6
5
4
3
2
0
0
0
0
KEYF
0
Write:
Reset:
ACKK
0
0
0
0
0
0
1
Bit 0
IMASKK
MODEK
0
0
= Unimplemented
Figure 22-3. Keyboard Status and Control Register (KBSCR)
Bits 7–4 — Not used
These read-only bits always read as logic 0s.
KEYF — Keyboard Flag Bit
This read-only bit is set when a keyboard interrupt is pending. Reset clears the KEYF bit.
1 = Keyboard interrupt pending
0 = No keyboard interrupt pending
MC68HC908AZ32A Data Sheet, Rev. 2
240
Freescale Semiconductor
I/O Registers
ACKK — Keyboard Acknowledge Bit
Writing a logic 1 to this write-only bit clears the keyboard interrupt request. ACKK always reads as logic
0. Reset clears ACKK.
IMASKK — Keyboard Interrupt Mask Bit
Writing a logic 1 to this read/write bit prevents the output of the keyboard interrupt mask from
generating interrupt requests. Reset clears the IMASKK bit.
1 = Keyboard interrupt requests masked
0 = Keyboard interrupt requests not masked
MODEK — Keyboard Triggering Sensitivity Bit
This read/write bit controls the triggering sensitivity of the keyboard interrupt pins. Reset clears
MODEK.
1 = Keyboard interrupt requests on falling edges and low levels
0 = Keyboard interrupt requests on falling edges only
22.7.2 Keyboard Interrupt Enable Register
The keyboard interrupt enable register enables or disables each port G and each port H pin to operate as
a keyboard interrupt pin.
Address: $0021
Read:
Bit 7
6
5
0
0
0
0
0
0
Write:
Reset:
4
3
2
1
Bit 0
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
0
0
0
0
0
= Unimplemented
Figure 22-4. Keyboard Interrupt Enable Register (KBIER)
KBIE4–KBIE0 — Keyboard Interrupt Enable Bits
Each of these read/write bits enables the corresponding keyboard interrupt pin to latch interrupt
requests. Reset clears the keyboard interrupt enable register.
1 = PDx pin enabled as keyboard interrupt pin
0 = PDx pin not enabled as keyboard interrupt pin
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
241
Keyboard Module (KBD)
MC68HC908AZ32A Data Sheet, Rev. 2
242
Freescale Semiconductor
Chapter 23
I/O Ports
23.1 Introduction
On the MC68HC908AZ32A, fifty bidirectional input/output (I/O) form seven parallel ports. All I/O pins are
programmable as inputs or outputs.
NOTE
Connect any unused I/O pins to an appropriate logic level, either VDD or
VSS. Although the I/O ports do not require termination for proper operation,
termination reduces excess current consumption and the possibility of
electrostatic damage.
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
$0000
Port A Data Register (PTA)
PTA7
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
$0001
Port B Data Register (PTB)
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
$0002
Port C Data Register (PTC)
0
0
PTC5
PTC4
PTC3
PTC2
PTC1
PTC0
$0003
Port D Data Register (PTD)
PTD7
PTD6
PTD5
PTD4
PTD3
PTD2
PTD1
PTD0
$0004
Data Direction Register A (DDRA)
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
$0005
Data Direction Register B (DDRB)
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
$0006
Data Direction Register C (DDRC)
MCLKEN
0
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
$0007
Data Direction Register D (DDRD)
DDRD7
DDRD6
DDRD5
DDRD4
DDRD3
DDRD2
DDRD1
DDRD0
$0008
Port E Data Register (PTE)
PTE7
PTE6
PTE5
PTE4
PTE3
PTE2
PTE1
PTE0
$0009
Port F Data Register (PTF)
0
PTF6
PTF5
PTF4
PTF3
PTF2
PTF1
PTF0
$000A
Port G Data Register (PTG)
0
0
0
0
0
PTG2
PTG1
PTG0
$000B
Port H Data Register (PTH)
0
0
0
0
0
0
PTH1
PTH0
$000C
Data Direction Register E (DDRE)
DDRE7
DDRE6
DDRE5
DDRE4
DDRE3
DDRE2
DDRE1
DDRE0
$000D
Data Direction Register F (DDRF)
0
DDRF6
DDRF5
DDRF4
DDRF3
DDRF2
DDRF1
DDRF0
$000E
Data Direction Register G (DDRG)
0
0
0
0
0
DDRG2
DDRG1
DDRG0
$000F
Data Direction Register H (DDRH)
0
0
0
0
0
0
DDRH1
DDRH0
Figure 23-1. I/O Port Register Summary
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
243
I/O Ports
23.2 Port A
Port A is an 8-bit general-purpose bidirectional I/O port.
23.2.1 Port A Data Register
The port A data register contains a data latch for each of the eight port A pins.
Address:
Read:
Write:
$0000
Bit 7
6
5
4
3
2
1
Bit 0
PTA7
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
Reset:
Unaffected by Reset
Figure 23-2. Port A Data Register (PTA)
PTA[7:0] — Port A Data Bits
These read/write bits are software programmable. Data direction of each port A pin is under the control
of the corresponding bit in data direction register A. Reset has no effect on port A data.
23.2.2 Data Direction Register A
Data direction register A determines whether each port A pin is an input or an output. Writing a logic 1 to
a DDRA bit enables the output buffer for the corresponding port A pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0004
Bit 7
6
5
4
3
2
1
Bit 0
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
0
0
0
0
0
0
0
0
Figure 23-3. Data Direction Register A (DDRA)
DDRA[7:0] — Data Direction Register A Bits
These read/write bits control port A data direction. Reset clears DDRA[7:0], configuring all port A pins
as inputs.
1 = Corresponding port A pin configured as output
0 = Corresponding port A pin configured as input
NOTE
Avoid glitches on port A pins by writing to the port A data register before
changing data direction register A bits from 0 to 1.
Figure 23-4 shows the port A I/O logic.
MC68HC908AZ32A Data Sheet, Rev. 2
244
Freescale Semiconductor
Port A
READ DDRA ($0004)
INTERNAL DATA BUS
WRITE DDRA ($0004)
DDRAx
RESET
WRITE PTA ($0000)
PTAx
PTAx
READ PTA ($0000)
Figure 23-4. Port A I/O Circuit
When bit DDRAx is a logic 1, reading address $0000 reads the PTAx data latch. When bit DDRAx is a
logic 0, reading address $0000 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-1 summarizes the operation of the port A pins.
Table 23-1. Port A Pin Functions
DDRA
Bit
PTA
Bit
I/O Pin Mode
0
X
1
X
Accesses to
DDRA
Accesses to PTA
Read/Write
Read
Write
Input, Hi-Z
DDRA[7:0]
Pin
PTA[7:0](1)
Output
DDRA[7:0]
PTA[7:0]
PTA[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
245
I/O Ports
23.3 Port B
Port B is an 8-bit special function port that shares all of its pins with the analog-to-digital converter.
23.3.1 Port B Data Register
The port B data register contains a data latch for each of the eight port B pins.
Address:
Read:
Write:
$0001
Bit 7
6
5
4
3
2
1
Bit 0
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
ATD2
ATD1
ATD0
Reset:
Alternate
Functions:
Unaffected by Reset
ATD7
ATD6
ATD5
ATD4
ATD3
Figure 23-5. Port B Data Register (PTB)
PTB[7:0] — Port B Data Bits
These read/write bits are software programmable. Data direction of each port B pin is under the control
of the corresponding bit in data direction register B. Reset has no effect on port B data.
ATD[7:0] — ADC Channels
PTB7–PTB0 are eight of the analog-to-digital converter channels. The ADC channel select bits,
CH[4:0], determine whether the PTB7–PTB0 pins are ADC channels or general-purpose I/O pins. If an
ADC channel is selected and a read of this corresponding bit in the port B data register occurs, the
data will be 0 if the data direction for this bit is programmed as an input. Otherwise, the data will reflect
the value in the data latch. (See Chapter 21 Analog-To-Digital Converter (ADC-15)). Data direction
register B (DDRB) does not affect the data direction of port B pins that are being used by the ADC.
However, the DDRB bits always determine whether reading port B returns to the states of the latches
or logic 0.
23.3.2 Data Direction Register B
Data direction register B determines whether each port B pin is an input or an output. Writing a logic 1 to
a DDRB bit enables the output buffer for the corresponding port B pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0005
Bit 7
6
5
4
3
2
1
Bit 0
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
0
0
0
0
0
0
0
0
Figure 23-6. Data Direction Register B (DDRB)
DDRB[7:0] — Data Direction Register B Bits
These read/write bits control port B data direction. Reset clears DDRB[7:0], configuring all port B pins
as inputs.
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
MC68HC908AZ32A Data Sheet, Rev. 2
246
Freescale Semiconductor
Port B
NOTE
Avoid glitches on port B pins by writing to the port B data register before
changing data direction register B bits from 0 to 1.
Figure 23-7 shows the port B I/O logic.
READ DDRB ($0005)
INTERNAL DATA BUS
WRITE DDRB ($0005)
DDRBx
RESET
WRITE PTB ($0001)
PTBx
PTBx
READ PTB ($0001)
Figure 23-7. Port B I/O Circuit
When bit DDRBx is a logic 1, reading address $0001 reads the PTBx data latch. When bit DDRBx is a
logic 0, reading address $0001 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-2 summarizes the operation of the port B pins.
Table 23-2. Port B Pin Functions
DDRB
Bit
PTB
Bit
I/O Pin
Mode
0
X
1
X
Accesses to
DDRB
Accesses to PTB
Read/Write
Read
Write
Input, Hi-Z
DDRB[7:0]
Pin
PTB[7:0](1)
Output
DDRB[7:0]
PTB[7:0]
PTB[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
247
I/O Ports
23.4 Port C
Port C is an 6-bit general-purpose bidirectional I/O port. Note that PTC5 is only available on 64-pin
package options.
23.4.1 Port C Data Register
The port C data register contains a data latch for each of the six port C pins.
Address:
$0002
Bit 7
6
Read:
0
0
Write:
R
R
R
= Reserved
5
4
3
2
1
Bit 0
PTC5
PTC4
PTC3
PTC2
PTC1
PTC0
Reset:
Unaffected by Reset
Alternate
Functions:
MCLK
Figure 23-8. Port C Data Register (PTC)
PTC[5:0] — Port C Data Bits
These read/write bits are software-programmable. Data direction of each port C pin is under the control
of the corresponding bit in data direction register C. Reset has no effect on port C data (5:0).
MCLK — System Clock Bit
The system clock is driven out of PTC2 when enabled by MCLKEN bit in PTCDDR7.
23.4.2 Data Direction Register C
Data direction register C determines whether each port C pin is an input or an output. Writing a logic 1 to
a DDRC bit enables the output buffer for the corresponding port C pin; a logic 0 disables the output buffer.
Address:
$0006
Bit 7
Read:
Write:
Reset:
6
MCLKEN
0
R
0
0
R
= Reserved
5
4
3
2
1
Bit 0
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
0
0
0
0
0
Figure 23-9. Data Direction Register C (DDRC)
MCLKEN — MCLK Enable Bit
This read/write bit enables MCLK to be an output signal on PTC2. If MCLK is enabled, DDRC2 has no
effect. Reset clears this bit.
1 = MCLK output enabled
0 = MCLK output disabled
DDRC[5:0] — Data Direction Register C Bits
These read/write bits control port C data direction. Reset clears DDRC[7:0], configuring all port C pins
as inputs.
1 = Corresponding port C pin configured as output
0 = Corresponding port C pin configured as input
MC68HC908AZ32A Data Sheet, Rev. 2
248
Freescale Semiconductor
Port C
NOTE
Avoid glitches on port C pins by writing to the port C data register before
changing data direction register C bits from 0 to 1.
Figure 23-10 shows the port C I/O logic.
READ DDRC ($0006)
INTERNAL DATA BUS
WRITE DDRC ($0006)
DDRCx
RESET
WRITE PTC ($0002)
PTCx
PTCx
READ PTC ($0002)
Figure 23-10. Port C I/O Circuit
When bit DDRCx is a logic 1, reading address $0002 reads the PTCx data latch. When bit DDRCx is a
logic 0, reading address $0002 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-3 summarizes the operation of the port C pins.
Table 23-3. Port C Pin Functions
Bit
Value
PTC
Bit
I/O Pin
Mode
0
2
1
Accesses to
DDRC
Accesses to PTC
Read/Write
Read
Write
Input, Hi-Z
DDRC[2]
Pin
PTC2
2
Output
DDRC[2]
0
—
0
X
Input, Hi-Z
DDRC[5:0]
Pin
PTC[5:0](1)
1
X
Output
DDRC[5:0]
PTC[5:0]
PTC[5:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
249
I/O Ports
23.5 Port D
Port D is an 8-bit general-purpose I/O port. Note that PTD7 is only available on 64-pin package options.
23.5.1 Port D Data Register
Port D is a 8-bit special function port that shares seven of its pins with the analog to digital converter and
two with the timer interface modules.
Address:
Read:
Write:
$0003
Bit 7
6
5
4
3
2
1
Bit 0
PTD7
PTD6
PTD5
PTD4
PTD3
PTD2
PTD1
PTD0
ATD10
ATD9
ATD8
Reset:
Alternate
Functions:
Unaffected by Reset
R
ATD14/
TACLK
ATD13
ATD12/
TBCLK
ATD11
Figure 23-11. Port D Data Register (PTD)
PTD[7:0] — Port D Data Bits
PTD[7:0] are read/write, software programmable bits. Data direction of PTD[7:0] pins are under the
control of the corresponding bit in data direction register D.
ATD[14:8] — ADC Channel Status Bits
PTD6/ATD14/TACLK–PTD0/ATD8 are seven of the 15 analog-to-digital converter channels. The ADC
channel select bits, CH[4:0], determine whether the PTD6/ATD14/TACLK–PTD0/ATD8 pins are ADC
channels or general-purpose I/O pins. If an ADC channel is selected and a read of this corresponding
bit in the port B data register occurs, the data will be 0 if the data direction for this bit is programmed
as an input. Otherwise, the data will reflect the value in the data latch. (See Chapter 21
Analog-To-Digital Converter (ADC-15)).
NOTE
Data direction register D (DDRD) does not affect the data direction of port
D pins that are being used by the TIMA or TIMB. However, the DDRD bits
always determine whether reading port D returns the states of the latches
or logic 0.
TACLK/TBCLK — Timer Clock Input Bit
The PTD6/ATD14/TCLK pin is the external clock input for the TIMA. The PTD4/ATD12 pin is the
external clock input for the TIMB. The prescaler select bits, PS[2:0], select PTD6/ATD14/TCLK or
PTD4/ATD12 as the TIM clock input. (See 18.8.4 TIMA Channel Status and Control Registers and
19.8.4 TIMB Channel Status and Control Registers). When not selected as the TIM clock,
PTD6/ATD14/TCLK and PTD4/ATD12 are available for general-purpose I/O. While TACLK/TBCLK are
selected corresponding DDRD bits have no effect.
MC68HC908AZ32A Data Sheet, Rev. 2
250
Freescale Semiconductor
Port D
23.5.2 Data Direction Register D
Data direction register D determines whether each port D pin is an input or an output. Writing a logic 1 to
a DDRD bit enables the output buffer for the corresponding port D pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0007
Bit 7
6
5
4
3
2
1
Bit 0
DDRD7
DDRD6
DDRD5
DDRD4
DDRD3
DDRD2
DDRD1
DDRD0
0
0
0
0
0
0
0
0
Figure 23-12. Data Direction Register D (DDRD)
DDRD[7:0] — Data Direction Register D Bits
These read/write bits control port D data direction. Reset clears DDRD[7:0], configuring all port D pins
as inputs.
1 = Corresponding port D pin configured as output
0 = Corresponding port D pin configured as input
NOTE
Avoid glitches on port D pins by writing to the port D data register before
changing data direction register D bits from 0 to 1.
Figure 23-13 shows the port D I/O logic.
READ DDRD ($0007)
INTERNAL DATA BUS
WRITE DDRD ($0007)
RESET
DDRDx
WRITE PTD ($0003)
PTDx
PTDx
READ PTD ($0003)
Figure 23-13. Port D I/O Circuit
When bit DDRDx is a logic 1, reading address $0003 reads the PTDx data latch. When bit DDRDx is a
logic 0, reading address $0003 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-4 summarizes the operation of the port D pins.
Table 23-4. Port D Pin Functions
Accesses to
DDRD
Accesses to PTD
DDRD
Bit
PTD
Bit
I/O Pin
Mode
Read/Write
Read
Write
0
X
Input, Hi-Z
DDRD[7:0]
Pin
PTD[7:0](1)
1
X
Output
DDRD[7:0]
PTD[7:0]
PTD[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
251
I/O Ports
23.6 Port E
Port E is an 8-bit special function port that shares two of its pins with the timer interface module (TIMA),
two of its pins with the serial communications interface module (SCI), and four of its pins with the serial
peripheral interface module (SPI).
23.6.1 Port E Data Register
The port E data register contains a data latch for each of the eight port E pins.
Address:
Read:
Write:
$0008
Bit 7
6
5
4
3
2
1
Bit 0
PTE7
PTE6
PTE5
PTE4
PTE3
PTE2
PTE1
PTE0
TACH0
RxD
TxD
Reset:
Alternate
Function:
Unaffected by Reset
SPSCK
MOSI
MISO
SS
TACH1
Figure 23-14. Port E Data Register (PTE)
PTE[7:0] — Port E Data Bits
PTE[7:0] are read/write, software programmable bits. Data direction of each port E pin is under the
control of the corresponding bit in data direction register E.
SPSCK — SPI Serial Clock Bit
The PTE7/SPSCK pin is the serial clock input of an SPI slave module and serial clock output of an SPI
master module. When the SPE bit is clear, the PTE7/SPSCK pin is available for general-purpose I/O.
(See 17.13.1 SPI Control Register).
MOSI — Master Out/Slave In Bit
The PTE6/MOSI pin is the master out/slave in terminal of the SPI module. When the SPE bit is clear,
the PTE6/MOSI pin is available for general-purpose I/O.
MISO — Master In/Slave Out Bit
The PTE5/MISO pin is the master in/slave out terminal of the SPI module. When the SPI enable bit,
SPE, is clear, the SPI module is disabled, and the PTE5/MISO pin is available for general-purpose I/O.
(See 17.13.1 SPI Control Register).
SS — Slave Select Bit
The PTE4/SS pin is the slave select input of the SPI module. When the SPE bit is clear, or when the
SPI master bit, SPMSTR, is set and MODFEN bit is low, the PTE4/SS pin is available for
general-purpose I/O. (See 17.12.4 SS (Slave Select)). When the SPI is enabled as a slave, the DDRF0
bit in data direction register E (DDRE) has no effect on the PTE4/SS pin.
NOTE
Data direction register E (DDRE) does not affect the data direction of port
E pins that are being used by the SPI module. However, the DDRE bits
always determine whether reading port E returns the states of the latches
or the states of the pins. (See Table 23-5).
MC68HC908AZ32A Data Sheet, Rev. 2
252
Freescale Semiconductor
Port E
TACH[1:0] — Timer Channel I/O Bits
The PTE3/TCH1–PTE2/TCH0 pins are the TIM input capture/output compare pins. The edge/level
select bits, ELSxB:ELSxA, determine whether the PTE3/TCH1–PTE2/TCH0 pins are timer channel I/O
pins or general-purpose I/O pins. (See 18.8.4 TIMA Channel Status and Control Registers).
NOTE
Data direction register E (DDRE) does not affect the data direction of port
E pins that are being used by the TIM. However, the DDRE bits always
determine whether reading port E returns the states of the latches or the
states of the pins. (See Table 23-5).
RxD — SCI Receive Data Input Bit
The PTE1/RxD pin is the receive data input for the SCI module. When the enable SCI bit, ENSCI, is
clear, the SCI module is disabled, and the PTE1/RxD pin is available for general-purpose I/O. (See
16.8.1 SCI Control Register 1).
TxD — SCI Transmit Data Output
The PTE0/TxD pin is the transmit data output for the SCI module. When the enable SCI bit, ENSCI, is
clear, the SCI module is disabled, and the PTE0/TxD pin is available for general-purpose I/O. (See
16.8.1 SCI Control Register 1).
NOTE
Data direction register E (DDRE) does not affect the data direction of port
E pins that are being used by the SCI module. However, the DDRE bits
always determine whether reading port E returns the states of the latches
or the states of the pins. (See Table 23-5).
23.6.2 Data Direction Register E
Data direction register E determines whether each port E pin is an input or an output. Writing a logic 1 to
a DDRE bit enables the output buffer for the corresponding port E pin; a logic 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$000C
Bit 7
6
5
4
3
2
1
Bit 0
DDRE7
DDRE6
DDRE5
DDRE4
DDRE3
DDRE2
DDRE1
DDRE0
0
0
0
0
0
0
0
0
Figure 23-15. Data Direction Register E (DDRE)
DDRE[7:0] — Data Direction Register E Bits
These read/write bits control port E data direction. Reset clears DDRE[7:0], configuring all port E pins
as inputs.
1 = Corresponding port E pin configured as output
0 = Corresponding port E pin configured as input
NOTE
Avoid glitches on port E pins by writing to the port E data register before
changing data direction register E bits from 0 to 1.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
253
I/O Ports
Figure 23-16 shows the port E I/O logic.
READ DDRE ($000C)
INTERNAL DATA BUS
WRITE DDRE ($000C)
DDREx
RESET
WRITE PTE ($0008)
PTEx
PTEx
READ PTE ($0008)
Figure 23-16. Port E I/O Circuit
When bit DDREx is a logic 1, reading address $0008 reads the PTEx data latch. When bit DDREx is a
logic 0, reading address $0008 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-5 summarizes the operation of the port E pins.
Table 23-5. Port E Pin Functions
DDRE
Bit
PTE
Bit
I/O Pin
Mode
0
X
1
X
Accesses to
DDRE
Accesses to PTE
Read/Write
Read
Write
Input, Hi-Z
DDRE[7:0]
Pin
PTE[7:0](1)
Output
DDRE[7:0]
PTE[7:0]
PTE[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908AZ32A Data Sheet, Rev. 2
254
Freescale Semiconductor
Port F
23.7 Port F
Port F is a 7-bit special function port that shares four of its pins with the timer interface module (TIMA-6)
and two of its pins with the timer interface module (TIMB) on the MC68HC908AZ32A. Note that PTF4,
PTF5 and PTF6 are only available on 64-pin package options.
23.7.1 Port F Data Register
The port F data register contains a data latch for each of the seven port F pins.
Address:
$0009
Bit 7
Read:
0
Write:
R
6
5
4
3
2
1
Bit 0
PTF6
PTF5
PTF4
PTF3
PTF2
PTF1
PTF0
TACH4
TACH3
TACH2
Reset:
Unaffected by Reset
Alternate
Function:
TBCH1
R
TBCH0
TACH5
= Reserved
Figure 23-17. Port F Data Register (PTF)
PTF[6:0] — Port F Data Bits
These read/write bits are software programmable. Data direction of each port F pin is under the control
of the corresponding bit in data direction register F. Reset has no effect on PTF[6:0].
TACH[5:2] — Timer A Channel I/O Bits
The PTF3/TCH5–PTF0/TCH2 pins are the TIM input capture/output compare pins. The edge/level
select bits, ELSxB:ELSxA, determine whether the PTF3/TCH5–PTF0/TCH2 pins are timer channel I/O
pins or general-purpose I/O pins. (See 18.8.1 TIMA Status and Control Register).
TBCH[1:0] — Timer B Channel I/O Bits
The PTF5/TBCH1–PTF4 pins are the TIMB input capture/output compare pins. The edge/level select
bits, ELSxB:ELSxA, determine whether the PTF5/TBCH1–PTF4 pins are timer channel I/O pins or
general-purpose I/O pins. (See 19.8.1 TIMB Status and Control Register).
NOTE
Data direction register F (DDRF) does not affect the data direction of port F
pins that are being used by the TIM. However, the DDRF bits always
determine whether reading port F returns the states of the latches or the
states of the pins. (See Table 23-6).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
255
I/O Ports
23.7.2 Data Direction Register F
Data direction register F determines whether each port F pin is an input or an output. Writing a logic 1 to
a DDRF bit enables the output buffer for the corresponding port F pin; a logic 0 disables the output buffer.
Address:
$000D
Bit 7
6
5
4
3
2
1
Bit 0
DDRF6
DDRF5
DDRF4
DDRF3
DDRF2
DDRF1
DDRF0
0
0
0
0
0
0
Read:
0
Write:
R
Reset:
0
0
R
= Reserved
Figure 23-18. Data Direction Register F (DDRF)
DDRF[6:0] — Data Direction Register F Bits
These read/write bits control port F data direction. Reset clears DDRF[6:0], configuring all port F pins
as inputs.
1 = Corresponding port F pin configured as output
0 = Corresponding port F pin configured as input
NOTE
Avoid glitches on port F pins by writing to the port F data register before
changing data direction register F bits from 0 to 1.
Figure 23-19 shows the port F I/O logic.
READ DDRF ($000D)
INTERNAL DATA BUS
WRITE DDRF ($000D)
RESET
DDRFx
WRITE PTF ($0009)
PTFx
PTFx
READ PTF ($0009)
Figure 23-19. Port F I/O Circuit
MC68HC908AZ32A Data Sheet, Rev. 2
256
Freescale Semiconductor
Port G
When bit DDRFx is a logic 1, reading address $0009 reads the PTFx data latch. When bit DDRFx is a
logic 0, reading address $0009 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-6 summarizes the operation of the port F pins.
Table 23-6. Port F Pin Functions
DDRF
Bit
PTF
Bit
I/O Pin
Mode
0
X
1
X
Accesses to
DDRF
Accesses to PTF
Read/Write
Read
Write
Input, Hi-Z
DDRF[6:0]
Pin
PTF[6:0](1)
Output
DDRF[6:0]
PTF[6:0]
PTF[6:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
23.8 Port G
Port G is a 3-bit special function port that shares all of its pins with the keyboard interrupt module (KBD).
Note that Port G is only available on 64-pin package options.
23.8.1 Port G Data Register
The port G data register contains a data latch for each of the three port G pins.
Address:
$000A
Bit 7
6
5
4
3
Read:
0
0
0
0
0
Write:
R
R
R
R
R
Reset:
2
1
Bit 0
PTG2
PTG1
PTG0
KBD2
KBD1
KBD0
Unaffected by Reset
Alternate
Function:
R
= Reserved
Figure 23-20. Port G Data Register (PTG)
PTG[2:0] — Port G Data Bits
These read/write bits are software programmable. Data direction of each port G pin is under the control
of the corresponding bit in data direction register G. Reset has no effect on PTG[2:0].
KBD[2:0] — Keyboard Wakeup pins
The keyboard interrupt enable bits, KBIE[2:0], in the keyboard interrupt control register, enable the port
G pins as external interrupt pins (See Chapter 22 Keyboard Module (KBD)). Enabling an external
interrupt pin will override the corresponding DDRGx.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
257
I/O Ports
23.8.2 Data Direction Register G
Data direction register G determines whether each port G pin is an input or an output. Writing a logic 1 to
a DDRG bit enables the output buffer for the corresponding port G pin; a logic 0 disables the output buffer.
Address:
$000E
Bit 7
6
5
4
3
Read:
0
0
0
0
0
Write:
R
R
R
R
R
Reset:
0
0
0
0
0
R
= Reserved
2
1
Bit 0
DDRG2
DDRG1
DDRG0
0
0
0
Figure 23-21. Data Direction Register G (DDRG)
DDRG[2:0] — Data Direction Register G Bits
These read/write bits control port G data direction. Reset clears DDRG[2:0], configuring all port G pins
as inputs.
1 = Corresponding port G pin configured as output
0 = Corresponding port G pin configured as input
NOTE
Avoid glitches on port G pins by writing to the port G data register before
changing data direction register G bits from 0 to 1.
Figure 23-22 shows the port G I/O logic.
READ DDRG ($000E)
INTERNAL DATA BUS
WRITE DDRG ($000E)
RESET
DDRGx
WRITE PTG ($000A)
PTGx
PTGx
READ PTG ($000A)
Figure 23-22. Port G I/O Circuit
MC68HC908AZ32A Data Sheet, Rev. 2
258
Freescale Semiconductor
Port H
When bit DDRGx is a logic 1, reading address $000A reads the PTGx data latch. When bit DDRGx is a
logic 0, reading address $000A reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-7 summarizes the operation of the port G pins.
Table 23-7. Port G Pin Functions
DDRG
Bit
PTG
Bit
I/O Pin
Mode
0
X
1
X
Accesses to
DDRG
Accesses to PTG
Read/Write
Read
Write
Input, Hi-Z
DDRG[2:0]
Pin
PTG[2:0](1)
Output
DDRG[2:0]
PTG[2:0]
PTG[2:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
23.9 Port H
Port H is a 2-bit special function port that shares all of its pins with the keyboard interrupt module (KBD).
Note that Port H is only available on 64-pin package options.
23.9.1 Port H Data Register
The port H data register contains a data latch for each of the two port H pins.
Address:
$000B
Bit 7
6
5
4
3
2
Read:
0
0
0
0
0
0
Write:
R
R
R
R
R
R
Reset:
1
Bit 0
PTH1
PTH0
KBD4
KBD3
Unaffected by Reset
Alternate
Function:
R
= Reserved
Figure 23-23. Port H Data Register (PTH)
PTH[1:0] — Port H Data Bits
These read/write bits are software programmable. Data direction of each port H pin is under the control
of the corresponding bit in data direction register H. Reset has no effect on PTH[1:0].
KBD[4:3] — Keyboard Wake-up pins
The keyboard interrupt enable bits, KBIE[4:3], in the keyboard interrupt control register, enable the port
H pins as external interrupt pins (See Chapter 22 Keyboard Module (KBD)).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
259
I/O Ports
23.9.2 Data Direction Register H
Data direction register H determines whether each port H pin is an input or an output. Writing a logic 1 to
a DDRH bit enables the output buffer for the corresponding port H pin; a logic 0 disables the output buffer.
Address:
$000F
Bit 7
6
5
4
3
2
Read:
0
0
0
0
0
0
Write:
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
R
= Reserved
1
Bit 0
DDRH1
DDRH0
0
0
Figure 23-24. Data Direction Register H (DDRH)
DDRH[1:0] — Data Direction Register H Bits
These read/write bits control port H data direction. Reset clears DDRG[1:0], configuring all port H pins
as inputs.
1 = Corresponding port H pin configured as output
0 = Corresponding port H pin configured as input
NOTE
Avoid glitches on port H pins by writing to the port H data register before
changing data direction register H bits from 0 to 1.
Figure 23-25 shows the port H I/O logic.
READ DDRH ($000F)
INTERNAL DATA BUS
WRITE DDRH ($000F)
RESET
DDRHx
WRITE PTH ($000B)
PTHx
PTHx
READ PTH ($000B)
Figure 23-25. Port H I/O Circuit
MC68HC908AZ32A Data Sheet, Rev. 2
260
Freescale Semiconductor
Port H
When bit DDRHx is a logic 1, reading address $000B reads the PTHx data latch. When bit DDRHx is a
logic 0, reading address $000B reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 23-8 summarizes the operation of the port H pins.
Table 23-8. Port H Pin Functions
DDRH
Bit
PTH
Bit
I/O Pin
Mode
0
X
1
X
Accesses to
DDRH
Accesses to PTH
Read/Write
Read
Write
Input, Hi-Z
DDRH[1:0]
Pin
PTH[1:0](1)
Output
DDRH[1:0]
PTH[1:0]
PTH[1:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
261
I/O Ports
MC68HC908AZ32A Data Sheet, Rev. 2
262
Freescale Semiconductor
Chapter 24
MSCAN Controller (MSCAN08)
24.1 Introduction
The MSCAN08 is the specific implementation of the scalable controller area network (MSCAN) concept
targeted for the Freescale M68HC08 Microcontroller Family.
The module is a communication controller implementing the CAN 2.0 A/B protocol as defined in the
BOSCH specification dated September 1991.
The CAN protocol was primarily, but not exclusively, designed to be used as a vehicle serial data bus,
meeting the specific requirements of this field: real-time processing, reliable operation in the
electromagnetic interference (EMI) environment of a vehicle, cost-effectiveness and required bandwidth.
MSCAN08 utilizes an advanced buffer arrangement, resulting in a predictable real-time behavior, and
simplifies the application software.
24.2 Features
Basic features of the MSCAN08 are:
• Modular Architecture
• Implementation of the CAN Protocol — Version 2.0A/B
– Standard and Extended Data Frames.
– 0–8 Bytes Data Length.
– Programmable Bit Rate up to 1 Mbps Depending on the Actual Bit Timing and the Clock Jitter
of the PLL
• Support for Remote Frames
• Double-Buffered Receive Storage Scheme
• Triple-Buffered Transmit Storage Scheme with Internal Prioritisation Using a “Local Priority”
Concept
• Flexible Maskable Identifier Filter Supports Alternatively One Full Size Extended Identifier Filter or
Two 16-Bit Filters or Four 8-Bit Filters
• Programmable Wakeup Functionality with Integrated Low-Pass Filter
• Programmable Loop-Back Mode Supports Self-Test Operation
• Separate Signalling and Interrupt Capabilities for All CAN Receiver and Transmitter Error States
(Warning, Error Passive, Bus Off)
• Programmable MSCAN08 Clock Source Either CPU Bus Clock or Crystal Oscillator Output
• Programmable Link to On-Chip Timer Interface Module (TIMB) for Time-Stamping and Network
Synchronization
• Low-Power Sleep Mode
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
263
MSCAN Controller (MSCAN08)
24.3 External Pins
The MSCAN08 uses two external pins, one input (RxCAN) and one output (TxCAN). The TxCAN output
pin represents the logic level on the CAN: 0 is for a dominant state, and 1 is for a recessive state.
A typical CAN system with MSCAN08 is shown in Figure 24-1.
CAN STATION 1
CAN NODE 1
CAN NODE 2
CAN NODE N
MCU
CAN CONTROLLER
(MSCAN08)
TXCAN
RXCAN
TRANSCEIVER
CAN_H
CAN_L
C A N BUS
Figure 24-1. The CAN System
Each CAN station is connected physically to the CAN bus lines through a transceiver chip. The
transceiver is capable of driving the large current needed for the CAN and has current protection against
defected CAN or defected stations.
24.4 Message Storage
MSCAN08 facilitates a sophisticated message storage system which addresses the requirements of a
broad range of network applications.
24.4.1 Background
Modern application layer software is built under two fundamental assumptions:
1. Any CAN node is able to send out a stream of scheduled messages without releasing the bus
between two messages. Such nodes will arbitrate for the bus right after sending the previous
message and will only release the bus in case of lost arbitration.
2. The internal message queue within any CAN node is organized as such that the highest priority
message will be sent out first if more than one message is ready to be sent.
MC68HC908AZ32A Data Sheet, Rev. 2
264
Freescale Semiconductor
Message Storage
Above behavior cannot be achieved with a single transmit buffer. That buffer must be reloaded right after
the previous message has been sent. This loading process lasts a definite amount of time and has to be
completed within the inter-frame sequence (IFS) to be able to send an uninterrupted stream of messages.
Even if this is feasible for limited CAN bus speeds, it requires that the CPU reacts with short latencies to
the transmit interrupt.
A double buffer scheme would de-couple the re-loading of the transmit buffers from the actual message
being sent and as such reduces the reactiveness requirements on the CPU. Problems may arise if the
sending of a message would be finished just while the CPU re-loads the second buffer. In that case, no
buffer would then be ready for transmission and the bus would be released.
At least three transmit buffers are required to meet the first of the above requirements under all
circumstances. The MSCAN08 has three transmit buffers.
The second requirement calls for some sort of internal prioritisation which the MSCAN08 implements with
the “local priority” concept described in 24.4.2 Receive Structures.
24.4.2 Receive Structures
The received messages are stored in a 2-stage input first in first out (FIFO). The two message buffers are
mapped using a Ping Pong arrangement into a single memory area (see Figure 24-2). While the
background receive buffer (RxBG) is exclusively associated to the MSCAN08, the foreground receive
buffer (RxFG) is addressable by the CPU08. This scheme simplifies the handler software, because only
one address area is applicable for the receive process.
Both buffers have a size of 13 bytes to store the CAN control bits, the identifier (standard or extended),
and the data content (for details, see 24.12 Programmer’s Model of Message Storage).
The receiver full flag (RXF) in the MSCAN08 receiver flag register (CRFLG) (see 24.13.5 MSCAN08
Receiver Flag Register (CRFLG)), signals the status of the foreground receive buffer. When the buffer
contains a correctly received message with matching identifier, this flag is set.
On reception, each message is checked to see if it passes the filter (for details see 24.5 Identifier
Acceptance Filter) and in parallel is written into RxBG. The MSCAN08 copies the content of RxBG into
RxFG(1), sets the RXF flag, and generates a receive interrupt to the CPU(2). The user’s receive handler
has to read the received message from RxFG and to reset the RXF flag to acknowledge the interrupt and
to release the foreground buffer. A new message which can follow immediately after the IFS field of the
CAN frame, is received into RxBG. The overwriting of the background buffer is independent of the
identifier filter function.
When the MSCAN08 module is transmitting, the MSCAN08 receives its own messages into the
background receive buffer, RxBG. It does NOT overwrite RxFG, generate a receive interrupt or
acknowledge its own messages on the CAN bus. The exception to this rule is in loop-back mode (see
24.13.2 MSCAN08 Module Control Register 1), where the MSCAN08 treats its own messages exactly like
all other incoming messages. The MSCAN08 receives its own transmitted messages in the event that it
loses arbitration. If arbitration is lost, the MSCAN08 must be prepared to become receiver.
An overrun condition occurs when both the foreground and the background receive message buffers are
filled with correctly received messages with accepted identifiers and another message is correctly
received from the bus with an accepted identifier. The latter message will be discarded and an error
1. Only if the RXF flag is not set.
2. The receive interrupt will occur only if not masked. A polling scheme can be applied on RXF also.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
265
MSCAN Controller (MSCAN08)
interrupt with overrun indication will be generated if enabled. The MSCAN08 is still able to transmit
messages with both receive message buffers filled, but all incoming messages are discarded.
CPU08 Ibus
MSCAN08
RxBG
RxFG
RXF
Tx0
TXE
PRIO
Tx1
TXE
PRIO
Tx2
TXE
PRIO
Figure 24-2. User Model for Message Buffer Organization
24.4.3 Transmit Structures
The MSCAN08 has a triple transmit buffer scheme to allow multiple messages to be set up in advance
and to achieve an optimized real-time performance. The three buffers are arranged as shown in Figure
24-2.
All three buffers have a 13-byte data structure similar to the outline of the receive buffers (see 24.12
Programmer’s Model of Message Storage). An additional transmit buffer priority register (TBPR) contains
an 8-bit “local priority” field (PRIO) (see 24.12.5 Transmit Buffer Priority Registers).
MC68HC908AZ32A Data Sheet, Rev. 2
266
Freescale Semiconductor
Identifier Acceptance Filter
To transmit a message, the CPU08 has to identify an available transmit buffer which is indicated by a set
transmit buffer empty (TXE) flag in the MSCAN08 transmitter flag register (CTFLG) (see 24.13.7
MSCAN08 Transmitter Flag Register).
The CPU08 then stores the identifier, the control bits and the data content into one of the transmit buffers.
Finally, the buffer has to be flagged ready for transmission by clearing the TXE flag.
The MSCAN08 then will schedule the message for transmission and will signal the successful
transmission of the buffer by setting the TXE flag. A transmit interrupt is generated(1) when TXE is set and
can be used to drive the application software to re-load the buffer.
In case more than one buffer is scheduled for transmission when the CAN bus becomes available for
arbitration, the MSCAN08 uses the local priority setting of the three buffers for prioritisation. For this
purpose, every transmit buffer has an 8-bit local priority field (PRIO). The application software sets this
field when the message is set up. The local priority reflects the priority of this particular message relative
to the set of messages being emitted from this node. The lowest binary value of the PRIO field is defined
as the highest priority.
The internal scheduling process takes place whenever the MSCAN08 arbitrates for the bus. This is also
the case after the occurrence of a transmission error.
When a high priority message is scheduled by the application software, it may become necessary to abort
a lower priority message being set up in one of the three transmit buffers. As messages that are already
under transmission cannot be aborted, the user has to request the abort by setting the corresponding
abort request flag (ABTRQ) in the transmission control register (CTCR). The MSCAN08 will then grant
the request, if possible, by setting the corresponding abort request acknowledge (ABTAK) and the TXE
flag in order to release the buffer and by generating a transmit interrupt. The transmit interrupt handler
software can tell from the setting of the ABTAK flag whether the message was actually aborted
(ABTAK = 1) or sent (ABTAK = 0).
24.5 Identifier Acceptance Filter
The Identifier Acceptance Registers (CIDAR0-3) define the acceptance patterns of the standard or
extended identifier (ID10-ID0 or ID28-ID0). Any of these bits can be marked ‘don’t care’ in the Identifier
Mask Registers (CIDMR0-3).
A filter hit is indicated to the application on software by a set RXF (Receive Buffer Full Flag, see 24.13.5
MSCAN08 Receiver Flag Register (CRFLG)) and two bits in the Identifier Acceptance Control Register
(see 24.13.9 MSCAN08 Identifier Acceptance Control Register). These Identifier Hit Flags (IDHIT1-0)
clearly identify the filter section that caused the acceptance. They simplify the application software’s task
to identify the cause of the receiver interrupt. In case that more than one hit occurs (two or more filters
match) the lower hit has priority.
A very flexible programmable generic identifier acceptance filter has been introduced to reduce the CPU
interrupt loading. The filter is programmable to operate in four different modes:
• Single identifier acceptance filter, each to be applied to a) the full 29 bits of the extended identifier
and to the following bits of the CAN frame: RTR, IDE, SRR or b) the 11 bits of the standard identifier
plus the RTR and IDE bits of CAN 2.0A/B messages. This mode implements a single filter for a full
length CAN 2.0B compliant extended identifier. Figure 24-3 shows how the 32-bit filter bank
(CIDAR0-3, CIDMR0-3) produces a filter 0 hit.
1. The transmit interrupt will occur only if not masked. A polling scheme can be applied on TXE also.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
267
MSCAN Controller (MSCAN08)
•
•
•
Two identifier acceptance filters, each to be applied to a) the 14 most significant bits of the
extended identifier plus the SRR and the IDE bits of CAN2.0B messages, or b) the 11 bits of the
identifier plus the RTR and IDE bits of CAN 2.0A/B messages. Figure 24-4 shows how the 32-bit
filter bank (CIDAR0-3, CIDMR0-3) produces filter 0 and 1 hits.
Four identifier acceptance filters, each to be applied to the first eight bits of the identifier. This mode
implements four independent filters for the first eight bits of a CAN 2.0A/B compliant standard
identifier. Figure 24-5 shows how the 32-bit filter bank (CIDAR0-3, CIDMR0-3) produces filter 0 to
3 hits.
Closed filter. No CAN message will be copied into the foreground buffer RxFG, and the RXF flag
will never be set.
ID28
IDR0
ID21 ID20
IDR1
ID15 ID14
ID10
IDR0
ID3 ID2
IDR1
AM7
CIDMR0
AM0 AM7
CIDMR1
AM0 AM7
CIDMR2
AC7
CIDAR0
AC0 AC7
CIDAR1
AC0 AC7
CIDAR2
IDE
ID10
IDR2
ID7 ID6
IDR3
RTR
IDR2
ID3 ID10
IDR3
ID3
AM0 AM7
CIDMR3
AM0
AC0 AC7
CIDAR3
AC0
ID Accepted (Filter 0 Hit)
Figure 24-3. Single 32-Bit Maskable Identifier Acceptance Filter
ID28
IDR0
ID21 ID20
IDR1
ID10
IDR0
ID3 ID2
IDR1
ID15 ID14
AM7
CIDMR0
AM0 AM7
CIDMR1
AM0
AC7
CIDAR0
AC0 AC7
CIDAR1
AC0
IDE
ID10
IDR2
ID7 ID6
IDR3
RTR
IDR2
ID3 ID10
IDR3
ID3
ID ACCEPTED (FILTER 0 HIT)
AM7
CIDMR2
AM0 AM7
CIDMR3
AM0
AC7
CIDAR2
AC0 AC7
CIDAR3
AC0
ID ACCEPTED (FILTER 1 HIT)
Figure 24-4. Dual 16-Bit Maskable Acceptance Filters
MC68HC908AZ32A Data Sheet, Rev. 2
268
Freescale Semiconductor
Identifier Acceptance Filter
ID28
IDR0
ID21 ID20
IDR1
ID10
IDR0
ID3 ID2
IDR1
AM7
CIDMR0
AM0
AC7
CIDAR0
AC0
ID15 ID14
IDE
ID10
IDR2
ID7 ID6
IDR3
RTR
IDR2
ID3 ID10
IDR3
ID3
ID ACCEPTED (FILTER 0 HIT)
AM7
CIDMR1
AM0
AC7
CIDAR1
AC0
ID ACCEPTED (FILTER 1 HIT)
AM7
CIDMR2
AM0
AC7
CIDAR2
AC0
ID ACCEPTED (FILTER 2 HIT)
AM7
CIDMR3
AM0
AC7
CIDAR3
AC0
ID ACCEPTED (FILTER 3 HIT)
Figure 24-5. Quadruple 8-Bit Maskable Acceptance Filters
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
269
MSCAN Controller (MSCAN08)
24.6 Interrupts
The MSCAN08 supports four interrupt vectors mapped onto eleven different interrupt sources, any of
which can be individually masked (for details see 24.13.5 MSCAN08 Receiver Flag Register (CRFLG), to
24.13.8 MSCAN08 Transmitter Control Register).
• Transmit Interrupt: At least one of the three transmit buffers is empty (not scheduled) and can be
loaded to schedule a message for transmission. The TXE flags of the empty message buffers are
set.
• Receive Interrupt: A message has been received successfully and loaded into the foreground
receive buffer. This interrupt will be emitted immediately after receiving the EOF symbol. The RXF
flag is set.
• Wakeup Interrupt: An activity on the CAN bus occurred during MSCAN08 internal sleep mode or
power-down mode (provided SLPAK = WUPIE = 1).
• Error Interrupt: An overrun, error, or warning condition occurred. The receiver flag register
(CRFLG) will indicate one of the following conditions:
– Overrun: An overrun condition as described in 24.4.2 Receive Structures, has occurred.
– Receiver Warning: The receive error counter has reached the CPU Warning limit of 96.
– Transmitter Warning: The transmit error counter has reached the CPU Warning limit of 96.
– Receiver Error Passive: The receive error counter has exceeded the error passive limit of 127
and MSCAN08 has gone to error passive state.
– Transmitter Error Passive: The transmit error counter has exceeded the error passive limit of
127 and MSCAN08 has gone to error passive state.
– Bus Off: The transmit error counter has exceeded 255 and MSCAN08 has gone to bus off state.
24.6.1 Interrupt Acknowledge
Interrupts are directly associated with one or more status flags in either the MSCAN08 receiver flag
register (CRFLG) or the MSCAN08 transmitter flag register (CTFLG). Interrupts are pending as long as
one of the corresponding flags is set. The flags in the above registers must be reset within the interrupt
handler in order to handshake the interrupt. The flags are reset through writing a ‘1’ to the corresponding
bit position. A flag cannot be cleared if the respective condition still prevails.
NOTE
Bit manipulation instructions (BSET) shall not be used to clear interrupt
flags.
24.6.2 Interrupt Vectors
The MSCAN08 supports four interrupt vectors as shown in Table 24-1. The vector addresses and the
relative interrupt priority are dependent on the chip integration and to be defined.
MC68HC908AZ32A Data Sheet, Rev. 2
270
Freescale Semiconductor
Protocol Violation Protection
Table 24-1. MSCAN08 Interrupt Vector Addresses
Function
Source
Local
Mask
Wakeup
WUPIF
WUPIE
RWRNIF
RWRNIE
TWRNIF
TWRNIE
RERRIF
RERRIE
TERRIF
TERRIE
BOFFIF
BOFFIE
OVRIF
OVRIE
RXF
RXFIE
TXE0
TXEIE0
TXE1
TXEIE1
TXE2
TXEIE2
Error
Interrupts
Receive
Transmit
Global
Mask
I Bit
24.7 Protocol Violation Protection
The MSCAN08 will protect the user from accidentally violating the CAN protocol through programming
errors. The protection logic implements the following features:
• The receive and transmit error counters cannot be written or otherwise manipulated.
• All registers which control the configuration of the MSCAN08 can not be modified while the
MSCAN08 is on-line. The SFTRES bit in the MSCAN08 module control register (see 24.13.1
MSCAN08 Module Control Register 0) serves as a lock to protect the following registers:
– MSCAN08 module control register 1 (CMCR1)
– MSCAN08 bus timing register 0 and 1 (CBTR0 and CBTR1)
– MSCAN08 identifier acceptance control register (CIDAC)
– MSCAN08 identifier acceptance registers (CIDAR0–3)
– MSCAN08 identifier mask registers (CIDMR0–3)
• The TxCAN pin is forced to recessive when the MSCAN08 is in any of the Low Power Modes.
24.8 Low Power Modes
In addition to normal mode, the MSCAN08 has three modes with reduced power consumption: Sleep, Soft
Reset and Power Down modes. In Sleep and Soft Reset mode, power consumption is reduced by
stopping all clocks except those to access the registers. In Power Down mode, all clocks are stopped and
no power is consumed.
The WAIT and STOP instructions put the MCU in low power consumption stand-by modes. summarizes
the combinations of MSCAN08 and CPU modes. A particular combination of modes is entered for the
given settings of the bits SLPAK and SFTRES. For all modes, an MSCAN wake-up interrupt can occur
only if SLPAK=WUPIE=1.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
271
MSCAN Controller (MSCAN08)
Table 24-2. MSCAN08 vs CPU Operating Modes
MSCAN Mode
CPU Mode
STOP
WAIT or RUN
SLPAK = X(1)
SFTRES = X
Power Down
Sleep
SLPAK = 1
SFTRES = 0
Soft Reset
SLPAK = 0
SFTRES = 1
Normal
SLPAK = 0
SFTRES = 0
1. ‘X’ means don’t care.
24.8.1 MSCAN08 Sleep Mode
The CPU can request the MSCAN08 to enter the low-power mode by asserting the SLPRQ bit in the
module configuration register (see Figure 24-6). The time when the MSCAN08 enters Sleep mode
depends on its activity:
• if it is transmitting, it continues to transmit until there is no more message to be transmitted, and
then goes into Sleep mode
• if it is receiving, it waits for the end of this message and then goes into Sleep mode
• if it is neither transmitting or receiving, it will immediately go into Sleep mode
NOTE
The application software must avoid setting up a transmission (by clearing
or more TXE flags) and immediately request Sleep mode (by setting
SLPRQ). It then depends on the exact sequence of operations whether
MSCAN08 starts transmitting or goes into Sleep mode directly.
MSCAN08 Running
SLPRQ = 0
SLPAK = 0
MCU
MCU
or MSCAN08
MSCAN08 Sleeping
Sleep Request
SLPRQ = 1
SLPAK = 1
SLPRQ = 1
SLPAK = 0
MSCAN08
Figure 24-6. Sleep Request/Acknowledge Cycle
MC68HC908AZ32A Data Sheet, Rev. 2
272
Freescale Semiconductor
Low Power Modes
During Sleep mode, the SLPAK flag is set. The application software should use SLPAK as a handshake
indication for the request (SLPRQ) to go into Sleep mode. When in Sleep mode, the MSCAN08 stops its
internal clocks. However, clocks to allow register accesses still run. If the MSCAN08 is in buss-off state,
it stops counting the 128*11 consecutive recessive bits due to the stopped clocks. The TxCAN pin stays
in recessive state. If RXF=1, the message can be read and RXF can be cleared. Copying of RxGB into
RxFG doesn’t take place while in Sleep mode. It is possible to access the transmit buffers and to clear
the TXE flags. No message abort takes place while in Sleep mode.
The MSCAN08 leaves Sleep mode (wake-up) when:
• bus activity occurs or
• the MCU clears the SLPRQ bit or
• the MCU sets the SFTRES bit
NOTE
The MCU cannot clear the SLPRQ bit before the MSCAN08 is in Sleep
mode (SLPAK=1).
After wake-up, the MSCAN08 waits for 11 consecutive recessive bits to synchronize to the bus. As a
consequence, if the MSCAN08 is woken-up by a CAN frame, this frame is not received. The receive
message buffers (RxFG and RxBG) contain messages if they were received before Sleep mode was
entered. All pending actions are executed upon wake-up: copying of RxBG into RxFG, message aborts
and message transmissions. If the MSCAN08 is still in bus-off state after Sleep mode was left, it continues
counting the 128*11 consecutive recessive bits.
24.8.2 MSCAN08 Soft Reset Mode
In Soft Reset mode, the MSCAN08 is stopped. Registers can still be accessed. This mode is used to
initialize the module configuration, bit timing and the CAN message filter. See 24.13.1 MSCAN08 Module
Control Register 0 for a complete description of the Soft Reset mode.
When setting the SFTRES bit, the MSCAN08 immediately stops all ongoing transmissions and
receptions, potentially causing CAN protocol violations.
NOTE
The user is responsible to take care that the MSCAN08 is not active when
Soft Reset mode is entered. The recommended procedure is to bring the
MSCAN08 into Sleep mode before the SFTRES bit is set.
24.8.3 MSCAN08 Power Down Mode
The MSCAN08 is in Power Down mode when the CPU is in Stop mode.
When entering the Power Down mode, the MSCAN08 immediately stops all ongoing transmissions and
receptions, potentially causing CAN protocol violations.
NOTE
The user is responsible to take care that the MSCAN08 is not active when
Power Down mode is entered. The recommended procedure is to bring the
MSCAN08 into Sleep mode before the STOP instruction is executed.
To protect the CAN bus system from fatal consequences of violations to the above rule, the MSCAN08
drives the TxCAN pin into recessive state.
In Power Down mode, no registers can be accessed.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
273
MSCAN Controller (MSCAN08)
MSCAN08 bus activity can wake the MCU from CPU Stop/MSCAN08 power-down mode. However, until
the oscillator starts up and synchronisation is achieved the MSCAN08 will not respond to incoming data.
24.8.4 CPU Wait Mode
The MSCAN08 module remains active during CPU wait mode. The MSCAN08 will stay synchronized to
the CAN bus and generates transmit, receive, and error interrupts to the CPU, if enabled. Any such
interrupt will bring the MCU out of wait mode.
24.8.5 Programmable Wakeup Function
The MSCAN08 can be programmed to apply a low-pass filter function to the RxCAN input line while in
internal sleep mode (see information on control bit WUPM in 24.13.2 MSCAN08 Module Control Register
1). This feature can be used to protect the MSCAN08 from wake-up due to short glitches on the CAN bus
lines. Such glitches can result from electromagnetic inference within noisy environments.
24.9 Timer Link
The MSCAN08 will generate a timer signal whenever a valid frame has been received. Because the CAN
specification defines a frame to be valid if no errors occurred before the EOF field has been transmitted
successfully, the timer signal will be generated right after the EOF. A pulse of one bit time is generated.
As the MSCAN08 receiver engine also receives the frames being sent by itself, a timer signal also will be
generated after a successful transmission.
The previously described timer signal can be routed into the on-chip timer interface module (TIM).This
signal is connected to the timer n channel m input(1) under the control of the timer link enable (TLNKEN)
bit in the CMCR0.
After timer n has been programmed to capture rising edge events, it can be used under software control
to generate 16-bit time stamps which can be stored with the received message.
24.10 Clock System
Figure 24-7 shows the structure of the MSCAN08 clock generation circuitry and its interaction with the
clock generation module (CGM). With this flexible clocking scheme the MSCAN08 is able to handle CAN
bus rates ranging from 10 kbps up to 1 Mbps.
The clock source bit (CLKSRC) in the MSCAN08 module control register (CMCR1) (see 24.13.1
MSCAN08 Module Control Register 0) defines whether the MSCAN08 is connected to the output of the
crystal oscillator or to the PLL output.
The clock source has to be chosen such that the tight oscillator tolerance requirements (up to 0.4%) of
the CAN protocol are met.
NOTE
If the system clock is generated from a PLL, it is recommended to select the
crystal clock source rather than the system clock source due to jitter
considerations, especially at faster CAN bus rates.
1. The timer channel being used for the timer link is integration dependent.
MC68HC908AZ32A Data Sheet, Rev. 2
274
Freescale Semiconductor
Clock System
CGMXCLK
÷2
OSC
CGMOUT
(TO SIM)
BCS
PLL
÷2
CGM
MSCAN08
(2 * BUS FREQ.)
÷2
MSCANCLK
PRESCALER
(1 .. 64)
CLKSRC
Figure 24-7. Clocking Scheme
A programmable prescaler is used to generate out of the MSCAN08 clock the time quanta (Tq) clock. A
time quantum is the atomic unit of time handled by the MSCAN08.
fTq =
fMSCANCLK
Presc value
A bit time is subdivided into three segments(1) (see Figure 24-8).
• SYNC_SEG: This segment has a fixed length of one time quantum. Signal edges are expected to
happen within this section.
• Time segment 1: This segment includes the PROP_SEG and the PHASE_SEG1 of the CAN
standard. It can be programmed by setting the parameter TSEG1 to consist of 4 to 16 time quanta.
• Time segment 2: This segment represents PHASE_SEG2 of the CAN standard. It can be
programmed by setting the TSEG2 parameter to be 2 to 8 time quanta long.
Bit rate =
fTq
No. of time quanta
The synchronization jump width (SJW) can be programmed in a range of 1 to 4 time quanta by setting the
SJW parameter.
1. For further explanation of the underlying concepts please refer to ISO/DIS 11 519-1, Section 10.3.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
275
MSCAN Controller (MSCAN08)
The above parameters can be set by programming the bus timing registers, CBTR0–CBTR1, see 24.13.3
MSCAN08 Bus Timing Register 0 and 24.13.4 MSCAN08 Bus Timing Register 1).
NOTE
It is the user’s responsibility to make sure that the bit timing settings are in
compliance with the CAN standard,
Table 24-8 gives an overview on the CAN conforming segment settings and the related parameter values.
NRZ SIGNAL
SYNC
_SEG
TIME SEGMENT 1
(PROP_SEG + PHASE_SEG1)
TIME SEG. 2
(PHASE_SEG2)
1
4 ... 16
2 ... 8
8... 25 TIME QUANTA
= 1 BIT TIME
SAMPLE POINT
(SINGLE OR TRIPLE SAMPLING)
Figure 24-8. Segments within the Bit Time
.
Table 24-3. Time Segment Syntax
SYNC_SEG
System expects transitions to occur on the bus during this period.
Transmit point
A node in transmit mode will transfer a new value to the CAN bus at this point.
Sample point
A node in receive mode will sample the bus at this point. If the three samples
per bit option is selected then this point marks the position of the third sample.
Table 24-4. CAN Standard Compliant Bit Time Segment Settings
Time
Segment 1
TSEG1
Time
Segment 2
TSEG2
Synchronization
Jump Width
SJW
5 .. 10
4 .. 9
2
1
1 .. 2
0 .. 1
4 .. 11
3 .. 10
3
2
1 .. 3
0 .. 2
5 .. 12
4 .. 11
4
3
1 .. 4
0 .. 3
6 .. 13
5 .. 12
5
4
1 .. 4
0 .. 3
7 .. 14
6 .. 13
6
5
1 .. 4
0 .. 3
8 .. 15
7 .. 14
7
6
1 .. 4
0 .. 3
9 .. 16
8 .. 15
8
7
1 .. 4
0 .. 3
MC68HC908AZ32A Data Sheet, Rev. 2
276
Freescale Semiconductor
Memory Map
24.11 Memory Map
The MSCAN08 occupies 128 bytes in the CPU08 memory space. The absolute mapping is
implementation dependent with the base address being a multiple of 128.
$xx00
$xx08
$xx09
$xx0D
$xx0E
$xx0F
$xx10
$xx17
$xx18
$xx3F
CONTROL REGISTERS
9 BYTES
RESERVED
5 BYTES
ERROR COUNTERS
2 BYTES
IDENTIFIER FILTER
8 BYTES
RESERVED
40 BYTES
$xx40
RECEIVE BUFFER
$xx4F
$xx50
TRANSMIT BUFFER 0
$xx5F
$xx60
TRANSMIT BUFFER 1
$xx6F
$xx70
TRANSMIT BUFFER 2
$xx7F
Figure 24-9. MSCAN08 Memory Map
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
277
MSCAN Controller (MSCAN08)
24.12 Programmer’s Model of Message Storage
This section details the organization of the receive and transmit message buffers and the associated
control registers. For reasons of programmer interface simplification, the receive and transmit message
buffers have the same outline. Each message buffer allocates 16 bytes in the memory map containing a
13-byte data structure. An additional transmit buffer priority register (TBPR) is defined for the transmit
buffers.
Addr
Register Name
$05b0
IDENTIFIER REGISTER 0
$05b1
IDENTIFIER REGISTER 1
$05b2
IDENTIFIER REGISTER 2
$05b3
IDENTIFIER REGISTER 3
$05b4
DATA SEGMENT REGISTER 0
$05b5
DATA SEGMENT REGISTER 1
$05b6
DATA SEGMENT REGISTER 2
$05b7
DATA SEGMENT REGISTER 3
$05b8
DATA SEGMENT REGISTER 4
$05b9
DATA SEGMENT REGISTER 5
$05bA
DATA SEGMENT REGISTER 6
$05bB
DATA SEGMENT REGISTER 7
$05bC
DATA LENGTH REGISTER
$05bD
TRANSMIT BUFFER PRIORITY REGISTER(1)
$05bE
UNUSED
$05bF
UNUSED
1. Not applicable for receive buffers
Figure 24-10. Message Buffer Organization
MC68HC908AZ32A Data Sheet, Rev. 2
278
Freescale Semiconductor
Programmer’s Model of Message Storage
24.12.1 Message Buffer Outline
Figure 24-11 shows the common 13-byte data structure of receive and transmit buffers for extended
identifiers. The mapping of standard identifiers into the IDR registers is shown in Figure 24-12. All bits of
the 13-byte data structure are undefined out of reset.
NOTE
The foreground receive buffer can be read anytime but cannot be written.
The transmit buffers can be read or written anytime.
Addr
Register
$05b0
IDR0
$05b1
IDR1
$05b2
IDR2
$05b3
IDR3
$05b4
DSR0
$05b5
DSR1
$05b6
DSR2
$05b7
DSR3
$05b8
DSR4
$05b9
DSR5
$05bA
DSR6
$05bB
DSR7
$05bC
DLR
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Bit 7
6
5
4
3
2
1
Bit 0
ID28
ID27
ID26
ID25
ID24
ID23
ID22
ID21
ID20
ID19
ID18
SRR (=1)
IDE (=1)
ID17
ID16
ID15
ID14
ID13
ID12
ID11
ID10
ID9
ID8
ID7
ID6
ID5
ID4
ID3
ID2
ID1
ID0
RTR
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
DLC3
DLC2
DLC1
DLC0
Read:
Write:
= Unimplemented
Figure 24-11. Receive/Transmit Message Buffer Extended Identifier (IDRn)
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
279
MSCAN Controller (MSCAN08)
Addr
Register
$05b0
IDR0
$05b1
IDR1
$05b2
IDR2
$05b3
IDR3
Read:
Write:
Read:
Write:
Bit 7
6
5
4
3
2
1
Bit 0
ID10
ID9
ID8
ID7
ID6
ID5
ID4
ID3
ID2
ID1
ID0
RTR
IDE(=0)
Read:
Write:
Read:
Write:
= Unimplemented
Figure 24-12. Standard Identifier Mapping
24.12.2 Identifier Registers
The identifiers consist of either 11 bits (ID10–ID0) for the standard, or 29 bits (ID28–ID0) for the extended
format. ID10/28 is the most significant bit and is transmitted first on the bus during the arbitration
procedure. The priority of an identifier is defined to be highest for the smallest binary number.
SRR — Substitute Remote Request
This fixed recessive bit is used only in extended format. It must be set to 1 by the user for transmission
buffers and will be stored as received on the CAN bus for receive buffers.
IDE — ID Extended
This flag indicates whether the extended or standard identifier format is applied in this buffer. In case
of a receive buffer, the flag is set as being received and indicates to the CPU how to process the buffer
identifier registers. In case of a transmit buffer, the flag indicates to the MSCAN08 what type of
identifier to send.
1 = Extended format, 29 bits
0 = Standard format, 11 bits
RTR — Remote Transmission Request
This flag reflects the status of the remote transmission request bit in the CAN frame. In case of a
receive buffer, it indicates the status of the received frame and supports the transmission of an
answering frame in software. In case of a transmit buffer, this flag defines the setting of the RTR bit to
be sent.
1 = Remote frame
0 = Data frame
24.12.3 Data Length Register (DLR)
This register keeps the data length field of the CAN frame.
DLC3–DLC0 — Data Length Code Bits
The data length code contains the number of bytes (data byte count) of the respective message. At
transmission of a remote frame, the data length code is transmitted as programmed while the number
of transmitted bytes is always 0. The data byte count ranges from 0 to 8 for a data frame. Table 24-5
shows the effect of setting the DLC bits.
MC68HC908AZ32A Data Sheet, Rev. 2
280
Freescale Semiconductor
Programmer’s Model of Control Registers
Table 24-5. Data Length Codes
Data Length Code
DLC3
DLC2
DLC1
DLC0
Data Byte
Count
0
0
0
0
0
0
0
0
1
1
0
0
1
0
2
0
0
1
1
3
0
1
0
0
4
0
1
0
1
5
0
1
1
0
6
0
1
1
1
7
1
0
0
0
8
24.12.4 Data Segment Registers (DSRn)
The eight data segment registers contain the data to be transmitted or received. The number of bytes to
be transmitted or being received is determined by the data length code in the corresponding DLR.
24.12.5 Transmit Buffer Priority Registers
Address:
Read:
Write:
Reset:
$05bD
Bit 7
6
5
4
3
2
1
Bit 0
PRIO7
PRIO6
PRIO5
PRIO4
PRIO3
PRIO2
PRIO1
PRIO0
u
u
u
u
u
u
u
u
Figure 24-13. Transmit Buffer Priority Register (TBPR)
PRIO7–PRIO0 — Local Priority
This field defines the local priority of the associated message buffer. The local priority is used for the
internal prioritisation process of the MSCAN08 and is defined to be highest for the smallest binary
number. The MSCAN08 implements the following internal prioritisation mechanism:
• All transmission buffers with a cleared TXE flag participate in the prioritisation right before the SOF
is sent.
• The transmission buffer with the lowest local priority field wins the prioritisation.
• In case more than one buffer has the same lowest priority, the message buffer with the lower index
number wins.
24.13 Programmer’s Model of Control Registers
The programmer’s model has been laid out for maximum simplicity and efficiency. Figure 24-14 gives an
overview on the control register block of the MSCAN08.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
281
MSCAN Controller (MSCAN08)
Addr
Register
$0500
CMCR0
$0501
CMCR1
$0502
CBTR0
$0503
CBTR1
$0504
CRFLG
$0505
CRIER
$0506
CTFLG
$0507
CTCR
$0508
CIDAC
$0509
Reserved
$050E
CRXERR
$050F
CTXERR
$0510
CIDAR0
$0511
CIDAR1
$0512
CIDAR2
$0513
CIDAR3
$0514
CIDMR0
$0515
CIDMR1
$0516
CIDMR2
$0517
CIDMR3
Read:
Bit 7
6
5
4
1
Bit 0
0
0
0
SYNCH
SLPRQ
SFTRES
0
0
0
0
0
LOOPB
WUPM
CLKSRC
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
SAMP
TSEG22
TSEG21
TSEG20
TSEG13
TSEG12
TSEG11
TSEG10
WUPIF
RWRNIF
TWRNIF
RERRIF
TERRIF
BOFFIF
OVRIF
RXF
WUPIE
RWRNIE
TWRNIE
RERRIE
TERRIE
BOFFIE
OVRIE
RXFIE
0
ABTAK2
ABTAK1
ABTAK0
0
TXE2
TXE1
TXE0
ABTRQ2
ABTRQ1
ABTRQ0
TXEIE2
TXEIE1
TXEIE0
IDAM1
IDAM0
0
0
IDHIT1
IDHIT0
Write:
Read:
3
TLNKEN
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
0
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
Read:
Write:
SLPAK
0
0
R
R
R
R
R
R
R
R
RXERR7
RXERR6
RXERR5
RXERR4
RXERR3
RXERR2
RXERR1
RXERR0
TXERR7
TXERR6
TXERR5
TXERR4
TXERR3
TXERR2
TXERR1
TXERR0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
R
= Reserved
Write:
Read:
0
2
= Unimplemented
Figure 24-14. MSCAN08 Control Register Structure
MC68HC908AZ32A Data Sheet, Rev. 2
282
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.1 MSCAN08 Module Control Register 0
Address:
Read:
$0500
Bit 7
6
5
4
0
0
0
SYNCH
0
0
0
0
Write:
Reset:
3
TLNKEN
2
SLPAK
0
0
1
Bit 0
SLPRQ
SFTRES
0
1
= Unimplemented
Figure 24-15. Module Control Register 0 (CMCR0)
SYNCH — Synchronized Status
This bit indicates whether the MSCAN08 is synchronized to the CAN bus and as such can participate
in the communication process.
1 = MSCAN08 synchronized to the CAN bus
0 = MSCAN08 not synchronized to the CAN bus
TLNKEN — Timer Enable
This flag is used to establish a link between the MSCAN08 and the on-chip timer (see 24.9 Timer Link).
1 = The MSCAN08 timer signal output is connected to the timer input.
0 = The port is connected to the timer input.
SLPAK — Sleep Mode Acknowledge
This flag indicates whether the MSCAN08 is in module internal sleep mode. It shall be used as a
handshake for the sleep mode request (see 24.8.1 MSCAN08 Sleep Mode). If the MSCAN08 detects
bus activity while in Sleep mode, it clears the flag.
1 = Sleep – MSCAN08 in internal sleep mode
0 = Wakeup – MSCAN08 is not in Sleep mode
SLPRQ — Sleep Request, Go to Internal Sleep Mode
This flag requests the MSCAN08 to go into an internal power-saving mode (see 24.8.1 MSCAN08
Sleep Mode).
1 = Sleep — The MSCAN08 will go into internal sleep mode.
0 = Wakeup — The MSCAN08 will function normally.
SFTRES — Soft Reset
When this bit is set by the CPU, the MSCAN08 immediately enters the soft reset state. Any ongoing
transmission or reception is aborted and synchronization to the bus is lost.
The following registers enter and stay in their hard reset state: CMCR0, CRFLG, CRIER, CTFLG, and
CTCR.
The registers CMCR1, CBTR0, CBTR1, CIDAC, CIDAR0–3, and CIDMR0–3 can only be written by
the CPU when the MSCAN08 is in soft reset state. The values of the error counters are not affected
by soft reset.
When this bit is cleared by the CPU, the MSCAN08 tries to synchronize to the CAN bus. If the
MSCAN08 is not in bus-off state, it will be synchronized after 11 recessive bits on the bus; if the
MSCAN08 is in bus-off state, it continues to wait for 128 occurrences of 11 recessive bits.
Clearing SFTRES and writing to other bits in CMCR0 must be in separate instructions.
1 = MSCAN08 in soft reset state
0 = Normal operation
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
283
MSCAN Controller (MSCAN08)
24.13.2 MSCAN08 Module Control Register 1
Address:
Read:
$0501
Bit 7
6
5
4
3
0
0
0
0
0
0
0
0
0
0
Write:
Reset:
2
1
Bit 0
LOOPB
WUPM
CLKSRC
0
0
0
= Unimplemented
Figure 24-16. Module Control Register (CMCR1)
LOOPB — Loop Back Self-Test Mode
When this bit is set, the MSCAN08 performs an internal loop back which can be used for self-test
operation: the bit stream output of the transmitter is fed back to the receiver internally. The RxCAN
input pin is ignored and the TxCAN output goes to the recessive state (logic ‘1’). The MSCAN08
behaves as it does normally when transmitting and treats its own transmitted message as a message
received from a remote node. In this state the MSCAN08 ignores the bit sent during the ACK slot of
the CAN frame Acknowledge field to insure proper reception of its own message. Both transmit and
receive interrupt are generated.
1 = Activate loop back self-test mode
0 = Normal operation
WUPM — Wakeup Mode
This flag defines whether the integrated low-pass filter is applied to protect the MSCAN08 from
spurious wakeups (see 24.8.5 Programmable Wakeup Function).
1 = MSCAN08 will wake up the CPU only in cases of a dominant pulse on the bus which has a
length of at least twup.
0 = MSCAN08 will wake up the CPU after any recessive to dominant edge on the CAN bus.
CLKSRC — Clock Source
This flag defines which clock source the MSCAN08 module is driven from (see 24.10 Clock System).
1 = The MSCAN08 clock source is CGMOUT (see Figure 24-7).
0 = The MSCAN08 clock source is CGMXCLK/2 (see Figure 24-7).
NOTE
The CMCR1 register can be written only if the SFTRES bit in the MSCAN08
module control register is set
MC68HC908AZ32A Data Sheet, Rev. 2
284
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.3 MSCAN08 Bus Timing Register 0
Address:
Read:
Write:
Reset:
$0502
Bit 7
6
5
4
3
2
1
Bit 0
SJW1
SJW0
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
0
0
0
0
0
0
0
0
Figure 24-17. Bus Timing Register 0 (CBTR0)
SJW1 and SJW0 — Synchronization Jump Width
The synchronization jump width (SJW) defines the maximum number of time quanta (Tq) clock cycles
by which a bit may be shortened, or lengthened, to achieve resynchronization on data transitions on
the bus (see Table 24-6).
Table 24-6. Synchronization Jump Width
SJW1
SJW0
Synchronization
Jump Width
0
0
1 Tq cycle
0
1
2 Tq cycle
1
0
3 Tq cycle
1
1
4 Tq cycle
BRP5–BRP0 — Baud Rate Prescaler
These bits determine the time quanta (Tq) clock, which is used to build up the individual bit timing,
according to Table 24-7.
Table 24-7. Baud Rate Prescaler
BRP5
BRP4
BRP3
BRP2
BRP1
BRP0
Prescaler
Value (P)
0
0
0
0
0
0
1
0
0
0
0
0
1
2
0
0
0
0
1
0
3
0
0
0
0
1
1
4
:
:
:
:
:
:
:
:
:
:
:
:
:
:
1
1
1
1
1
1
64
NOTE
The CBTR0 register can be written only if the SFTRES bit in the MSCAN08
module control register is set.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
285
286 MSCAN Controller (MSCAN08)
24.13.4 MSCAN08 Bus Timing Register 1
Address:
Read:
Write:
Reset:
$0503
Bit 7
6
5
4
3
2
1
Bit 0
SAMP
TSEG22
TSEG21
TSEG20
TSEG13
TSEG12
TSEG11
TSEG10
0
0
0
0
0
0
0
0
Figure 24-18. Bus Timing Register 1 (CBTR1)
SAMP — Sampling
This bit determines the number of serial bus samples to be taken per bit time. If set, three samples per
bit are taken, the regular one (sample point) and two preceding samples, using a majority rule. For
higher bit rates, SAMP should be cleared, which means that only one sample will be taken per bit.
1 = Three samples per bit(1)
0 = One sample per bit
TSEG22–TSEG10 — Time Segment
Time segments within the bit time fix the number of clock cycles per bit time and the location of the
sample point. Time segment 1 (TSEG1) and time segment 2 (TSEG2) are programmable as shown in
Table 24-8.
Table 24-8. Time Segment Values
TSEG13
TSEG12
TSEG11
TSEG10
Time
Segment 1
TSEG22
TSEG21
TSEG20
Time
Segment 2
0
0
0
0
1 Tq Cycle(1)
0
0
0
1 Tq Cycle(1)
0
0
0
1
2 Tq Cycles(1)
0
0
1
2 Tq Cycles
0
0
1
0
3Tq Cycles(1)
.
.
.
.
0
0
1
1
4 Tq Cycles
.
.
.
.
.
.
.
.
.
1
1
1
8Tq Cycles
.
.
.
.
.
1
1
1
1
16 Tq Cycles
1. This setting is not valid. Please refer to Table 24-4 for valid settings.
The bit time is determined by the oscillator frequency, the baud rate prescaler, and the number of time
quanta (Tq) clock cycles per bit as shown in Table 24-8).
Bit time =
Pres value
fMSCANCLK
• number of Time Quanta
NOTE
The CBTR1 register can only be written if the SFTRES bit in the MSCAN08
module control register is set.
1. In this case PHASE_SEG1 must be at least 2 time quanta.
MC68HC908AZ32A Data Sheet, Rev. 2
286
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.5 MSCAN08 Receiver Flag Register (CRFLG)
All bits of this register are read and clear only. A flag can be cleared by writing a 1 to the corresponding
bit position. A flag can be cleared only when the condition which caused the setting is valid no more.
Writing a 0 has no effect on the flag setting. Every flag has an associated interrupt enable flag in the
CRIER register. A hard or soft reset will clear the register.
Address:
Read:
Write:
Reset:
$0504
Bit 7
6
5
4
3
2
1
Bit 0
WUPIF
RWRNIF
TWRNIF
RERRIF
TERRIF
BOFFIF
OVRIF
RXF
0
0
0
0
0
0
0
0
Figure 24-19. Receiver Flag Register (CRFLG)
WUPIF — Wakeup Interrupt Flag
If the MSCAN08 detects bus activity while in Sleep mode, it sets the WUPIF flag. If not masked, a
wake-up interrupt is pending while this flag is set.
1 = MSCAN08 has detected activity on the bus and requested wake-up.
0 = No wake-up interrupt has occurred.
RWRNIF — Receiver Warning Interrupt Flag
This flag is set when the MSCAN08 goes into warning status due to the receive error counter (REC)
exceeding 96 and neither one of the Error Interrupt flags or the Bus-off Interrupt flag is set(1). If not
masked, an error interrupt is pending while this flag is set.
1 = MSCAN08 has gone into receiver warning status.
0 = No receiver warning status has been reached.
TWRNIF — Transmitter Warning Interrupt Flag
This flag is set when the MSCAN08 goes into warning status due to the transmit error counter (TEC)
exceeding 96 and neither one of the error interrupt flags or the bus-off interrupt flag is set(2). If not
masked, an error interrupt is pending while this flag is set.
1 = MSCAN08 has gone into transmitter warning status.
0 = No transmitter warning status has been reached.
RERRIF — Receiver Error Passive Interrupt Flag
This flag is set when the MSCAN08 goes into error passive status due to the receive error counter
exceeding 127 and the bus-off interrupt flag is not set(3). If not masked, an Error interrupt is pending
while this flag is set.
1 = MSCAN08 has gone into receiver error passive status.
0 = No receiver error passive status has been reached.
1. Condition to set the flag: RWRNIF = (96 ð REC) & RERRIF & TERRIF & BOFFIF
2. Condition to set the flag: TWRNIF = (96 ð TEC) & RERRIF & TERRIF & BOFFIF
3. Condition to set the flag: RERRIF = (127 ð REC ð 255) & BOFFIF
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
287
MSCAN Controller (MSCAN08)
TERRIF — Transmitter Error Passive Interrupt Flag
This flag is set when the MSCAN08 goes into error passive status due to the Transmit Error counter
exceeding 127 and the Bus-off interrupt flag is not set(1). If not masked, an Error interrupt is pending
while this flag is set.
1 = MSCAN08 went into transmit error passive status.
0 = No transmit error passive status has been reached.
BOFFIF — Bus-Off Interrupt Flag
This flag is set when the MSCAN08 goes into bus-off status, due to the transmit error counter
exceeding 255. It cannot be cleared before the MSCAN08 has monitored 128 times 11 consecutive
‘recessive’ bits on the bus. If not masked, an Error interrupt is pending while this flag is set.
1 = MSCAN08has gone into bus-off status.
0 = No bus-off status has bee reached.
OVRIF — Overrun Interrupt Flag
This flag is set when a data overrun condition occurs. If not masked, an error interrupt is pending while
this flag is set.
1 = A data overrun has been detected since last clearing the flag.
0 = No data overrun has occurred.
RXF — Receive Buffer Full
The RXF flag is set by the MSCAN08 when a new message is available in the foreground receive
buffer. This flag indicates whether the buffer is loaded with a correctly received message. After the
CPU has read that message from the receive buffer the RXF flag must be cleared to release the buffer.
A set RXF flag prohibits the exchange of the background receive buffer into the foreground buffer. If
not masked, a receive interrupt is pending while this flag is set.
1 = The receive buffer is full. A new message is available.
0 = The receive buffer is released (not full).
NOTE
To ensure data integrity, no registers of the receive buffer shall be read
while the RXF flag is cleared.
NOTE
The CRFLG register is held in the reset state when the SFTRES bit in
CMCR0 is set.
1. Condition to set the flag: TERRIF = (128 ð TEC ð 255) & BOFFIF
MC68HC908AZ32A Data Sheet, Rev. 2
288
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.6 MSCAN08 Receiver Interrupt Enable Register
Address:
Read:
Write:
Reset:
$0505
Bit 7
6
5
4
3
2
1
Bit 0
WUPIE
RWRNIE
TWRNIE
RERRIE
TERRIE
BOFFIE
OVRIE
RXFIE
0
0
0
0
0
0
0
0
Figure 24-20. Receiver Interrupt Enable Register (CRIER)
WUPIE — Wakeup Interrupt Enable
1 = A wakeup event will result in a wakeup interrupt.
0 = No interrupt will be generated from this event.
RWRNIE — Receiver Warning Interrupt Enable
1 = A receiver warning status event will result in an error interrupt.
0 = No interrupt is generated from this event.
TWRNIE — Transmitter Warning Interrupt Enable
1 = A transmitter warning status event will result in an error interrupt.
0 = No interrupt is generated from this event.
RERRIE — Receiver Error Passive Interrupt Enable
1 = A receiver error passive status event will result in an error interrupt.
0 = No interrupt is generated from this event.
TERRIE — Transmitter Error Passive Interrupt Enable
1 = A transmitter error passive status event will result in an error interrupt.
0 = No interrupt is generated from this event.
BOFFIE — Bus-Off Interrupt Enable
1 = A bus-off event will result in an error interrupt.
0 = No interrupt is generated from this event.
OVRIE — Overrun Interrupt Enable
1 = An overrun event will result in an error interrupt.
0 = No interrupt is generated from this event.
RXFIE — Receiver Full Interrupt Enable
1 = A receive buffer full (successful message reception) event will result in a receive interrupt.
0 = No interrupt will be generated from this event.
NOTE
The CRIER register is held in the reset state when the SFTRES bit in
CMCR0 is set.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
289
MSCAN Controller (MSCAN08)
24.13.7 MSCAN08 Transmitter Flag Register
The Abort Acknowledge flags are read only. The Transmitter Buffer Empty flags are read and clear only.
A flag can be cleared by writing a 1 to the corresponding bit position. Writing a 0 has no effect on the flag
setting. The Transmitter Buffer Empty flags each have an associated interrupt enable bit in the CTCR
register. A hard or soft reset will resets the register.
Address:
Read:
$0506
5
Bit 7
6
5
4
3
0
ABTAK2
ABTAK1
ABTAK0
0
0
0
0
0
0
Write:
Reset:
2
1
Bit 0
TXE2
TXE1
TXE0
1
1
1
= Unimplemented
Figure 24-21. Transmitter Flag Register (CTFLG)
ABTAK2–ABTAK0 — Abort Acknowledge
This flag acknowledges that a message has been aborted due to a pending abort request from the
CPU. After a particular message buffer has been flagged empty, this flag can be used by the
application software to identify whether the message has been aborted successfully or has been sent.
The ABTAKx flag is cleared implicitly whenever the corresponding TXE flag is cleared.
1 = The message has been aborted.
0 = The message has not been aborted, thus has been sent out.
TXE2–TXE0 — Transmitter Empty
This flag indicates that the associated transmit message buffer is empty, thus not scheduled for
transmission. The CPU must handshake (clear) the flag after a message has been set up in the
transmit buffer and is due for transmission. The MSCAN08 sets the flag after the message has been
sent successfully. The flag is also set by the MSCAN08 when the transmission request was
successfully aborted due to a pending abort request (see 24.12.5 Transmit Buffer Priority Registers).
If not masked, a receive interrupt is pending while this flag is set.
Clearing a TXEx flag also clears the corresponding ABTAKx flag (ABTAK, see above). When a TXEx
flag is set, the corresponding ABTRQx bit (ABTRQ, see 24.13.8 MSCAN08 Transmitter Control
Register) is cleared.
1 = The associated message buffer is empty (not scheduled).
0 = The associated message buffer is full (loaded with a message due for transmission).
NOTE
To ensure data integrity, no registers of the transmit buffers should be
written to while the associated TXE flag is cleared.
NOTE
The CTFLG register is held in the reset state when the SFTRES bit in
CMCR0 is set.
MC68HC908AZ32A Data Sheet, Rev. 2
290
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.8 MSCAN08 Transmitter Control Register
Address:
$0507
Bit 7
Read:
0
Write:
Reset:
0
6
5
4
ABTRQ2
ABTRQ1
ABTRQ0
0
0
0
3
0
2
1
Bit 0
TXEIE2
TXEIE1
TXEIE0
0
0
0
0
= Unimplemented
Figure 24-22. Transmitter Control Register (CTCR)
ABTRQ2–ABTRQ0 — Abort Request
The CPU sets an ABTRQx bit to request that an already scheduled message buffer (TXE = 0) be
aborted. The MSCAN08 will grant the request if the message has not already started transmission, or
if the transmission is not successful (lost arbitration or error). When a message is aborted the
associated TXE and the abort acknowledge flag (ABTAK) (see 24.13.7 MSCAN08 Transmitter Flag
Register) will be set and an TXE interrupt is generated if enabled. The CPU cannot reset ABTRQx.
ABTRQx is cleared implicitly whenever the associated TXE flag is set.
1 = Abort request pending
0 = No abort request
NOTE
The software must not clear one or more of the TXE flags in CTFLG and
simultaneously set the respective ABTRQ bit(s).
TXEIE2–TXEIE0 — Transmitter Empty Interrupt Enable
1 = A transmitter empty (transmit buffer available for transmission) event results in a transmitter
empty interrupt.
0 = No interrupt is generated from this event.
NOTE
The CTCR register is held in the reset state when the SFTRES bit in
CMCR0 is set.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
291
MSCAN Controller (MSCAN08)
24.13.9 MSCAN08 Identifier Acceptance Control Register
Address:
Read:
$0508
Bit 7
6
0
0
0
0
Write:
Reset:
5
4
IDAM1
IDAM0
0
0
3
2
1
Bit 0
0
0
IDHIT1
IDHIT0
0
0
0
0
= Unimplemented
Figure 24-23. Identifier Acceptance Control Register (CIDAC)
IDAM1–IDAM0— Identifier Acceptance Mode
The CPU sets these flags to define the identifier acceptance filter organization (see 24.5 Identifier
Acceptance Filter). Table 24-9 summarizes the different settings. In “filter closed” mode no messages
will be accepted so that the foreground buffer will never be reloaded.
Table 24-9. Identifier Acceptance Mode Settings
IDAM1
IDAM0
Identifier Acceptance Mode
0
0
Single 32-Bit Acceptance Filter
0
1
Two 16-Bit Acceptance Filter
1
0
Four 8-Bit Acceptance Filters
1
1
Filter Closed
IDHIT1–IDHIT0— Identifier Acceptance Hit Indicator
The MSCAN08 sets these flags to indicate an identifier acceptance hit (see 24.5 Identifier Acceptance
Filter). Table 24-9 summarizes the different settings.
Table 24-10. Identifier Acceptance Hit Indication
IDHIT1
IDHIT0
Identifier Acceptance Hit
0
0
Filter 0 Hit
0
1
Filter 1 Hit
1
0
Filter 2 Hit
1
1
Filter 3 Hit
The IDHIT indicators are always related to the message in the foreground buffer. When a message gets
copied from the background to the foreground buffer, the indicators are updated as well.
NOTE
The CIDAC register can be written only if the SFTRES bit in the CMCR0 is
set.
MC68HC908AZ32A Data Sheet, Rev. 2
292
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.10 MSCAN08 Receive Error Counter
Address:
Read:
$050E
Bit 7
6
5
4
3
2
1
Bit 0
RXERR7
RXERR6
RXERR5
RXERR4
RXERR3
RXERR2
RXERR1
RXERR0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 24-24. Receiver Error Counter (CRXERR)
This register reflects the status of the MSCAN08 receive error counter. The register is read only.
24.13.11 MSCAN08 Transmit Error Counter
Address:
Read:
$050F
Bit 7
6
5
4
3
2
1
Bit 0
TXERR7
TXERR6
TXERR5
TXERR4
TXERR3
TXERR2
TXERR1
TXERR0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 24-25. Transmit Error Counter (CTXERR)
This register reflects the status of the MSCAN08 transmit error counter. The register is read only.
NOTE
Both error counters may only be read when in Sleep or Soft Reset mode.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
293
MSCAN Controller (MSCAN08)
24.13.12 MSCAN08 Identifier Acceptance Registers
On reception each message is written into the background receive buffer. The CPU is only signalled to
read the message, however, if it passes the criteria in the identifier acceptance and identifier mask
registers (accepted); otherwise, the message will be overwritten by the next message (dropped).
The acceptance registers of the MSCAN08 are applied on the IDR0 to IDR3 registers of incoming
messages in a bit by bit manner.
For extended identifiers, all four acceptance and mask registers are applied. For standard identifiers only
the first two (CIDMR0/1 and CIDAR0/1) are applied.
CIDAR0
Read:
Write:
Address: $0510
Bit 7
6
5
4
3
2
1
Bit 0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
Reset:
CIDAR1
Read:
Write:
Unaffected by Reset
Address: $050511
Bit 7
6
5
4
3
2
1
Bit 0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
Reset:
CIDAR2
Read:
Write:
Unaffected by Reset
Address: $0512
Bit 7
6
5
4
3
2
1
Bit 0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
Reset:
CIDAR3
Read:
Write:
Reset:
Unaffected by Reset
Address: $0513
Bit 7
6
5
4
3
2
1
Bit 0
AC7
AC6
AC5
AC4
AC3
AC2
AC1
AC0
Unaffected by Reset
Figure 24-26. Identifier Acceptance Registers (CIDAR0–CIDAR3)
AC7–AC0 — Acceptance Code Bits
AC7–AC0 comprise a user-defined sequence of bits with which the corresponding bits of the related
identifier register (IDRn) of the receive message buffer are compared. The result of this comparison is
then masked with the corresponding identifier mask register.
NOTE
The CIDAR0–3 registers can be written only if the SFTRES bit in CMCR0
is set
MC68HC908AZ32A Data Sheet, Rev. 2
294
Freescale Semiconductor
Programmer’s Model of Control Registers
24.13.13 MSCAN08 Identifier Mask Registers (CIDMR0–3)
The identifier mask registers specify which of the corresponding bits in the identifier acceptance register
are relevant for acceptance filtering. For standard identifiers it is required to program the last three bits
(AM2-AM0) in the mask register CIDMR1 to ‘don’t care’.
CIDMRO
Address: $0514
Read:
Write:
Bit 7
6
5
4
3
2
1
Bit 0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
Reset:
Unaffected by Reset
CIDMR1
Address: $0515
Read:
Write:
Bit 7
6
5
4
3
2
1
Bit 0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
Reset:
Unaffected by Reset
CIDMR2
Address: $0516
Read:
Write:
Bit 7
6
5
4
3
2
1
Bit 0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
Reset:
Unaffected by Reset
CIDMR3
Address: $0517
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
AM7
AM6
AM5
AM4
AM3
AM2
AM1
AM0
Unaffected by Reset
Figure 24-27. Identifier Mask Registers (CIDMR0–CIDMR3)
AM7–AM0 — Acceptance Mask Bits
If a particular bit in this register is cleared, this indicates that the corresponding bit in the identifier
acceptance register must be the same as its identifier bit before a match will be detected. The message
will be accepted if all such bits match. If a bit is set, it indicates that the state of the corresponding bit
in the identifier acceptance register will not affect whether or not the message is accepted.
1 = Ignore corresponding acceptance code register bit.
0 = Match corresponding acceptance code register and identifier bits.
NOTE
The CIDMR0-3 registers can be written only if the SFTRES bit in the
CMCR0 is set
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
295
MSCAN Controller (MSCAN08)
MC68HC908AZ32A Data Sheet, Rev. 2
296
Freescale Semiconductor
Chapter 25
Electrical Specifications
25.1 Electrical Specifications
25.1.1 Maximum Ratings
Maximum ratings are the extreme limits to which the microcontroller unit (MCU) can be exposed without
permanently damaging it.
NOTE
This device is not guaranteed to operate properly at the maximum ratings.
Refer to 25.1.4 5.0 Volt DC Electrical Characteristics for guaranteed
operating conditions.
Rating
Symbol
Value
Unit
Supply Voltage
VDD
–0.3 to +6.0
V
Input Voltage
VIN
VSS –0.3 to VDD +0.3
V
I
± 25
mA
Storage Temperature
TSTG
–55 to +150
°C
Maximum Current out of VSS
IMVSS
100
mA
Maximum Current into VDD
IMVDD
100
mA
VHI
VDD + 4.5
V
Maximum Current Per Pin Excluding VDD and VSS
Reset and IRQ Input Voltage
NOTE: Voltages are referenced to VSS.
NOTE
This device contains circuitry to protect the inputs against damage due to
high static voltages or electric fields; however, it is advised that normal
precautions be taken to avoid application of any voltage higher than
maximum-rated voltages to this high-impedance circuit. For proper
operation, it is recommended that VIN and VOUT be constrained to the
range VSS ≤ (VIN or VOUT) ≤ VDD. Reliability of operation is enhanced if
unused inputs are connected to an appropriate logic voltage level (for
example, either VSS or VDD).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
297
Electrical Specifications
25.1.2 Functional Operating Range
Rating
Operating Temperature Range(1)
Operating Voltage Range
Symbol
Value
Unit
TA
–40 to TA(MAX)
°C
VDD
5.0 ± 0.5
V
1. TA(MAX) = 125°C for part suffix MFU/MFN
TA(MAX) = 105°C for part suffix VFU/VFN
TA(MAX) = 85°C for part suffix CFU/CFN
NOTE
For applications which use the LVI, Freescale guarantee the functionality of
the device down to the LVI trip point (VLVI) within the constraints outlined in
Chapter 14 Low Voltage Inhibit (LVI).
25.1.3 Thermal Characteristics
Characteristic
Symbol
Value
Unit
Thermal Resistance
QFP (64 Pins)
θJA
70
°C/W
I/O Pin Power Dissipation
PI/O
User Determined
W
Power Dissipation(1)
PD
PD = (IDD x VDD) + PI/O =
K/(TJ + 273 °C)
W
Constant(2)
K
Average Junction Temperature
TJ
PD x (TA + 273 °C)
+ (PD2 x θJA)
TA + PD
x θJA
W/°C
°C
1. Power dissipation is a function of temperature
2. K is a constant unique to the device. K can be determined from a known TA and measured PD. With this value of K, PD and
TJ can be determined for any value of TA.
MC68HC908AZ32A Data Sheet, Rev. 2
298
Freescale Semiconductor
Electrical Specifications
25.1.4 5.0 Volt DC Electrical Characteristics
Characteristic(1)
Symbol
Min
Typical
Max
Unit
VOH
VDD –0.8
VDD –1.5
—
—
—
—
V
IOH(TOT)
—
—
10
mA
VOL
—
—
—
—
0.4
1.5
V
IOL(TOT)
—
—
15
mA
Input High Voltage
All Ports, IRQs, RESET, OSC1
VIH
0.7 x VDD
—
VDD
V
Input Low Voltage
All Ports, IRQs, RESET, OSC1
VIL
VSS
—
0.3 x VDD
V
—
—
25
14
35
20
mA
mA
—
—
—
—
100
35
400
50
500
100
μA
μA
μA
μA
Output High Voltage
(ILOAD = –2.0 mA) All Ports
(ILOAD = –5.0 mA) All Ports
Total source current
Output Low Voltage
(ILOAD = 1.6 mA) All Ports
(ILOAD = 10.0 mA) All Ports
Total sink current
VDD Supply Current
Run(2)
Wait(3)
Stop(4)
LVI enabled, TA=25 °C
LVI disabled, TA=25 °C
LVI enabled, –40 °C to +125 °C
LVI disabled, –40 °C to +125 °C
IDD(5)
I/O Ports Hi-Z Leakage Current
IL
–1
1
μA
Input Current
IIN
–1
1
μA
COUT
CIN
—
—
12
8
pF
VLVI
3.80
4.49
V
POR ReArm Voltage(6)
VPOR
0
200
mV
POR Reset Voltage(7)
VPORRST
0
800
mV
RPOR
0.02
—
V/ms
VHI
VDD + 3.0
VDD + 4.5
V
VHI
VDD + 3.0
VDD + 4.5
V
RPU
20
200
kΩ
Capacitance
Ports (As Input or Output)
Low-Voltage Reset Inhibit (trip recover)
POR Rise Time Ramp Rate(8)
High COP Disable Voltage(9)
Monitor mode entry voltage on
Keyboard pullup resistor
IRQ(10)
90
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = –40 °C to +TA(MAX), unless otherwise noted.
2. Run (Operating) IDD measured using external square wave clock source (fBUS = 8.4 MHz). All inputs 0.2 V from rail. No dc
loads. Less than 100 pF on all outputs. CL = 20 pF on OSC2. All ports configured as inputs. OSC2 capacitance linearly
affects run IDD. Measured with all modules enabled. Typical values at midpoint of voltage range, 25C only.
3. Wait IDD measured using external square wave clock source (fBUS = 8.4 MHz). All inputs 0.2 Vdc from rail. No dc loads.
Less than 100 pF on all outputs, CL = 20 pF on OSC2. All ports configured as inputs. OSC2 capacitance linearly affects
wait IDD. Measured with all modules enabled. Typical values at midpoint of voltage range, 25C only.
4. Stop IDD measured with OSC1 = VSS. Typical values at midpoint of voltage range, 25C only.
5. Although IDD is proportional to bus frequency, a current of several mA is present even at very low frequencies.
6. Maximum is highest voltage that POR is guaranteed.
7. Maximum is highest voltage that POR is possible.
8. If minimum VDD is not reached before the internal POR reset is released, RST must be driven low externally until minimum
VDD is reached.
9. See Chapter 13 Computer Operating Properly (COP. VHI applied to RST.
10. See Monitor mode description within Chapter 13 Computer Operating Properly (COP. VHI applied to IRQ or RST
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
299
Electrical Specifications
25.1.5 Control Timing
Characteristic(1)
Symbol
Min
Max
Unit
fBUS
—
8.4
MHz
RESET Pulse Width Low
tRL
1.5
—
tcyc
IRQ Interrupt Pulse Width Low (Edge-Triggered)
tILHI
1.5
—
tcyc
IRQ Interrupt Pulse Period
tILIL
Note(2)
—
tcyc
tTH, tTL
tTLTL
2
Note(2)
—
—
tcyc
tWUP
2
5
μs
Bus Operating Frequency (4.5–5.5 V — VDD Only)
16-Bit Timer(3)
Input Capture Pulse Width(4)
Input Capture Period
MSCAN Wake-up Filter Pulse Width(5)
1. VDD = 5.0 Vdc ± 0.5v, VSS = 0 Vdc, TA = –40°C to TA(MAX), unless otherwise noted.
2. The minimum period tTLTL or tILIL should not be less than the number of cycles it takes to execute the capture interrupt
service routine plus TBD tcyc.
3. The 2-bit timer prescaler is the limiting factor in determining timer resolution.
4. Refer to Table 18-2. Mode, Edge, and Level Selection, and supporting note.
5. The minimum pulse width to wake up the MSCAN module is guaranteed by design but not tested.
25.1.6 ADC Characteristics
Characteristic(1)
Min
Max
Unit
Resolution
8
8
Bits
Absolute Accuracy
(VREFL = 0 V, VDDA/VDDAREF = VREFH = 5 V ± 0.5v)
–1
+1
LSB
Includes Quantization
VREFL
VREFH
V
VREFL = VSSA
16
17
μs
Conversion Time Period
Input Leakage
Ports B and D
–1
1
μA
Conversion Time
16
17
ADC
Clock
Cycles
Conversion Range
Power-Up Time
(2)
Monotonicity
Comments
Includes Sampling Time
Inherent within Total Error
Zero Input Reading
00
01
Hex
VIN = VREFL
Full-Scale Reading
FE
FF
Hex
VIN = VREFH
Sample Time(3)
5
—
ADC
Clock
Cycles
Input Capacitance
—
8
pF
Not Tested
ADC Internal Clock
500 k
1.048 M
Hz
Tested Only at 1 MHz
Analog Input Voltage
VREFL
VREFH
V
1. VDD = 5.0 Vdc ± 0.5v, VSS = 0 Vdc, VDDA/VDDAREF = 5.0 Vdc ± 0.5v, VSSA = 0 Vdc, VREFH = 5.0 Vdc ± 0.5v
2. The external system error caused by input leakage current is approximately equal to the product of R source and input
current.
3. Source impedances greater than 10 kΩ adversely affect internal RC charging time during input sampling.
MC68HC908AZ32A Data Sheet, Rev. 2
300
Freescale Semiconductor
Electrical Specifications
25.1.7 5.0 Vdc ± 0.5 V Serial Peripheral Interface (SPI) Timing
Num(1)
Characteristic(2)
Symbol
Min
Max
Unit
Operating Frequency(3)
Master
Slave
fBUS(M)
fBUS(S)
fBUS/128
dc
fBUS/2
fBUS
MHz
1
Cycle Time
Master
Slave
tcyc(M)
tcyc(S)
2
1
128
—
tcyc
2
Enable Lead Time
tLead
15
—
ns
3
Enable Lag Time
tLag
15
—
ns
4
Clock (SCK) High Time
Master
Slave
tW(SCKH)M
tW(SCKH)S
100
50
—
—
ns
5
Clock (SCK) Low Time
Master
Slave
tW(SCKL)M
tW(SCKL)S
100
50
—
—
ns
6
Data Setup Time (Inputs)
Master
Slave
tSU(M)
tSU(S)
45
5
—
—
ns
7
Data Hold Time (Inputs)
Master
Slave
tH(M)
tH(S)
0
15
—
—
ns
tA(CP0)
tA(CP1)
0
0
40
20
ns
tDIS
—
25
ns
8
Access Time, Slave(4)
CPHA = 0
CPHA = 1
9
Slave Disable Time (Hold Time to High-Impedance State)
10
Enable Edge Lead Time to Data Valid(5)
Master
Slave
tEV(M)
tEV(S)
—
—
10
40
ns
11
Data Hold Time (Outputs, after Enable Edge)
Master
Slave
tHO(M)
tHO(S)
0
5
—
—
ns
12
Data Valid
Master (Before Capture Edge)
tV(M)
90
—
ns
13
Data Hold Time (Outputs)
Master (Before Capture Edge)
tHO(M)
100
—
ns
1. Item numbers refer to dimensions in Figure 25-1 and Figure 25-2.
2. All timing is shown with respect to 30% VDD and 70% VDD, unless otherwise noted; assumes 100 pF load on all SPI pins.
3. fBUS = the currently active bus frequency for the microcontroller.
4. Time to data active from high-impedance state.
5. With 100 pF on all SPI pins
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
301
Electrical Specifications
SS
(INPUT)
SS pin of master held high.
1
SCK (CPOL = 0)
(OUTPUT)
NOTE
SCK (CPOL = 1)
(OUTPUT)
NOTE
5
4
5
4
6
MISO
(INPUT)
MSB IN
BITS 6–1
10
11
MOSI
(OUTPUT)
MASTER MSB OUT
7
LSB IN
10
11
BITS 6–1
MASTER LSB OUT
13
12
NOTE: This first clock edge is generated internally, but is not seen at the SCK pin.
a) SPI Master Timing (CPHA = 0)
SS
(INPUT)
SS pin of master held high.
1
SCK (CPOL = 0)
(OUTPUT)
SCK (CPOL = 1)
(OUTPUT)
5
NOTE
4
5
NOTE
4
6
MISO
(INPUT)
MSB IN
10
MOSI
(OUTPUT)
BITS 6–1
11
MASTER MSB OUT
12
7
LSB IN
10
BITS 6–1
11
MASTER LSB OUT
13
NOTE: This last clock edge is generated internally, but is not seen at the SCK pin.
b) SPI Master Timing (CPHA = 1)
Figure 25-1. SPI Master Timing Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
302
Freescale Semiconductor
Electrical Specifications
SS
(INPUT)
3
1
SCK (CPOL = 0)
(INPUT)
11
5
4
2
SCK (CPOL = 1)
(INPUT)
5
4
9
8
MISO
(INPUT)
SLAVE
MSB OUT
6
MOSI
(OUTPUT)
BITS 6–1
7
NOTE
11
11
10
MSB IN
SLAVE LSB OUT
BITS 6–1
LSB IN
NOTE: Not defined but normally MSB of character just received
a) SPI Slave Timing (CPHA = 0)
SS
(INPUT)
1
SCK (CPOL = 0)
(INPUT)
5
4
2
3
SCK (CPOL = 1)
(INPUT)
8
MISO
(OUTPUT)
MOSI
(INPUT)
5
4
10
NOTE
9
SLAVE
MSB OUT
6
7
BITS 6–1
11
10
MSB IN
SLAVE LSB OUT
BITS 6–1
LSB IN
NOTE: Not defined but normally LSB of character previously transmitted
b) SPI Slave Timing (CPHA = 1)
Figure 25-2. SPI Slave Timing Diagram
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
303
Electrical Specifications
25.1.8 CGM Operating Conditions
Characteristic
Symbol
Min
Typ
Max
Unit
VDDA
VDD-0.3
—
VDD+0.3
V
VSSA
VSS-0.3
—
VSS+0.3
V
Crystal Reference Frequency
fCGMRCLK
1
4.9152
16
MHz
Module Crystal Reference
Frequency
fCGMXCLK
—
4.9152
—
MHz
fNOM
—
4.9152
—
MHz
Operating Voltage
Range Nom. Multiplier
Comments
Same Frequency
as fCGMRCLK
MHz
fCGMVRS is a nominal
value described and
calculated as an
example in the Chapter
8 Clock Generator
Module (CGM) section
for the desired VCO
operating frequency,
fCGMVCLK.
Max
Unit
Comments
—
—
—
Consult Crystal
Manufacturer’s Data
—
2 x CL
—
—
Consult Crystal
Manufacturer’s Data
C2
—
2 x CL
—
—
Consult Crystal
Manufacturer’s Data
Cfact
—
0.0154
—
F/s V
—
CFACT x
(VDDA/
fXCLK)
—
—
See 8.4.3 External
Filter Capacitor Pin
(CGMXFC)
μF
CBYP must provide
low AC impedance
from f = fCGMXCLK/100
to 100 x fCGMVCLK, so
series resistance must
be considered.
VCO Center-of-Range Frequency
fCGMVRS
4.9152
—
Note 1
VCO Operating Frequency
fCGMVCLK
4.9152
—
32.0
Symbol
Min
Typ
Crystal Load Capacitance
CL
—
Crystal Fixed Capacitance
C1
Crystal Tuning Capacitance
25.1.9 CGM Component Information
Description
Filter Capacitor Multiply Factor
Filter Capacitor
Bypass Capacitor
CF
CBYP
—
0.1
—
MC68HC908AZ32A Data Sheet, Rev. 2
304
Freescale Semiconductor
Electrical Specifications
25.1.10 CGM Acquisition/Lock Time Information
Description(1)
Symbol
Min
Typ(2)
Max(2)
Unit
Manual Mode Time to Stable
tACQ
—
(8 x VDDA) /
(fCGMXCLK x KACQ)
—
s
If CF Chosen
Correctly
Manual Stable to Lock Time
tAL
—
(4 x VDDA) /
(fCGMXCLK x KTRK)
—
s
If CF Chosen
Correctly
Manual Acquisition Time
tLOCK
—
tACQ+tAL
—
s
Tracking Mode Entry Frequency
Tolerance
DTRK
0
—
± 3.6
%
Acquisition Mode Entry Frequency
Tolerance
DUNT
± 6.3
—
± 7.2
%
LOCK Entry Frequency Tolerance
DLOCK
0
—
± 0.9
%
LOCK Exit Frequency Tolerance
DUNL
± 0.9
—
± 1.8
%
Reference Cycles per Acquisition
Mode Measurement
nACQ
—
32
—
—
Reference Cycles per Tracking
Mode Measurement
nTRK
—
128
—
—
Automatic Mode Time to Stable
tACQ
nACQ/fXCLK
(8 x VDDA) /
(fXCLK x KACQ)
Automatic Stable to Lock Time
tAL
nTRK/fXCLK
(4 x VDDA) /
(fXCLK x KTRK)
tLOCK
—
Automatic Lock Time
PLL Jitter, Deviation of Average Bus
Frequency over 2 ms(3)
Notes
s
If CF Chosen
Correctly
—
s
If CF Chosen
Correctly
0.65
25
ms
0
—
± (fCRYS)
x (.025%)
x (N/4)
Hz
K value for automatic mode time to
stable
Kacq
—
0.2
—
—
K value
Ktrk
—
0.004
—
—
N = VCO Freq.
Mult.
1. VDD = 5.0 Vdc ± 0.5 V, VSS = 0 Vdc, TA = -40C to TA (MAX), unless otherwise noted.
2. Conditions for typical and maximum values are for Run mode with fCGMXCLK = 8MHz, fBUSDES = 8MHz, N = 4, L = 7,
discharged CF = 15 nF, VDD = 5Vdc.
3. Guaranteed but not tested. Refer to Chapter 8 Clock Generator Module (CGM) for guidance on the use of the PLL.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
305
Electrical Specifications
25.1.11 Timer Module Characteristics
Characteristic
Symbol
Min
Max
Unit
tTIH, tTIL
125
—
ns
tTCH, tTCL
(1/fOP) + 5
—
ns
Symbol
Min
Max
Unit
VRDR
0.7
—
V
Symbol
Min
Max
Unit
EEPROM Programming Time per Byte
tEEPGM
10
—
ms
EEPROM Erasing Time per Byte
tEEBYTE
10
—
ms
EEPROM Erasing Time per Block
tEEBLOCK
10
—
ms
EEPROM Erasing Time per Bulk
tEEBULK
10
—
ms
EEPROM Programming Voltage Discharge Period
tEEFPV
100
—
μs
Number of Programming Operations to the Same EEPROM Byte
Before Erase(1)
—
—
8
—
EEPROM Write/Erase Cycles @ 10 ms Write Time
—
10,000
—
Cycles
EEPROM Data Retention After 10,000 Write/Erase Cycles
—
10
—
Years
EEPROM Programming Maximum Time to ‘AUTO’ Bit Set
—
—
500
μs
EEPROM Erasing Maximum Time to ‘AUTO’ Bit Set
—
—
8
ms
Input Capture Pulse Width
Input Clock Pulse Width
25.1.12 RAM Memory Characteristics
Characteristic
RAM Data Retention Voltage
25.1.13 EEPROM Memory Characteristics
Characteristic
1. Programming a byte more times than the specified maximum may affect the data integrity of that byte. The byte must be
erased before it can be programmed again.
MC68HC908AZ32A Data Sheet, Rev. 2
306
Freescale Semiconductor
Mechanical Specifications
25.1.14 FLASH Memory Characteristics
Characteristic
Symbol
Min
Max
Unit
—
1
—
MHz
FLASH Read Bus Clock Frequency
fREAD(1)
32K
8.4M
Hz
FLASH Page Erase Time (0 to 1k cycles)
tERASE(2)
1
—
ms
FLASH Page Erase Time (1 to 10k cycles)
tERASE(2)
4
—
ms
tMERASE(3)
4
—
ms
FLASH PGM/ERASE to HVEN Set Up Time
tNVS
10
—
μs
FLASH High Voltage Hold Time
tNVH
5
—
μs
FLASH High Voltage Hold Time (Mass)
tNVHL
100
—
μs
FLASH Program Hold Time
tPGS
5
—
μs
FLASH Program Time
tPROG
30
40
μs
FLASH Return to Read Time
tRCV(4)
1
FLASH Cumulative Program HV Period
tHV(5)
—
4
ms
FLASH Row Erase Endurance(6)
10,000
—
cycles
FLASH Row Program Endurance(7)
10,000
—
cycles
10
—
years
FLASH Program Bus Clock Frequency
FLASH Mass Erase Time
FLASH Data Retention Time(8)
μs
1. fREAD is defined as the frequency range for which the FLASH memory can be read.
2. If the page erase time is longer than tERASE(MIN), there is no erase-disturb, but it reduces the endurance of the FLASH
memory.
3. If the mass erase time is longer than tMERASE(MIN), there is no erase-disturb, but it reduces the endurance of the FLASH
memory.
4. tRCV is defined as the time it needs before the FLASH can be read after turning off the high voltage charge pump by clearing
HVEN to logic 0.
5. tHV is defined as the cumulative high voltage programming time to the same row before next erase.
tHV must satisfy this condition: tNVS+ tNVH + tPGS + (tPROGX 64) ð tHV max.
6. The minimum row erase endurance value specifies each row of the FLASH memory is guaranteed to work for at least this
many erase cycles.
7. The minimum row program endurance value specifies each row of the FLASH memory is guaranteed to work for at least
this many program cycles.
8. The FLASH is guaranteed to retain data over the entire operating temperature range for at least the minimum time
specified.
25.2 Mechanical Specifications
Refer to the following pages for detailed package dimensions.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
307
Chapter 26
Revision History
26.1 Major Changes Between Revision 2.0 and Revision 1.0
The following table lists the major changes between the current revision of the MC68HC908AZ32A
Technical Data Sheet, Rev 2.0, and the previous revision, Rev 1.0.
Section affected
Description of change
Timer Interface Module A (TIMA)
TSTOP — TIMA Stop Bit — Added note to bit definition for clarity.
Timer Interface Module B (TIMB)
TSTOP — TIMB Stop Bit — Added note to bit definition for clarity.
Chapter 25 Electrical
Specifications
25.1.10 CGM Acquisition/Lock Time Information — Corrected unit value for PLL jitter
deviation of average bus frequency over 2 ms.
26.2 Major Changes Between Revision 1.0 and Revision 0.0
The following table lists the major changes between the current revision of the MC68HC908AZ32A
Technical Data Sheet, Rev 1.0, and the previous revision, Rev 0.0.
Section affected
Chapter 25 Electrical
Specifications
Description of change
Updated case outline drawing for 64-Pin Quad Flat Pack (Case 840B)
Section 22.8 Changed KBSCR and KBIER addresses to match the Section Memory
Map.
Added to Electrical Specs, an entry for keyboard pullup resistor.
Updated the Flash Page Erase Time, terase to
1 ms min, 0 to 1k cycles
4 ms min, 1k to 10k cycles
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
311
Revision History
MC68HC908AZ32A Data Sheet, Rev. 2
312
Freescale Semiconductor
Glossary
A — See “accumulator (A).”
accumulator (A) — An 8-bit general-purpose register in the CPU08. The CPU08 uses the accumulator
to hold operands and results of arithmetic and logic operations.
acquisition mode — A mode of PLL operation during startup before the PLL locks on a frequency. Also
see "tracking mode."
address bus — The set of wires that the CPU or DMA uses to read and write memory locations.
addressing mode — The way that the CPU determines the operand address for an instruction. The
M68HC08 CPU has 16 addressing modes.
ALU — See “arithmetic logic unit (ALU).”
arithmetic logic unit (ALU) — The portion of the CPU that contains the logic circuitry to perform
arithmetic, logic, and manipulation operations on operands.
asynchronous — Refers to logic circuits and operations that are not synchronized by a common
reference signal.
baud rate — The total number of bits transmitted per unit of time.
BCD — See “binary-coded decimal (BCD).”
binary — Relating to the base 2 number system.
binary number system — The base 2 number system, having two digits, 0 and 1. Binary arithmetic is
convenient in digital circuit design because digital circuits have two permissible voltage levels, low
and high. The binary digits 0 and 1 can be interpreted to correspond to the two digital voltage
levels.
binary-coded decimal (BCD) — A notation that uses 4-bit binary numbers to represent the 10 decimal
digits and that retains the same positional structure of a decimal number. For example,
234 (decimal) = 0010 0011 0100 (BCD)
bit — A binary digit. A bit has a value of either logic 0 or logic 1.
branch instruction — An instruction that causes the CPU to continue processing at a memory location
other than the next sequential address.
break module — A module in the M68HC08 Family. The break module allows software to halt program
execution at a programmable point in order to enter a background routine.
breakpoint — A number written into the break address registers of the break module. When a number
appears on the internal address bus that is the same as the number in the break address registers,
the CPU executes the software interrupt instruction (SWI).
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
313
Glossary
break interrupt — A software interrupt caused by the appearance on the internal address bus of the
same value that is written in the break address registers.
bus — A set of wires that transfers logic signals.
bus clock — The bus clock is derived from the CGMOUT output from the CGM. The bus clock frequency,
fop, is equal to the frequency of the oscillator output, CGMXCLK, divided by four.
byte — A set of eight bits.
C — The carry/borrow bit in the condition code register. The CPU08 sets the carry/borrow bit when an
addition operation produces a carry out of bit 7 of the accumulator or when a subtraction operation
requires a borrow. Some logical operations and data manipulation instructions also clear or set
the carry/borrow bit (as in bit test and branch instructions and shifts and rotates).
CCR — See “condition code register.”
central processor unit (CPU) — The primary functioning unit of any computer system. The CPU controls
the execution of instructions.
CGM — See “clock generator module (CGM).”
clear — To change a bit from logic 1 to logic 0; the opposite of set.
clock — A square wave signal used to synchronize events in a computer.
clock generator module (CGM) — A module in the M68HC08 Family. The CGM generates a base clock
signal from which the system clocks are derived. The CGM may include a crystal oscillator circuit
and or phase-locked loop (PLL) circuit.
comparator — A device that compares the magnitude of two inputs. A digital comparator defines the
equality or relative differences between two binary numbers.
computer operating properly module (COP) — A counter module in the M68HC08 Family that resets
the MCU if allowed to overflow.
condition code register (CCR) — An 8-bit register in the CPU08 that contains the interrupt mask bit and
five bits that indicate the results of the instruction just executed.
control bit — One bit of a register manipulated by software to control the operation of the module.
control unit — One of two major units of the CPU. The control unit contains logic functions that
synchronize the machine and direct various operations. The control unit decodes instructions and
generates the internal control signals that perform the requested operations. The outputs of the
control unit drive the execution unit, which contains the arithmetic logic unit (ALU), CPU registers,
and bus interface.
COP — See "computer operating properly module (COP)."
counter clock — The input clock to the TIM counter. This clock is the output of the TIM prescaler.
CPU — See “central processor unit (CPU).”
CPU08 — The central processor unit of the M68HC08 Family.
MC68HC908AZ32A Data Sheet, Rev. 2
314
Freescale Semiconductor
CPU clock — The CPU clock is derived from the CGMOUT output from the CGM. The CPU clock
frequency is equal to the frequency of the oscillator output, CGMXCLK, divided by four.
CPU cycles — A CPU cycle is one period of the internal bus clock, normally derived by dividing a crystal
oscillator source by two or more so the high and low times will be equal. The length of time
required to execute an instruction is measured in CPU clock cycles.
CPU registers — Memory locations that are wired directly into the CPU logic instead of being part of the
addressable memory map. The CPU always has direct access to the information in these
registers. The CPU registers in an M68HC08 are:
• A (8-bit accumulator)
• H:X (16-bit index register)
• SP (16-bit stack pointer)
• PC (16-bit program counter)
• CCR (condition code register containing the V, H, I, N, Z, and C bits)
CSIC — customer-specified integrated circuit
cycle time — The period of the operating frequency: tCYC = 1/fOP.
decimal number system — Base 10 numbering system that uses the digits zero through nine.
direct memory access module (DMA) — A M68HC08 Family module that can perform data transfers
between any two CPU-addressable locations without CPU intervention. For transmitting or
receiving blocks of data to or from peripherals, DMA transfers are faster and more code-efficient
than CPU interrupts.
DMA — See "direct memory access module (DMA)."
DMA service request — A signal from a peripheral to the DMA module that enables the DMA module to
transfer data.
duty cycle — A ratio of the amount of time the signal is on versus the time it is off. Duty cycle is usually
represented by a percentage.
EEPROM — Electrically erasable, programmable, read-only memory. A nonvolatile type of memory that
can be electrically reprogrammed.
EPROM — Erasable, programmable, read-only memory. A nonvolatile type of memory that can be erased
by exposure to an ultraviolet light source and then reprogrammed.
exception — An event such as an interrupt or a reset that stops the sequential execution of the
instructions in the main program.
external interrupt module (IRQ) — A module in the M68HC08 Family with both dedicated external
interrupt pins and port pins that can be enabled as interrupt pins.
fetch — To copy data from a memory location into the accumulator.
firmware — Instructions and data programmed into nonvolatile memory.
free-running counter — A device that counts from zero to a predetermined number, then rolls over to
zero and begins counting again.
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
315
Glossary
full-duplex transmission — Communication on a channel in which data can be sent and received
simultaneously.
H — The upper byte of the 16-bit index register (H:X) in the CPU08.
H — The half-carry bit in the condition code register of the CPU08. This bit indicates a carry from the
low-order four bits of the accumulator value to the high-order four bits. The half-carry bit is required
for binary-coded decimal arithmetic operations. The decimal adjust accumulator (DAA) instruction
uses the state of the H and C bits to determine the appropriate correction factor.
hexadecimal — Base 16 numbering system that uses the digits 0 through 9 and the letters A through F.
high byte — The most significant eight bits of a word.
illegal address — An address not within the memory map
illegal opcode — A nonexistent opcode.
I — The interrupt mask bit in the condition code register of the CPU08. When I is set, all interrupts are
disabled.
index register (H:X) — A 16-bit register in the CPU08. The upper byte of H:X is called H. The lower
byte is called X. In the indexed addressing modes, the CPU uses the contents of H:X to determine
the effective address of the operand. H:X can also serve as a temporary data storage location.
input/output (I/O) — Input/output interfaces between a computer system and the external world. A CPU
reads an input to sense the level of an external signal and writes to an output to change the level
on an external signal.
instructions — Operations that a CPU can perform. Instructions are expressed by programmers as
assembly language mnemonics. A CPU interprets an opcode and its associated operand(s) and
instruction.
interrupt — A temporary break in the sequential execution of a program to respond to signals from
peripheral devices by executing a subroutine.
interrupt request — A signal from a peripheral to the CPU intended to cause the CPU to execute a
subroutine.
I/O — See “input/output (I/0).”
IRQ — See "external interrupt module (IRQ)."
jitter — Short-term signal instability.
latch — A circuit that retains the voltage level (logic 1 or logic 0) written to it for as long as power is applied
to the circuit.
latency — The time lag between instruction completion and data movement.
least significant bit (LSB) — The rightmost digit of a binary number.
logic 1 — A voltage level approximately equal to the input power voltage (VDD).
MC68HC908AZ32A Data Sheet, Rev. 2
316
Freescale Semiconductor
logic 0 — A voltage level approximately equal to the ground voltage (VSS).
low byte — The least significant eight bits of a word.
low voltage inhibit module (LVI) — A module in the M68HC08 Family that monitors power supply
voltage.
LVI — See "low voltage inhibit module (LVI)."
M68HC08 — A Freescale family of 8-bit MCUs.
mark/space — The logic 1/logic 0 convention used in formatting data in serial communication.
mask — 1. A logic circuit that forces a bit or group of bits to a desired state. 2. A photomask used in
integrated circuit fabrication to transfer an image onto silicon.
mask option — A optional microcontroller feature that the customer chooses to enable or disable.
mask option register (MOR) — An EPROM location containing bits that enable or disable certain MCU
features.
MCU — Microcontroller unit. See “microcontroller.”
memory location — Each M68HC08 memory location holds one byte of data and has a unique address.
To store information in a memory location, the CPU places the address of the location on the
address bus, the data information on the data bus, and asserts the write signal. To read
information from a memory location, the CPU places the address of the location on the address
bus and asserts the read signal. In response to the read signal, the selected memory location
places its data onto the data bus.
memory map — A pictorial representation of all memory locations in a computer system.
microcontroller — Microcontroller unit (MCU). A complete computer system, including a CPU, memory,
a clock oscillator, and input/output (I/O) on a single integrated circuit.
modulo counter — A counter that can be programmed to count to any number from zero to its maximum
possible modulus.
monitor ROM — A section of ROM that can execute commands from a host computer for testing
purposes.
MOR — See "mask option register (MOR)."
most significant bit (MSB) — The leftmost digit of a binary number.
multiplexer — A device that can select one of a number of inputs and pass the logic level of that input
on to the output.
N — The negative bit in the condition code register of the CPU08. The CPU sets the negative bit when
an arithmetic operation, logical operation, or data manipulation produces a negative result.
nibble — A set of four bits (half of a byte).
object code — The output from an assembler or compiler that is itself executable machine code, or is
suitable for processing to produce executable machine code.
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opcode — A binary code that instructs the CPU to perform an operation.
open-drain — An output that has no pullup transistor. An external pullup device can be connected to the
power supply to provide the logic 1 output voltage.
operand — Data on which an operation is performed. Usually a statement consists of an operator and
an operand. For example, the operator may be an add instruction, and the operand may be the
quantity to be added.
oscillator — A circuit that produces a constant frequency square wave that is used by the computer as
a timing and sequencing reference.
OTPROM — One-time programmable read-only memory. A nonvolatile type of memory that cannot be
reprogrammed.
overflow — A quantity that is too large to be contained in one byte or one word.
page zero — The first 256 bytes of memory (addresses $0000–$00FF).
parity — An error-checking scheme that counts the number of logic 1s in each byte transmitted. In a
system that uses odd parity, every byte is expected to have an odd number of logic 1s. In an even
parity system, every byte should have an even number of logic 1s. In the transmitter, a parity
generator appends an extra bit to each byte to make the number of logic 1s odd for odd parity or
even for even parity. A parity checker in the receiver counts the number of logic 1s in each byte.
The parity checker generates an error signal if it finds a byte with an incorrect number of logic 1s.
PC — See “program counter (PC).”
peripheral — A circuit not under direct CPU control.
phase-locked loop (PLL) — A oscillator circuit in which the frequency of the oscillator is synchronized
to a reference signal.
PLL — See "phase-locked loop (PLL)."
pointer — Pointer register. An index register is sometimes called a pointer register because its contents
are used in the calculation of the address of an operand, and therefore points to the operand.
polarity — The two opposite logic levels, logic 1 and logic 0, which correspond to two different voltage
levels, VDD and VSS.
polling — Periodically reading a status bit to monitor the condition of a peripheral device.
port — A set of wires for communicating with off-chip devices.
prescaler — A circuit that generates an output signal related to the input signal by a fractional scale factor
such as 1/2, 1/8, 1/10 etc.
program — A set of computer instructions that cause a computer to perform a desired operation or
operations.
program counter (PC) — A 16-bit register in the CPU08. The PC register holds the address of the next
instruction or operand that the CPU will use.
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pull — An instruction that copies into the accumulator the contents of a stack RAM location. The stack
RAM address is in the stack pointer.
pullup — A transistor in the output of a logic gate that connects the output to the logic 1 voltage of the
power supply.
pulse-width — The amount of time a signal is on as opposed to being in its off state.
pulse-width modulation (PWM) — Controlled variation (modulation) of the pulse width of a signal with
a constant frequency.
push — An instruction that copies the contents of the accumulator to the stack RAM. The stack RAM
address is in the stack pointer.
PWM period — The time required for one complete cycle of a PWM waveform.
RAM — Random access memory. All RAM locations can be read or written by the CPU. The contents of
a RAM memory location remain valid until the CPU writes a different value or until power is turned
off.
RC circuit — A circuit consisting of capacitors and resistors having a defined time constant.
read — To copy the contents of a memory location to the accumulator.
register — A circuit that stores a group of bits.
reserved memory location — A memory location that is used only in special factory test modes. Writing
to a reserved location has no effect. Reading a reserved location returns an unpredictable value.
reset — To force a device to a known condition.
ROM — Read-only memory. A type of memory that can be read but cannot be changed (written). The
contents of ROM must be specified before manufacturing the MCU.
SCI — See "serial communication interface module (SCI)."
serial — Pertaining to sequential transmission over a single line.
serial communications interface module (SCI) — A module in the M68HC08 Family that supports
asynchronous communication.
serial peripheral interface module (SPI) — A module in the M68HC08 Family that supports
synchronous communication.
set — To change a bit from logic 0 to logic 1; opposite of clear.
shift register — A chain of circuits that can retain the logic levels (logic 1 or logic 0) written to them and
that can shift the logic levels to the right or left through adjacent circuits in the chain.
signed — A binary number notation that accommodates both positive and negative numbers. The most
significant bit is used to indicate whether the number is positive or negative, normally logic 0 for
positive and logic 1 for negative. The other seven bits indicate the magnitude of the number.
software — Instructions and data that control the operation of a microcontroller.
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Glossary
software interrupt (SWI) — An instruction that causes an interrupt and its associated vector fetch.
SPI — See "serial peripheral interface module (SPI)."
stack — A portion of RAM reserved for storage of CPU register contents and subroutine return
addresses.
stack pointer (SP) — A 16-bit register in the CPU08 containing the address of the next available storage
location on the stack.
start bit — A bit that signals the beginning of an asynchronous serial transmission.
status bit — A register bit that indicates the condition of a device.
stop bit — A bit that signals the end of an asynchronous serial transmission.
subroutine — A sequence of instructions to be used more than once in the course of a program. The last
instruction in a subroutine is a return from subroutine (RTS) instruction. At each place in the main
program where the subroutine instructions are needed, a jump or branch to subroutine (JSR or
BSR) instruction is used to call the subroutine. The CPU leaves the flow of the main program to
execute the instructions in the subroutine. When the RTS instruction is executed, the CPU returns
to the main program where it left off.
synchronous — Refers to logic circuits and operations that are synchronized by a common reference
signal.
TIM — See "timer interface module (TIM)."
timer interface module (TIM) — A module used to relate events in a system to a point in time.
timer — A module used to relate events in a system to a point in time.
toggle — To change the state of an output from a logic 0 to a logic 1 or from a logic 1 to a logic 0.
tracking mode — Mode of low-jitter PLL operation during which the PLL is locked on a frequency. Also
see "acquisition mode."
two’s complement — A means of performing binary subtraction using addition techniques. The most
significant bit of a two’s complement number indicates the sign of the number (1 indicates
negative). The two’s complement negative of a number is obtained by inverting each bit in the
number and then adding 1 to the result.
unbuffered — Utilizes only one register for data; new data overwrites current data.
unimplemented memory location — A memory location that is not used. Writing to an unimplemented
location has no effect. Reading an unimplemented location returns an unpredictable value.
Executing an opcode at an unimplemented location causes an illegal address reset.
V —The overflow bit in the condition code register of the CPU08. The CPU08 sets the V bit when a two's
complement overflow occurs. The signed branch instructions BGT, BGE, BLE, and BLT use the
overflow bit.
variable — A value that changes during the course of program execution.
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VCO — See "voltage-controlled oscillator."
vector — A memory location that contains the address of the beginning of a subroutine written to service
an interrupt or reset.
voltage-controlled oscillator (VCO) — A circuit that produces an oscillating output signal of a frequency
that is controlled by a dc voltage applied to a control input.
waveform — A graphical representation in which the amplitude of a wave is plotted against time.
wired-OR — Connection of circuit outputs so that if any output is high, the connection point is high.
word — A set of two bytes (16 bits).
write — The transfer of a byte of data from the CPU to a memory location.
X — The lower byte of the index register (H:X) in the CPU08.
Z — The zero bit in the condition code register of the CPU08. The CPU08 sets the zero bit when an
arithmetic operation, logical operation, or data manipulation produces a result of $00.
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MC68HC908AZ32A
Rev. 2, 10/2006
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