Freescale MC68HC908EY16KFAE M68hc08 microcontroller Datasheet

MC68HC908EY16
MC68HC908EY8
Data Sheet
M68HC08
Microcontrollers
MC68HC908EY16
Rev. 10
10/2005
freescale.com
MC68HC908EY16
MC68HC908EY8
Data Sheet
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MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
List of Chapters
Chapter 1
General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Chapter 2
Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Chapter 3
Analog-to-Digital Converter (ADC) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Chapter 4
BEMF Counter Module (BEMF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Chapter 5
Configuration Registers (CONFIG1 and CONFIG2) . . . . . . . . . . . . . . . . . . . . . . . 57
Chapter 6
Computer Operating Properly (COP) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Chapter 7
Central Processor Unit (CPU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Chapter 8
Internal Clock Generator (ICG) Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Chapter 9
External Interrupt (IRQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Chapter 10
Keyboard Interrupt (KBD) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Chapter 11
Low-Voltage Inhibit (LVI) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Chapter 12
Input/Output (I/O) Ports (PORTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Chapter 13
Enhanced Serial Communications Interface (ESCI) Module. . . . . . . . . . . . . . . 125
Chapter 14
System Integration Module (SIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Chapter 15
Serial Peripheral Interface (SPI) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Chapter 16
Timebase Module (TBM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Chapter 17
Timer Interface A (TIMA) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Chapter 18
Timer Interface B (TIMB) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
Chapter 19
Development Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225
Chapter 20
Electrical Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Chapter 21
Ordering Information and Mechanical Specifications . . . . . . . . . . . . . . . . . . . . 253
Appendix A
MC68HC908EY8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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List of Chapters
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Table of Contents
Chapter 1
General Description
1.1
1.2
1.3
1.4
1.5
1.5.1
1.5.2
1.5.3
1.5.4
1.5.5
1.5.6
1.5.7
1.5.8
1.5.9
1.5.10
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MCU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply Pins (VDD and VSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oscillator Pins (PTC4/OSC1 and PTC3/OSC2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Reset Pin (RST). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Interrupt Pin (IRQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog Power Supply/Reference Pins (VDDA, VREFH, VSSA and VREFL) . . . . . . . . . . . . . . .
Port A I/O Pins (PTA6/SS, PTA5/SPSCK, PTA4/KBD4–PTA0/KBD0) . . . . . . . . . . . . . . . .
Port B I/O Pins (PTB7/AD7/TBCH1, PTB6/AD6/TBCH0, PTB5/AD5–PTB0/AD0) . . . . . . .
Port C I/O Pins (PTC4/OSC1, PTC3/OSC2, PTC2/MCLK, PTC1/MOSI, PTC0/MISO). . . .
Port D I/O Pins (PTD1/TACH1–PTD0/TACH0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E I/O Pins (PTE1/RxD–PTE0/TxD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
19
21
22
22
22
23
23
23
23
24
24
24
24
24
Chapter 2
Memory
2.1
2.2
2.3
2.4
2.5
2.6
2.6.1
2.6.2
2.6.3
2.6.4
2.6.5
2.6.6
2.6.7
2.6.8
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unimplemented Memory Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reserved Memory Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input/Output (I/O) Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Random Access Memory (RAM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Memory (FLASH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Page Erase Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Mass Erase Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Program/Read Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Block Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
FLASH Block Protect Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
25
25
25
35
35
36
37
38
39
41
41
42
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Table of Contents
Chapter 3
Analog-to-Digital Converter (ADC) Module
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.1
ADC Port I/O Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.2
Voltage Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3
Conversion Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4
Continuous Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.5
Result Justification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.6
Monotonicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.1
ADC Analog Power Pin (VDDA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.2
ADC Analog Ground Pin (VSSA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.3
ADC Voltage Reference Pin (VREFH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.4
ADC Voltage Reference Low Pin (VREFL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.5
ADC Voltage In (ADVIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.6
ADC External Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.6.1
VREFH and VREFL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.6.2
ANx. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.6.3
Grounding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.1
ADC Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.2
ADC Data Register High (ADRH) and Data Register Low (ADRL) . . . . . . . . . . . . . . . . . . .
3.7.2.1
Left Justified Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.2.2
Right Justified Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.2.3
Left Justified Signed Data Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.2.4
Eight Bit Truncation Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.3
ADC Clock Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
43
43
45
45
46
46
46
47
47
48
48
48
48
48
48
48
48
49
49
49
49
49
51
51
51
52
52
53
Chapter 4
BEMF Counter Module (BEMF)
4.1
4.2
4.3
4.4
4.5
4.5.1
4.5.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BEMF Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
55
55
55
55
55
55
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Chapter 5
Configuration Registers (CONFIG1 and CONFIG2)
5.1
5.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Chapter 6
Computer Operating Properly (COP) Module
6.1
6.2
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.3.7
6.3.8
6.4
6.5
6.6
6.7
6.7.1
6.7.2
6.8
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61
61
62
62
62
62
62
62
62
62
63
63
63
63
63
63
63
63
Chapter 7
Central Processor Unit (CPU)
7.1
7.2
7.3
7.3.1
7.3.2
7.3.3
7.3.4
7.3.5
7.4
7.5
7.5.1
7.5.2
7.6
7.7
7.8
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Index Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stack Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Program Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Condition Code Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arithmetic/Logic Unit (ALU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instruction Set Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Opcode Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
65
65
66
66
67
67
67
69
69
69
69
69
70
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Table of Contents
Chapter 8
Internal Clock Generator (ICG) Module
8.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.1
Clock Enable Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2
Internal Clock Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2.1
Digitally Controlled Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2.2
Modulo N Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2.3
Frequency Comparator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.2.4
Digital Loop Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.3
External Clock Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.3.1
External Oscillator Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.3.2
External Clock Input Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.4
Clock Monitor Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.4.1
Clock Monitor Reference Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.4.2
Internal Clock Activity Detector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.4.3
External Clock Activity Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.5
Clock Selection Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.5.1
Clock Selection Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3.5.2
Clock Switching Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4
Usage Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.1
Switching Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.2
Enabling the Clock Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.3
Using Clock Monitor Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.4
Quantization Error in DCO Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.4.1
Digitally Controlled Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.4.2
Binary Weighted Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.4.3
Variable-Delay Ring Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.4.4
Ring Oscillator Fine-Adjust Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.5
Switching Internal Clock Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.6
Nominal Frequency Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.6.1
Settling to Within 15 Percent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.6.2
Settling to Within 5 Percent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.6.3
Total Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4.7
Trimming Frequency on the Internal Clock Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6
CONFIG Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6.1
External Clock Enable (EXTCLKEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6.2
External Crystal Enable (EXTXTALEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6.3
Slow External Clock (EXTSLOW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6.4
Oscillator Enable In Stop (OSCENINSTOP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
77
77
80
80
81
81
81
82
82
83
84
84
85
85
86
87
87
87
88
88
89
90
90
90
91
91
91
92
92
92
93
93
94
94
94
94
95
95
95
95
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Freescale Semiconductor
8.7
8.7.1
8.7.2
8.7.3
8.7.4
8.7.5
8.7.6
Input/Output (I/O) Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
ICG Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
ICG Multiplier Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
ICG Trim Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
ICG Trim Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
ICG DCO Divider Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
ICG DCO Stage Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Chapter 9
External Interrupt (IRQ)
9.1
9.2
9.3
9.4
9.5
9.6
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Module During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
101
101
102
104
104
Chapter 10
Keyboard Interrupt (KBD) Module
10.1
10.2
10.3
10.4
10.5
10.5.1
10.5.2
10.6
10.7
10.7.1
10.7.2
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
105
105
105
108
108
108
108
108
109
109
110
Chapter 11
Low-Voltage Inhibit (LVI) Module
11.1
11.2
11.3
11.3.1
11.3.2
11.3.3
11.3.4
11.4
11.5
11.5.1
11.5.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Polled LVI Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forced Reset Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
False Reset Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LVI Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LVI Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111
111
111
112
112
112
112
113
113
113
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Table of Contents
Chapter 12
Input/Output (I/O) Ports (PORTS)
12.1
12.2
12.2.1
12.2.2
12.3
12.3.1
12.3.2
12.4
12.4.1
12.4.2
12.5
12.5.1
12.5.2
12.6
12.6.1
12.6.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port B Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
115
115
115
115
117
117
118
119
119
119
120
120
121
122
122
123
Chapter 13
Enhanced Serial Communications Interface (ESCI) Module
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3 Pin Name Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.1
Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2
Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2.1
Character Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2.2
Character Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2.3
Break Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2.4
Idle Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2.5
Inversion of Transmitted Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.2.6
Transmitter Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3
Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.1
Character Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.2
Character Reception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.3
Data Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.4
Framing Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.5
Baud Rate Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.6
Receiver Wakeup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.7
Receiver Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4.3.8
Error Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.5 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
125
125
125
127
128
128
129
129
129
130
130
130
131
132
132
132
134
134
135
136
136
136
136
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13.6
13.7
13.7.1
13.7.2
13.8
13.8.1
13.8.2
13.8.3
13.8.4
13.8.5
13.8.6
13.8.7
13.9
13.9.1
13.9.2
13.9.3
13.9.4
ESCI During Break Module Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
PTE0/TxD (Transmit Data). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
PTE1/RxD (Receive Data) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
ESCI Control Register 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
ESCI Control Register 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
ESCI Control Register 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
ESCI Status Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
ESCI Status Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
ESCI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
ESCI Baud Rate Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
ESCI Arbiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
ESCI Arbiter Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
ESCI Arbiter Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Bit Time Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Arbitration Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Chapter 14
System Integration Module (SIM)
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2 SIM Bus Clock Control and Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2.1
Bus Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2.2
Clock Startup from POR or LVI Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2.3
Clocks in Stop Mode and Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3 Reset and System Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.1
External Pin Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2
Active Resets from Internal Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2.1
Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2.2
Computer Operating Properly (COP) Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2.3
Illegal Opcode Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2.4
Illegal Address Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2.5
Forced Monitor Mode Entry Reset (MENRST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3.2.6
Low-Voltage Inhibit (LVI) Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4 SIM Counter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.1
SIM Counter During Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2
SIM Counter During Stop Mode Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.3
SIM Counter and Reset States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5 Program Exception Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5.1
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5.1.1
Hardware Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5.1.2
SWI Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5.2
Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5.3
Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5.4
Status Flag Protection in Break Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
155
155
157
157
157
157
157
158
158
159
159
159
159
160
160
160
160
160
160
161
162
163
163
164
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Table of Contents
14.6 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.7 SIM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.7.1
SIM Break Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.7.2
SIM Reset Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.7.3
SIM Break Flag Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
164
164
165
166
166
167
168
Chapter 15
Serial Peripheral Interface (SPI) Module
15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3 Pin Name and Register Name Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4.1
Master Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4.2
Slave Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5 Transmission Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.1
Clock Phase and Polarity Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.2
Transmission Format When CPHA = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.3
Transmission Format When CPHA = 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.4
Transmission Initiation Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6 Error Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6.1
Overflow Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6.2
Mode Fault Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.8 Queuing Transmission Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.9 Resetting the SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.10 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.10.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.10.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.11 SPI During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.12 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.12.1
MISO (Master In/Slave Out). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.12.2
MOSI (Master Out/Slave In). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.12.3
SPSCK (Serial Clock) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.12.4
SS (Slave Select) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.12.5
VSS (Clock Ground) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.13 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.13.1
SPI Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.13.2
SPI Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.13.3
SPI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
169
169
169
171
172
172
173
173
174
174
175
176
177
178
180
180
181
182
182
182
182
182
183
183
183
183
184
184
184
186
188
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Chapter 16
Timebase Module (TBM)
16.1
16.2
16.3
16.4
16.5
16.6
16.6.1
16.6.2
16.7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TBM Interrupt Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timebase Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
189
189
189
190
191
191
191
191
192
Chapter 17
Timer Interface A (TIMA) Module
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.1
TIMA Counter Prescaler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.2
Input Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.3
Output Compare. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.3.1
Unbuffered Output Compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.3.2
Buffered Output Compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.4
Pulse Width Modulation (PWM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.4.1
Unbuffered PWM Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.4.2
Buffered PWM Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.3.4.3
PWM Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.4 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.6 TIMA During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.7 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.7.1
TIMA Channel I/O Pins (PTD0/TACH0, PTD1/TACH1) . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8.1
TIMA Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8.2
TIMA Counter Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8.3
TIMA Counter Modulo Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8.4
TIMA Channel Status and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.8.5
TIMA Channel Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
193
193
193
195
195
196
196
197
197
198
198
199
200
200
200
200
200
201
201
201
201
203
203
204
207
Chapter 18
Timer Interface B (TIMB) Module
18.1
18.2
18.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
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Table of Contents
18.3.1
TIMB Counter Prescaler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.2
Input Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.3
Output Compare. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.3.1
Unbuffered Output Compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.3.2
Buffered Output Compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.4
Pulse Width Modulation (PWM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.4.1
Unbuffered PWM Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.4.2
Buffered PWM Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3.4.3
PWM Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.5 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.6 TIMB During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.7 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.7.1
TIMB Channel I/O Pins (PTB7/TBCH1–PTB6/TBCH0) . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.1
TIMB Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.2
TIMB Counter Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.3
TIMB Counter Modulo Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.4
TIMB Channel Status and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8.5
TIMB Channel Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
211
211
212
212
213
213
214
214
215
215
216
216
216
216
216
216
217
217
219
219
220
223
Chapter 19
Development Support
19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2 Break Module (BRK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1.1
Flag Protection During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1.2
TIM During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1.3
COP During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2
Break Module Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.1
Break Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.2
Break Address Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.3
Break Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.4
Break Flag Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.3
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3 Monitor Module (MON) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.1
Normal Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.2
Forced Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.3
Monitor Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.4
Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.5
Break Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.6
Baud Rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.7
Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.2
Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
225
225
225
227
227
227
227
228
228
229
229
229
230
230
233
234
235
235
235
235
236
239
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Chapter 20
Electrical Specifications
20.1
20.2
20.3
20.4
20.5
20.6
20.7
20.8
20.9
20.9.1
20.10
20.11
20.12
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Operating Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thermal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trimmed Accuracy of the Internal Clock Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trimmed Internal Clock Generator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog-to-Digital Converter (ADC) Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SPI Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Memory Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
241
241
242
242
242
244
244
245
246
246
247
248
251
Chapter 21
Ordering Information and Mechanical Specifications
21.1
21.2
21.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
MC Order Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
32-Pin QFP (Case Number 873) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Appendix A
MC68HC908EY8
A.1
A.2
A.3
A.4
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MC Order Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
255
255
255
258
Glossary
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Revision History
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Table of Contents
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
18
Freescale Semiconductor
Chapter 1
General Description
1.1 Introduction
The MC68HC908EY16 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.
The information contained in this document pertains to the MC68HC908EY8 with the exceptions noted in
Appendix A MC68HC908EY8.
1.2 Features
For convenience, features have been organized to reflect:
• Standard features of the MC68HC908EY16
• Features of the CPU08
Standard features of the MC68HC908EY16 include:
• High-performance M68HC08 architecture optimized for C-compilers
• Fully upward-compatible object code with M6805, M146805, and M68HC05 Families
• 8-MHz internal bus frequency at 5V
• Internal oscillator requiring no external components:
– Software selectable bus frequencies
– 25 percent accuracy with a trimming capability of better than 1 percent
– Clock monitor
– Option to allow use of external clock source or external crystal/ceramic resonator
• 15,872 bytes of on-chip FLASH memory with in-circuit programming
• FLASH program memory security(1)
• 512 bytes of on-chip random-access memory (RAM)
• Low voltage inhibit (LVI) module
• Internal clock generator module (ICG)
• Two 16-bit, 2-channel timer (TIMA and TIMB) interface modules with selectable input capture,
output compare, and pulse-width modulation (PWM) capability on each channel
• 8-channel, 10-bit successive approximation analog-to-digital converter (ADC)
• Enhanced serial communications interface module (ESCI) for local interconnect network (LIN)
connectivity
• Serial peripheral interface (SPI)
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
19
General Description
•
•
•
•
•
•
•
•
•
•
•
•
Timebase Module (TBM)
5-bit keyboard interrupt (KBI) with wakeup feature
24 general-purpose input/output (I/O) pins
External asynchronous interrupt pin with internal pullup (IRQ)
System protection features:
– Optional computer operating properly (COP) reset
– Illegal opcode detection with reset
– Illegal address detection with reset
32-pin quad flat pack (QFP) package
Low-power design; fully static with stop and wait modes
Internal pullups on IRQ and RST to reduce customer system cost
Standard low-power modes of operation:
– Wait mode
– Stop mode
Master reset pin (RST) and power-on reset (POR)
BREAK module (BRK) to allow single breakpoint setting during in-circuit debugging
Higher current source capability on nine port lines for LED drive (PTA6/SS, PTA5/SPSCK,
PTA4/KBD4, PTA3/KBD3, PTA2/KBD2, PTA1/KBD1, PTA0/KBD0, PTC1/MOSI, and PTC0/MISO)
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
• Third party C language support
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
20
Freescale Semiconductor
MCU Block Diagram
1.3 MCU Block Diagram
Figure 1-1 shows the structure of the MC68HC908EY16.
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
VDD
VSS
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
SINGLE BREAKPOINT
BREAK MODULE
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 1-1. MCU Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
21
General Description
1.4 Pin Assignments
PTA4/KBD4
VREFH
VDDA
VDD
VSS
VSSA
VREFL
30
29
28
27
26
25
PTA2/KBD2 1
31
32 PTA3/KBD3
Figure 1-2 shows the pin assignments for the MC68HC908EY16.
24
PTE1/RxD
PTB7/AD7/TBCH1
4
21
PTC1/MOSI
PTB6/AD6/TBCH0
5
20
PTA5/SPSCK
PTC4/OSC1
6
19
PTA6/SS
PTC3/OSC2
7
18
PTB0/AD0
PTC2/MCLK
8
17
IRQ
PTD1/TACH1
PTD0/TACH0
PTB1/AD1
RST
PTB2/AD2
PTB3/AD3
PTB4/AD4
PTB5/AD5
16
PTC0/MISO
15
22
14
3
13
PTA0/KBD0
12
PTE0/TxD
11
23
10
2
9
PTA1/KBD1
Figure 1-2. Pin Assignments
1.5 Pin Functions
Descriptions of the pin functions are provided here.
1.5.1 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 Figure 1-3
shows. 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
22
Freescale Semiconductor
Pin Functions
MCU
VSS
VDD
C1
0.1 µF
+
C2
VDD
Note: Component values shown represent typical applications.
Figure 1-3. Power Supply Bypassing
1.5.2 Oscillator Pins (PTC4/OSC1 and PTC3/OSC2)
The OSC1 and OSC2 pins are available through programming options in the configuration register. These
pins then become the connections to an external clock source or crystal/ceramic resonator.
When selecting PTC4 and PTC3 as I/O, OSC1 and OSC2 functions are not available.
1.5.3 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. This pin contains an
internal pullup resistor that is always activated, even when the reset pin is pulled low. See Chapter 14
System Integration Module (SIM).
1.5.4 External Interrupt Pin (IRQ)
IRQ is an asynchronous external interrupt pin. This pin contains an internal pullup resistor that is always
activated, even when the IRQ pin is pulled low. See Chapter 9 External Interrupt (IRQ).
1.5.5 Analog Power Supply/Reference Pins (VDDA, VREFH, VSSA and VREFL)
VDDA and VSSA are the power supply pins for the analog-to-digital converter (ADC). Decoupling of these
pins should be as per the digital supply.
NOTE
VREFH is the high reference supply for the ADC. VDDA should be tied to the
same potential as VDD via separate traces.
VREFL is the low reference supply for the ADC. VSSA should be tied to the
same potential as VSS via separate traces.
See Chapter 3 Analog-to-Digital Converter (ADC) Module.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
23
General Description
1.5.6 Port A I/O Pins (PTA6/SS, PTA5/SPSCK, PTA4/KBD4–PTA0/KBD0)
Port A input/output (I/O) pins (PTA6/SS, PTA5/SPSCK, PTA4/KBD4, PTA3/KBD3, PTA2/KBD2,
PTA1/KBD1, and PTA0/KBD0) are special-function, bidirectional I/O port pins. PTA5 and PTA6 are
shared with the serial peripheral interface (SPI). PTA4-PTA0 can be programmed to serve as keyboard
interrupt pins.
See Chapter 12 Input/Output (I/O) Ports (PORTS) and Chapter 9 External Interrupt (IRQ).
1.5.7 Port B I/O Pins (PTB7/AD7/TBCH1, PTB6/AD6/TBCH0, PTB5/AD5–PTB0/AD0)
PTB7/AD7/TBCH1, PTB6/AD6/TBCH0, and PTB5/AD5–PTB0/AD0 are special-function, bidirectional I/O
port pins that can also be used for ADC inputs. PTB7/AD7/TBCH1 and PTB6/AD6/TBCH0 are special
function bidirectional I/O port pins that can also be used for timer interface pins.
See and Chapter 3 Analog-to-Digital Converter (ADC) Module and Chapter 17 Timer Interface A (TIMA)
Module.
1.5.8 Port C I/O Pins (PTC4/OSC1, PTC3/OSC2, PTC2/MCLK, PTC1/MOSI, PTC0/MISO)
PTC4/OSC1–PTC0/MISO are special-function, bidirectional I/O port pins. See Chapter 12 Input/Output
(I/O) Ports (PORTS). PTC3/OSC2 and PTC4/OSC1 are shared with the on-chip oscillator circuit through
configuration options. See Chapter 8 Internal Clock Generator (ICG) Module.
When applications require:
• PTC3/OSC2 can be programmed to be OSC2
• PTC4/OSC1 can be programmed to be OSC1
PTC2/MCLK is software selectable to be MCLK, or bus clock out. PTC1/MOSI can be programmed to be
the MOSI signal for the SPI. PTC0/MISO can be programmed to be the MISO signal for the SPI.
1.5.9 Port D I/O Pins (PTD1/TACH1–PTD0/TACH0)
PTD1/TACH1–PTD0/TACH0 are special-function, bidirectional I/O port pins that can also be programmed
to be timer pins.
See Chapter 17 Timer Interface A (TIMA) Module and Chapter 12 Input/Output (I/O) Ports (PORTS).
1.5.10 Port E I/O Pins (PTE1/RxD–PTE0/TxD)
PTE1/RxD–PTE0/TxD are special-function, bidirectional I/O port pins that can also be programmed to be
enhanced serial communication interface (ESCI) pins.
See Chapter 13 Enhanced Serial Communications Interface (ESCI) Module and Chapter 12 Input/Output
(I/O) Ports (PORTS).
NOTE
Any unused inputs and I/O ports should be tied to an appropriate logic level
(either VDD or VSS). Although the I/O ports of the MC68HC908EY16 do not
require termination, termination is recommended to reduce the possibility
of electro-static discharge damage.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
24
Freescale Semiconductor
Chapter 2
Memory
2.1 Introduction
The M68HC08 central processor unit (CPU08) can address 64 Kbytes of memory space. The memory
map, shown in Figure 2-1, includes:
• 16 Kbytes of FLASH memory, 15, 872 bytes of user space
• 512 bytes of random-access memory (RAM)
• 36 bytes of user-defined vectors
• 310 bytes of monitor routines in read-only memory (ROM)
• 1024 bytes of integrated FLASH burn-in routines in ROM
2.2 Unimplemented Memory Locations
Accessing an unimplemented location can cause an illegal address reset. In the memory map
(Figure 2-1) and in register figures in this document, unimplemented locations are shaded.
2.3 Reserved Memory Locations
Accessing a reserved location can have unpredictable effects on microcontroller unit (MCU) operation. In
the Figure 2-1 and in register figures in this document, reserved locations are marked with the word
reserved or with the letter R.
2.4 Input/Output (I/O) Section
Most of the control, status, and data registers are in the zero page area of $0000–$003F. Additional I/O
registers have these addresses:
• $FE00; SIM break status register, SBSR
• $FE01; SIM reset status register, SRSR
• $FE03; SIM break flag control register, SBFCR
• $FE08; FLASH control register, FLCR
• $FE09; break address register high, BRKH
• $FE0A; break address register low, BRKL
• $FE0B; break status and control register, BRKSCR
• $FE0C; LVI status register, LVISR
• $FF7E; FLASH block protect register, FLBPR
• $FF80; ICG trim value (optional), ICGT
Data registers are shown in Figure 2-2. and Table 2-1 is a list of vector locations.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
25
Memory
$0000
$FE09
Break Address Register High (BRKH)
$FE0A
Break Address Register Low (BRKL)
$003F
$FE0B
Break Status and Control Register (BRKSCR)
$0040
$FE0C
LVI Status Register (LVISR)
↓
↓
I/O Registers
64 Bytes
RAM
512 Bytes
$FE0D
$0240
↓
$FE0F
Unimplemented
3520 Bytes
$FE10
↓
$0FFF
$1000
↓
$FE1F
Reserved for Integrated FLASH Burn-in Routines
1024 Bytes
↓
$1400
FF55
Unimplemented
44,032 Bytes
Monitor ROM 310 Bytes
FF56
$BFFF
↓
$C000
FF7D
↓
Reserved
16 Bytes
Reserved for Compatibility with Monitor Code
for A-Family Parts
$FE20
$13FF
↓
Reserved
3 Bytes
↓
$023F
FLASH Memory
15,872 Bytes
$FDFF
Unimplemented
40 Bytes
$FF7E
FLASH Block Protect Register (FLBPR)
$FF80
ICG Trim Value (Optional) (ICGT)
$FE00
SIM Break Status Register (SBSR)
$FF7F
$FE01
SIM Reset Status Register (SRSR)
↓
$FE02
Reserved
$FFDB
$FE03
SIM Break Flag Control Register (SBFCR)
$FFDC
$FE04
RESERVED
↓
$FE05
RESERVED
$FFFF
$FE06
RESERVED
$FE07
Reserved for FLASH Test Control Register (FLTCR)
$FE08
FLASH Control Register (FLCR)
Unimplemented
93 Bytes
FLASH Vectors
36 Bytes
Note:
Locations $FFF6–$FFFD are reserved for eight
security bytes.
Figure 2-1. Memory Map
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
26
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
$0000
$0001
$0002
$0003
$0004
$0005
$0006
$0007
$0008
Register Name
Bit 7
Read:
Port A Data Register
(PTA) Write:
See page 115.
Reset:
Read:
Port B Data Register
(PTB) Write:
See page 117.
Reset:
0
6
5
4
3
2
1
Bit 0
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
PTB2
PTB1
PTB0
PTC2
PTC1
PTC0
PTD1
PTD0
Unaffected by reset
PTB7
PTB6
PTB5
PTB4
PTB3
Unaffected by reset
Read:
Port C Data Register
(PTC) Write:
See page 119.
Reset:
0
Port D Data Register Read:
(PTD)
Write:
See page 120.
Reset:
0
Read:
Data Direction
Register A (DDRA) Write:
See page 115.
Reset:
0
0
0
PTC4
PTC3
Unaffected by reset
0
0
0
0
0
Unaffected by reset
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
0
0
0
0
0
0
0
0
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
0
0
0
0
0
0
0
0
Read:
Data Direction
MCLKEN
Register C (DDRC) Write:
See page 119.
Reset:
0
0
0
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
0
0
0
0
0
0
Data Direction Read:
Register D (DDRD)
Write:
See page 121.
Reset:
0
0
0
0
0
0
DDRD1
DDRD0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
PTE1
PTE0
R
R
DDRE1
DDRE0
Read:
Data Direction
Register B (DDRB) Write:
See page 118.
Reset:
Read:
Port E Data Register
(PTE) Write:
See page 122.
Reset:
Unaffected by reset
$0009
Reserved
R
R
R
R
R
R
0
0
0
0
0
0
$000A
Read:
Data Direction
Register E (DDRE) Write:
See page 123.
Reset:
0
0
0
0
0
0
0
0
BEMF7
BEMF6
BEMF5
BEMF4
BEMF3
BEMF2
BEMF1
BEMF0
0
0
0
0
0
0
0
0
$000B
Read:
BEMF Register
(BEMF) Write:
See page 55.
Reset:
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 1 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
27
Memory
Addr.
$000C
$000D
$000E
$000F
$0010
$0011
$0012
$0013
$0014
$0015
$0016
$0017
Register Name
Reserved
Read:
SPI Control Register
(SPCR) Write:
See page 184.
Reset:
Read:
SPI Status and Control
Register (SPSCR) Write:
See page 186.
Reset:
Read:
SPI Data Register
(SPDR) Write:
See page 188.
Reset:
Read:
ESCI Control Register 1
(SCC1) Write:
See page 138.
Reset:
Read:
ESCI Control Register 2
(SCC2) Write:
See page 140.
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
R
R
R
R
R
R
R
R
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
0
0
1
0
1
0
0
0
OVRF
MODF
SPTE
MODFEN
SPR1
SPR0
SPRF
ERRIE
0
0
0
0
1
0
0
0
R7
R6
R5
R4
R3
R2
R1
R0
T7
T6
T5
T4
T3
T2
T1
T0
Indeterminate after reset
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
0
0
0
0
0
0
0
0
T8
R
R
ORIE
NEIE
FEIE
PEIE
Read:
ESCI Control Register 3
(SCC3) Write:
See page 142.
Reset:
R8
U
0
0
0
0
0
0
0
Read:
ESCI Status Register 1
(SCS1) Write:
See page 143.
Reset:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
1
1
0
0
0
0
0
0
Read:
ESCI Status Register 2
(SCS2) Write:
See page 145.
Reset:
0
0
0
0
0
0
BKF
RPF
0
0
0
0
0
0
0
0
Read:
ESCI Data Register
(SCDR) Write:
See page 146.
Reset:
R7
R6
R5
R4
R3
R2
R1
R0
T7
T6
T5
T4
T3
T2
T1
T0
Read:
ESCI Baud Rate Register
(SCBR) Write:
See page 146.
Reset:
Read:
ESCI Prescale Register
(SCPSC) Write:
See page 147.
Reset:
Unaffected by reset
R
LINR
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
0
0
PDS2
PDS1
PDS0
PSSB4
PSSB3
PSSB2
PSSB1
PSSB0
0
0
0
0
0
0
0
0
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 2 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
28
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
$0018
$0019
$001A
$001B
$001C
$001D
$001E
$001F
Register Name
Bit 7
ESCII Arbiter Control Read:
Register
Write:
(SCIACTL)
See page 151. Reset:
Read:
ESCI Arbiter Data Register
(SCIACTL) Write:
See page 152.
Reset:
Keyboard Status Read:
and Control Register
Write:
(INTKBSCR)
See page 109. Reset:
Read:
Keyboard Interrupt Enable
Register (INTKBIER) Write:
See page 110.
Reset:
Read:
Timebase Control Register
Write:
(TBCR)
See page 192. Reset:
Read:
IRQ Status and Control
Register (INTSCR) Write:
See page 104.
Reset:
6
ALOST
AM1
5
4
AM0
ACLK
3
2
1
Bit 0
AFIN
ARUN
AROVFL
ARD8
0
0
0
0
0
0
0
0
ARD7
ARD6
ARD5
ARD4
ARD3
ARD2
ARD1
ARD0
0
0
0
0
0
0
0
0
0
0
0
0
KEYF
0
IMASKK
MODEK
ACKK
0
0
0
0
0
0
0
0
0
0
0
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
0
0
0
0
0
0
0
0
TBR2
TBR1
TBR0
TBIE
TBON
R
0
0
0
0
0
0
0
0
0
0
0
0
IRQF
0
IMASK
MODE
TBIF
0
TACK
ACK
0
0
0
0
0
0
0
0
R
ESCI
BDSRC
EXTXTALEN
EXTSLOW
EXTCLKEN
TMBCLKSEL
OSCENINSTOP
SSBPUENB
0
0
0
0
0
0
0
1
COPRS
LVISTOP
LVIRSTD
LVIPWRD
LVI5OR3(1)
SSREC
STOP
COPD
0
0
0
0
0
0
0
0
TOIE
TSTOP
R
PS2
PS1
PS0
0
0
1
0
0
0
0
0
Read:
Timer A Counter Register
High (TACNTH) Write:
See page 203.
Reset:
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
0
0
0
0
0
0
0
0
Read:
Timer A Counter Register
Low (TACNTL) Write:
See page 203.
Reset:
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
0
0
0
0
0
Read:
Configuration Register 2
Write:
(CONFIG2)
See page 57. Reset:
Read:
Configuration Register 1
(CONFIG1) Write:
See page 58.
Reset:
1. The LVI5OR3 bit is cleared only by a power-on reset (POR).
Read:
Timer A Status and Control
$0020
Register (TASC) Write:
See page 201.
Reset:
$0021
$0022
TOF
0
= Unimplemented
0
TRST
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 3 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
29
Memory
Addr.
$0023
$0024
$0025
$0026
$0027
$0028
$0029
$002A
Register Name
Read:
Timer A Counter Modulo
Register High (TAMODH) Write:
See page 203.
Reset:
Read:
Timer A Counter Modulo
Register Low (TAMODL) Write:
See page 203.
Reset:
Timer A Channel 0 Status Read:
and Control Register
Write:
(TASC0)
See page 204. Reset:
Read:
Timer A Channel 0
Register High (TACH0H) Write:
See page 207.
Reset:
Read:
Timer A Channel 0
Register Low (TACH0L) Write:
See page 207.
Reset:
Timer A Channel 1 Status Read:
and Control Register
Write:
(TASC1)
See page 207. Reset:
Read:
Timer A Channel 1
Register High (TACH1H) Write:
See page 207.
Reset:
Read:
Timer A Channel 1
Register Low (TACH1L) Write:
See page 207.
Reset:
Read:
Timer B Status and Control
$002B
Register (TBSC) Write:
See page 217.
Reset:
$002C
$002D
$002E
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
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1
1
1
1
1
1
1
1
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
BIT 2
BIT 1
BIT 0
CH0F
0
Indeterminate after reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Indeterminate after reset
CH1F
0
0
CH1IE
R
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
0
0
0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
BIT 2
BIT 1
BIT 0
R
PS2
PS1
PS0
Indeterminate after reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Indeterminate after reset
TOF
0
TOIE
TSTOP
0
0
1
0
0
0
0
0
Read:
Timer B Counter Register
High (TBCNTH) Write:
See page 219.
Reset:
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
0
0
0
0
0
0
0
0
Read:
Timer B Counter Register
Low (TBCNTL) Write:
See page 219.
Reset:
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
0
0
0
0
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
Read:
Timer B Counter Modulo
Register High (TBMODH) Write:
See page 219.
Reset:
0
= Unimplemented
TRST
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 4 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
30
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
$002F
$0030
$0031
$0032
$0033
$0034
$0035
$0036
$0037
$0038
$0039
$003A
Register Name
Read:
Timer B Counter Modulo
Register Low (TBMODL) Write:
See page 219.
Reset:
Timer B Channel 0 Status Read:
and Control Register
Write:
(TBSC0)
See page 220. Reset:
Read:
Timer B Channel 0
Register High (TBCH0H) Write:
See page 223.
Reset:
Read:
Timer B Channel 0
Register Low (TBCH0L) Write:
See page 223.
Reset:
Timer B Channel 1 Status Read:
and Control Register
Write:
(TBSC1)
See page 220. Reset:
Read:
Timer B Channel 1
Register High (TBCH1H) Write:
See page 223.
Reset:
Read:
Timer B Channel 1
Register Low (TBCH1L) Write:
See page 223.
Reset:
Read:
ICG Control Register
(ICGCR) Write:
See page 97.
Reset:
Read:
ICG Multiplier Register
(ICGMR) Write:
See page 98.
Reset:
Read:
ICG Trim Register (ICGTR)
Write:
See page 99.
Reset:
Read:
ICG Divider Control
Register (ICGDVR) Write:
See page 99.
Reset:
Read:
ICG DCO Stage Control
Register (ICGDSR) Write:
See page 100.
Reset:
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
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
BIT 2
BIT 1
BIT 0
CH0F
0
Indeterminate after reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Indeterminate after reset
CH1F
0
0
CH1IE
R
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
0
0
0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
BIT 2
BIT 1
BIT 0
Indeterminate after reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Indeterminate after reset
CMIE
CMF
ICGS
CS
ICGON
0
0
0
1
0
0
0
N6
N5
N4
N3
N2
N1
N0
0
0
0
1
0
1
0
1
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
1
0
0
0
0
0
0
0
DDIV3
DDIV2
DDIV1
DDIV0
0
0
ECGON
ECGS
CMON
0
0
0
0
U
U
U
U
DSTG7
DSTG6
DSTG5
DSTG4
DDSTG3
DSTG2
DSTG1
DSTG0
R
R
R
R
R
R
R
R
U
U
U
U
U
U
U
U
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 5 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
31
Memory
Addr.
$003B
$003C
$003D
$003E
$003F
$FE00
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
R
R
R
R
R
R
R
R
COCO
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
0
0
0
1
1
1
1
1
Read:
Analog-to-Digital Data
Register High (ADRH) Write:
See page 51.
Reset:
0
0
0
0
0
0
AD9
AD8
Read:
Analog-to-Digital Data
Register Low (ADRL) Write:
See page 53.
Reset:
AD7
AD2
AD1
AD0
Reserved
Analog-to-Digital Status Read:
and Control Register
Write:
(ADSCR)
See page 49. Reset:
Read:
Analog-to-Digital Clock
Register (ADCLK) Write:
See page 53.
Reset:
Read:
SIM Break Status Register
(SBSR) Write:
See page 166.
Reset:
Unaffected by reset
AD6
AD5
AD4
AD3
Unaffected by reset
0
ADIV2
ADIV1
ADIV0
ADICLK
MODE1
MODE0
R
0
0
0
0
0
1
0
R
R
R
R
R
R
0
0
0
0
0
0
0
0
POR
PIN
COP
ILOP
ILAD
MENRST
LVI
0
1
0
0
0
0
0
0
0
BCFE
R
R
R
R
R
R
R
0
0
0
0
HVEN
MASS
ERASE
PGM
0
0
0
0
0
0
0
0
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
0
0
0
0
0
0
0
0
SBSW
NOTE
0
R
Note: Writing a 0 clears SBSW.
$FE01
Read:
SIM Reset Status Register
(SRSR) Write:
See page 167.
POR:
$FE02
Reserved
$FE03
SIM Break Flag Control
Register (SBFCR)
$FE04
Reserved
↓
$FE07
$FE08
$FE09
Reserved
Read:
FLASH Control Register
(FLCR) Write:
See page 36.
Reset:
Read:
Break Address Register
High (BRKH) Write:
See page 228.
Reset:
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 6 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
32
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
Register Name
$FE0A
Read:
Break Address Register
Low (BRKL) Write:
See page 228.
Reset:
$FE0B
$FE0C
$FF7E
$FF7F
$FF80
Read:
Break Status and Control
Register (BSCR) Write:
See page 228.
Reset:
Read:
LVI Status Register
(LVISR) Write:
See page 112.
Reset:
Read:
FLASH Block Protect
(1)
Register (FLBPR)
Write:
See page 99.
Reset:
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
0
0
0
0
0
0
0
0
BRKE
BRKA
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LVIOUT
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
BPR7
BPR6
BPR5
BPR4
BPR3
BPR2
BPR1
BPR0
BPR2
BPR1
BPR0
Unaffected by reset
Reserved
Read:
ICG Trim Value
(2) Write:
(ICGT)
See page 41.
Reset:
BPR7
BPR6
BPR5
BPR4
BPR3
Unaffected by reset
1. Non-volatile FLASH register.
$FFFF
Read:
COP Control Register
(COPCTL) Write:
See page 63.
Reset:
Low byte of reset vector
Writing clears COP counter (any value)
Unaffected by reset
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 7 of 7)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
33
Memory
Table 2-1. Vector Addresses
Vector Priority
Lowest
Vector
IF16
IF15
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
IF6
IF5
IF4
IF3
IF2
IF1
—
Highest
—
Address
Vector
$FFDC
Timebase interrupt vector (high)
$FFDD
Timebase interrupt vector (low)
$FFDE
SPI transmit vector (high)
$FFDF
SPI transmit vector (low)
$FFE0
SPI receive vector (high)
$FFE1
SPI receive vector (low)
$FFE2
ADC conversion complete vector (high)
$FFE3
ADC conversion complete vector (low)
$FFE4
Keyboard vector (high)
$FFE5
Keyboard vector (low)
$FFE6
ESCI transmit vector (high)
$FFE7
ESCI transmit vector (low)
$FFE8
ESCI receive vector (high)
$FFE9
ESCI receive vector (low)
$FFEA
ESCI error vector (high)
$FFEB
ESCI error vector (low)
$FFEC
TIMB overflow vector (high)
$FFED
TIMB overflow vector (low)
$FFEE
TIMB channel 1 vector (high)
$FFEF
TIMB channel 1 vector (low)
$FFF0
TIMB channel 0 vector (high)
$FFF1
TIMB channel 0 vector (low)
$FFF2
TIMA overflow vector (high)
$FFF3
TIMA overflow vector (low)
$FFF4
TIMA channel 1 vector (high)
$FFF5
TIMA channel 1 vector (low)
$FFF6
TIMA channel 0 vector (high)
$FFF7
TIMA channel 0 vector (low)
$FFF8
CMIREQ (high)
$FFF9
CMIREQ (low)
$FFFA
IRQ vector (high)
$FFFB
IRQ vector (low)
$FFFC
SWI vector (high)
$FFFD
SWI vector (low)
$FFFE
Reset vector (high)
$FFFF
Reset vector (low)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
34
Freescale Semiconductor
Random Access Memory (RAM)
2.5 Random Access Memory (RAM)
Addresses $0040–$00FF and $0100–$023F 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 192 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 central
processor unit (CPU) registers.
NOTE
For M6805, M146805, and M68HC05 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.
2.6 FLASH Memory (FLASH)
The FLASH memory is an array of 15,872 bytes with an additional 36 bytes of user vectors and one byte
used for block protection.
NOTE
An erased bit reads as 1 and a programmed bit reads as 0.
The program and erase operations are facilitated through control bits in the FLASH control register
(FLCR). See 2.6.1 FLASH Control Register.
The FLASH is organized internally as an 16,384-word by 8-bit complementary metal-oxide semiconductor
(CMOS) page erase, byte (8-bit) program embedded FLASH memory. Each page consists of 64 bytes.
The page erase operation erases all words within a page. A page is composed of two adjacent rows.
A security feature prevents viewing of the FLASH contents.(1)
In the 125°C to 135°C temperature range, the FLASH is guaranteed as read only.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
35
Memory
2.6.1 FLASH Control Register
The FLASH control register (FLCR) controls FLASH program and erase operations.
Address:
Read:
$FE08
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 2-3. 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 be set only 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 16-Kbyte 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 equal to 1 or set to 1 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
36
Freescale Semiconductor
FLASH Memory (FLASH)
2.6.2 FLASH Page Erase Operation
Use this step-by-step procedure to erase a page (64 bytes) of FLASH memory to read as logic 1:
1. Set the ERASE bit and clear the MASS bit in the FLASH control register.
2. Read the FLASH block protect register.
3. Write any data to any FLASH location within the address range of the block to be erased.
4. Wait for a time, tNVS (minimum 10 µs).
5. Set the HVEN bit.
6. Wait for a time, tErase (minimum 1 ms or 4 ms).
7. Clear the ERASE bit.
8. Wait for a time, tNVH (minimum 5 µs).
9. Clear the HVEN bit.
10. After time, tRCV (typical 1 µs), the memory can be accessed in read mode again.
NOTE
While these operations must be performed in the order shown, other
unrelated operations may occur between the steps.
NOTE
Due to the security feature (see 19.3 Monitor Module (MON)) the last page
of the FLASH (0xFFDC–0xFFFF), which contains the security bytes,
cannot be erased by Page Erase Operation. It can only be erased with the
Mass Erase Operation.
In applications that require more than 1000 program/erase cycles, use the 4 ms page erase specification
to get improved long-term reliability. Any application can use this 4 ms page erase specification. However,
in applications where a FLASH location will be erased and reprogrammed less than 1000 times, and
speed is important, use the 1 ms page erase specification to get a shorter cycle time.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
37
Memory
2.6.3 FLASH Mass Erase Operation
Use this step-by-step procedure to erase entire FLASH memory to read as logic 1:
1. Set both the ERASE bit and the MASS bit in the FLASH control register.
2. Read the FLASH block protect register.
3. Write any data to any FLASH address(1) within the FLASH memory address range.
4. Wait for a time, tNVS (minimum 10 µs).
5. Set the HVEN bit.
6. Wait for a time, tMErase (minimum 4 ms).
7. Clear the ERASE and MASS bits.
NOTE
Mass erase is disabled whenever any block is protected (FLBPR does not
equal $FF).
8. Wait for a time, tNVHL (minimum 100 µs).
9. Clear the HVEN bit.
10. After time, tRCV (typical 1 µs), the memory can be accessed in read mode again.
NOTE
Programming and erasing of FLASH locations cannot be performed by
code being executed from the FLASH memory. While these operations
must be performed in the order as shown, but other unrelated operations
may occur between the steps.
1. When in monitor mode, with security sequence failed (see 19.3.2 Security), write to the FLASH block protect register instead of any FLASH address.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
38
Freescale Semiconductor
FLASH Memory (FLASH)
2.6.4 FLASH Program/Read Operation
Programming of the FLASH memory is done on a row basis. A row consists of 32 consecutive bytes
starting from addresses $XX00, $XX20, $XX40, $XX60, $XX80, $XXA0, $XXC0, and $XXE0. Use this
step-by-step procedure to program a row of FLASH memory (Figure 2-4 is a flowchart representation).
NOTE
To avoid program disturbs, the row must be erased before any byte on that
row is programmed.
1. Set the PGM bit. This configures the memory for program operation and enables the latching of
address and data for programming.
2. Read from the FLASH block protect register.
3. Write any data to any FLASH address within the row address range desired.
4. Wait for a time, tNVS (minimum of 10 µs).
5. Set the HVEN bit.
6. Wait for a time, tPGS (minimum of 5 µs).
7. Write data to the FLASH address(1) to be programmed.
8. Wait for a time, tPROG (minimum of 30 µs).
9. Repeat steps 7 and 8 until all the bytes within the row are programmed.
10. Clear the PGM bit.(1)
11. Wait for a time, tNVH (minimum of 5 µs).
12. Clear the HVEN bit.
13. After a time, tRCV (minimum of 1 µs), the memory can be accessed in read mode again.
This program sequence is repeated throughout the memory until all data is programmed.
NOTE
Programming and erasing of FLASH locations cannot be performed by
code being executed from the FLASH memory. While these operations
must be performed in the order shown, other unrelated operations may
occur between the steps. Do not exceed tPROG maximum.
1. The time between each FLASH address change, or the time between the last FLASH address programmed to clearing the
PGM bit, must not exceed the maximum programming time, tPROG maximum.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
39
Memory
Algorithm for Programming
a Row (32 bytes) of FLASH Memory
1
SET PGM BIT
2
READ THE FLASH BLOCK
PROTECT REGISTER
3
WRITE ANY DATA TO ANY FLASH ADDRESS
WITHIN THE ROW ADDRESS RANGE DESIRED
4
5
6
7
8
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?
YES
NO
10
11
CLEAR PGM BIT
WAIT FOR A TIME, tNVH
Notes:
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 maximum.
12
13
This row program algorithm assumes the row/s
to be programmed are initially erased.
CLEAR HVEN BIT
WAIT FOR A TIME, tRCV
END OF PROGRAMMING
Figure 2-4. FLASH Programming Flowchart
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
40
Freescale Semiconductor
FLASH Memory (FLASH)
2.6.5 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 a block of memory from unintentional erase or program
operations due to system malfunction. This protection is done by using the FLASH block protect register
(FLBPR). The 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 cannot be set in either erase or program
operations.
NOTE
In performing a program or erase operation, FLBPR must be read after
setting the PGM or ERASE bit and before asserting the HVEN bit.
When FLBPR is programmed with all 0s, the entire memory is protected from being programmed and
erased. When all the bits are erased (all 1s), the entire memory is accessible for program and erase.
When bits within the FLBPR are programmed, they lock a block of memory address ranges as shown in
2.6.6 FLASH Block Protect Register. Once the FLBPR is programmed with a value other than $FF or $FE,
any erase or program of the FLBPR or the protected block of FLASH memory is prohibited. Mass erase
is disabled whenever any block is protected (FLBPR does not equal $FF). The presence of a VTST on the
IRQ pin will bypass the block protection so that all of the memory included in the block protect register is
open for program and erase operations.
2.6.6 FLASH Block Protect Register
The FLASH block protect register (FLBPR) is implemented as a byte within the FLASH memory, and
therefore can be written only during a programming sequence of the FLASH memory. The value in this
register determines the starting location of the protected range within the FLASH memory.
Address:
$FF7E
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
BPR7
BPR6
BPR5
BPR4
BPR3
BPR2
BPR1
BPR0
Unaffected by reset. Initial value from factory is $FF.
Write to this register is by a programming sequence to the FLASH memory.
Figure 2-5. FLASH Block Protect Register (FLBPR)
BPR7–BPR0 — FLASH Block Protect Bits
These eight bits represent bits [13:6] of a 16-bit memory address. Bit 15 and Bit 14 are 1s and bits [5:0]
are 0s.
The resultant 16-bit address is used for specifying the start address of the FLASH memory for block
protection. The 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, $XX40, $XX80, and $XXC0 (64 bytes
page boundaries) within the FLASH memory.
16-BIT MEMORY ADDRESS
START ADDRESS OF FLASH
1
BLOCK PROTECT
1
FLBPR VALUE
0
0
0
0
0
0
Figure 2-6. FLASH Block Protect Start Address
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
41
Memory
Table 2-2. Examples of Protect Address Ranges
BPR[7:0]
Addresses of Protect Range
$00
The entire FLASH memory is protected.
$01 (0000 0001)
$C040 (1100 0000 0100 0000) — $FFFF
$02 (0000 0010)
$C080 (1100 0000 1000 0000) — $FFFF
$03 (0000 0011)
$C0C0 (1100 0000 1100 0000) — $FFFF
$04 (0000 0100)
$C100 (1100 0001 0000 0000) — $FFFF
and so on...
$FC (1111 1100)
$FF00 (1111 1111 0000 0000) — FFFF
$FD (1111 1101)
$FF40 (1111 1111 0100 0000) — $FFFF
FLBPR and vectors are protected
$FE (1111 1110)
$FF80 (1111 1111 1000 0000) — FFFF
Vectors are protected
$FF
The entire FLASH memory is not protected.
2.6.7 Wait Mode
Putting the microcontroller unit (MCU) into wait mode while the FLASH is in read mode does not affect
the operation of the FLASH memory directly, but there will not be any memory activity since the CPU is
inactive.
The WAIT instruction should not be executed while performing a program or erase operation on the
FLASH, or the operation will discontinue and the FLASH will be on standby mode.
2.6.8 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, but there will not be any memory activity since the CPU is inactive.
The STOP instruction should not be executed while performing a program or erase operation on the
FLASH, or the operation will discontinue and the FLASH will be on 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 at a minimum.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
42
Freescale Semiconductor
Chapter 3
Analog-to-Digital Converter (ADC) Module
3.1 Introduction
This section describes the 10-bit analog-to-digital converter (ADC).
For further information regarding analog-to-digital converters on Freescale microcontrollers, please
consult the HC08 ADC Reference Manual, ADCRM/AD.
3.2 Features
Features of the ADC module include:
• 8 channels with multiplexed input
• Linear successive approximation
• 10-bit resolution, 8-bit accuracy
• Single or continuous conversion
• Conversion complete flag or conversion complete interrupt
• Selectable ADC clock
• Left or right justified result
• Left justified sign data mode
• High impedance buffered ADC input
3.3 Functional Description
Eight ADC channels are available for sampling external sources at pins PTB7:PTB0. To achieve the best
possible accuracy, these pins are implemented as input-only pins when the analog-to-digital (A/D) feature
is enabled. An analog multiplexer allows the single ADC to select one of the 8 ADC channels as ADC
voltage IN (ADCVIN). ADCVIN is converted by the successive approximation algorithm. When the
conversion is completed, the ADC places the result in the ADC data register (ADRH and ADRL) and sets
a flag or generates an interrupt. See Figure 3-2.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
43
Analog-to-Digital Converter (ADC) Module
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 3-1. Block Diagram Highlighting ADC Block and Pins
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
44
Freescale Semiconductor
Functional Description
INTERNAL
DATA BUS
PTB
ADC CHANNEL x
READ PTB
DISABLE
ADC DATA REGISTERS
INTERRUPT
LOGIC
AIEN
ADC VOLTAGE IN
ADVIN
CONVERSION
COMPLETE
ADC
CHANNEL
SELECT
ADCH[4:0]
COCO/IDMAS
ADC CLOCK
PTx
CGMXCLK
BUS CLOCK
CLOCK
GENERATOR
ADIV[2:0]
ADICLK
Figure 3-2. ADC Block Diagram
3.3.1 ADC Port I/O Pins
PTB7:PTB0 are general-purpose I/O pins that are shared with the ADC channels. See Chapter 12
Input/Output (I/O) Ports (PORTS).
The channel select bits define which ADC channel/port pin will be used as the input signal. The ADC
overrides the port logic when that port is selected by the ADC multiplexer. The remaining ADC
channels/port pins are controlled by the port logic and can be used as general-purpose input/output (I/O)
pins. Writes to the port register or DDR will not have any effect 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.
3.3.2 Voltage Conversion
When the input voltage to the ADC equals VREFH, the ADC converts the signal to $3FF (full scale). If the
input voltage equals VREFL, the ADC converts it to $000. Input voltages between VREFH and VREFL are
straight-line linear conversions. All other input voltages will result in $3FF if greater than VREFH and $000
if less than VREFL.
NOTE
Input voltage should not exceed the analog supply voltages. See 20.10
Analog-to-Digital Converter (ADC) Characteristics.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
45
Analog-to-Digital Converter (ADC) Module
3.3.3 Conversion Time
Conversion starts after a write to the ADSCR. A conversion is between 16 and 17 ADC clock cycles,
therefore:
16 to17 ADC Cycles
Conversion time =
ADC Frequency
Number of Bus Cycles = Conversion Time x Bus Frequency
The ADC conversion time is determined by the clock source chosen and the divide ratio selected. The
clock source is either the bus clock or CGMXCLK and is selectable by ADICLK located in the ADC clock
register. For example, if CGMXCLK is 4 MHz and is selected as the ADC input clock source, the ADC
input clock divide-by-2 prescale is selected and the bus frequency is 8 MHz:
Conversion Time =
16 to17 ADC Cycles
= 8 to 8.5 µs
4 MHz/2
Number of bus cycles = (8 to 8.5µs) x 8 MHz = 64 to 68 cycles
The ADC frequency must be between fADIC minimum and fADIC maximum
to meet A/D specifications. See 20.10 Analog-to-Digital Converter (ADC)
Characteristics.
Since an ADC cycle may be comprised of several bus cycles (four in the previous example) and the start
of a conversion is initiated by a bus cycle write to the ADSCR, from zero to four additional bus cycles may
occur before the start of the initial ADC cycle. This results in a fractional ADC cycle and is represented as
the 17th cycle.
3.3.4 Continuous Conversion
In continuous conversion mode, the ADC data registers ADRH and ADRL 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 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.
3.3.5 Result Justification
The conversion result may be formatted in four different ways:
1. Left justified
2. Right justified
3. Left Justified sign data mode
4. 8-bit truncation mode
All four of these modes are controlled using MODE0 and MODE1 bits located in the ADC clock register
(ADCLK).
Left justification will place the eight most significant bits (MSB) in the corresponding ADC data register
high, ADRH. This may be useful if the result is to be treated as an 8-bit result where the two least
significant bits (LSB), located in the ADC data register low, ADRL, can be ignored. However, ADRL must
be read after ADRH or else the interlocking will prevent all new conversions from being stored.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
46
Freescale Semiconductor
Interrupts
Right justification will place only the two MSBs in the corresponding ADC data register high, ADRH, and
the eight LSBs in ADC data register low, ADRL. This mode of operation typically is used when a 10-bit
unsigned result is desired.
Left justified sign data mode is similar to left justified mode with one exception. The MSB of the 10-bit
result, AD9 located in ADRH, is complemented. This mode of operation is useful when a result,
represented as a signed magnitude from mid-scale, is needed. Finally, 8-bit truncation mode will place
the eight MSBs in ADC data register low, ADRL. The two LSBs are dropped. This mode of operation is
used when compatibility with 8-bit ADC designs are required. No interlocking between ADRH and ADRL
is present.
NOTE
Quantization error is affected when only the most significant eight bits are
used as a result. See Figure 3-3.
8-BIT 10-BIT
RESULT RESULT
IDEAL 8-BIT CHARACTERISTIC
WITH QUANTIZATION = ±1/2
10-BIT TRUNCATED
TO 8-BIT RESULT
003
00B
00A
009
002
IDEAL 10-BIT CHARACTERISTIC
WITH QUANTIZATION = ±1/2
008
007
006
005
001
004
WHEN TRUNCATION IS USED,
ERROR FROM IDEAL 8-BIT = 3/8 LSB
DUE TO NON-IDEAL QUANTIZATION.
003
002
001
000
000
1/2
2 1/2
1 1/2
1/2
4 1/2
3 1/2
6 1/2
5 1/2
1 1/2
8 1/2
7 1/2
9 1/2
2 1/2
INPUT VOLTAGE
REPRESENTED AS 10-BIT
INPUT VOLTAGE
REPRESENTED AS 8-BIT
Figure 3-3. 8-Bit Truncation Mode Error
3.3.6 Monotonicity
The conversion process is monotonic and has no missing codes.
3.4 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 is at 0. The COCO bit is not used as a
conversion complete flag when interrupts are enabled.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
47
Analog-to-Digital Converter (ADC) Module
3.5 Wait Mode
The WAIT instruction can put the MCU in low power-consumption standby 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 ADCH[4:0] in the ADC status and control register before executing the WAIT
instruction.
3.6 I/O Signals
The ADC module has eight input signals.
3.6.1 ADC Analog Power Pin (VDDA)
The ADC analog portion uses VDDA as its power pin. Connect the VDDA pin to the same voltage potential
as VDD. External filtering may be necessary to ensure clean VDDA for good results.
NOTE
Route VDDA carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
3.6.2 ADC Analog Ground Pin (VSSA)
The ADC analog portion uses VSSA as its ground pin. Connect the VSSA pin to the same voltage potential
as VSS.
3.6.3 ADC Voltage Reference Pin (VREFH)
VREFH is the power supply for setting the reference voltage VREFH. Connect the VREFH pin to the same
voltage potential as VDDA. There will be a finite current associated with VREFH. See Chapter 20 Electrical
Specifications.
NOTE
Route VREFH carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
3.6.4 ADC Voltage Reference Low Pin (VREFL)
VREFL is the lower reference supply for the ADC. Connect the VREFL pin to the same voltage potential as
VSSA. A finite current will be associated with VREFL. See Chapter 20 Electrical Specifications.
3.6.5 ADC Voltage In (ADVIN)
ADVIN is the input voltage signal from one of the 8 ADC channels to the ADC module.
3.6.6 ADC External Connections
This section describes the ADC external connections: VREFH and VREFL, ANx, and grounding.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
48
Freescale Semiconductor
I/O Registers
3.6.6.1 VREFH and VREFL
Both ac and dc current are drawn through the VREFH and VREFL loop. The AC current is in the form of
current spikes required to supply charge to the capacitor array at each successive approximation step.
The current flows through the internal resistor string. The best external component to meet both these
current demands is a capacitor in the 0.01 µF to 1 µF range with good high frequency characteristics. This
capacitor is connected between VREFH and VREFL and must be placed as close as possible to the
package pins. Resistance in the path is not recommended because the dc current will cause a voltage
drop which could result in conversion errors.
3.6.6.2 ANx
Empirical data shows that capacitors from the analog inputs to VREFL improve ADC performance. 0.01-µF
and 0.1-µF capacitors with good high-frequency characteristics are sufficient. These capacitors must be
placed as close as possible to the package pins.
3.6.6.3 Grounding
In cases where separate power supplies are used for analog and digital power, the ground connection
between these supplies should be at the VSSA pin. This should be the only ground connection between
these supplies if possible. The VSSA pin makes a good single point ground location. Connect the VREFL
pin to the same potential as VSSA at the single point ground location.
3.7 I/O Registers
These I/O registers control and monitor operation of the ADC:
• ADC status and control register, ADSCR
• ADC data registers, ADRH and ARDL
• ADC clock register, ADCLK
3.7.1 ADC Status and Control Register
This section describes the function of the ADC status and control register (ADSCR). Writing ADSCR
aborts the current conversion and initiates a new conversion.
Address:
Read:
Write:
Reset:
$003C
Bit 7
6
5
4
3
2
1
Bit 0
COCO
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
0
0
0
1
1
1
1
1
Figure 3-4. ADC Status and Control Register (ADSCR)
COCO — Conversions Complete Bit
When AIEN bit is 0, the COCO is a read-only bit which is set each time a conversion is completed
except in the continuous conversion mode where it is set after the first conversion. This bit is cleared
whenever the ADC status and control register is written or whenever the ADC data register is read.
If AIEN bit is 1, the COCO is a read/write bit. Reset clears this bit.
1 = Conversion completed (AIEN = 0)
0 = Conversion not completed (AIEN = 0)/CPU interrupt (AIEN = 1)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
49
Analog-to-Digital Converter (ADC) Module
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 8 ADC
channels. The ADC channels are detailed in Table 3-1.
NOTE
Take care to prevent switching noise from corrupting the analog signal
when simultaneously using a port pin as both an analog and digital input.
The ADC subsystem is turned off when the channel select bits are all set to 1. This feature allows for
reduced power consumption for the MCU when the ADC is not used.
NOTE
Recovery from the disabled state requires one conversion cycle to stabilize.
The voltage levels supplied from internal reference nodes as specified in
Table 3-1 are used to verify the operation of the ADC both in production test and for user applications.
Table 3-1. 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
to
Unused *
1
1
0
1
0
1
1
0
1
1
Reserved **
1
1
1
0
0
Unused *
1
1
1
0
1
VREFH
1
1
1
1
0
VREFL
1
1
1
1
1
ADC power off
* If any unused channels are selected, the resulting ADC conversion will be unknown.
** Used for factory testing.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
50
Freescale Semiconductor
I/O Registers
3.7.2 ADC Data Register High (ADRH) and Data Register Low (ADRL)
3.7.2.1 Left Justified Mode
In left justified mode the ADRH register holds the eight MSBs of the 10-bit result. The ADRL register holds
the two LSBs of the 10-bit result. All other bits read as 0. ADRH and ADRL are updated each time an ADC
single channel conversion completes. Reading ADRH latches the contents of ADRL until ADRL is read.
Until ADRL is read, all subsequent results will be lost.
Address:
Read:
$003D
ADRH
Bit 7
6
5
4
3
2
1
Bit 0
AD9
AD8
AD7
AD6
AD5
AD4
AD3
AD2
Write:
Reset:
Address:
Read:
Unaffected by reset
$003E
ADRL
AD1
AD0
0
0
0
0
0
0
Write:
Reset:
Unaffected by reset
= Unimplemented
Figure 3-5. ADC Data Register High (ADRH) and Low (ADRL)
3.7.2.2 Right Justified Mode
In right justified mode the ADRH register holds the two MSBs of the 10-bit result. All other bits read as 0.
The ADRL register holds the eight LSBs of the 10-bit result. ADRH and ADRL are updated each time an
ADC single channel conversion completes. Reading ADRH latches the contents of ADRL until ADRL is
read. Until ADRL is read, all subsequent ADC results will be lost.
Address:
Read:
$003D
ADRH
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
AD9
AD8
Write:
Reset:
Address:
Read:
Unaffected by reset
$003E
AD7
ADRL
AD6
AD5
AD4
AD3
AD2
AD1
AD0
Write:
Reset:
Unaffected by reset
= Unimplemented
Figure 3-6. ADC Data Register High (ADRH) and Low (ADRL)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
51
Analog-to-Digital Converter (ADC) Module
3.7.2.3 Left Justified Signed Data Mode
In left justified signed data mode the ADRH register holds the eight MSBs of the 10-bit result. The only
difference from left justified mode is that the AD9 is complemented. The ADRL register holds the two
LSBs of the 10-bit result. All other bits read as 0. ADRH and ADRL are updated each time an ADC single
channel conversion completes. Reading ADRH latches the contents of ADRL until ADRL is read. Until
ADRL is read, all subsequent results will be lost.
Address:
Read:
$003D
ADRH
Bit 7
6
5
4
3
2
1
Bit 0
AD9
AD8
AD7
AD6
AD5
AD4
AD3
AD2
Write:
Reset:
Address:
Read:
Unaffected by reset
$003E
AD1
ADRL
AD0
0
0
0
0
0
0
Write:
Reset:
Unaffected by reset
= Unimplemented
Figure 3-7. ADC Data Register High (ADRH) and Low (ADRL)
3.7.2.4 Eight Bit Truncation Mode
In 8-bit truncation mode the ADRL register holds the eight MSBs of the 10-bit result. The ADRH register
is unused and reads as 0. The ADRL register is updated each time an ADC single channel conversion
completes. In 8-bit mode, the ADRL register contains no interlocking with ADRH.
Address:
Read:
$003D
ADRH
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
Write:
Reset:
Address:
Read:
Unaffected by reset
$003E
AD9
ADRL
AD8
AD7
AD6
AD5
AD4
AD3
AD2
Write:
Reset:
Unaffected by reset
= Unimplemented
Figure 3-8. ADC Data Register High (ADRH) and Low (ADRL)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
52
Freescale Semiconductor
I/O Registers
3.7.3 ADC Clock Register
This register selects the clock frequency for the ADC, selecting between modes of operation.
Address:
Read:
Write:
$003F
Address:
Bit 7
6
5
4
3
2
1
ADIV2
ADIV1
ADIV0
ADICLK
MODE1
MODE0
R
0
0
0
0
0
1
0
Reset:
Bit 0
0
0
= Unimplemented
Figure 3-9. ADC Clock Register (ADCLK)
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 3-2 shows the available clock configurations.
Table 3-2. 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 Select 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 fADIC, correct operation can be guaranteed. See
20.10 Analog-to-Digital Converter (ADC) Characteristics.
1 = Internal bus clock
0 = External clock, CGMXCLK
fADIC =
CGMXCLK or bus frequency
ADIV[2:0]
MODE1:MODE0 — Modes of Result Justification Bits
MODE1:MODE0 selects among four modes of operation. The manner in which the ADC conversion
results will be placed in the ADC data registers is controlled by these modes of operation. Reset returns
right-justified mode.
00 = 8-bit truncation mode
01 = Right justified mode
10 = Left justified mode
11 = Left justified sign data mode
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
53
Analog-to-Digital Converter (ADC) Module
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
54
Freescale Semiconductor
Chapter 4
BEMF Counter Module (BEMF)
4.1 Introduction
This section describes the BEMF module. The BEMF counter integrates over time, while the
PTD0/TACH0 pin is active. This function is useful for measuring recirculation currents in motors occurring
on switching of inductive loads.
BEMF is the abbreviation for Back ElectroMagnetic Force.
4.2 Functional Description
The 8-bit BEMF counter runs at the internal bus frequency divided by 64. Whenever PTD0/TACH0 is a
logic 1, the counter increments by 1 with each period.
4.3 BEMF Register
The BEMF register contains the eight read-only bits of the BEMF counter, showing its actual value. A read
access to the BEMF register resets all counter bits to 0.
Address:
Read:
$000B
Bit 7
6
5
4
3
2
1
Bit 0
BEMF7
BEMF6
BEMF5
BEMF4
BEMF3
BEMF2
BEMF1
BEMF0
0
0
0
0
0
0
0
Write:
Reset:
0
= Unimplemented
Figure 4-1. BEMF Register (BEMF)
4.4 Input Signal
Port D shares the PTD0/TACH0 pin with the BEMF module. To measure an external signal with the BEMF
module, PTD0/TACH0 must be configured as an input (DDRD0 = 0).
4.5 Low Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
4.5.1 Wait Mode
The BEMF module remains active after execution of the WAIT instruction. In WAIT mode the BEMF
register is not accessible by the CPU.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
55
BEMF Counter Module (BEMF)
4.5.2 Stop Mode
The BEMF module is inactive after execution of the STOP instruction. In STOP mode the BEMF register
is not accessible by the CPU.
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
DDRD
PORT D
PORT E
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA1/KBD1
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 4-2. Block Diagram Highlighting BEMF Block and Pins
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
56
Freescale Semiconductor
Chapter 5
Configuration Registers (CONFIG1 and CONFIG2)
5.1 Introduction
This section describes the configuration registers, CONFIG1 and CONFIG2. The configuration registers
control these options:
• Stop mode recovery time, 32 CGMXCLK cycles or 4096 CGMXCLK cycles
• Computer operating properly (COP) timeout period, 262,128 or 8176 CGMXCLK cycles
• STOP instruction
• Computer operating properly (COP) module
• Low-voltage inhibit (LVI) module control and voltage trip point selection
• Enable/disable the oscillator (OSC) during stop mode
• External clock/crystal source control
• Enhanced SCI clock source selection
5.2 Functional Description
The configuration registers are used in the initialization of various options and can be written once after
each reset. All of the configuration register bits are cleared during reset. Since the various options affect
the operation of the microcontroller unit (MCU), it is recommended that these registers be written
immediately after reset. The configuration registers are located at $001E and $001F. For compatibility, a
write to a read-only memory (ROM) version of the MCU at this location will have no effect. The
configuration register may be read at anytime.
NOTE
The CONFIG module is known as an MOR (mask option register) on a
ROM device. On a ROM device, the options are fixed at the time of device
fabrication and are neither writable nor changeable by the user.
On a FLASH device, the CONFIG registers are special registers containing
one-time writable latches after each reset. Upon a reset, the CONFIG
registers default to predetermined settings as shown in Figure 5-1 and
Figure 5-2.
Address:
$001E
Bit 7
Read:
Write:
R
Reset:
6
5
4
3
2
1
Bit 0
ESCIBDSRC EXTXTALEN EXTSLOW EXTCLKEN TMBCLKSEL OSCENINSTOP SSBPUENB
0
0
R
= Reserved
0
0
0
0
0
1
Figure 5-1. Configuration Register 2 (CONFIG2)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
57
Configuration Registers (CONFIG1 and CONFIG2)
Address:
Read:
Write:
$001F
Bit 7
6
5
4
3
2
1
Bit 0
COPRS
LVISTOP
LVIRSTD
LVIPWRD
LVI5OR3(1)
SSREC
STOP
COPD
0
0
0
0
0
0
0
0
Reset:
1. The LVI5OR3 bit is cleared only by a power-on reset (POR).
Figure 5-2. Configuration Register 1 (CONFIG1)
ESCIBDSRC — ESCI Baud Rate Clock Source Bit
ESCIBDSRC controls the clock source used for the ESCI. The setting of the bit affects the frequency
at which the ESCI operates.
1 = Internal data bus clock used as clock source for ESCI
0 = CGMXCLK used as clock source for ESCI
EXTXTALEN — External Crystal Enable Bit
EXTXTALEN enables the external oscillator circuits to be configured for a crystal configuration where
the PTC4/OSC1 and PTC3/OSC2 pins are the connections for an external crystal.
NOTE
This bit does not function without setting the EXTCLKEN bit also.
Clearing the EXTXTALEN bit (default setting) allows the PTC3/OSC2 pin to function as a
general-purpose I/O pin. Refer to Table 5-1 for configuration options for the external source. See
Chapter 8 Internal Clock Generator (ICG) Module for a more detailed description of the external clock
operation.
Table 5-1. External Clock Option Settings
External Clock
Configuration Bits
Pin Function
Description
EXTCLKEN EXTXTALEN PTC4/OSC1 PTC3/OSC2
0
0
PTC4
PTC3
Default setting — external oscillator disabled
0
1
PTC4
PTC3
External oscillator disabled since EXTCLKEN not set
1
0
OSC1
PTC3
External oscillator configured for an external clock
source input (square wave) on OSC1
1
1
OSC1
OSC2
External oscillator configured for an external crystal
configuration on OSC1 and OSC2. System will also
operate with square-wave clock source in OSC1.
EXTXTALEN, when set, also configures the clock monitor to expect an external clock source in the
valid range of crystals (30 kHz to 100 kHz or 1 MHz to 8 MHz). When EXTXTALEN is clear, the clock
monitor will expect an external clock source in the valid range for externally generated clocks when
using the clock monitor (60 Hz to 32 MHz).
EXTXTALEN, when set, also configures the external clock stabilization divider in the clock monitor for
a 4096-cycle timeout to allow the proper stabilization time for a crystal. When EXTXTALEN is clear,
the stabilization divider is configured to 16 cycles since an external clock source does not need a
startup time.
1 = Allows PTC3/OSC2 to be an external crystal connection.
0 = PTC3/OSC2 functions as an I/O port pin (default).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
58
Freescale Semiconductor
Functional Description
EXTSLOW — Slow External Crystal Enable Bit
The EXTSLOW bit has two functions. It configures the ICG module for a fast (1 MHz to 8 MHz) or slow
(30 kHz to 100 kHz) speed crystal. The option also configures the clock monitor operation in the ICG
module to expect an external frequency higher (307.2 kHz to 32 MHz) or lower (60 Hz to 307.2 kHz)
than the base frequency of the internal oscillator. See Chapter 8 Internal Clock Generator (ICG)
Module.
1 = ICG set for slow external crystal operation
0 = ICG set for fast external crystal operation
EXTCLKEN — External Clock Enable Bit
EXTCLKEN enables an external clock source or crystal/ceramic resonator to be used as a clock input.
Setting this bit enables PTC4/OSC1 pin to be a clock input pin. Clearing this bit (default setting) allows
the PTC4/OSC1 and PTC3/OSC2 pins to function as general-purpose input/output (I/O) pins. Refer to
Table 5-1 for configuration options for the external source. See Chapter 8 Internal Clock Generator
(ICG) Module for a more detailed description of the external clock operation.
1 = Allows PTC4/OSC1 to be an external clock connection
0 = PTC4/OSC1 and PTC3/OSC2 function as I/O port pins (default).
TMBCLKSEL — Timebase Clock Select Bit
TMBCLKSEL enables an enable the extra divide by 128 prescaler in the timebase module. Setting this
bit enables the extra prescaler and clearing this bit disables it. Refer to Table 16-1 for timebase divider
selection details.
1 = Enables extra divide by 128 prescaler in timebase module.
0 = Disables extra divide by 128 prescaler in timebase module.
OSCENINSTOP — Oscillator Enable In Stop Mode Bit
OSCENINSTOP, when set, will enable the internal clock generator module to continue to generate
clocks (either internal, ICLK, or external, ECLK) in stop mode. See Chapter 8 Internal Clock Generator
(ICG) Module. This function is used to keep the timebase running while the rest of the microcontroller
stops. When clear, all clock generation will cease and both ICLK and ECLK will be forced low during
stop mode. The default state for this option is clear, disabling the ICG in stop mode.
1 = Oscillator enabled to operate during stop mode
0 = Oscillator disabled during stop mode (default)
NOTE
This bit has the same functionality as the OSCSTOPENB CONFIG bit in
MC68HC908GP20 and MC68HC908GR8 parts.
SSBPUENB — SS Pullup Enable Bit
Clearing SSBPUENB enables the SS pullup resistor.
1 = Disables SS pullup resistor.
0 = Enables SS pullup resistor.
COPRS — COP Rate Select Bit
COPRS selects the COP timeout period. Reset clears COPRS. See Chapter 6 Computer Operating
Properly (COP) Module.
1 = COP timeout period = 8176 CGMXCLK cycles
0 = COP timeout period = 262,128 CGMXCLK cycles
LVISTOP — LVI Enable in Stop Mode Bit
When the LVIPWRD bit is clear, setting the LVISTOP bit enables the LVI to operate during stop mode.
Reset clears LVISTOP.
1 = LVI enabled during stop mode
0 = LVI disabled during stop mode
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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59
Configuration Registers (CONFIG1 and CONFIG2)
LVIRSTD — LVI Reset Disable Bit
LVIRSTD disables the reset signal from the LVI module. See Chapter 11 Low-Voltage Inhibit (LVI)
Module.
1 = LVI module resets disabled
0 = LVI module resets enabled
LVIPWRD — LVI Power Disable Bit
LVIPWRD disables the LVI module. See Chapter 11 Low-Voltage Inhibit (LVI) Module.
1 = LVI module power disabled
0 = LVI module power enabled
LVI5OR3 — LVI 5-V or 3-V Operating Mode Bit
LVI5OR3 selects the voltage operating mode of the LVI module. See Chapter 11 Low-Voltage Inhibit
(LVI) Module. The voltage mode selected for the LVI will typically be 5 V. However, users may choose
to operate the LVI in 3-V mode if desired. See Chapter 20 Electrical Specifications for the LVI’s voltage
trip points for each of the modes.
1 = LVI operates in 5-V mode.
0 = LVI operates in 3-V mode.
NOTE
The LVI5OR3 bit is cleared by a power-on reset (POR) only. Other resets
will leave this bit unaffected.
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.
1 = Stop mode recovery after 32 CGMXCLK cycles
0 = Stop mode recovery after 4096 CGMXCLCK cycles
NOTE
Exiting stop mode by an LVI reset will result in the long stop recovery.
If the system clock source selected is the internal oscillator or the external crystal and the
OSCENINSTOP configuration bit is not set, the oscillator will be disabled during stop mode. The short
stop recovery does not provide enough time for oscillator stabilization and thus the SSREC bit should
not be set.
When using the LVI during normal operation but disabling during stop mode, the LVI will have an
enable time of tEN. The system stabilization time for power-on reset and long stop recovery (both 4096
CGMXCLK cycles) gives a delay longer than the LVI enable time for these startup scenarios. There is
no period where the MCU is not protected from a low-power condition. However, when using the short
stop recovery configuration option, the 32-CGMXCLK delay must be greater than the LVI’s turn on time
to avoid a period in startup where the LVI is not protecting the MCU.
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 6 Computer Operating Properly (COP) Module.
1 = COP module disabled
0 = COP module enabled
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Chapter 6
Computer Operating Properly (COP) Module
6.1 Introduction
The computer operating properly (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.
6.2 Functional Description
SIM MODULE
RESET VECTOR FETCH
RESET STATUS REGISTER
COP TIMEOUT
CLEAR STAGES 5–12
CLEAR ALL STAGES
INTERNAL RESET SOURCES(1)
SIM RESET CIRCUIT
12-BIT SIM COUNTER
BUSCLKX4
COPCTL WRITE
COP CLOCK
COP MODULE
6-BIT COP COUNTER
COPEN (FROM SIM)
COPD (FROM CONFIG1)
RESET
CLEAR
COP COUNTER
COPCTL WRITE
COP RATE SELECT
(COPRS FROM CONFIG1)
1. See Chapter 14 System Integration Module (SIM) for more details.
Figure 6-1. COP Block Diagram
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. When COPRS = 0,
a 4.9152-MHz crystal gives a COP timeout period of 53.3 ms. Writing any value to location $FFFF before
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
61
Computer Operating Properly (COP) Module
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 VTST. During the break state,
VTST 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.
6.3 I/O Signals
The following paragraphs describe the signals shown in Figure 6-1.
6.3.1 CGMXCLK
CGMXCLK is the crystal oscillator output signal. CGMXCLK frequency is equal to the crystal frequency.
6.3.2 STOP Instruction
The STOP instruction signal clears the COP prescaler.
6.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) (see 6.4 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.
6.3.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK cycles after power-up.
6.3.5 Internal Reset
An internal reset clears the COP prescaler and the COP counter.
6.3.6 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.
6.3.7 COPD
The COPD signal reflects the state of the COP disable bit (COPD) in the configuration register. See
Chapter 5 Configuration Registers (CONFIG1 and CONFIG2).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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COP Control Register
6.3.8 COPRS
The COPRS signal reflects the state of the COP rate select bit (COPRS) in the configuration register. See
Chapter 5 Configuration Registers (CONFIG1 and CONFIG2).
6.4 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 6-2. COP Control Register (COPCTL)
6.5 Interrupts
The COP does not generate CPU interrupt requests.
6.6 Monitor Mode
The COP is disabled in monitor mode when VTST is present on the IRQ pin or on the RST pin.
6.7 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
6.7.1 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.
6.7.2 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) enables the STOP instruction. To prevent
inadvertently turning off the COP with a STOP instruction, disable the STOP instruction by clearing the
STOP bit.
6.8 COP Module During Break Interrupts
The COP is disabled during a break interrupt when VTST is present on the RST pin.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Computer Operating Properly (COP) Module
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Chapter 7
Central Processor Unit (CPU)
7.1 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.
7.2 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
7.3 CPU Registers
Figure 7-1 shows the five CPU registers. CPU registers are not part of the memory map.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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65
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 7-1. CPU Registers
7.3.1 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 7-2. Accumulator (A)
7.3.2 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 7-3. Index Register (H:X)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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CPU Registers
7.3.3 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 7-4. 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.
7.3.4 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 7-5. Program Counter (PC)
7.3.5 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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67
Central Processor Unit (CPU)
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 7-6. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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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
7.4 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.
7.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
7.5.1 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
7.5.2 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.
7.6 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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69
Central Processor Unit (CPU)
7.7 Instruction Set Summary
Table 7-1 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
V H I N Z C
A ← (A) + (M) + (C)
Add with 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
Description
Operand
Operation
Effect
on CCR
Opcode
Source
Form
Address
Mode
Table 7-1. 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
ii
2
ADD #opr
ADD opr
ADD opr
ADD opr,X
ADD opr,X
ADD ,X
ADD opr,SP
ADD opr,SP
Add without Carry
AIS #opr
Add Immediate Value (Signed) to SP
SP ← (SP) + (16 « M)
– – – – – – IMM
A7
AIX #opr
Add Immediate Value (Signed) to H:X
H:X ← (H:X) + (16 « M)
– – – – – – IMM
AF
A ← (A) & (M)
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
A4
B4
C4
D4
E4
F4
9EE4
9ED4
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
A ← (A) + (M)
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
ii
2
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
70
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 7-1. 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
PC ← (PC) + 3 + rel ? (Mn) = 0
PC ← (PC) + 2
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
– – – – – – 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
71
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
Clear
Compare A with M
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
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)
(A)10
Exclusive OR M with A
Increment
M ← $00
A ← $00
X ← $00
H ← $00
M ← $00
M ← $00
M ← $00
(X) – (M)
DBNZ opr,rel
DBNZA rel
DBNZX rel
Decrement and Branch if Not Zero
DBNZ opr,X,rel
DBNZ X,rel
DBNZ opr,SP,rel
INC opr
INCA
INCX
INC opr,X
INC ,X
INC opr,SP
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
Effect
on CCR
V H I N Z C
COM opr
COMA
COMX
COM opr,X
COM ,X
COM opr,SP
EOR #opr
EOR opr
EOR opr
EOR opr,X
EOR opr,X
EOR ,X
EOR opr,SP
EOR opr,SP
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 7-1. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
72
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)
MOV opr,opr
MOV opr,X+
MOV #opr,opr
MOV X+,opr
Move
MUL
Unsigned multiply
C
b7
b7
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
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
Negate (Two’s Complement)
45
55
AE
BE
CE
DE
EE
FE
9EEE
9EDE
b0
0
IMM
DIR
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
X ← (M)
Logical Shift Left
(Same as ASL)
Logical Shift Right
0 – – –
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 7-1. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
73
Central Processor Unit (CPU)
V H I N Z C
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 7-1. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
74
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 7-1. 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
7.8 Opcode Map
See Table 7-2.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
75
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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
3
4
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)
76
Table 7-2. Opcode Map
Bit Manipulation
DIR
DIR
Chapter 8
Internal Clock Generator (ICG) Module
8.1 Introduction
The internal clock generator (ICG) module is used to create a stable clock source for the microcontroller
without using any external components. The ICG generates the oscillator output clock (CGMXCLK),
which is used by the computer operating properly (COP), low-voltage inhibit (LVI), and other modules.
The ICG also generates the clock generator output (CGMOUT), which is fed to the system integration
module (SIM) to create the bus clocks. The bus frequency will be one-fourth the frequency of CGMXCLK
and one-half the frequency of CGMOUT. Finally, the ICG generates the timebase clock (TBMCLK), which
is used in the timebase module (TBM).
8.2 Features
The ICG has these features:
• Selectable external clock generator, either 1-pin external source or 2-pin crystal, multiplexed with
port pins
• Internal clock generator with programmable frequency output in integer multiples of a nominal
frequency (307.2 kHz ± 25 percent)
• Internal oscillator trimmed accuracy of ±3.5 percent
• Bus clock software selectable from either internal or external clock (bus frequency range from 76.8
kHz ± 25 percent to 9.75 MHz ± 25 percent in 76.8-kHz increments)
NOTE
For the MC68HC908EY16, do not exceed the maximum bus frequency of
8 MHz at 5.0 V.
•
•
Timebase clock automatically selected from external clock if external clock is available
Clock monitor for both internal and external clocks
8.3 Functional Description
The ICG, shown in Figure 8-2, contains these major submodules:
• Clock enable circuit
• Internal clock generator
• External clock generator
• Clock monitor circuit
• Clock selection circuit
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
77
Internal Clock Generator (ICG) Module
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
MONITOR ROM
310 BYTES
PTA0/KBD0
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
PORT B
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
24 INTERNAL SYSTEM
INTEGRATION MODULE
CONFIGURATION REGISTER
MODULE
PTB3/AD3
PTD1/TACH1
PTE1/RxD
SERIAL PERIPHERAL
INTERFACE MODULE
DDRE
IRQ
INTERNAL CLOCK
GENERATOR MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
RST
PTA3/KBD3
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PTA4/KBD4
PTA2/KBD2
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 8-1. Block Diagram Highlighting ICG Block and Pins
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
78
Freescale Semiconductor
Functional Description
CS
CGMOUT
RESET
CGMXCLK
CLOCK
SELECTION
CIRCUIT
TBMCLK
IOFF
EOFF
CMON
ECGS
ICGS
CLOCK
MONITOR
CIRCUIT
FICGS
DDIV[3:0]
INTERNAL CLOCK
GENERATOR
N[6:0}
DSTG[7:0]
TRIM[7:0]
ICLK
IBASE
ICGEN
SIMOSCEN
CLOCK/PIN
ENABLE
CIRCUIT
OSCENINSTOP
EXTCLKEN
ECGON
ICGON
ECGEN
EXTXTALEN
EXTERNAL CLOCK
GENERATOR
EXTSLOW
INTERNAL
TO MCU
PTC4
LOGIC
ECLK
PTC3
LOGIC
OSC1
PTC4
OSC2
PTC3
EXTERNAL
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-2. ICG Module Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
79
Internal Clock Generator (ICG) Module
8.3.1 Clock Enable Circuit
The clock enable circuit is used to enable the internal clock (ICLK) or external clock (ECLK) and the port
logic which is shared with the oscillator pins (OSC1 and OSC2). The clock enable circuit generates an
ICG stop (ICGSTOP) signal which stops all clocks (ICLK, ECLK, and the low-frequency base clock,
IBASE). ICGSTOP is set and the ICG is disabled in stop mode if the oscillator enable stop bit
(OSCENINSTOP) in the configuration (CONFIG) register is clear. The ICG clocks will be enabled in stop
mode if OSCENINSTOP is high.
The internal clock enable signal (ICGEN) turns on the internal clock generator which generates ICLK.
ICGEN is set (active) whenever the ICGON bit is set and the ICGSTOP signal is clear. When ICGEN is
clear, ICLK and IBASE are both low.
The external clock enable signal (ECGEN) turns on the external clock generator which generates ECLK.
ECGEN is set (active) whenever the ECGON bit is set and the ICGSTOP signal is clear. ECGON cannot
be set unless the external clock enable (EXTCLKEN) bit in the CONFIG is set. when ECGEN is clear,
ECLK is low.
The port C4 enable signal (PC4EN) turns on the port C4 logic. Since port C4 is on the same pin as OSC1,
this signal is only active (set) when the external clock function is not desired. Therefore, PC4EN is clear
when ECGON is set. PC4EN is not gated with ICGSTOP, which means that if the ECGON bit is set, the
port C4 logic will remain disabled in stop mode.
The port C3 enable signal (PC3EN) turns on the port C3 logic. Since port C3 is on the same pin as OSC2,
this signal is only active (set) when 2-pin oscillator function is not desired. Therefore, PC3EN is clear when
ECGON and the external crystal enable (EXTXTALEN) bit in the CONFIG are both set. PC4EN is not
gated with ICGSTOP, which means that if ECGON and EXTXTALEN are set, the port C3 logic will remain
disabled in stop mode.
8.3.2 Internal Clock Generator
The internal clock generator, shown in Figure 8-3, creates a low frequency base clock (IBASE), which
operates at a nominal frequency (fNOM) of 307.2 kHz ± 25 percent, and an internal clock (ICLK) which is
an integer multiple of IBASE. This multiple is the ICG multiplier factor (N), which is programmed in the
ICG multiplier register (ICGMR). The internal clock generator is turned off and the output clocks (IBASE
and ICLK) are held low when the internal clock generator enable signal (ICGEN) is clear.
The internal clock generator contains:
• A digitally controlled oscillator
• A modulo N divider
• A frequency comparator, which contains voltage and current references, a frequency to voltage
converter, and comparators
• A digital loop filter
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
80
Freescale Semiconductor
Functional Description
ICGEN
FICGS
++
VOLTAGE AND
CURRENT
REFERENCES
DSTG[7:0]
+
DDIV[3:0]
DIGITAL
LOOP
FILTER
DIGITALLY
CONTROLLED
OSCILLATOR
–
ICLK
––
TRIM[7:0]
FREQUENCY
COMPARATOR
CLOCK GENERATOR
N[6:0]
MODULO
N
DIVIDER
IBASE
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-3. Internal Clock Generator Block Diagram
8.3.2.1 Digitally Controlled Oscillator
The digitally controlled oscillator (DCO) is an inaccurate oscillator which generates the internal clock
(ICLK). The clock period of ICLK is dependent on the digital loop filter outputs (DSTG[7:0] and DDIV[3:0]).
Because of only a limited number of bits in DDIV and DSTG, the precision of the output (ICLK) is restricted
to a precision of approximately ±0.202 percent to ±0.368 percent when measured over several cycles (of
the desired frequency). Additionally, since the propagation delays of the devices used in the DCO ring
oscillator are a measurable fraction of the bus clock period, reaching the long-term precision may require
alternately running faster and slower than desired, making the worst case cycle-to-cycle frequency
variation ±6.45 percent to ±11.8 percent (of the desired frequency). The valid values of DDIV:DSTG range
from $000 to $9FF. For more information on the quantization error in the DCO, see 8.4.4 Quantization
Error in DCO Output.
8.3.2.2 Modulo N Divider
The modulo N divider creates the low-frequency base clock (IBASE) by dividing the internal clock (ICLK)
by the ICG multiplier factor (N), contained in the ICG multiplier register (ICGMR). When N is programmed
to a $01 or $00, the divider is disabled and ICLK is passed through to IBASE undivided. When the internal
clock generator is stable, the frequency of IBASE will be equal to the nominal frequency (fNOM) of
307.2 kHz ± 25 percent.
8.3.2.3 Frequency Comparator
The frequency comparator effectively compares the low-frequency base clock (IBASE) to a nominal
frequency, fNOM. First, the frequency comparator converts IBASE to a voltage by charging a known
capacitor with a current reference for a period dependent on IBASE. This voltage is compared to a voltage
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
81
Internal Clock Generator (ICG) Module
reference with comparators, whose outputs are fed to the digital loop filter. The dependence of these
outputs on the capacitor size, current reference, and voltage reference causes up to ±25 percent error in
fNOM.
8.3.2.4 Digital Loop Filter
The digital loop filter (DLF) uses the outputs of the frequency comparator to adjust the internal clock
(ICLK) clock period. The DLF generates the DCO divider control bits (DDIV[3:0]) and the DCO stage
control bits (DSTG[7:0]), which are fed to the DCO. The DLF first concatenates the DDIV and DSTG
registers (DDIV[3:0]:DSTG[7:0]) and then adds or subtracts a value dependent on the relative error in the
low-frequency base clock’s period, as shown in Table 8-1. In some extreme error conditions, such as
operating at a VDD level which is out of specification, the DLF may attempt to use a value above the
maximum ($9FF) or below the minimum ($000). In both cases, the value for DDIV will be between $A and
$F. In this range, the DDIV value will be interpreted the same as $9 (the slowest condition). Recovering
from this condition requires subtracting (increasing frequency) in the normal fashion until the value is
again below $9FF. (If the desired value is $9xx, the value may settle at $Axx through $Fxx. This is an
acceptable operating condition.) If the error is less than ±5 percent, the internal clock generator’s filter
stable indicator (FICGS) is set, indicating relative frequency accuracy to the clock monitor.
Table 8-1. Correction Sizes from DLF to DCO
Frequency Error
of IBASE Compared
to fNOM
DDVI[3:0]:DSTG[7:0]
Correction
IBASE < 0.85 fNOM
–32 (–$020)
0.85 fNOM < IBASE
IBASE < 0.95 fNOM
–8 (–$008)
0.95 fNOM < IBASE
IBASE < fNOM
–1 (–$001)
fNOM < IBASE
IBASE < 1.05 fNOM
+1 (+$001)
1.05 fNOM < IBASE
IBASE < 1.15 fNOM
+8 (+$008)
1.15 fNOM < IBASE
+32 (+$020)
Current to New
DDIV[3:0]:DSTG[7:0](1)
Relative Correction
in DCO
Minimum
$xFF to $xDF
–2/31
–6.45%
Maximum
$x20 to $x00
–2/19
–10.5%
Minimum
$xFF to $xF7
–0.5/31
–1.61%
Maximum
$x08 to $x00
–0.5/17.5
–2.86%
Minimum
$xFF to $xFE
–0.0625/31
–0.202%
Maximum
$x01 to $x00
–0.0625/17.0625
–0.366%
Minimum
$xFE to $xFF
+0.0625/30.9375
+0.202%
Maximum
$x00 to $x01
+0.0625/17
+0.368%
Minimum
$xF7 to $xFF
+0.5/30.5
+1.64%
Maximum
$x00 to $x08
+0.5/17
+2.94%
Minimum
$xDF to $xFF
+2/29
+6.90%
Maximum
$x00 to $x20
+2/17
+11.8%
1. x = Maximum error is independent of value in DDIV[3:0]. DDIV increments or decrements when an addition to DSTG[7:0]
carries or borrows.
8.3.3 External Clock Generator
The ICG also provides for an external oscillator or external clock source, if desired. The external clock
generator, shown in Figure 8-4, contains an external oscillator amplifier and an external clock input path.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
82
Freescale Semiconductor
Functional Description
8.3.3.1 External Oscillator Amplifier
The external oscillator amplifier provides the gain required by an external crystal connected in a Pierce
oscillator configuration. The amount of this gain is controlled by the slow external (EXTSLOW) bit in the
CONFIG. When EXTSLOW is set, the amplifier gain is reduced for operating low-frequency crystals (32
kHz to 100 kHz). When EXTSLOW is clear, the amplifier gain will be sufficient for 1-MHz to 8-MHz
crystals. EXTSLOW must be configured correctly for the given crystal or the circuit may not operate.
The amplifier is enabled when the external clock generator enable (ECGEN) signal is set and when the
external crystal enable (EXTXTALEN) bit in the CONFIG is set. ECGEN is controlled by the clock enable
circuit (see 8.3.1 Clock Enable Circuit) and indicates that the external clock function is desired. When
enabled, the amplifier will be connected between the PTC4/OSC1 and PTC3/OSC2 pins. Otherwise, the
PTC3/OSC2 pin reverts to its port function.
ECGEN
INPUT PATH
ECLK
EXTXTALEN
AMPLIFIER
EXTERNAL
CLOCK
GENERATOR
EXTSLOW
INTERNAL TO MCU
OSC1
PTC4
OSC2
PTC3
EXTERNAL
NAME
NAME
RB
R S*
CONFIGURATION BIT
X1
TOP LEVEL SIGNAL
NAME
REGISTER BIT
NAME
MODULE SIGNAL
C1
*RS can be 0 (shorted)
when used with higherfrequency crystals. Refer
to manufacturer’s data.
C2
These components are required
for external crystal use only.
Figure 8-4. External Clock Generator Block Diagram
In its typical configuration, the external oscillator requires five external components:
1. Crystal, X1
2. Fixed capacitor, C1
3. Tuning capacitor, C2 (can also be a fixed capacitor)
4. Feedback resistor, RB
5. Series resistor, RS (included in Figure 8-4 to follow strict Pierce oscillator guidelines and may not
be required for all ranges of operation, especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
83
Internal Clock Generator (ICG) Module
8.3.3.2 External Clock Input Path
The external clock input path is the means by which the microcontroller uses an external clock source.
The input to the path is the PTC4/OSC1 pin and the output is the external clock (ECLK). The path, which
contains input buffering, is enabled when the external clock generator enable signal (ECGEN) is set.
When not enabled, the PTC4/OSC1 pin reverts to its port function.
8.3.4 Clock Monitor Circuit
The ICG contains a clock monitor circuit which, when enabled, will continuously monitor both the external
clock (ECLK) and the internal clock (ICLK) to determine if either clock source has been corrupted. The
clock monitor circuit, shown in Figure 8-5, contains these blocks:
• Clock monitor reference generator
• Internal clock activity detector
• External clock activity detector
IOFF
IOFF
EREF
ICGS
ICGS
IBASE
EREF
CMON
CMON
FICGS
FICGS
IBASE
IBASE
ICGEN
ICGEN
ICLK
ACTIVITY
DETECTOR
ICGON
EXTXTALEN
EXTSLOW
EXTXTALEN
REFERENCE
GENERATOR
EXTSLOW
ECGS
ESTBCLK
ECLK
ECGEN
IREF
ESTBCLK
ECGS
ECGS
IREF
ECGEN
ECLK
ECGEN
ECLK
ECLK
ACTIVITY
DETECTOR
CMON
EOFF
EOFF
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-5. Clock Monitor Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
84
Freescale Semiconductor
Functional Description
8.3.4.1 Clock Monitor Reference Generator
The clock monitor uses a reference based on one clock source to monitor the other clock source. The
clock monitor reference generator generates the external reference clock (EREF) based on the external
clock (ECLK) and the internal reference clock (IREF) based on the internal clock (ICLK). To simplify the
circuit, the low-frequency base clock (IBASE) is used in place of ICLK because it always operates at or
near 307.2 kHz. For proper operation, EREF must be at least twice as slow as IBASE and IREF must be
at least twice as slow as ECLK.
To guarantee that IREF is slower than ECLK and EREF is slower than IBASE, one of the signals is divided
down. Which signal is divided and by how much is determined by the external slow (EXTSLOW) and
external crystal enable (EXTXTALEN) bits in the CONFIG, according to the rules in Table 8-2.
NOTE
Each signal (IBASE and ECLK) is always divided by four. A longer divider
is used on either IBASE or ECLK based on the EXTSLOW bit.
To conserve size, the long divider (divide by 4096) is also used as an external crystal stabilization divider.
The divider is reset when the external clock generator is turned off or in stop mode (ECGEN is clear).
When the external clock generator is first turned on, the external clock generator stable bit (ECGS) will
be clear. This condition automatically selects ECLK as the input to the long divider. The external
stabilization clock (ESTBCLK) will be ECLK divided by 16 when EXTXTALEN is low or 4096 when
EXTXTALEN is high. This timeout allows the crystal to stabilize. The falling edge of ESTBCLK is used to
set ECGS, which will set after a full 16 or 4096 cycles. When ECGS is set, the divider returns to its normal
function. ESTBCLK may be generated by either IBASE or ECLK, but any clocking will only reinforce the
set condition. If ECGS is cleared because the clock monitor determined that ECLK was inactive, the
divider will revert to a stabilization divider. Since this will change the EREF and IREF divide ratios, it is
important to turn the clock monitor off (CMON = 0) after inactivity is detected to ensure valid recovery.
8.3.4.2 Internal Clock Activity Detector
The internal clock activity detector, shown in Figure 8-6, looks for at least one falling edge on the
low-frequency base clock (IBASE) every time the external reference (EREF) is low. Since EREF is less
than half the frequency of IBASE, this should occur every time. If it does not occur two consecutive times,
the internal clock inactivity indicator (IOFF) is set. IOFF will be cleared the next time there is a falling edge
of IBASE while EREF is low.
The internal clock stable bit (ICGS) is also generated in the internal clock activity detector. ICGS is set
when the internal clock generator’s filter stable signal (FICGS) indicates that IBASE is within about 5
percent of the target 307.2 kHz ± 25 percent for two consecutive measurements. ICGS is cleared when
FICGS is clear, the internal clock generator is turned off or is in stop mode (ICGEN is clear), or when IOFF
is set.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
85
Internal Clock Generator (ICG) Module
CMON
CK
EREF
IOFF
Q
1/4
R
R
R
D
D
DFFRS
IBASE
CK
R
Q
DFFRR
CK
Q
S
D
Q
ICGS
DFFRR
CK
R
R
DLF MEASURE
OUTPUT CLOCK
ICGEN
FICGS
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-6. Internal Clock Activity Detector
8.3.4.3 External Clock Activity Detector
The external clock activity detector, shown in Figure 8-7, looks for at least one falling edge on the external
clock (ECLK) every time the internal reference (IREF) is low. Since IREF is less than half the frequency
of ECLK, this should occur every time. If it does not occur two consecutive times, the external clock
inactivity indicator (EOFF) is set. EOFF will be cleared the next time there is a falling edge of ECLK while
IREF is low.
The external clock stable bit (ECGS) is also generated in the external clock activity detector. ECGS is set
on a falling edge of the external stabilization clock (ESTBCLK). This will be 4096 ECLK cycles after the
external clock generator on bit is set, or the MCU exits stop mode (ECGEN = 1) if the external crystal
enable (EXTXTALEN) in the CONFIG is set, or 16 cycles when EXTXTALEN is clear. ECGS is cleared
when the external clock generator is turned off or in stop mode (ECGEN is clear) or when EOFF is set.
CMON
CK
IREF
EOFF
Q
1/4
R
R
R
D
D
DFFRS
ECLK
CK
Q
DFFRR
CK
S
Q
EGGS
R
ESTBCLK
ECGEN
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-7. External Clock Activity Detector
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
86
Freescale Semiconductor
Functional Description
8.3.5 Clock Selection Circuit
The clock selection circuit, shown in Figure 8-8, contains two clock switches which generate the oscillator
output clock (CGMXCLK) and the timebase clock (TBMCLK) from either the internal clock (ICLK) or the
external clock (ECLK). The clock selection circuit also contains a divide-by-two circuit which creates the
clock generator output clock (CGMOUT), which generates the bus clocks.
CS
ICLK
ICLK
ECLK
ECLK
IOFF
IOFF
EOFF
EOFF
CGMXCLK
OUTPUT
SELECT
SYNCHRONIZING
CLOCK
SWITCHER
DIV2
CGMOUT
FORCE_I
RESET
VSS
FORCE_E
TBMCLK
OUTPUT
SELECT
ECGON
ICLK
ECLK
IOFF
EOFF
SYNCHRONIZING
CLOCK
SWITCHER
FORCE_I
FORCE_E
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-8. Clock Selection Circuit Block Diagram
8.3.5.1 Clock Selection Switches
The first switch creates the oscillator output clock (CGMXCLK) from either the internal clock (ICLK) or the
external clock (ECLK), based on the clock select bit (CS; set selects ECLK, clear selects ICLK). When
switching the CS bit, both ICLK and ECLK must be on (ICGON and ECGON set). The clock being
switched to also must be stable (ICGS or ECGS set).
The second switch creates the timebase clock (TBMCLK) from ICLK or ECLK based on the external clock
on bit. When ECGON is set, the switch automatically selects the external clock, regardless of the state of
the ECGS bit.
8.3.5.2 Clock Switching Circuit
To robustly switch between the internal clock (ICLK) and the external clock (ECLK), the switch assumes
the clocks are completely asynchronous, so a synchronizing circuit is required to make the transition.
When the select input (the clock select bit for the oscillator output clock switch or the external clock on bit
for the timebase clock switch) is changed, the switch will continue to operate off the original clock for
between one and two cycles as the select input is transitioned through one side of the synchronizer. Next,
the output will be held low for between one and two cycles of the new clock as the select input transitions
through the other side. Then the output starts switching at the new clock’s frequency. This transition
guarantees that no glitches will be seen on the output even though the select input may change
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
87
Internal Clock Generator (ICG) Module
asynchronously to the clocks. The unpredictably of the transition period is a necessary result of the
asynchronicity.
The switch automatically selects ICLK during reset. When the clock monitor is on (CMON is set) and it
determines one of the clock sources is inactive (as indicated by the IOFF or EOFF signals), the circuit is
forced to select the active clock. There are no clocks for the inactive side of the synchronizer to properly
operate, so that side is forced deselected. However, the active side will not be selected until one to two
clock cycles after the IOFF or EOFF signal transitions.
8.4 Usage Notes
The ICG has several features which can provide protection to the microcontroller if properly used. Other
features can greatly simplify usage of the ICG if certain techniques are employed. This section describes
several possible ways to use the ICG and its features. These techniques are not the only ways to use the
ICG and may not be optimum for all environments. In any case, these techniques should be used only as
a template, and the user should modify them according to the application’s requirements.
These notes include:
• Switching clock sources
• Enabling the clock monitor
• Using clock monitor interrupts
• Quantization error in digitally controlled oscillator (DCO) output
• Switching internal clock frequencies
• Nominal frequency settling time
• Improving frequency settling time
• Trimming frequency
8.4.1 Switching Clock Sources
Switching from one clock source to another requires both clock sources to be enabled and stable. A
simple flow requires:
• Enable desired clock source
• Wait for it to become stable
• Switch clocks
• Disable previous clock source
The key point to remember in this flow is that the clock source cannot be switched (CS cannot be written)
unless the desired clock is on and stable. A short assembly code example of how to employ this flow is
shown in Figure 8-9. This code is for illustrative purposes only and does not represent valid syntax for any
particular assembler.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
88
Freescale Semiconductor
Usage Notes
start
lda
#$13
loop
**
**
sta
icgcr
cmpa
bne
icgcr
loop
;Clock Switching Code Example
;This code switches from Internal to External clock
;Clock Monitor and interrupts are not enabled
;Mask for CS, ECGON, ECGS
; If switching from External to Internal, mask is $0C.
;Other code here, such as writing the COP, since ECGS may
; take some time to set
;Try to set CS, ECGON and clear ICGON. ICGON will not
; clear until CS is set, and CS will not set until
; ECGON and ECGS are set.
;Check to see if ECGS set, then CS set, then ICGON clear
;Keep looping until ICGON is clear.
Figure 8-9. Code Example for Switching Clock Sources
8.4.2 Enabling the Clock Monitor
Many applications require the clock monitor to determine if one of the clock sources has become inactive,
so the other can be used to recover from a potentially dangerous situation. Using the clock monitor
requires both clocks to be active (ECGON and ICGON both set). To enable the clock monitor, both clocks
also must be stable (ECGS and ICGS both set). This is to prevent the use of the clock monitor when a
clock is first turned on and potentially unstable.
Enabling the clock monitor and clock monitor interrupts requires a flow similar to this:
• Enable the alternate clock source
• Wait for both clock sources to be stable
• Switch to the desired clock source if necessary
• Enable the clock monitor
• Enable clock monitor interrupts
These events must happen in sequence. A short assembly code example of how to employ this flow is
shown in Figure 8-10. This code is for illustrative purposes only and does not represent valid syntax for
any particular assembler.
start
lda
loop
**
sta
brset
cmpa
bne
;Clock Monitor Enabling Code Example
;This code turns on both clocks, selects the desired
; one, then turns on the Clock Monitor and Interrupts
#$AF
;Mask for CMIE, CMON, ICGON, ICGS, ECGON, ECGS
; If Internal Clock desired, mask is $AF
; If External Clock desired, mask is $BF
; If interrupts not desired mask is $2F int; $3F ext
**
;Other code here, such as writing the COP, since ECGS
; and ICGS may take some time to set.
icgcr
;Try to set CMIE. CMIE wont set until CMON set; CMON
; won’t set until ICGON, ICGS, ECGON, ECGS set.
6,ICGCR,error ;Verify CMF is not set
icgcr
;Check if ECGS set, then CMON set, then CMIE set
loop
;Keep looping until CMIE is set.
Figure 8-10. Code Example for Enabling the Clock Monitor
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
89
Internal Clock Generator (ICG) Module
8.4.3 Using Clock Monitor Interrupts
The clock monitor circuit can be used to recover from perilous situations such as crystal loss. To use the
clock monitor effectively, these points should be observed:
• Enable the clock monitor and clock monitor interrupts.
• The first statement in the clock monitor interrupt service routine (CMISR) should be a read to the
ICG control register (ICGCR) to verify that the clock monitor flag (CMF) is set. This is also the first
step in clearing the CMF bit.
• The second statement in the CMISR should be a write to the ICGCR to clear the CMF bit (write the
bit low). Writing the bit high will not affect it. This statement does not need to immediately follow
the first, but must be contained in the CMISR.
• The third statement in the CMISR should be to clear the CMON bit. This is required to ensure
proper reconfiguration of the reference dividers. This statement also must be contained in the
CMISR.
• Although the clock monitor can be enabled only when both clocks are stable (ICGS is set or ECGS
is set), it will remain set if one of the clocks goes unstable.
• The clock monitor only works if the external slow (EXTSLOW) bit in the CONFIG is set to the
correct value.
• The internal and external clocks must both be enabled and running to use the clock monitor.
• When the clock monitor detects inactivity, the inactive clock is automatically deselected and the
active clock selected as the source for CGMXCLK and TBMCLK. The CMISR can use the state of
the CS bit to check which clock is inactive.
• When the clock monitor detects inactivity, the application may have been subjected to extreme
conditions which may have affected other circuits. The CMISR should take any appropriate
precautions.
8.4.4 Quantization Error in DCO Output
The digitally controlled oscillator (DCO) is comprised of three major sub-blocks:
1. Binary weighted divider
2. Variable-delay ring oscillator
3. Ring oscillator fine-adjust circuit
Each of these blocks affects the clock period of the internal clock (ICLK). Since these blocks are controlled
by the digital loop filter (DLF) outputs DDIV and DSTG, the output of the DCO can change only in
quantized steps as the DLF increments or decrements its output. The following sections describe how
each block will affect the output frequency.
8.4.4.1 Digitally Controlled Oscillator
The digitally controlled oscillator (DCO) is an inaccurate oscillator which generates the internal clock
(ICLK), whose clock period is dependent on the digital loop filter outputs (DSTG[7:0] and DDIV[3:0]).
Because of the digital nature of the DCO, the clock period of ICLK will change in quantized steps. This
will create a clock period difference or quantization error (Q-ERR) from one cycle to the next. Over several
cycles or for longer periods, this error is divided out until it reaches a minimum error of 0.202 percent to
0.368 percent. The dependence of this error on the DDIV[3:0] value and the number of cycles the error is
measured over is shown in Table 8-2.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
90
Freescale Semiconductor
Usage Notes
Table 8-2. Quantization Error in ICLK
DDIV[3:0]
ICLK Cycles
Bus Cycles
τICLK Q-ERR
%0000 (min)
1
NA
6.45%–11.8%
%0000 (min)
4
1
1.61%–2.94%
%0000 (min)
≥ 32
≥8
0.202%–0.368%
%0001
1
NA
3.23%–5.88%
%0001
4
1
0.806%–1.47%
%0001
≥ 16
≥4
0.202%–0.368%
%0010
1
NA
1.61%–2.94%
%0010
4
1
0.403%–0.735%
%0010
≥8
≥2
0.202%–0.368%
%0011
1
NA
0.806%–1.47%
%0011
≥4
≥1
0.202%–0.368%
%0100
1
NA
0.403%–0.735%
%0100
≥2
≥1
0.202%–0.368%
%0101–%1001 (max)
≥1
≥1
0.202%–0.368%
8.4.4.2 Binary Weighted Divider
The binary weighted divider divides the output of the ring oscillator by a power of two, specified by the
DCO divider control bits (DDIV[3:0]). DDIV maximizes at %1001 (values of %1010 through %1111 are
interpreted as %1001), which corresponds to a divide by 512. When DDIV is %0000, the ring oscillator’s
output is divided by 1. Incrementing DDIV by one will double the period; decrementing DDIV will halve the
period. The DLF cannot directly increment or decrement DDIV; DDIV is only incremented or decremented
when an addition or subtraction to DSTG carries or borrows.
8.4.4.3 Variable-Delay Ring Oscillator
The variable-delay ring oscillator’s period is adjustable from 17 to 31 stage delays, in increments of two,
based on the upper three DCO stage control bits (DSTG[7:5]). A DSTG[7:5] of %000 corresponds to 17
stage delays; DSTG[7:5] of %111 corresponds to 31 stage delays. Adjusting the DSTG[5] bit has a 6.45
percent to 11.8 percent effect on the output frequency. This also corresponds to the size correction made
when the frequency error is greater than ±15 percent. The value of the binary weighted divider does not
affect the relative change in output clock period for a given change in DSTG[7:5].
8.4.4.4 Ring Oscillator Fine-Adjust Circuit
The ring oscillator fine-adjust circuit causes the ring oscillator to effectively operate at non-integer
numbers of stage delays by operating at two different points for a variable number of cycles specified by
the lower five DCO stage control bits (DSTG[4:0]). For example:
• When DSTG[7:5] is %011, the ring oscillator nominally operates at 23 stage delays.
• When DSTG[4:0] is %00000, the ring will always operate at 23 stage delays.
• When DSTG[4:0] is %00001, the ring will operate at 25 stage delays for one of 32 cycles and at 23
stage delays for 31 of 32 cycles.
• Likewise, when DSTG[4:0] is %11111, the ring operates at 25 stage delays for 31 of 32 cycles and
at 23 stage delays for one of 32 cycles.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
91
Internal Clock Generator (ICG) Module
•
When DSTG[7:5] is %111, similar results are achieved by including a variable divide-by-two, so the
ring operates at 31 stages for some cycles and at 17 stage delays, with a divide-by-two for an
effective 34 stage delays, for the remainder of the cycles.
Adjusting the DSTG[0] bit has a 0.202 percent to 0.368 percent effect on the output clock period. This
corresponds to the minimum size correction made by the DLF, and the inherent, long-term quantization
error in the output frequency.
8.4.5 Switching Internal Clock Frequencies
The frequency of the internal clock (ICLK) may need to be changed for some applications. For example,
if the reset condition does not provide the correct frequency, or if the clock is slowed down for a low-power
mode (or sped up after a low-power mode), the frequency must be changed by programming the internal
clock multiplier factor (N). The frequency of ICLK is N times the frequency of IBASE, which is 307.2 kHz
±25 percent.
Before switching frequencies by changing the N value, the clock monitor must be disabled. This is
because when N is changed, the frequency of the low-frequency base clock (IBASE) will change
proportionally until the digital loop filter has corrected the error. Since the clock monitor uses IBASE, it
could erroneously detect an inactive clock. The clock monitor cannot be re-enabled until the internal clock
is stable again (ICGS is set).
The following flow is an example of how to change the clock frequency:
• Verify there is no clock monitor interrupt by reading the CMF bit.
• Turn off the clock monitor.
• If desired, switch to the external clock (see 8.4.1 Switching Clock Sources).
• Change the value of N.
• Switch back to internal (see 8.4.1 Switching Clock Sources),
if desired.
• Turn on the clock monitor (see 8.4.2 Enabling the Clock Monitor), if desired.
8.4.6 Nominal Frequency Settling Time
Because the clock period of the internal clock (ICLK) is dependent on the digital loop filter outputs (DDIV
and DSTG) which cannot change instantaneously, ICLK temporarily will operate at an incorrect clock
period when any operating condition changes. This happens whenever the part is reset, the ICG multiply
factor (N) is changed, the ICG trim factor (TRIM) is changed, or the internal clock is enabled after inactivity
(stop mode or disabled operation). The time that the ICLK takes to adjust to the correct period is known
as the settling time.
Settling time depends primarily on how many corrections it takes to change the clock period and the
period of each correction. Since the corrections require four periods of the low-frequency base clock
(4*τIBASE), and since ICLK is N (the ICG multiply factor for the desired frequency) times faster than
IBASE, each correction takes 4*N*τICLK. The period of ICLK, however, will vary as the corrections occur.
8.4.6.1 Settling to Within 15 Percent
When the error is greater than 15 percent, the filter takes eight corrections to double or halve the clock
period. Due to how the DCO increases or decreases the clock period, the total period of these eight
corrections is approximately 11 times the period of the fastest correction. (If the corrections were perfectly
linear, the total period would be 11.5 times the minimum period; however, the ring must be slightly
nonlinear.) Therefore, the total time it takes to double or halve the clock period is 44*N*τICLKFAST.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
92
Freescale Semiconductor
Usage Notes
If the clock period needs more than doubled or halved, the same relationship applies, only for each time
the clock period needs doubled, the total number of cycles doubles. That is, when transitioning from fast
to slow, going from the initial speed to half speed takes 44*N*τICLKFAST; from half speed to quarter speed
takes 88*N*τICLKFAST; going from quarter speed to eighth speed takes 176*N*τICLKFAST; and so on. This
series can be expressed as (2x–1)*44*N*τICLKFAST, where x is the number of times the speed needs
doubled or halved. Since 2x happens to be equal to τICLKSLOW/τICLKFAST, the equation reduces to
44*N*(τICLKSLOW–τICLKFAST).
Note that increasing speed takes much longer than decreasing speed since N is higher. This can be
expressed in terms of the initial clock period (τ1) minus the final clock period (τ2) as such:
τ 15 = abs [ 44N ( τ 1 – τ 2 ) ]
8.4.6.2 Settling to Within 5 Percent
Once the clock period is within 15 percent of the desired clock period, the filter starts making smaller
adjustments. When between 15 percent and 5 percent error, each correction will adjust the clock period
between 1.61 percent and 2.94 percent. In this mode, a maximum of eight corrections will be required to
get to less than 5 percent error. Since the clock period is relatively close to desired, each correction takes
approximately the same period of time, or 4*τIBASE. At this point, the internal clock stable bit (ICGS) will
be set and the clock frequency is usable, although the error will be as high as 5 percent. The total time to
this point is:
τ 5 = abs [ 44N ( τ 1 – τ 2 ) ] + 32τ IBASE
8.4.6.3 Total Settling Time
Once the clock period is within 5 percent of the desired clock period, the filter starts making minimum
adjustments. In this mode, each correction will adjust the frequency between 0.202 percent and 0.368
percent. A maximum of 24 corrections will be required to get to the minimum error. Each correction takes
approximately the same period of time, or 4*τIBASE. Added to the corrections for 15 percent to 5 percent,
this makes 32 corrections (128*τIBASE) to get from 15 percent to the minimum error. The total time to the
minimum error is:
τ tot = abs [ 44N ( τ 1 – τ 2 ) ] + 128τ IBASE
The equations for τ15, τ5, and τtot are dependent on the actual initial and final clock periods τ1 and τ2, not
the nominal. This means the variability in the ICLK frequency due to process, temperature, and voltage
must be considered. Additionally, other process factors and noise can affect the actual tolerances of the
points at which the filter changes modes. This means a worst case adjustment of up to 35 percent (ICLK
clock period tolerance plus 10 percent) must be added. This adjustment can be reduced with trimming.
Table 8-3 shows some typical values for settling time.
Table 8-3. Typical Settling Time Examples
τ1
τ2
N
τ15
τ5
τtot
1/ (6.45 MHz)
1/ (25.8 MHz)
84
430 µs
535 µs
850 µs
1/ (25.8 MHz)
1/ (6.45 MHz)
21
107 µs
212 µs
525 µs
1/ (25.8 MHz)
1/ (307.2 kHz)
1
141 µs
246 µs
560 µs
1/ (307.2 kHz)
1/ (25.8 MHz)
84
11.9 ms
12.0 ms
12.3 ms
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
93
Internal Clock Generator (ICG) Module
8.4.7 Trimming Frequency on the Internal Clock Generator
The unadjusted frequency of the low-frequency base clock (IBASE), when the comparators in the
frequency comparator indicate zero error, will vary as much as ±25 percent due to process, temperature,
and voltage dependencies. These dependencies are in the voltage and current references, the offset of
the comparators, and the internal capacitor.
The method of changing the unadjusted operating point is by changing the size of the capacitor. This
capacitor is designed with 639 equally sized units. Of that number, 384 of these units are always
connected. The remaining 255 units are put in by adjusting the ICG trim factor (TRIM). The default value
for TRIM is $80, or 128 units, making the default capacitor size 512. Each unit added or removed will
adjust the output frequency by about ±0.195 percent of the unadjusted frequency (adding to TRIM will
decrease frequency). Therefore, the frequency of IBASE can be changed to ±25 percent of its unadjusted
value, which is enough to cancel the process variability mentioned before.
The best way to trim the internal clock is to use the timer to measure the width of an input pulse on an
input capture pin (this pulse must be supplied by the application and should be as long or wide as
possible). Considering the prescale value of the timer and the theoretical (zero error) frequency of the bus
(307.2 kHz *N/4), the error can be calculated. This error, expressed as a percentage, can be divided by
0.195 percent and the resultant factor added or subtracted from TRIM. This process should be repeated
to eliminate any residual error.
8.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power- consumption standby modes.
8.5.1 Wait Mode
The ICG remains active in wait mode. If enabled, the ICG interrupt to the CPU can bring the MCU out of
wait mode.
In some applications, low power-consumption is desired in wait mode and a high-frequency clock is not
needed. In these applications, reduce power consumption by either selecting a low-frequency external
clock and turn the internal clock generator off or reduce the bus frequency by minimizing the ICG multiplier
factor (N) before executing the WAIT instruction.
8.5.2 Stop Mode
The value of the oscillator enable in stop (OSCENINSTOP) bit in the CONFIG determines the behavior
of the ICG in stop mode. If OSCENINSTOP is low, the ICG is disabled in stop and, upon execution of the
STOP instruction, all ICG activity will cease and the output clocks (CGMXCLK, CGMOUT, and TBMCLK)
will be held low. Power consumption will be minimal.
If OSCENINSTOP is high, the ICG is enabled in stop and activity will continue. This is useful if the
timebase module (TBM) is required to bring the MCU out of stop mode. ICG interrupts will not bring the
MCU out of stop mode in this case.
During stop mode, if OSCENINSTOP is low, several functions in the ICG are affected. The stable bits
(ECGS and ICGS) are cleared, which will enable the external clock stabilization divider upon recovery.
The clock monitor is disabled (CMON = 0) which will also clear the clock monitor interrupt enable (CMIE)
and clock monitor flag (CMF) bits. The CS, ICGON, ECGON, N, TRIM, DDIV, and DSTG bits are
unaffected.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
94
Freescale Semiconductor
CONFIG Options
8.6 CONFIG Options
Four CONFIG options affect the functionality of the ICG. These options are:
1. EXTCLKEN, external clock enable
2. EXTXTALEN, external crystal enable
3. EXTSLOW, slow external clock
4. OSCENINSTOP, oscillator enable in stop
All CONFIG options will have a default setting. Refer to Chapter 5 Configuration Registers (CONFIG1 and
CONFIG2) on how the CONFIG is used.
8.6.1 External Clock Enable (EXTCLKEN)
External clock enable (EXTCLKEN), when set, enables the ECGON bit to be set. ECGON turns on the
external clock input path through the PTC4/OSC1 pin. When EXTCLKEN is clear, ECGON cannot be set
and PTC4/OSC1 will always perform the PTC4 function.
The default state for this option is clear.
8.6.2 External Crystal Enable (EXTXTALEN)
External crystal enable (EXTXTALEN), when set, will enable an amplifier to drive the PTC3/OSC2 pin
from the PTC4/OSC1 pin. The amplifier will drive only if the external clock enable (EXTCLKEN) bit and
the ECGON bit are also set. If EXTCLKEN or ECGON are clear, PTC3/OSC2 will perform the PTC3
function. When EXTXTALEN is clear, PTC3/OSC2 will always perform the PTC3 function.
EXTXTALEN, when set, also configures the clock monitor to expect an external clock source in the valid
range of crystals (30 kHz to 100 kHz or 1 MHz to 8 MHz). When EXTXTALEN is clear, the clock monitor
will expect an external clock source in the valid range for externally generated clocks when using the clock
monitor (60 Hz to 32 MHz).
EXTXTALEN, when set, also configures the external clock stabilization divider in the clock monitor for a
4096 cycle timeout to allow the proper stabilization time for a crystal. When EXTXTALEN is clear, the
stabilization divider is configured to 16 cycles since an external clock source does not need a startup time.
The default state for this option is clear.
8.6.3 Slow External Clock (EXTSLOW)
Slow external clock (EXTSLOW), when set, will decrease the drive strength of the oscillator amplifier,
enabling low-frequency crystal operation (30 kHz–100 kHz) if properly enabled with the external clock
enable (EXTCLKEN) and external crystal enable (EXTXTALEN) bits. When clear, EXTSLOW enables
high-frequency crystal operation (1 MHz to 8 MHz).
EXTSLOW, when set, also configures the clock monitor to expect an external clock source that is slower
than the low-frequency base clock (60 Hz to 307.2 kHz). When EXTSLOW is clear, the clock monitor will
expect an external clock faster than the low-frequency base clock (307.2 kHz to 32 MHz).
The default state for this option is clear.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
95
Internal Clock Generator (ICG) Module
8.6.4 Oscillator Enable In Stop (OSCENINSTOP)
Oscillator enable in stop (OSCENINSTOP), when set, will enable the ICG to continue to generate clocks
(either CGMXCLK, CGMOUT, or TBMCLK) in stop mode. This function is used to keep the timebase
running while the rest of the microcontroller stops. When OSCENINSTOP is clear, all clock generation
will cease and CGMXCLK, CGMOUT, and TBMCLK will be forced low during stop mode.
The default state for this option is clear.
8.7 Input/Output (I/O) Registers
The ICG contains five registers. These registers are:
1. ICG control register, ICGCR
2. ICG multiplier register, ICGMR
3. ICG trim register, ICGTR
4. ICG DCO divider control register, ICGDVR
5. ICG DCO stage control register, ICGDSR
Several of the bits in these registers have interaction where the state of one bit may force another bit to
a particular state or prevent another bit from being set or cleared. A summary of this interaction is shown
in Table 8-4.
Table 8-4. ICG Module Register Bit Interaction Summary
Condition
Register Bit Results for Given Condition
CMIE CMF CMON CS ICGON ICGS ECQON ECQ N[6:0] TRIM[7:0] DDIV[3:0] DSTQ[7:0]
Reset
0
0
0
0
1
0
0
0
$15
$80
—
—
OSCENINSTOP = 0,
STOP = 1
0
0
0
—
—
0
—
0
—
—
—
—
EXTCLKEN = 0
0
0
0
0
1
—
0
0
—
—
uw
uw
CMF = 1
—
(1)
1
—
1
—
1
—
uw
uw
uw
uw
CMON = 0
0
0
(0)
—
—
—
—
—
—
—
—
—
CMON = 1
—
—
(1)
—
1
—
1
—
uw
uw
uw
uw
CS = 0
—
—
—
(0)
1
—
—
—
—
—
uw
uw
CS = 1
—
—
—
(1)
—
—
1
—
—
—
—
—
ICGON = 0
0
0
0
1
(0)
0
1
—
—
—
—
—
ICGON = 1
—
—
—
—
(1)
—
—
—
—
—
uw
uw
ICGS = 0
us
—
us
uc
—
(0)
—
—
—
—
—
—
ECGON = 0
0
0
0
0
1
—
(0)
0
—
—
uw
uw
ECGS = 0
us
—
us
us
—
—
—
(0)
—
—
—
—
IOFF = 1
—
1*
(1)
1
(1)
0
(1)
—
uw
uw
uw
uw
EOFF = 1
—
1*
(1)
0
(1)
—
(1)
0
uw
uw
uw
uw
N = written
(0)
(0)
(0)
—
—
0*
—
—
—
—
—
—
TRIM = written
(0)
(0)
(0)
—
—
0*
—
—
—
—
—
—
—
0, 1
0*, 1*
(0), (1)
us, uc, uw
Register bit is unaffected by the given condition.
Register bit is forced clear or set (respectively) in the given condition.
Register bit is temporarily forced clear or set (respectively) in the given condition.
Register bit must be clear or set (respectively) for the given condition to occur.
Register bit cannot be set, cleared, or written (respectively) in the given condition.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
96
Freescale Semiconductor
Input/Output (I/O) Registers
8.7.1 ICG Control Register
The ICG control register (ICGCR) contains the control and status bits for the internal clock generator,
external clock generator, and clock monitor as well as the clock select and interrupt enable bits.
Address: $0036
Bit 7
Read:
CMIE
Write:
Reset:
0
6
CMF
0(1)
5
4
3
CMON
CS
ICGON
0
0
1
0
2
ICGS
0
1
ECGON
0
Bit 0
ECGS
0
1. See CMF bit description for method of clearing CMF bit.
= Unimplemented
Figure 8-11. ICG Control Register (ICGCR)
CMIE — Clock Monitor Interrupt Enable Bit
This read/write bit enables clock monitor interrupts. An interrupt will occur when both CMIE and CMF
are set. CMIE can be set when the CMON bit has been set for at least one cycle. CMIE is forced clear
when CMON is clear or during reset.
1 = Clock monitor interrupts enabled
0 = Clock monitor interrupts disabled
CMF — Clock Monitor Interrupt Flag
This read-only bit is set when the clock monitor determines that either ICLK or ECLK becomes inactive
and the CMON bit is set. This bit is cleared by first reading the bit while it is set, followed by writing the
bit low. This bit is forced clear when CMON is clear or during reset.
1 = Either ICLK or ECLK has become inactive.
0 = ICLK and ECLK have not become inactive since the last read of the ICGCR, or the clock monitor
is disabled.
CMON — Clock Monitor On Bit
This read/write bit enables the clock monitor. CMON can be set when both ICLK and ECLK have been
on and stable for at least one bus cycle. (ICGON, ECGON, ICGS, and ECGS are all set.) CMON is
forced set when CMF is set, to avoid inadvertent clearing of CMF. CMON is forced clear when either
ICGON or ECGON is clear, during stop mode with OSCENINSTOP low, or during reset.
1 = Clock monitor output enabled
0 = Clock monitor output disabled
CS — Clock Select Bit
This read/write bit determines which clock will generate the oscillator output clock (CGMXCLK). This
bit can be set when ECGON and ECGS have been set for at least one bus cycle and can be cleared
when ICGON and ICGS have been set for at least one bus cycle. This bit is forced set when the clock
monitor determines the internal clock (ICLK) is inactive or when ICGON is clear. This bit is forced clear
when the clock monitor determines that the external clock (ECLK) is inactive, when ECGON is clear,
or during reset.
1 = External clock (ECLK) sources CGMXCLK
0 = Internal clock (ICLK) sources CGMXCLK
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
97
Internal Clock Generator (ICG) Module
ICGON — Internal Clock Generator On Bit
This read/write bit enables the internal clock generator. ICGON can be cleared when the CS bit has
been set and the CMON bit has been clear for at least one bus cycle. ICGON is forced set when the
CMON bit is set, the CS bit is clear, or during reset.
1 = Internal clock generator enabled
0 = Internal clock generator disabled
ICGS — Internal Clock Generator Stable Bit
This read-only bit indicates when the internal clock generator has determined that the internal clock
(ICLK) is within about 5 percent of the desired value. This bit is forced clear when the clock monitor
determines the ICLK is inactive, when ICGON is clear, when the ICG multiplier register (ICGMR) is
written, when the ICG TRIM register (ICGTR) is written, during stop mode with OSCENINSTOP low,
or during reset.
1 = Internal clock is within 5 percent of the desired value.
0 = Internal clock may not be within 5 percent of the desired value.
ECGON — External Clock Generator On Bit
This read/write bit enables the external clock generator. ECGON can be cleared when the CS and
CMON bits have been clear for at least one bus cycle. ECGON is forced set when the CMON bit or the
CS bit is set. ECGON is forced clear during reset.
1 = External clock generator enabled
0 = External clock generator disabled
ECGS — External Clock Generator Stable Bit
This read-only bit indicates when at least 4096 external clock (ECLK) cycles have elapsed since the
external clock generator was enabled. This is not an assurance of the stability of ECLK but is meant
to provide a startup delay. This bit is forced clear when the clock monitor determines ECLK is inactive,
when ECGON is clear, during stop mode with OSCENINSTOP low, or during reset.
1 = 4096 ECLK cycles have elapsed since ECGON was set.
0 = External clock is unstable, inactive, or disabled.
8.7.2 ICG Multiplier Register
Address: $0037
Bit 7
Read:
Write:
Reset:
0
6
5
4
3
2
1
Bit 0
N6
N5
N4
N3
N2
N1
N0
0
0
1
0
1
0
1
= Unimplemented
Figure 8-12. ICG Multiplier Register (ICGMR)
N6:N0 — ICG Multiplier Factor Bits
These read/write bits change the multiplier used by the internal clock generator. The internal clock
(ICLK) will be:
(307.2 kHz ± 25 percent) * N
A value of $00 in this register is interpreted the same as a value of $01. This register cannot be written
when the CMON bit is set. Reset sets this factor to $15 (decimal 21) for default frequency of 6.45 MHz
± 25 percent (1.613 MHz ± 25 percent bus).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
98
Freescale Semiconductor
Input/Output (I/O) Registers
8.7.3 ICG Trim Register
Address: $0038
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
1
0
0
0
0
0
0
0
Figure 8-13. ICG Trim Register (ICGTR)
TRIM7:TRIM0 — ICG Trim Factor Bits
These read/write bits change the size of the internal capacitor used by the internal clock generator. By
testing the frequency of the internal clock and incrementing or decrementing this factor accordingly,
the accuracy of the internal clock can be improved (see 20.9.1 Trimmed Internal Clock Generator
Characteristics). Incrementing this register by one decreases the frequency by 0.195 percent of the
unadjusted value. Decrementing this register by one increases the frequency by 0.195 percent. This
register cannot be written when the CMON bit is set. Reset sets these bits to $80, centering the range
of possible adjustment.
8.7.4 ICG Trim Value
Address: $FF80
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
1
0
0
0
0
0
0
0
Figure 8-14. Internal Oscillator Trim Value (ICGT)
This register provides non-volatile storage for an optional oscillator trim value, which can be transferred
by the user software to the ICG Trim Register (ICGTR) when the device comes out of reset. (See 8.7.3
ICG Trim Register.)
8.7.5 ICG DCO Divider Register
Address: $0039
Bit 7
6
5
4
Read:
3
2
1
Bit 0
DDIV3
DDIV2
DDIV1
DDIV0
U
U
U
U
Write:
Reset:
0
0
= Unimplemented
0
0
U = Unaffected
Figure 8-15. ICG DCO Divider Control Register (ICGDVR)
DDIV3:DDIV0 — ICG DCO Divider Control Bits
These bits indicate the number of divide-by-twos (DDIV) that follow the digitally controlled oscillator.
When ICGON is set, DDIV is controlled by the digital loop filter. The range of valid values for DDIV is
from $0 to $9. Values of $A through $F are interpreted the same as $9. Since the DCO is active during
reset, reset has no effect on DSTG and the value may vary.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
99
Internal Clock Generator (ICG) Module
8.7.6 ICG DCO Stage Register
Address: $003A
Bit 7
6
5
4
3
2
1
Bit 0
Read:
DSTG7
DSTG6
DSTG5
DSTG4
DSTG3
DSTG2
DSTG1
DSTG0
Write:
R
R
R
R
R
R
R
R
Reset:
Unaffected by reset
R
= Reserved
Figure 8-16. ICG DCO Stage Control Register (ICGDSR)
DSTG7:DSTG0 — ICG DCO Stage Control Bits
These bits indicate the number of stages (above the minimum) in the digitally controlled oscillator. The
total number of stages is approximately equal to $1FF, so changing DSTG from $00 to $FF will
approximately double the period. Incrementing DSTG will increase the period (decrease the
frequency) by 0.202 percent to 0.368 percent (decrementing has the opposite effect). DSTG cannot
be written when ICGON is set to prevent inadvertent frequency shifting. When ICGON is set, DSTG is
controlled by the digital loop filter. Since the DCO is active during reset, reset has no effect on DSTG
and the value may vary.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
100
Freescale Semiconductor
Chapter 9
External Interrupt (IRQ)
9.1 Introduction
This section describes the non-maskable external interrupt (IRQ) input.
9.2 Features
Features include:
• Dedicated external interrupt pin (IRQ)
• Hysteresis buffer
• Programmable edge-only or edge- and level-interrupt sensitivity
• Automatic interrupt acknowledge
9.3 Functional Description
A logic 0 applied to the external interrupt pin can latch a central processor unit (CPU) interrupt request.
Figure 9-1 shows the structure of the IRQ module.
INTERNAL ADDRESS BUS
ACK
TO CPU FOR
BIL/BIH
INSTRUCTIONS
VECTOR
FETCH
DECODER
VDD
IRQF
D
IRQ
CLR
Q
SYNCHRONIZER
CK
IRQ
INTERRUPT
REQUEST
IRQ
LATCH
IMASK
MODE
HIGH
VOLTAGE
DETECT
TO MODE
SELECT
LOGIC
Figure 9-1. IRQ Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
101
External Interrupt (IRQ)
Interrupt signals on the IRQ pin are latched into the IRQ latch. An interrupt latch remains set until one of
these 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 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 IRQ 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 these occur:
• Vector fetch or software clear
• Return of the interrupt pin to logic 1
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 MODE 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 9-2.
9.4 IRQ Pin
A logic 0 on the IRQ 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 IRQ pin is both falling-edge sensitive and low-level sensitive. With MODE set,
both of these 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 1 to the ACK bit in
the interrupt status and control register (ISCR). The ACK bit is useful in applications that poll the
IRQ 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 IRQ
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 IRQ pin to logic 1 — As long as the IRQ pin is at logic 0, the IRQ latch remains set.
The vector fetch or software clear and the return of the IRQ pin to logic 1 can occur in any order. The
interrupt request remains pending as long as the IRQ 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
102
Freescale Semiconductor
IRQ Pin
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 9-2. IRQ Interrupt Flowchart
If the MODE bit is clear, the IRQ 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 IRQ pin.
NOTE
When using the level-sensitive interrupt trigger, avoid false interrupts by
masking interrupt requests in the interrupt routine.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
103
External Interrupt (IRQ)
9.5 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.
To allow software to clear the IRQ latch during a break interrupt, write a 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 0 to the BCFE bit. With BCFE at 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.
9.6 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 IRQ interrupt pin
Address:
$001D
Bit 7
6
5
4
3
2
Read:
0
0
0
0
IRQF
0
Write:
R
R
R
R
R
ACK
0
0
0
0
0
0
R
= Reserved
Reset:
1
Bit 0
IMASK
MODE
0
0
Figure 9-3. 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 1 to this write-only bit clears the IRQ latch. ACK always reads as 0. Reset clears ACK.
IMASK — IRQ Interrupt Mask Bit
Writing a 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 IRQ pin. Reset clears MODE.
1 = IRQ interrupt requests on falling edges and low levels
0 = IRQ interrupt requests on falling edges only
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
104
Freescale Semiconductor
Chapter 10
Keyboard Interrupt (KBD) Module
10.1 Introduction
The keyboard interrupt (KBD) module provides five independently maskable external interrupt pins.
10.2 Features
KBD features include:
• Five keyboard interrupt pins (PTA4/KBD4–PTA0/KBD0) with internal pullups, 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
10.3 Functional Description
Writing to the KBIE4–KBIE0 bits in the keyboard interrupt enable register independently enables or
disables each port 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 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 $FFE4 and $FFE5.
• 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
105
Keyboard Interrupt (KBD) Module
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA2/KBD2
PTA1/KBD1
PTA0/KBD0
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
DDRD
PORT D
PORT E
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
DDRE
IRQ
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PTB5/AD5
PTB4/AD4
PORT B
MONITOR ROM
310 BYTES
RST
PTA3/KBD3
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PTA4/KBD4
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 10-1. Block Diagram Highlighting Keyboard Block and Pins
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
106
Freescale Semiconductor
Functional Description
INTERNAL BUS
VECTOR FETCH
DECODER
ACKK
KBD0
VDD
.
TO PULLUP
ENABLE
RESET
D
CLR
KEYF
Q
SYNCHRONIZER
.
CK
KB0IE
.
KEYBOARD
INTERRUPT FF
KBD4
TO PULLUP
ENABLE
IMASKK
KEYBOARD
INTERRUPT
REQUEST
MODEK
KB4IE
Figure 10-2. Keyboard Module Block Diagram
The vector fetch or software clear and the return of all enabled keyboard interrupt pins to logic 1 may occur
in any order.
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 0 for software to read the
pin.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
107
Keyboard Interrupt (KBD) Module
10.4 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 DDRA bits in data direction
register A.
2. Write 1s to the appropriate port A data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard interrupt enable register.
10.5 Low-Power Modes
The WAIT and STOP instructions put the microcontroller unit (MCU) in low power-consumption standby
modes.
10.5.1 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.
10.5.2 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.
10.6 Keyboard Module During Break Interrupts
The BCFE bit in the break flag control register (SBFCR) enables software to clear status bits during the
break state.
To allow software to clear the KEYF bit during a break interrupt, write a 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 0 to the BCFE bit. With BCFE at 0, writing to the
keyboard acknowledge bit (ACKK) in the keyboard status and control register during the break state has
no effect. See 10.7.1 Keyboard Status and Control Register.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
108
Freescale Semiconductor
I/O Registers
10.7 I/O Registers
These registers control and monitor operation of the keyboard module:
• Keyboard status and control register, KBSCR
• Keyboard interrupt enable register, KBIER
10.7.1 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: $001A
Read:
Bit 7
6
5
4
3
2
0
0
0
0
KEYF
0
Write:
ACKK
Reset:
0
0
0
0
0
1
Bit 0
IMASKK
MODEK
0
0
0
= Unimplemented
Figure 10-3. Keyboard Status and Control Register (KBSCR)
Bits 7–4 — Not used
These read-only bits always read as 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
ACKK — Keyboard Acknowledge Bit
Writing a 1 to this write-only bit clears the keyboard interrupt request. ACKK always reads as 0. Reset
clears ACKK.
IMASKK — Keyboard Interrupt Mask Bit
Writing a 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
109
Keyboard Interrupt (KBD) Module
10.7.2 Keyboard Interrupt Enable Register
The keyboard interrupt enable register enables or disables each port A pin to operate as a keyboard
interrupt pin.
Address: $001B
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 10-4. 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 = KBDx pin enabled as keyboard interrupt pin
0 = KBDx pin not enabled as keyboard interrupt pin
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Chapter 11
Low-Voltage Inhibit (LVI) Module
11.1 Introduction
This section describes the low-voltage inhibit (LVI) module, which monitors the voltage on the VDD pin
and can force a reset when the VDD voltage falls to the LVI trip voltage.
11.2 Features
Features include:
• Programmable LVI reset
• Programmable power consumption
• 3 V or 5 V selectable trip point
11.3 Functional Description
Figure 11-1 shows the structure of the LVI module. The LVI is enabled out of reset. The following bits,
located in the configuration register, can alter the default conditions.
• Setting the LVI power disable bit, LVIPWRD, disables the LVI.
• Setting the LVI reset disable bit, LVIRSTD, prevents the LVI module from generating a reset.
• Setting the LVI enable in stop mode bit, LVISTOP, enables the LVI to continue monitoring the
voltage level on VDD, while in stop mode.
VDD
STOP INSTRUCTION
LVISTOP
FROM CONFIG-1
FROM CONFIG-1
LVIRSTD
LVIPWRD
FROM CONFIG-1
LOW VDD
DETECTOR
VDD > LVITRIPR = 0
LVI RESET
VDD < LVITRIPF = 1
LVI5OR3
FROM CONFIG-1
LVIOUT
Figure 11-1. LVI Module Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
111
Low-Voltage Inhibit (LVI) Module
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 11.3.2 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.
11.3.1 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 LVIPWRD bit must be at 0 to enable the LVI
module, and the LVIRSTD bit must be at 1 to disable LVI resets.
11.3.2 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. In the configuration register, the LVIPWRD
and LVIRSTD bits must be at 0 to enable the LVI module and to enable LVI resets.
11.3.3 False Reset Protection
False reset protection is provided by the hysteresis in the LVI trip circuit (refer to Table 11-1). Please refer
to 20.5 DC Electrical Characteristics for hysteresis value (VHYS) and rising and falling LVI trip values.
11.3.4 LVI Status Register
The LVI status register flags VDD voltages below the LVITRIPF level.
Address:
Read:
$FE0C
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 11-2. LVI Status Register (LVISR)
LVIOUT — LVI Output Bit
This read-only flag becomes set when the VDD voltage falls below the LVITRIPF voltage. (See
Table 11-1.) Reset clears the LVIOUT bit.
Table 11-1. LVIOUT Bit Indication
VDD
LVIOUT
At Level:
VDD > LVITRIPR
0
VDD < LVITRIPF
1
LVITRIPF < VDD < LVITRIPR
Previous Value
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
112
Freescale Semiconductor
LVI Interrupts
11.4 LVI Interrupts
The LVI module does not generate interrupt requests.
11.5 Low-Power Modes
The WAIT and STOP instructions put the microcontroller unit (MCU) in low power-consumption standby
modes.
11.5.1 Wait Mode
With the LVIPWRD bit in the configuration register programmed to 0, the LVI module is active after a
WAIT instruction.
With the LVIRSTD bit in the configuration register programmed to 0, the LVI module can generate a reset
and bring the MCU out of wait mode.
11.5.2 Stop Mode
With the LVISTOP bit in the configuration register programmed to a 1, and the LVIPWRD bit programmed
to a 0, the LVI module will be active after a STOP instruction.
With the LVIPWRD bit in the configuration register programmed to 1, and the LVISTOP bit programmed
to a 0, the LVI module will be inactive after a STOP instruction.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
113
Low-Voltage Inhibit (LVI) Module
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
114
Freescale Semiconductor
Chapter 12
Input/Output (I/O) Ports (PORTS)
12.1 Introduction
Twenty-four bidirectional input/output (I/O) pins form five 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.
12.2 Port A
Port A is a 7-bit general-purpose bidirectional I/O port that shares pin functions with the serial peripheral
interface (SPI) and keyboard (KBD) modules.
12.2.1 Port A Data Register
The port A data register contains a data latch for each of the seven port A pins.
Address:
$0000
Bit 7
Read:
Write:
0
6
5
4
3
2
1
Bit 0
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
KBD2
KBD1
KBD0
Reset:
Alternative Function:
Unaffected by reset
SS
SPSCK
KBD4
KBD3
= Unimplemented
Figure 12-1. Port A Data Register (PTA)
PTA[6:0] — 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.
12.2.2 Data Direction Register A
Data direction register A determines whether each port A pin is an input or an output. Writing a 1 to a
DDRA bit enables the output buffer for the corresponding port A pin; a 0 disables the output buffer.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
115
Input/Output (I/O) Ports (PORTS)
Address:
$0004
Bit 7
Read:
0
Write:
Reset:
0
6
5
4
3
2
1
Bit 0
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
0
0
0
0
0
0
0
= Unimplemented
Figure 12-2. Data Direction Register A (DDRA)
DDRA[6:0] — Data Direction Register A Bits
These read/write bits control port A data direction. Reset clears DDRA[6:0], 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 12-3 shows the port A I/O logic.
READ DDRA ($0004)
INTERNAL DATA BUS
WRITE DDRA ($0004)
RESET
DDRAx
WRITE PTA ($0000)
PTAx
PTAx
READ PTA ($0000)
Figure 12-3. Port A I/O Circuit
When bit DDRAx is a 1, reading address $0000 reads the PTAx data latch. When bit DDRAx is a 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 12-1 summarizes the operation of the port A pins.
Table 12-1. Port A Pin Functions
DDRA
Bit
PTA
Bit
I/O Pin
Mode
Accesses to DDRA
Read/Write
Read
Accesses to PTA
Write
0
X
Input, Hi-Z
DDRA[6:0]
Pin
PTA[6:0](1)
1
X
Output
DDRA[6:0]
PTA[6:0]
PTA[6:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
116
Freescale Semiconductor
Port B
12.3 Port B
Port B is an 8-bit special-function port that shares all of its pins with the analog-to-digital converter (ADC)
and some pin functions with TIMB.
Port B is designed so that the ADC function will take priority over the timer functionality on PTB6 and
PTB7. If the ADC is selected for a conversion on a previously enabled timer pin, the port pin will be
connected to the ADC and disconnected from the timer. If both the timer input capture and ADC functions
are being used on the same port pin, it is recommended that the timer channel be diabled before the pin
is enabled as an ADC input to avoid glitches. If both the timer output compare (or PWM) and ADC
functions are being used on the same port pin, it is recommended that the timer channel be disabled
before the pin is enabled as an ADC input.
12.3.1 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
AD2
AD1
AD0
Reset:
Unaffected by reset
Alternative Function:
AD7
AD6
Alternative Function:
TBCH1
TBCH0
AD5
AD4
AD3
Figure 12-4. 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.
AD[7:0] — ADC Channels
PTB7–PTB0 are eight ADC 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 a 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 3 Analog-to-Digital Converter (ADC) Module). 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 0.
TBCH[1:0] — Timer Channel I/O Bits
The PTB7/TBCH1–PTB6/TBCH0 pins are the TIMB input capture/output compare pins. The
edge/level select bits, ELSxB–ELSxA, determine whether the PTB7/TBCH1–PTB6/TBCH0 pins are
timer channel I/O pins or general-purpose I/O pins. See 18.8.1 TIMB Status and Control Register.
NOTE
Data direction register B (DDRB) does not affect the data direction of port
B pins that are being used by the TIMB. However, the DDRB bits always
determine whether reading port B returns the states of the latches or the
states of the pins. See Table 12-2.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
117
Input/Output (I/O) Ports (PORTS)
12.3.2 Data Direction Register B
Data direction register B determines whether each port B pin is an input or an output. Writing a 1 to a
DDRB bit enables the output buffer for the corresponding port B pin; a 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 12-5. 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
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 12-6 shows the port B I/O logic.
READ DDRB ($0005)
INTERNAL DATA BUS
WRITE DDRB ($0005)
RESET
DDRBx
WRITE PTB ($0001)
PTBx
PTBx
READ PTB ($0001)
Figure 12-6. Port B I/O Circuit
When DDRBx is a 1, reading address $0001 reads the PTBx data latch. When DDRBx is a 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 12-2 summarizes the operation of the port B pins.
Table 12-2. Port B Pin Functions
DDRB
Bit
PTB
Bit
I/O Pin
Mode
Accesses to DDRB
Accesses to PTB
Read/Write
Read
Write
0
X
Input, Hi-Z
DDRB[7:0]
Pin
PTB[7:0](1)
1
X
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
118
Freescale Semiconductor
Port C
12.4 Port C
Port C is an 5-bit general-purpose bidirectional I/O port that shares pin functions with the internal clock
generator (ICG) and serial peripheral interface (SPI) modules.
12.4.1 Port C Data Register
The port C data register contains a data latch for each of the five port C pins.
Address:
$0002
Bit 7
6
5
0
0
0
Read:
Write:
Reset:
4
3
2
1
Bit 0
PTC4
PTC3
PTC2
PTC1
PTC0
MCLK
MOSI
MISO
Unaffected by reset
Alternative Function:
OSC1
OSC2
= Unimplemented
Figure 12-7. Port C Data Register (PTC)
PTC[4:0] — 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.
MCLK — T12 System Clock Bit
The system clock is driven out of PTC2 when enabled by MCLKEN bit in PTCDDR7.
12.4.2 Data Direction Register C
Data direction register C determines whether each port C pin is an input or an output. Writing a 1 to a
DDRC bit enables the output buffer for the corresponding port C pin; a 0 disables the output buffer.
Address:
$0006
Bit 7
Read:
Write:
Reset:
MCLKEN
0
6
5
0
0
0
0
4
3
2
1
Bit 0
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
0
0
0
0
= Unimplemented
Figure 12-8. 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, PTC2 is under
the control of MCLKEN. Reset clears this bit.
1 = MCLK output enabled
0 = MCLK output disabled
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
119
Input/Output (I/O) Ports (PORTS)
DDRC[4:0] — Data Direction Register C Bits
These read/write bits control port C data direction. Reset clears DDRC[4:0] and MCLKEN, configuring
all port C pins as inputs.
1 = Corresponding port C pin configured as output
0 = Corresponding port C pin configured as input
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 12-9 shows the port C I/O logic.
READ DDRC ($0006)
INTERNAL DATA BUS
WRITE DDRC ($0006)
RESET
DDRCx
WRITE PTC ($0002)
PTCx
PTCx
READ PTC ($0002)
Figure 12-9. Port C I/O Circuit
When bit DDRCx is a 1, reading address $0002 reads the PTCx data latch. When bit DDRCx is a 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 12-3 summarizes the operation of the port C pins.
Table 12-3. Port C Pin Functions
DDRC
Bit
PTC
Bit
I/O Pin
Mode
Accesses to DDRC
Accesses to PTC
Read/Write
Read
Write
0
2
Input, Hi-Z
DDRC[7]
Pin
PTC2
1
2
Output
DDRC[7]
0
—
0
X
Input, Hi-Z
DDRC[4:0]
Pin
PTC[4:0](1)
1
X
Output
DDRC[4:0]
PTC[4:0]
PTC[4:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
12.5 Port D
Port D is a 2-bit special function port that shares its pins with the timer interface module (TIMA).
12.5.1 Port D Data Register
The port D data register contains a data latch for each of the two port D pins.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
120
Freescale Semiconductor
Port D
Address:
$0003
Bit 7
6
5
4
3
2
0
0
0
0
0
0
Read:
Write:
Reset:
1
Bit 0
PTD1
PTD0
TACH1
TACH0
Unaffected by reset
Alternative Function:
= Unimplemented
Figure 12-10. Port D Data Register (PTD)
PTD[1:0] — Port D Data Bits
PTD[1:0] are read/write, software programmable bits. Data direction of each port D pin is under the
control of the corresponding bit in data direction register D.
TACH[1:0] — Timer Channel I/O Bits
The PTD1/TACH1–PTD0/TACH0 pins are the TIMA input capture/output compare pins. The
edge/level select bits, ELSxB–ELSxA, determine whether the PTD1/TACH1–PTD0/TACH0 pins are
timer channel I/O pins or general-purpose I/O pins. See 17.8.1 TIMA Status and Control Register.
NOTE
Data direction register D (DDRD) does not affect the data direction of port
D pins that are being used by the TIMA. However, the DDRD bits always
determine whether reading port D returns the states of the latches or the
states of the pins. See Table 12-4.
12.5.2 Data Direction Register D
Data direction register D determines whether each port D pin is an input or an output. Writing a 1 to a
DDRD bit enables the output buffer for the corresponding port D pin; a 0 disables the output buffer.
Address:
Read:
$0007
Bit 7
6
5
4
3
2
0
0
0
0
0
0
0
0
0
0
0
0
Write:
Reset:
1
Bit 0
DDRD1
DDRD0
0
0
= Unimplemented
Figure 12-11. Data Direction Register D (DDRD)
DDRD[1:0] — Data Direction Register D Bits
These read/write bits control port D data direction. Reset clears DDRD[1:0], 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
121
Input/Output (I/O) Ports (PORTS)
Figure 12-12 shows the port D I/O logic.
READ DDRD ($0007)
INTERNAL DATA BUS
WRITE DDRD ($0007)
DDRDx
RESET
WRITE PTD ($0003)
PTDx
PTDx
READ PTD ($0003)
Figure 12-12. Port D I/O Circuit
When bit DDRDx is a 1, reading address $0003 reads the PTDx data latch. When bit DDRDx is a 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 12-4 summarizes the operation of the port D pins.
Table 12-4. Port D Pin Functions
DDRD
Bit
PTD
Bit
I/O Pin
Mode
Accesses to DDRD
Accesses to PTD
Read/Write
Read
Write
0
X
Input, Hi-Z
DDRD[1:0]
Pin
PTD[1:0](1)
1
X
Output
DDRD[1:0]
PTD[1:0]
PTD[1:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
12.6 Port E
Port E is a 2-bit special function port that shares its pins with the enhanced serial communications
interface module (ESCI).
12.6.1 Port E Data Register
The port E data register contains a data latch for each of the port E pins.
Address:
Read:
$0008
Bit 7
6
5
4
3
2
0
0
0
0
0
0
Write:
Reset:
1
Bit 0
PTE1
PTE0
RXD
TXD
Unaffected by reset
Alternative Function:
= Unimplemented
Figure 12-13. Port E Data Register (PTE)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
122
Freescale Semiconductor
Port E
PTE[1:0] — Port E Data Bits
These read/write bits are software programmable. Data direction of each port E pin is under the control
of the corresponding bit in data direction register E. Reset has no effect on PTE[1:0].
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
13.8.1 ESCI 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
13.8.1 ESCI 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 ESCI. However, the DDRE bits always
determine whether reading port E returns the states of the latches or the
states of the pins. See Table 12-5.
12.6.2 Data Direction Register E
Data direction register E determines whether each port E pin is an input or an output. Writing a 1 to a
DDRE bit enables the output buffer for the corresponding port E pin; a 0 disables the output buffer.
Address:
Read:
$000A
Bit 7
6
5
4
3
2
0
0
0
0
0
0
0
0
0
0
0
0
Write:
Reset:
1
Bit 0
DDRE1
DDRE0
0
0
= Unimplemented
Figure 12-14. Data Direction Register E (DDRE)
DDRE[1:0] — Data Direction Register E Bits
These read/write bits control port E data direction. Reset clears DDRE[1:0], 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
123
Input/Output (I/O) Ports (PORTS)
Figure 12-15 shows the port E I/O logic.
READ DDRE ($000A)
INTERNAL DATA BUS
WRITE DDRE ($000A)
RESET
DDREx
WRITE PTE ($0008)
PTEx
PTEx
READ PTE($0008)
Figure 12-15. Port E I/O Circuit
When bit DDREx is a 1, reading address $0008 reads the PTEx data latch. When bit DDREx is a 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 12-5 summarizes the operation of the port E pins.
Table 12-5. Port E Pin Functions
DDRE
Bit
PTE
Bit
I/O Pin
Mode
Accesses to DDRE
Accesses to PTE
Read/Write
Read
Write
0
X
Input, Hi-Z
DDRE[1:0]
Pin
PTE[1:0](1)
1
X
Output
DDRE[1:0]
PTE[1:0]
PTE[1:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
124
Freescale Semiconductor
Chapter 13
Enhanced Serial Communications Interface (ESCI) Module
13.1 Introduction
The enhanced serial communications interface (ESCI) module allows asynchronous communications
with peripheral devices and other microcontroller units (MCU).
13.2 Features
Features include:
• Full-duplex operation
• Standard mark/space non-return-to-zero (NRZ) format
• Programmable baud rates
• Programmable 8-bit or 9-bit character length
• Separately enabled transmitter and receiver
• Separate receiver and transmitter central processor unit (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
13.3 Pin Name Conventions
The generic names of the ESCI input/output (I/O) pins are:
• RxD (receive data)
• TxD (transmit data)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
125
Enhanced Serial Communications Interface (ESCI) Module
INTERNAL BUS
M68HC08 CPU
5-BIT KEYBOARD
INTERRUPT MODULE
USER FLASH
15,872 BYTES
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
PTE1/RxD
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
DDRE
CONFIGURATION REGISTER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
SINGLE EXTERNAL IRQ
MODULE
PTB3/AD3
DDRD
INTERNAL CLOCK
GENERATOR MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 13-1. Block Diagram Highlighting ESCI Block and Pins
ESCI I/O lines are implemented by sharing parallel I/O port pins. The full name of an ESCI input or output
reflects the name of the shared port pin. Table 13-1 shows the full names and the generic names of the
ESCI I/O pins. The generic pin names appear in the text of this section.
Table 13-1. Pin Name Conventions
Generic Pin Names
Full Pin Names
RxD
TxD
PTE1/RxD
PTE0/TxD
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
126
Freescale Semiconductor
Functional Description
13.4 Functional Description
Figure 13-2 shows the structure of the ESCI module. The ESCI allows full-duplex, asynchronous, NRZ
serial communication between the MCU and remote devices, including other MCUs. The transmitter and
receiver of the ESCI operate independently, although they use the same baud rate generator. During
normal operation, the CPU monitors the status of the ESCI, writes the data to be transmitted, and
processes received data.
The baud rate clock source for the ESCI can be selected via the configuration bit, ESCIBDSRC, of the
CONFIG2 register ($001E).
INTERNAL BUS
ERROR
INTERRUPT
CONTROL
RECEIVE
SHIFT REGISTER
RxD
ESCI DATA
REGISTER
RECEIVER
INTERRUPT
CONTROL
TRANSMITTER
INTERRUPT
CONTROL
ESCI DATA
REGISTER
RxD
SCI_TxD
TRANSMIT
SHIFT REGISTER
TXINV
LINR
SCTIE
ARBITER-
BUS_CLK
R8
TCIE
TxD
SL
T8
SCRIE
ILIE
ACLK bit in SCIACTL
TE
RE
TC
RWU
SBK
SCRF
OR
ORIE
IDLE
NF
NEIE
FE
FEIE
PE
SCI_CLK
SCTE
PEIE
LOOPS
LOOPS
WAKEUP
CONTROL
BUS CLOCK
CGMXCLK
ENSCI
Enhanced
PRESCALER
TRANSMIT
CONTROL
FLAG
CONTROL
BKF
M
RPF
WAKE
ILTY
÷4
PRESCALER
ESCIBDSRC
FROM
CONFIG2
SL
RECEIVE
CONTROL
ENSCI
BAUD RATE
GENERATOR
÷ 16
PEN
PTY
DATA SELECTION
CONTROL
SL=1 -> SCI_CLK = BUSCLK
SL=0 -> SCI_CLK = CGMXCLK (4x BUSCLK)
Figure 13-2. ESCI Module Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
127
Enhanced Serial Communications Interface (ESCI) Module
13.4.1 Data Format
The SCI uses the standard non-return-to-zero mark/space data format illustrated in Figure 13-3.
PARITY
OR DATA
BIT
8-BIT DATA FORMAT
(BIT M IN SCC1 CLEAR)
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
STOP
BIT
PARITY
OR DATA
BIT
9-BIT DATA FORMAT
(BIT M IN SCC1 SET)
START
BIT
NEXT
START
BIT
BIT 6
BIT 7
BIT 8
NEXT
START
BIT
STOP
BIT
Figure 13-3. SCI Data Formats
13.4.2 Transmitter
Figure 13-4 shows the structure of the SCI transmitter. The baud rate clock source for the ESCI can be
selected via the configuration bit, ESCIBDSRC.
INTERNAL BUS
BAUD
DIVIDER
÷ 16
ESCI DATA REGISTER
SCP1
11-BIT
TRANSMIT
SHIFT REGISTER
STOP
SCP0
SCR1
H
SCR2
8
7
6
5
4
3
2
START
PRESCALER
÷4
1
0
L
SCI_TxD
PSSB4
PSSB3
PSSB2
PTY
MSB
PARITY
GENERATION
BREAK
(ALL ZEROS)
PEN
PREAMBLE
(ALL ONES)
PDS0
M
SHIFT ENABLE
PDS1
TXINV
LOAD FROM SCDR
PDS2
TRANSMITTER CPU INTERRUPT REQUEST
BUS CLOCK
PRESCALER
SCR0
T8
TRANSMITTER
CONTROL LOGIC
PSSB1
SCTE
SBK
PSSB0
SCTE
SCTIE
TC
TCIE
LOOPS
SCTIE
ENSCI
TC
TE
TCIE
LINT
Figure 13-4. ESCI Transmitter
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
128
Freescale Semiconductor
Functional Description
13.4.2.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in ESCI control
register 1 (SCC1) determines character length. When transmitting 9-bit data, bit T8 in ESCI control
register 3 (SCC3) is the ninth bit (bit 8).
13.4.2.2 Character Transmission
During an ESCI transmission, the transmit shift register shifts a character out to the TxD pin. The ESCI
data register (SCDR) is the write-only buffer between the internal data bus and the transmit shift register.
To initiate an ESCI transmission:
1. Enable the ESCI by writing a 1 to the enable ESCI bit (ENSCI) in ESCI control register 1 (SCC1).
2. Enable the transmitter by writing a 1 to the transmitter enable bit (TE) in ESCI control register 2
(SCC2).
3. Clear the ESCI transmitter empty bit (SCTE) by first reading ESCI status register 1 (SCS1) and
then writing to the SCDR. For 9-bit data, also write the T8 bit in SCC3.
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 1s. After the preamble shifts out, control logic transfers the SCDR data into the transmit
shift register. A 0 start bit automatically goes into the least significant bit (LSB) position of the transmit shift
register. A 1 stop bit goes into the most significant bit (MSB) position.
The ESCI 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 ESCI 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 ESCI control register 1 (SCC1), the transmitter and
receiver relinquish control of the port E pins.
13.4.2.3 Break Characters
Writing a 1 to the send break bit, SBK, in SCC2 loads the transmit shift register with a break character.
For TXINV = 0 (output not inverted), a transmitted break character contains all 0s and has no start, stop,
or parity bit. Break character length depends on the M bit in SCC1 and the LINR bits in SCBR. As long as
SBK is at 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 1. The automatic 1 at the end of a break character guarantees the recognition of
the start bit of the next character.
When LINR is cleared in SCBR, the ESCI recognizes a break character when a start bit is followed by
eight or nine 0 data bits and a 0 where the stop bit should be, resulting in a total of 10 or 11 consecutive
0 data bits. When LINR is set in SCBR, the ESCI recognizes a break character when a start bit is followed
by 9 or 10 consecutive 0 data bits and a 0 where the stop bit should be, resulting in a total of 11 or 12
consecutive 0 data bits.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
129
Enhanced Serial Communications Interface (ESCI) Module
Receiving a break character has these effects on ESCI registers:
• Sets the framing error bit (FE) in SCS1
• Sets the ESCI receiver full bit (SCRF) in SCS1
• Clears the ESCI 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
13.4.2.4 Idle Characters
For TXINV = 0 (output not inverted), a transmitted idle character contains all 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 0 and one half data bit length of 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.
When queueing an idle character, return the TE bit to 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.
13.4.2.5 Inversion of Transmitted Output
The transmit inversion bit (TXINV) in ESCI 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 1. See
13.8.1 ESCI Control Register 1.
13.4.2.6 Transmitter Interrupts
These conditions can generate CPU interrupt requests from the ESCI transmitter:
• ESCI 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 ESCI 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
130
Freescale Semiconductor
Functional Description
13.4.3 Receiver
Figure 13-5 shows the structure of the ESCI receiver.
INTERNAL BUS
SCP1
SCR2
SCP0
SCR0
BUS CLOCK
BAUD
DIVIDER
DATA
RECOVERY
RxD
BKF
PDS2
STOP
÷ 16
ALL ZEROS
RPF
H
ALL ONES
PRESCALER
PRESCALER
÷4
ESCI DATA REGISTER
START
SCR1
11-BIT
RECEIVE SHIFT REGISTER
8
7
6
5
4
3
2
1
0
L
MSB
LINR
PDS1
PDS0
PSSB4
PSSB3
PSSB2
M
WAKE
ILTY
PSSB1
PEN
PSSB0
PTY
SCRF
WAKEUP
LOGIC
IDLE
R8
PARITY
CHECKING
IDLE
ILIE
CPU INTERRUPT
REQUEST
SCRF
SCRIE
ILIE
SCRIE
OR
ORIE
ERROR CPU
INTERRUPT REQUEST
RWU
NF
NEIE
FE
FEIE
PE
PEIE
OR
ORIE
NF
NEIE
FE
FEIE
PE
PEIE
Figure 13-5. ESCI Receiver Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
131
Enhanced Serial Communications Interface (ESCI) Module
13.4.3.1 Character Length
The receiver can accommodate either 8-bit or 9-bit data. The state of the M bit in ESCI control register 1
(SCC1) determines character length. When receiving 9-bit data, bit R8 in ESCI control register 3 (SCC3)
is the ninth bit (bit 8). When receiving 8-bit data, bit R8 is a copy of the eighth bit (bit 7).
13.4.3.2 Character Reception
During an ESCI reception, the receive shift register shifts characters in from the RxD pin. The ESCI 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 ESCI receiver full bit, SCRF, in ESCI status register 1 (SCS1) becomes set, indicating
that the received byte can be read. If the ESCI receive interrupt enable bit, SCRIE, in SCC2 is also set,
the SCRF bit generates a receiver CPU interrupt request.
13.4.3.3 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 these times
(see Figure 13-6):
• After every start bit
• After the receiver detects a data bit change from 1 to 0 (after the majority of data bit samples at
RT8, RT9, and RT10 returns a valid 1 and the majority of the next RT8, RT9, and RT10 samples
returns a valid 0)
To locate the start bit, data recovery logic does an asynchronous search for a 0 preceded by three 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 13-6. Receiver Data Sampling
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
132
Freescale Semiconductor
Functional Description
To verify the start bit and to detect noise, data recovery logic takes samples at RT3, RT5, and RT7.
Table 13-2 summarizes the results of the start bit verification samples.
Table 13-2. Start Bit Verification
RT3, RT5, and RT7 Samples
000
001
010
011
100
101
110
111
Start Bit Verification
Yes
Yes
Yes
No
Yes
No
No
No
Noise Flag
0
1
1
0
1
0
0
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 13-3 summarizes the results of the data bit samples.
Table 13-3. Data Bit Recovery
RT8, RT9, and RT10 Samples
000
001
010
011
100
101
110
111
Data Bit Determination
0
0
0
1
0
1
1
1
Noise Flag
0
1
1
1
1
1
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 1s following a
successful start bit verification, the noise flag (NF) is set and the receiver
assumes that the bit is a start bit.
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and RT10. Table 13-4
summarizes the results of the stop bit samples.
Table 13-4. Stop Bit Recovery
RT8, RT9, and RT10 Samples
000
001
010
011
100
101
110
111
Framing Error Flag
1
1
1
0
1
0
0
0
Noise Flag
0
1
1
1
1
1
1
0
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
133
Enhanced Serial Communications Interface (ESCI) Module
13.4.3.4 Framing Errors
If the data recovery logic does not detect a 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.
13.4.3.5 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 13-7 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 13-7. Slow 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 13-7, 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 13-7, 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
134
Freescale Semiconductor
Functional Description
Fast Data Tolerance
Figure 13-8 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 13-8. 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 13-8, 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 13-8, 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
13.4.3.6 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:
1. Address mark — An address mark is a 1 in the MSB 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 ESCI 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.
2. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
135
Enhanced Serial Communications Interface (ESCI) Module
does not set the receiver idle bit, IDLE, or the ESCI receiver full bit, SCRF. The idle line type bit,
ILTY, determines whether the receiver begins counting 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 will cause the receiver to wake up.
13.4.3.7 Receiver Interrupts
These sources can generate CPU interrupt requests from the ESCI receiver:
• ESCI 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 ESCI 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 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.
13.4.3.8 Error Interrupts
These 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 ESCI error CPU interrupt requests.
• Noise flag (NF) — The NF bit is set when the ESCI 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 ESCI error CPU interrupt requests.
• Framing error (FE) — The FE bit in SCS1 is set when a 0 occurs where the receiver expects a stop
bit. The framing error interrupt enable bit, FEIE, in SCC3 enables FE to generate ESCI error CPU
interrupt requests.
• Parity error (PE) — The PE bit in SCS1 is set when the ESCI detects a parity error in incoming
data. The parity error interrupt enable bit, PEIE, in SCC3 enables PE to generate ESCI error CPU
interrupt requests.
13.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
13.5.1 Wait Mode
The ESCI module remains active in wait mode. Any enabled CPU interrupt request from the ESCI module
can bring the MCU out of wait mode.
If ESCI module functions are not required during wait mode, reduce power consumption by disabling the
module before executing the WAIT instruction.
13.5.2 Stop Mode
The ESCI module is inactive in stop mode. The STOP instruction does not affect ESCI register states.
ESCI module operation resumes after the MCU exits stop mode.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
136
Freescale Semiconductor
ESCI During Break Module Interrupts
Because the internal clock is inactive during stop mode, entering stop mode during an ESCI transmission
or reception results in invalid data.
13.6 ESCI During Break Module Interrupts
The BCFE bit in the break flag control register (SBFCR) enables software to clear status bits during the
break state. See 19.2 Break Module (BRK).
To allow software to clear status bits during a break interrupt, write a 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 0 to the BCFE bit. With BCFE at 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 0. After the break, doing the
second step clears the status bit.
13.7 I/O Signals
Port E shares two of its pins with the ESCI module. The two ESCI I/O pins are:
• PTE0/TxD — transmit data
• PTE1/RxD — receive data
13.7.1 PTE0/TxD (Transmit Data)
The PTE0/TxD pin is the serial data output from the ESCI transmitter. The ESCI shares the PTE0/TxD
pin with port E. When the ESCI is enabled, the PTE0/TxD pin is an output regardless of the state of the
DDRE0 bit in data direction register E (DDRE).
13.7.2 PTE1/RxD (Receive Data)
The PTE1/RxD pin is the serial data input to the ESCI receiver. The ESCI shares the PTE1/RxD pin with
port E. When the ESCI is enabled, the PTE1/RxD pin is an input regardless of the state of the DDRE1 bit
in data direction register E (DDRE).
13.8 I/O Registers
These I/O registers control and monitor ESCI operation:
• ESCI control register 1, SCC1
• ESCI control register 2, SCC2
• ESCI control register 3, SCC3
• ESCI status register 1, SCS1
• ESCI status register 2, SCS2
• ESCI data register, SCDR
• ESCI baud rate register, SCBR
• ESCI prescaler register, SCPSC
• ESCI arbiter control register, SCIACTL
• ESCI arbiter data register, SCIADAT
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
137
Enhanced Serial Communications Interface (ESCI) Module
13.8.1 ESCI Control Register 1
ESCI control register 1 (SCC1):
• Enables loop mode operation
• Enables the ESCI
• Controls output polarity
• Controls character length
• Controls ESCI wakeup method
• Controls idle character detection
• Enables parity function
• Controls parity type
Address: $0010
Read:
Write:
Reset:
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
Figure 13-9. ESCI 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
ESCI, 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
ENSCI — Enable ESCI Bit
This read/write bit enables the ESCI and the ESCI baud rate generator. Clearing ENSCI sets the SCTE
and TC bits in ESCI status register 1 and disables transmitter interrupts. Reset clears the ENSCI bit.
1 = ESCI enabled
0 = ESCI 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 ESCI characters are eight or nine bits long (See
Table 13-5).The ninth bit can serve as a receiver wakeup signal or as a parity bit. Reset clears the M
bit.
1 = 9-bit ESCI characters
0 = 8-bit ESCI characters
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
138
Freescale Semiconductor
I/O Registers
Table 13-5. Character Format Selection
Control Bits
Character Format
M
PEN:PTY
Start Bits
Data Bits
Parity
Stop Bits
Character Length
0
0 X
1
8
None
1
10 bits
1
0 X
1
9
None
1
11 bits
0
1 0
1
7
Even
1
10 bits
0
1 1
1
7
Odd
1
10 bits
1
1 0
1
8
Even
1
11 bits
1
1 1
1
8
Odd
1
11 bits
WAKE — Wakeup Condition Bit
This read/write bit determines which condition wakes up the ESCI: a 1 (address mark) in the MSB
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 ESCI starts counting 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 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 ESCI parity function (see Table 13-5). When enabled, the parity
function inserts a parity bit in the MSB position (see Table 13-3). Reset clears the PEN bit.
1 = Parity function enabled
0 = Parity function disabled
PTY — Parity Bit
This read/write bit determines whether the ESCI generates and checks for odd parity or even parity
(see Table 13-5). 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
139
Enhanced Serial Communications Interface (ESCI) Module
13.8.2 ESCI Control Register 2
ESCI control register 2 (SCC2):
• Enables these CPU interrupt requests:
– SCTE bit to generate transmitter CPU interrupt requests
– TC bit to generate transmitter CPU interrupt requests
– SCRF bit to generate receiver CPU interrupt requests
– IDLE bit to generate receiver CPU interrupt requests
• Enables the transmitter
• Enables the receiver
• Enables ESCI wakeup
• Transmits ESCI break characters
Address: $0011
Read:
Write:
Reset:
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 13-10. ESCI Control Register 2 (SCC2)
SCTIE — ESCI Transmit Interrupt Enable Bit
This read/write bit enables the SCTE bit to generate ESCI transmitter CPU interrupt requests. Setting
the SCTIE bit in SCC2 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 ESCI 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
SCRIE — ESCI Receive Interrupt Enable Bit
This read/write bit enables the SCRF bit to generate ESCI receiver CPU interrupt requests. Setting the
SCRIE bit in SCC2 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 ESCI 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
140
Freescale Semiconductor
I/O Registers
TE — Transmitter Enable Bit
Setting this read/write bit begins the transmission by sending a preamble of 10 or 11 consecutive 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 (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 ESCI bit (ENSCI) is
clear. ENSCI is in ESCI 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 ESCI bit (ENSCI) is
clear. ENSCI is in ESCI 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 1. The 1 after the
break character guarantees recognition of a valid start bit. If SBK remains set, the transmitter
continuously transmits break characters with no 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 ESCI to send a break
character instead of a preamble.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
141
Enhanced Serial Communications Interface (ESCI) Module
13.8.3 ESCI Control Register 3
ESCI control register 3 (SCC3):
• Stores the ninth ESCI data bit received and the ninth ESCI data bit to be transmitted.
• Enables these interrupts:
– Receiver overrun
– Noise error
– Framing error
– Parity error
Address:
$0012
Bit 7
Read:
R8
Write:
Reset:
U
6
5
4
3
2
1
Bit 0
T8
R
R
ORIE
NEIE
FEIE
PEIE
0
0
0
0
0
0
0
R
= Reserved
= Unimplemented
U = Unaffected
Figure 13-11. ESCI Control Register 3 (SCC3)
R8 — Received Bit 8
When the ESCI 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 ESCI 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 ESCI 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 clears the T8 bit.
ORIE — Receiver Overrun Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the receiver overrun bit,
OR. Reset clears ORIE.
1 = ESCI error CPU interrupt requests from OR bit enabled
0 = ESCI error CPU interrupt requests from OR bit disabled
NEIE — Receiver Noise Error Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the noise error bit, NE.
Reset clears NEIE.
1 = ESCI error CPU interrupt requests from NE bit enabled
0 = ESCI error CPU interrupt requests from NE bit disabled
FEIE — Receiver Framing Error Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the framing error bit, FE.
Reset clears FEIE.
1 = ESCI error CPU interrupt requests from FE bit enabled
0 = ESCI error CPU interrupt requests from FE bit disabled
PEIE — Receiver Parity Error Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the parity error bit, PE.
Reset clears PEIE.
1 = ESCI error CPU interrupt requests from PE bit enabled
0 = ESCI error CPU interrupt requests from PE bit disabled
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
142
Freescale Semiconductor
I/O Registers
13.8.4 ESCI Status Register 1
ESCI status register 1 (SCS1) contains flags to signal these 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:
$0013
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 13-12. ESCI Status Register 1 (SCS1)
SCTE — ESCI 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 ESCI transmitter CPU interrupt request. When the SCTIE bit in SCC2 is set,
SCTE generates an ESCI 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 ESCI 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 — ESCI Receiver Full Bit
This clearable, read-only bit is set when the data in the receive shift register transfers to the ESCI data
register. SCRF can generate an ESCI 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 1s appear on the receiver input. IDLE
generates an ESCI receiver 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
143
Enhanced Serial Communications Interface (ESCI) Module
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 ESCI 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 13-13 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.
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 13-13. Flag Clearing Sequence
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
144
Freescale Semiconductor
I/O Registers
NF — Receiver Noise Flag Bit
This clearable, read-only bit is set when the ESCI 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
FE — Receiver Framing Error Bit
This clearable, read-only bit is set when a 0 is accepted as the stop bit. FE generates an ESCI 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 ESCI 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
13.8.5 ESCI Status Register 2
ESCI status register 2 (SCS2) contains flags to signal these conditions:
• Break character detected
• Incoming data
Address:
Read:
Write:
Reset:
$0014
Bit 7
0
0
6
0
5
0
4
0
3
0
2
0
1
BKF
Bit 0
RPF
0
0
= Unimplemented
0
0
0
0
0
Figure 13-14. ESCI Status Register 2 (SCS2)
BKF — Break Flag Bit
This clearable, read-only bit is set when the ESCI 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 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 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 ESCI module or entering stop mode can show whether a reception is in
progress.
1 = Reception in progress
0 = No reception in progress
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
145
Enhanced Serial Communications Interface (ESCI) Module
13.8.6 ESCI Data Register
The ESCI data register (SCDR) is the buffer between the internal data bus and the receive and transmit
shift registers. Reset has no effect on data in the ESCI data register.
Address:
$0015
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 13-15. ESCI Data Register (SCDR)
R7/T7:R0/T0 — Receive/Transmit Data Bits
Reading address $0015 accesses the read-only received data bits, R7:R0. Writing to address $0015
writes the data to be transmitted, T7:T0. Reset has no effect on the ESCI data register.
NOTE
Do not use read-modify-write instructions on the ESCI data register.
13.8.7 ESCI Baud Rate Register
The ESCI baud rate register (SCBR) together with the ESCI prescaler register selects the baud rate for
both the receiver and the transmitter.
NOTE
There are two prescalers available to adjust the baud rate. One in the ESCI
baud rate register and one in the ESCI prescaler register.
Address:
Read:
Write:
Reset:
$0016
Bit 7
6
5
4
3
2
1
Bit 0
R
LINR
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
0
0
R
= Reserved
Figure 13-16. ESCI Baud Rate Register (SCBR)
LINR — LIN Receiver Bit
This read/write bit selects the enhanced ESCI features for slave nodes in the local interconnect
network (LIN) protocol as shown in Table 13-6. Reset clears LINR.
Table 13-6. ESCI LIN Control Bits
LINR
M
0
X
Normal ESCI functionality
Functionality
1
0
13-bit break detect enabled for LIN receiver
1
1
14-bit break detect enabled for LIN receiver
In LIN (version 1.2) systems, the master node transmits a break character which will appear as
11.05–14.95 dominant bits to the slave node. A data character of 0x00 sent from the master might
appear as 7.65–10.35 dominant bit times. This is due to the oscillator tolerance requirement that the
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
146
Freescale Semiconductor
I/O Registers
slave node must be within ±15% of the master node's oscillator. Since a slave node cannot know if it
is running faster or slower than the master node (prior to synchronization), the LINR bit allows the slave
node to differentiate between a 0x00 character of 10.35 bits and a break character of 11.05 bits. The
break symbol length must be verified in software in any case, but the LINR bit serves as a filter,
preventing false detections of break characters that are really 0x00 data characters.
SCP1 and SCP0 — ESCI Baud Rate Register Prescaler Bits
These read/write bits select the baud rate register prescaler divisor as shown in Table 13-7. Reset
clears SCP1 and SCP0.
Table 13-7. ESCI Baud Rate Prescaling
Baud Rate Register
Prescaler Divisor (BPD)
1
3
4
13
SCP[1:0]
0
0
1
1
0
1
0
1
SCR2–SCR0 — ESCI Baud Rate Select Bits
These read/write bits select the ESCI baud rate divisor as shown in Table 13-8. Reset clears
SCR2–SCR0.
Table 13-8. ESCI Baud Rate Selection
SCR[2:1:0]
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
Baud Rate Divisor (BD)
1
2
4
8
16
32
64
128
ESCI Prescaler Register
The ESCI prescaler register (SCPSC) together with the ESCI baud rate register selects the baud rate for
both the receiver and the transmitter.
NOTE
There are two prescalers available to adjust the baud rate. One in the ESCI
baud rate register and one in the ESCI prescaler register.
Address:
Read:
Write:
Reset:
$0017
Bit 7
6
5
4
3
2
1
Bit 0
PDS2
PDS1
PDS0
PSSB4
PSSB3
PSSB2
PSSB1
PSSB0
0
0
0
0
0
0
0
0
Figure 13-17. ESCI Prescaler Register (SCPSC)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
147
Enhanced Serial Communications Interface (ESCI) Module
PDS2–PDS0 — Prescaler Divisor Select Bits
These read/write bits select the prescaler divisor as shown in Table 13-9. Reset clears PDS2–PDS0.
NOTE
The setting of ‘000’ will bypass not only this prescaler but also the Prescaler
Divisor Fine Adjust (PDFA). It is not recommended to bypass the prescaler
while ENSCI is set, because the switching is not glitch free.
Table 13-9. ESCI Prescaler Division Ratio
PDS[2:1:0]
Prescaler Divisor (PD)
0 0 0
Bypass this prescaler
0 0 1
2
0 1 0
3
0 1 1
4
1 0 0
5
1 0 1
6
1 1 0
7
1 1 1
8
PSSB4–PSSB0 — Clock Insertion Select Bits
These read/write bits select the number of clocks inserted in each 32 output cycle frame to achieve
more timing resolution on the average prescaler frequency as shown in Table 13-10. Reset clears
PSSB4–PSSB0.
Use the following formula to calculate the ESCI baud rate:
Baud rate =
Frequency of the SCI clock source
64 x BPD x BD x (PD + PDFA)
where:
Frequency of the SCI clock source = fBus or CGMXCLK (selected by
ESCIBDSRC in the CONFIG2 register)
BPD = Baud rate register prescaler divisor
BD = Baud rate divisor
PD = Prescaler divisor
PDFA = Prescaler divisor fine adjust
Table 13-11 shows the ESCI baud rates that can be generated with a 4.9152-MHz clock frequency.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
148
Freescale Semiconductor
I/O Registers
Table 13-10. ESCI Prescaler Divisor Fine Adjust
PSSB[4:3:2:1:0]
Prescaler Divisor Fine Adjust (PDFA)
0 0 0 0 0
0/32 = 0
0 0 0 0 1
1/32 = 0.03125
0 0 0 1 0
2/32 = 0.0625
0 0 0 1 1
3/32 = 0.09375
0 0 1 0 0
4/32 = 0.125
0 0 1 0 1
5/32 = 0.15625
0 0 1 1 0
6/32 = 0.1875
0 0 1 1 1
7/32 = 0.21875
0 1 0 0 0
8/32 = 0.25
0 1 0 0 1
9/32 = 0.28125
0 1 0 1 0
10/32 = 0.3125
0 1 0 1 1
11/32 = 0.34375
0 1 1 0 0
12/32 = 0.375
0 1 1 0 1
13/32 = 0.40625
0 1 1 1 0
14/32 = 0.4375
0 1 1 1 1
15/32 = 0.46875
1 0 0 0 0
16/32 = 0.5
1 0 0 0 1
17/32 = 0.53125
1 0 0 1 0
18/32 = 0.5625
1 0 0 1 1
19/32 = 0.59375
1 0 1 0 0
20/32 = 0.625
1 0 1 0 1
21/32 = 0.65625
1 0 1 1 0
22/32 = 0.6875
1 0 1 1 1
23/32 = 0.71875
1 1 0 0 0
24/32 = 0.75
1 1 0 0 1
25/32 = 0.78125
1 1 0 1 0
26/32 = 0.8125
1 1 0 1 1
27/32 = 0.84375
1 1 1 0 0
28/32 = 0.875
1 1 1 0 1
29/32 = 0.90625
1 1 1 1 0
30/32 = 0.9375
1 1 1 1 1
31/32 = 0.96875
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
149
Enhanced Serial Communications Interface (ESCI) Module
Table 13-11. ESCI Baud Rate Selection Examples
PDS[2:1:0]
PSSB[4:3:2:1:0]
SCP[1:0]
Prescaler
Divisor
(BPD)
SCR[2:1:0]
Baud Rate
Divisor
(BD)
0 0 0
X X X X X
0 0
1
0 0 0
1
76,800
1 1 1
0 0 0 0 0
0 0
1
0 0 0
1
9600
1 1 1
0 0 0 0 1
0 0
1
0 0 0
1
9562.65
1 1 1
0 0 0 1 0
0 0
1
0 0 0
1
9525.58
1 1 1
1 1 1 1 1
0 0
1
0 0 0
1
8563.07
0 0 0
X X X X X
0 0
1
0 0 1
2
38,400
0 0 0
X X X X X
0 0
1
0 1 0
4
19,200
0 0 0
X X X X X
0 0
1
0 1 1
8
9600
0 0 0
X X X X X
0 0
1
1 0 0
16
4800
0 0 0
X X X X X
0 0
1
1 0 1
32
2400
0 0 0
X X X X X
0 0
1
1 1 0
64
1200
0 0 0
X X X X X
0 0
1
1 1 1
128
600
0 0 0
X X X X X
0 1
3
0 0 0
1
25,600
0 0 0
X X X X X
0 1
3
0 0 1
2
12,800
0 0 0
X X X X X
0 1
3
0 1 0
4
6400
0 0 0
X X X X X
0 1
3
0 1 1
8
3200
0 0 0
X X X X X
0 1
3
1 0 0
16
1600
0 0 0
X X X X X
0 1
3
1 0 1
32
800
0 0 0
X X X X X
0 1
3
1 1 0
64
400
0 0 0
X X X X X
0 1
3
1 1 1
128
200
0 0 0
X X X X X
1 0
4
0 0 0
1
19,200
0 0 0
X X X X X
1 0
4
0 0 1
2
9600
0 0 0
X X X X X
1 0
4
0 1 0
4
4800
0 0 0
X X X X X
1 0
4
0 1 1
8
2400
0 0 0
X X X X X
1 0
4
1 0 0
16
1200
0 0 0
X X X X X
1 0
4
1 0 1
32
600
0 0 0
X X X X X
1 0
4
1 1 0
64
300
0 0 0
X X X X X
1 0
4
1 1 1
128
150
0 0 0
X X X X X
1 1
13
0 0 0
1
5908
0 0 0
X X X X X
1 1
13
0 0 1
2
2954
0 0 0
X X X X X
1 1
13
0 1 0
4
1477
0 0 0
X X X X X
1 1
13
0 1 1
8
739
0 0 0
X X X X X
1 1
13
1 0 0
16
369
0 0 0
X X X X X
1 1
13
1 0 1
32
185
0 0 0
X X X X X
1 1
13
1 1 0
64
92
0 0 0
X X X X X
1 1
13
1 1 1
128
46
Baud Rate
(ESCI Clock = 4.9152 MHz)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
150
Freescale Semiconductor
ESCI Arbiter
13.9 ESCI Arbiter
The ESCI module comprises an arbiter module designed to support software for communication tasks as
bus arbitration, baud rate recovery and break time detection. The arbiter module consists of an 9-bit
counter with 1-bit overflow and control logic. The CPU can control operation mode via the ESCI arbiter
control register (SCIACTL).
13.9.1 ESCI Arbiter Control Register
Address:
$0018
Bit 7
Read:
Write:
Reset:
AM1
0
6
ALOST
0
5
4
AM0
ACLK
0
0
3
2
1
Bit 0
AFIN
ARUN
AROVFL
ARD8
0
0
0
0
= Unimplemented
Figure 13-18. ESCI Arbiter Control Register (SCIACTL)
AM1 and AM0 — Arbiter Mode Select Bits
As shown in Table 13-12, these read/write bits select the mode of the arbiter module. Reset clears
AM1 and AM0.
Table 13-12. ESCI Arbiter Selectable Modes
AM[1:0]
ESCI Arbiter Mode
0 0
Idle / counter reset
0 1
Bit time measurement
1 0
Bus arbitration
1 1
Reserved / do not use
ALOST — Arbitration Lost Flag
This read-only bit indicates loss of arbitration. Clear ALOST by writing a 0 to AM1. Reset clears
ALOST.
ACLK — Arbiter Counter Clock Select Bit
This read/write bit selects the arbiter counter clock source. Reset clears ACLK.
1 = Arbiter counter is clocked with one quarter of the ESCI input clock generated by the ESCI
prescaler.
0 = Arbiter counter is clocked with the bus clock divided by four
NOTE
For ACLK=1, the Arbiter input clock is driven from the ESCI prescaler. The
prescaler can be clocked by either the bus clock or CGMXCLK depending
on the state of the ESCIBDSRC bit in CONFIG2.
AFIN— Arbiter Bit Time Measurement Finish Flag
This read-only bit indicates bit time measurement has finished. Clear AFIN by writing any value to
SCIACTL. Reset clears AFIN.
1 = Bit time measurement has finished
0 = Bit time measurement not yet finished
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
151
Enhanced Serial Communications Interface (ESCI) Module
ARUN— Arbiter Counter Running Flag
This read-only bit indicates the arbiter counter is running. Reset clears ARUN.
1 = Arbiter counter running
0 = Arbiter counter stopped
AROVFL— Arbiter Counter Overflow Bit
This read-only bit indicates an arbiter counter overflow. Clear AROVFL by writing any value to
SCIACTL. Writing 0s to AM1 and AM0 resets the counter keeps it in this idle state. Reset clears
AROVFL.
1 = Arbiter counter overflow has occurred
0 = No arbiter counter overflow has occurred
ARD8— Arbiter Counter MSB
This read-only bit is the MSB of the 9-bit arbiter counter. Clear ARD8 by writing any value to SCIACTL.
Reset clears ARD8.
13.9.2 ESCI Arbiter Data Register
Address: $0019
Read:
Bit 7
6
5
4
3
2
1
Bit 0
ARD7
ARD6
ARD5
ARD4
ARD3
ARD2
ARD1
ARD0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 13-19. ESCI Arbiter Data Register (SCIADAT)
ARD7–ARD0 — Arbiter Least Significant Counter Bits
These read-only bits are the eight LSBs of the 9-bit arbiter counter. Clear ARD7–ARD0 by writing any
value to SCIACTL. Writing 0s to AM1 and AM0 permanently resets the counter and keeps it in this idle
state. Reset clears ARD7–ARD0.
13.9.3 Bit Time Measurement
Two bit time measurement modes, described here, are available according to the state of ACLK.
1. ACLK = 0 — The counter is clocked with one quarter of the bus clock. The counter is started when
a falling edge on the RxD pin is detected. The counter will be stopped on the next falling edge.
ARUN is set while the counter is running, AFIN is set on the second falling edge on RxD (for
instance, the counter is stopped). This mode is used to recover the received baud rate. See
Figure 13-20.
2. ACLK = 1 — The counter is clocked with one quarter of the ESCI input clock generated by the ESCI
prescaler. The counter is started when a logic 0 is detected on RxD (see Figure 13-21). A logic 0
on RxD on enabling the bit time measurement with ACLK = 1 leads to immediate start of the
counter (see Figure 13-22). The counter will be stopped on the next rising edge of RxD. This mode
is used to measure the length of a received break.
13.9.4 Arbitration Mode
If AM[1:0] is set to 10, the arbiter module operates in arbitration mode. On every rising edge of SCI_TxD
(output of the ESCI module, internal chip signal), the counter is started. When the counter reaches $38
(ACLK = 0) or $08 (ACLK = 1), RxD is statically sensed. If in this case, RxD is sensed low (for example,
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
152
Freescale Semiconductor
ESCI Arbiter
another bus is driving the bus dominant) ALOST is set. As long as ALOST is set, the TxD pin is forced
to 1, resulting in a seized transmission.
If SCI_TxD is sensed logic 0 without having sensed a logic 0 before on RxD, the counter will be reset,
arbitration operation will be restarted after the next rising edge of SCI_TxD.
MEASURED TIME
CPU READS RESULT
OUT OF SCIADAT
COUNTER STOPS,
AFIN = 1
COUNTER STARTS,
ARUN = 1
CPU WRITES SCIACTL
WITH $20
RXD
Figure 13-20. Bit Time Measurement with ACLK = 0
MEASURED TIME
CPU READS RESULT OUT
OF SCIADAT
COUNTER STOPS, AFIN = 1
CPU WRITES SCIACTL WITH $30
COUNTER STARTS, ARUN = 1
RXD
Figure 13-21. Bit Time Measurement with ACLK = 1, Scenario A
MEASURED TIME
CPU READS RESULT
OUT OF SCIADAT
COUNTER STOPS,
AFIN = 1
COUNTER STARTS,
ARUN = 1
CPU WRITES SCIACTL
WITH $30
RXD
Figure 13-22. Bit Time Measurement with ACLK = 1, Scenario B
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
153
Enhanced Serial Communications Interface (ESCI) Module
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
154
Freescale Semiconductor
Chapter 14
System Integration Module (SIM)
14.1 Introduction
This section describes the system integration module (SIM), which supports up to 24 external and/or
internal interrupts. The SIM is a system state controller that coordinates the central processor unit (CPU)
and exception timing. Together with the CPU, the SIM controls all microcontroller unit (MCU) activities. A
block diagram of the SIM is shown in Figure 14-1.
The SIM is responsible for:
• Bus clock generation and control for CPU and peripherals:
– Stop/wait/reset 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
• Modular architecture expandable to 128 interrupt sources
Table 14-1 shows the internal signal names used in this section.
Table 14-1. Signal Name Conventions
Signal Name
Description
CGMXCLK
Selected clock source from internal clock generator module (ICG)
CGMOUT
Clock output from ICG module (bus clock = CGMOUT divided by two)
IAB
Internal address bus
IDB
Internal data bus
PORRST
Signal from the power-on reset (POR) module to the SIM
IRST
Internal reset signal
R/W
Read/write signal
14.2 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 14-2. This clock
originates from either an external oscillator or from the internal clock generator.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
155
System Integration Module (SIM)
MODULE STOP
MODULE WAIT
CPU STOP (FROM CPU)
CPU WAIT (FROM CPU)
STOP/WAIT
CONTROL
SIMOSCEN (TO ICG)
SIM
COUNTER
COP CLOCK
CGMXCLK (FROM ICG)
CGMOUT (FROM ICG)
÷2
CLOCK
CONTROL
INTERNAL CLOCKS
CLOCK GENERATORS
FORCED MON MODE ENTRY
(FROM MENRST MODULE)
POR CONTROL
LVI (FROM LVI MODULE)
ILLEGAL OPCODE (FROM CPU)
ILLEGAL ADDRESS (FROM ADDRESS
MAP DECODERS)
COP (FROM COP MODULE)
MASTER
RESET
CONTROL
SIM RESET STATUS REGISTER
RESET
INTERRUPT SOURCES
INTERRUPT CONTROL
AND PRIORITY DECODE
CPU INTERFACE
Figure 14-1. SIM Block Diagram
CGMXCLK
ECLK
CLOCK
SELECT
CIRCUIT
÷2
ICLK
ICG
GENERATOR
A
CGMOUT
B S*
*WHEN S = 1,
CGMOUT = B
SIM COUNTER
÷2
BUS CLOCK
GENERATORS
SIM
CS
MONITOR MODE
USER MODE
ICG
Figure 14-2. System Clock Signals
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
156
Freescale Semiconductor
Reset and System Initialization
14.2.1 Bus Timing
In user mode, the internal bus frequency is the internal clock generator output (CGMXCLK) divided by
four.
14.2.2 Clock Startup from POR or LVI Reset
When the power-on reset (POR) module or the low-voltage inhibit (LVI) 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 MCU is held in reset by the SIM during this entire period. The bus clocks start upon completion
of the timeout.
14.2.3 Clocks in Stop Mode and Wait Mode
Upon exit from stop mode by an interrupt 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. Stop mode
recovery timing is discussed in detail in 14.6.2 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.
14.3 Reset and System Initialization
The MCU has these internal reset sources:
• Power-on reset (POR) module
• Computer operating properly (COP) module
• Low-voltage inhibit (LVI) module
• Illegal opcode
• Illegal address
• Forced monitor mode entry reset (MENRST) module
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.
These internal resets clear the SIM counter and set a corresponding bit in the SIM reset status register
(SRSR). See 14.4 SIM Counter and 14.7.2 SIM Reset Status Register.
14.3.1 External Pin Reset
The RST pin circuits include an internal pullup device. 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 at
least the minimum tIRL time. Figure 14-3 shows the relative timing.
CGMOUT
RST
IAB
PC
VECT H
VECT L
Figure 14-3. External Reset Timing
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
157
System Integration Module (SIM)
14.3.2 Active Resets from Internal Sources
An internal reset can be caused by an illegal address, illegal opcode, COP timeout, LVI, POR, or
MENRST as shown in Figure 14-4.
NOTE
For LVI or POR resets, the SIM cycles through 4096 CGMXCLK cycles
during which the SIM asserts IRST. The internal reset signal then follows
with the 64-cycle phase as shown in Figure 14-5.
The COP reset is asynchronous to the bus clock.
ILLEGAL ADDRESS RESET
ILLEGAL OPCODE RESET
COP RESET
LVI
POR
MENRST
INTERNAL RESET
Figure 14-4. Sources of Internal Reset
Table 14-2. Reset Recovery Timing
Reset Type
Actual Number of Cycles
POR/LVI
4163 (4096 + 64 + 3)
All Others
67 (64 + 3)
RST
RST PULLED LOW BY MCU
32 CYCLES
32 CYCLES
CGMXCLK
IAB
VECTOR HIGH
Figure 14-5. Internal Reset Timing
14.3.2.1 Power-On Reset
When power is first applied to the MCU, the power-on reset (POR) module generates a pulse to indicate
that power-on has occurred. The MCU is held in reset while the SIM counter counts out 4096 CGMXCLK
cycles. Another 64 CGMXCLK cycles later, the CPU and memories are released from reset to allow the
reset vector sequence to occur.
At power-on, these 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 internal clock generator.
• The POR bit of the SIM reset status register (SRSR) is set and all other bits in the register are
cleared.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
158
Freescale Semiconductor
Reset and System Initialization
OSC1
PORRST
4096
CYCLES
32
CYCLES
CGMXCLK
CGMOUT
RST
$FFFE
IAB
$FFFF
Figure 14-6. POR Recovery
14.3.2.2 Computer Operating Properly (COP) Reset
An input to the SIM is reserved for the COP reset signal. The overflow of the COP counter causes an
internal reset and sets the COP bit in the reset status register (SRSR).
To prevent a COP module timeout, write any value to location $FFFF. Writing to location $FFFF clears
the COP counter and stages 12–5 of the SIM counter. The SIM counter output, which occurs at least
every 4080 CGMXCLK cycles, drives the COP counter. The COP should be serviced as soon as possible
out of reset to guarantee the maximum amount of time before the first timeout.
The COP module is disabled if the IRQ pin is held at VTST while the MCU is in monitor mode. The COP
module can be disabled only through combinational logic conditioned with the high-voltage signal on the
IRQ pin. This prevents the COP from becoming disabled as a result of external noise.
14.3.2.3 Illegal Opcode Reset
The SIM decodes signals from the CPU to detect illegal instructions. An illegal instruction sets the ILOP
bit in the SIM reset status register (SRSR) and causes a reset.
If the stop enable bit, STOP, in the configuration register (CONFIG1) is 0, the SIM treats the STOP
instruction as an illegal opcode and causes an illegal opcode reset.
14.3.2.4 Illegal Address Reset
An opcode fetch from an unmapped address generates an illegal address reset. The SIM verifies that the
CPU is fetching an opcode prior to asserting the ILAD bit in the SIM reset status register (SRSR) and
resetting the MCU. A data fetch from an unmapped address does not generate a reset.
14.3.2.5 Forced Monitor Mode Entry Reset (MENRST)
The MENRST module is monitoring the reset vector fetches and will assert an internal reset if it detects
that the reset vectors are erased ($FF). When the MCU comes out of reset, it is forced into monitor mode.
See 19.3 Monitor Module (MON).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
159
System Integration Module (SIM)
14.3.2.6 Low-Voltage Inhibit (LVI) Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when the VDD voltage falls to the VTRIPF
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 register are at 0. The MCU is held in reset until VDD rises
above VTRIPR. The MCU remains in reset until the SIM counts 4096 CGMXCLK to begin a reset recovery.
Another 64 CGMXCLK cycles later, the CPU is released from reset to allow the reset vector sequence to
occur. See Chapter 11 Low-Voltage Inhibit (LVI) Module.
14.4 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.
14.4.1 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 internal clock generator to drive the
bus clock state machine.
14.4.2 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 configuration
register. If the SSREC bit is a 1, then the stop recovery is reduced from the normal delay of 4096
CGMXCLK cycles down to 32 CGMXCLK cycles.
14.4.3 SIM Counter and Reset States
The SIM counter is free-running after all reset states. See 14.3.2 Active Resets from Internal Sources for
counter control and internal reset recovery sequences.
14.5 Program Exception Control
Normal, sequential program execution can be changed in two ways:
1. Interrupts
a. Maskable hardware CPU interrupts
b. Non-maskable software interrupt instruction (SWI)
2. Reset
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
160
Freescale Semiconductor
Program Exception Control
14.5.1 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 return-from-interrupt
(RTI) instruction recovers the CPU register contents from the stack so that normal processing can
resume. Figure 14-7 shows interrupt entry timing. Figure 14-8 shows interrupt recovery timing.
MODULE
INTERRUPT
I BIT
IAB
IDB
SP
DUMMY
DUMMY
SP – 1
SP – 2
PC – 1[7:0] PC – 1[15:8]
SP – 3
X
SP – 4
A
VECT H
CCR
VECT L
V DATA H
START ADDR
V DATA L
OPCODE
R/W
Figure 14-7. Interrupt Entry
MODULE
INTERRUPT
I BIT
IAB
IDB
SP – 4
SP – 3
CCR
SP – 2
A
SP – 1
X
SP
PC
PC + 1
PC – 1 [7:0] PC – 1 [15:8] OPCODE
OPERAND
R/W
Figure 14-8. Interrupt Recovery
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. As shown in
Figure 14-9, 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
161
System Integration Module (SIM)
FROM RESET
YES
BITSET?
SET?
IIBIT
NO
IRQ
INTERRUPT
?
NO
ICG CLK MON
INTERRUPT
?
NO
OTHER
INTERRUPTS
?
NO
YES
YES
YES
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 14-9. Interrupt Processing
14.5.1.1 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Program Exception Control
If more than one interrupt is pending at the end of an instruction execution, the highest priority interrupt is
serviced first. Figure 14-10 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
load-accumulator- from-memory (LDA) instruction is executed.
CLI
BACKGROUND
ROUTINE
LDA #$FF
INT1
PSHH
INT1 INTERRUPT SERVICE ROUTINE
PULH
RTI
INT2
PSHH
INT2 INTERRUPT SERVICE ROUTINE
PULH
RTI
Figure 14-10. Interrupt Recognition Example
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 M6805, M146805, and MC68HC05
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.
14.5.1.2 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.
14.5.2 Reset
All reset sources always have higher priority than interrupts and cannot be arbitrated.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
163
System Integration Module (SIM)
14.5.3 Break Interrupts
The break module can stop normal program flow at a software-programmable break point by asserting its
break interrupt output. See 19.2 Break Module (BRK). 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.
14.5.4 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.
14.6 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. Both STOP and WAIT clear the interrupt mask
(I) in the condition code register, allowing interrupts to occur. Low-power modes are exited via an interrupt
or reset.
14.6.1 Wait Mode
In wait mode, the CPU clocks are inactive while one set of peripheral clocks continues to run.
Figure 14-11 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. If the COP disable bit, COPD, in the configuration register is 0,
then the computer operating properly module (COP) is enabled and remains active in wait mode.
IAB
IDB
WAIT ADDR
WAIT ADDR + 1
PREVIOUS DATA
NEXT OPCODE
SAME
SAME
SAME
SAME
R/W
Note: Previous data can be operand data or the WAIT opcode, depending on the last instruction.
Figure 14-11. Wait Mode Entry Timing
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
164
Freescale Semiconductor
Low-Power Modes
Figure 14-12 and Figure 14-13 show the timing for WAIT recovery.
IAB
$DE0B
IDB
$A6
$A6
$DE0C
$A6
$01
$00FF
$0B
$00FE
$00FD
$00FC
$DE
EXITSTOPWAIT
Note: EXITSTOPWAIT = CPU interrupt
Figure 14-12. Wait Recovery from Interrupt
64
CYCLES
$DE0B
IAB
IDB
$A6
$A6
RST VCT H RST VCT L
$A6
IRST
CGMXCLK
Figure 14-13. Wait Recovery from Internal Reset
14.6.2 Stop Mode
In stop mode, the SIM counter is held in reset and the CPU and peripheral clocks are held inactive. If the
STOPOSCEN bit in the configuration register is not enabled, the SIM also disables the internal clock
generator module outputs (CGMOUT and CGMXCLK).
The CPU and peripheral clocks do not become active until after the stop delay timeout. Stop mode is
exited via an interrupt request from a module that is still active in stop mode or from a system reset.
An interrupt request from a module that is still active in stop mode can cause an exit from stop mode. Stop
recovery time is selectable using the SSREC bit in the configuration register. If SSREC is set, stop
recovery is reduced from the normal delay of 4096 CGMXCLK cycles down to 32. Stacking for interrupts
begins after the selected stop recovery time has elapsed.
When stop mode is exited due to a reset condition, the SIM forces a long stop recovery time of 4096
CGMXCLK cycles.
NOTE
Short stop recovery is ideal for applications using canned oscillators that do
not require long startup times for stop mode. External crystal applications
should use the full stop recovery time by clearing the SSREC bit.
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 14-14 shows stop mode entry timing.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
165
System Integration Module (SIM)
CPUSTOP
IAB
STOP ADDR + 1
STOP ADDR
IDB
PREVIOUS DATA
SAME
SAME
NEXT OPCODE
SAME
SAME
R/W
Note: Previous data can be operand data or the STOP opcode, depending on the last instruction.
Figure 14-14. Stop Mode Entry Timing
STOP RECOVERY PERIOD
CGMXCLK
INT
IAB
STOP + 2
STOP +1
STOP + 2
SP
SP – 1
SP – 2
SP – 3
Figure 14-15. Stop Mode Recovery from Interrupt
14.7 SIM Registers
The SIM has three memory mapped registers. Table 14-3 shows the mapping of these registers.
Table 14-3. SIM Registers
Address
Register
Access Mode
$FE00
SBSR
User
$FE01
SRSR
User
$FE03
SBFCR
User
14.7.1 SIM Break Status Register
The SIM break status register (SBSR) contains a flag to indicate that a break caused an exit from stop or
wait mode.
Address: $FE00
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
R
R
R
R
R
R
0
0
0
0
0
0
R
1
SBSW
Note(1)
0
Bit 0
R
0
= Reserved
Note: 1. Writing a 0 clears SBSW
Figure 14-16. SIM Break Status Register (SBSR)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
166
Freescale Semiconductor
SIM Registers
SBSW — SIM Break STOP/WAIT
SBSW can be read within the break state SWI routine. The user can modify the return address on the
stack by subtracting one from it.
1 = Wait mode was exited by break interrupt
0 = Wait mode was not exited by break interrupt
14.7.2 SIM Reset Status Register
This register contains seven bits that show the source of the last reset. The status register will clear
automatically 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
MENRST
LVI
0
1
0
0
0
0
0
0
0
Write:
POR:
= Unimplemented
Figure 14-17. 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 SPSR
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
MENRST — Forced Monitor Mode Entry Reset Bit
1 = Last reset was caused by the MENRST circuit
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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
167
System Integration Module (SIM)
14.7.3 SIM Break Flag Control Register
The SIM break flag control register (SBFCR) contains a bit that enables software to clear status bits while
the MCU is in a break state.
Address: $FE03
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
BCFE
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
R
= Reserved
Figure 14-18. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
168
Freescale Semiconductor
Chapter 15
Serial Peripheral Interface (SPI) Module
15.1 Introduction
This section describes the serial peripheral interface (SPI) module, which allows full-duplex, synchronous,
serial communications with peripheral devices.
15.2 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
15.3 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 15-1 shows the full names of the SPI I/O pins. The generic pin names appear in
the text that follows.
Table 15-1. Pin Name Conventions
SPI Generic Pin Name
Full SPI Pin Name
MISO
MOSI
SS
SPSCK
PTC0/MISO
PTC1/MOSI
PTA6/SS
PTA5/SPSCK
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
169
Serial Peripheral Interface (SPI) Module
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 15-1. Block Diagram Highlighting SPI Block and Pins
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 15-2 shows the names and the addresses of the SPI I/O registers.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Functional Description
Table 15-2. I/O Register Addresses
Register Name
Address
SPI control register (SPCR)
$000D
SPI status and control register (SPSCR)
$000E
SPI data register (SPDR)
$000F
15.4 Functional Description
Figure 15-2 shows the structure of the SPI module.
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 15-2. SPI Module Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
171
Serial Peripheral Interface (SPI) Module
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.
15.4.1 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 15.13.1 SPI Control Register.
MASTER MCU
SHIFT REGISTER
SLAVE MCU
MISO
MISO
MOSI
MOSI
SPSCK
BAUD RATE
GENERATOR
SS
SHIFT REGISTER
SPSCK
VDD
SS
Figure 15-3. Full-Duplex Master-Slave Connections
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 15-3).
The SPR1 and SPR0 bits control the baud rate generator and determine the speed of the shift register.
(See 15.13.2 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.
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.
15.4.2 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 15.6.2
Mode Fault Error.)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
172
Freescale Semiconductor
Transmission Formats
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.
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 15.5 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.
15.5 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.
15.5.1 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).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
173
Serial Peripheral Interface (SPI) Module
15.5.2 Transmission Format When CPHA = 0
Figure 15-4 shows an SPI transmission in which CPHA (SPCR) is 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 15.6.2
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 15-4. Transmission Format (CPHA = 0)
15.5.3 Transmission Format When CPHA = 1
Figure 15-5 shows an SPI transmission in which CPHA (SPCR) is 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 15.6.2
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
174
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 15-5. Transmission Format (CPHA = 1)
15.5.4 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 15-6.) 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 15-6. 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
175
Serial Peripheral Interface (SPI) Module
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 15-6. Transmission Start Delay (Master)
15.6 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
176
Freescale Semiconductor
Error Conditions
15.6.1 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 15-4 and Figure 15-5.) 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 15-9.) 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 15-7 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
7
1
BYTE 1 SETS SPRF BIT.
5
CPU READS SPSCRW WITH SPRF BIT SET AND OVRF BIT CLEAR.
2
CPU READS SPSCR WITH SPRF BIT SET AND OVRF BIT CLEAR.
6
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
3
CPU READS BYTE 1 IN SPDR, CLEARING SPRF BIT.
7
CPU READS BYTE 2 IN SPDR, CLEARING SPRF BIT, BUT NOT OVRF BIT.
4
BYTE 2 SETS SPRF BIT.
8
BYTE 4 FAILS TO SET SPRF BIT BECAUSE OVRF BIT IS SET. BYTE 4 IS LOST.
Figure 15-7. Missed Read of Overflow Condition
The first part of Figure 15-7 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 15-8 illustrates this process. Generally, to
avoid this second SPSCR read, enable the OVRF to the CPU by setting the ERRIE bit (SPSCR).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
177
Serial Peripheral Interface (SPI) Module
SPI RECEIVE
COMPLETE
BYTE 1
BYTE 2
BYTE 3
BYTE 4
1
5
7
11
SPRF
OVRF
2
READ SPSCR
BYTE 1 SETS SPRF BIT.
2
3
6
3
READ SPDR
1
4
9
8
12
10
14
13
8
CPU READS BYTE 2 IN SPDR, CLEARING SPRF BIT.
CPU READS SPSCR WITH SPRF BIT SET AND OVRF BIT CLEAR.
9
CPU READS SPSCR AGAIN TO CHECK OVRF BIT.
CPU READS BYTE 1 IN SPDR, CLEARING SPRF BIT.
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 15-8. Clearing SPRF When OVRF Interrupt Is Not Enabled
15.6.2 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 15-9). 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.
SPTE
SPTIE
SPE
SPI TRANSMITTER
CPU INTERRUPT REQUEST
SPRIE
ERRIE
SPRF
SPI RECEIVER/ERROR
CPU INTERRUPT REQUEST
MODF
OVRF
Figure 15-9. SPI Interrupt Request Generation
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
178
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 15.5 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
179
Serial Peripheral Interface (SPI) Module
15.7 Interrupts
Four SPI status flags can be enabled to generate CPU interrupt requests:
Table 15-3. 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.
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.
15.8 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 15-10
shows the timing associated with doing back-to-back transmissions with the SPI (SPSCK has
CPHA:CPOL = 1:0).
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Resetting the SPI
WRITE TO SPDR
1
3
SPTE
8
5
2
10
SPSCK (CPHA:CPOL = 1:0)
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
MOSI
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 15-10. SPRF/SPTE CPU Interrupt Timing
15.9 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 a 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
181
Serial Peripheral Interface (SPI) Module
15.10 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
15.10.1 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 15.7 Interrupts.)
15.10.2 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.
15.11 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 19.2.1.1 Flag Protection During Break Interrupts.)
To allow software to clear status bits during a break interrupt, write a 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 0 to the BCFE bit. With BCFE at 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 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.
15.12 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Signals
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.
15.12.1 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 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.
15.12.2 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.
15.12.3 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.
15.12.4 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.
(See 15.5 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 15-11.
MISO/MOSI
BYTE 1
BYTE 2
BYTE 3
MASTER SS
SLAVE SS
CPHA = 0
SLAVE SS
CPHA = 1
Figure 15-11. CPHA/SS Timing
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
183
Serial Peripheral Interface (SPI) Module
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 15.13.2 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 15.6.2 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 15-4.)
Table 15-4. 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
15.12.5 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.
15.13 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)
15.13.1 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
184
Freescale Semiconductor
I/O Registers
Address:
Read:
Write:
Reset:
$000D
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 15-12. 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 15-4 and Figure 15-5.) To transmit data between SPI modules, the SPI modules must have
identical CPOL bits. Reset clears the CPOL bit.
CPHA — Clock Phase Bit
This read/write bit controls the timing relationship between the serial clock and SPI data. (See
Figure 15-4 and Figure 15-5.) 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 15-11). 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
15.6.2 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
185
Serial Peripheral Interface (SPI) Module
SPE — SPI Enable Bit
This read/write bit enables the SPI module. Clearing SPE causes a partial reset of the SPI (see 15.9
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
15.13.2 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
Address:
$000E
Bit 7
Read:
SPRF
Write:
Reset:
0
6
ERRIE
0
5
4
3
OVRF
MODF
SPTE
0
0
1
2
1
Bit 0
MODFEN
SPR1
SPR0
0
0
0
= Unimplemented
Figure 15-13. 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Registers
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.
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 15.12.4 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 15.6.2 Mode
Fault Error).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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187
Serial Peripheral Interface (SPI) Module
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 15-5. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Table 15-5. 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 internal clock generator module (ICG),
see Chapter 8 Internal Clock Generator (ICG) Module.
BD = baud rate divisor
15.13.3 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 15-2
Address:
$000F
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 15-14. 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.
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Freescale Semiconductor
Chapter 16
Timebase Module (TBM)
16.1 Introduction
This section describes the timebase module (TBM). The TBM will generate periodic interrupts at user
selectable rates using a counter clocked by either the internal or external clock sources. This TBM version
uses 15 divider stages, eight of which are user selectable.
NOTE
The TBM on this device differs from that of the MC68HC908KX8 in that it
has an additional divide-by-128 at the front end of the divider chain.
For further information regarding timers on M68HC08 family devices, please consult the HC08 Timer
Reference Manual, Freescale order number TIM08RM/AD.
16.2 Features
Features of the TBM module include:
• Software configurable periodic interrupts with divide-by-1024, 2048, 4096, 8192, 16384, 262144,
1048576, and 4194304 taps of the selected clock source
• Configurable for operation during stop mode to allow periodic wake up from stop
16.3 Functional Description
This module can generate a periodic interrupt by dividing the clock source supplied from the internal clock
generator module, TBMCLK. Note that this clock source is the external clock ECLK when the ECGON bit
in the ICG control register (ICGCR) is set. Otherwise, TBMCLK is driven at the internally generated clock
frequency (ICLK). In other words, if the external clock is enabled it will be used as the TBMCLK, even if
the MCU bus clock is based on the internal clock.
The counter is initialized to all 0s when TBON bit is cleared. The counter, shown in Figure 16-1, starts
counting when the TBON bit is set. When the counter overflows at the tap selected by TBR2–TBR0, the
TBIF bit gets set. If the TBIE bit is set, an interrupt request is sent to the CPU. The TBIF flag is cleared
by writing a 1 to the TACK bit. The first time the TBIF flag is set after enabling the timebase module, the
interrupt is generated at approximately half of the overflow period. Subsequent events occur at the exact
period.
The timebase module may remain active after execution of the STOP instruction if the internal clock
generator has been enabled to operate during stop mode through the OSCENINSTOP bit in the
configuration register. The timebase module can be used in this mode to generate a periodic wakeup from
stop mode.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
189
Timebase Module (TBM)
TMBCLKSEL
FROM CONFIG2
0
DIVIDE
BY 128
PRESCALER
TBMCLK
FROM ICG MODULE
1
TBON
÷2
÷2
÷2
÷2
÷2
÷2
÷2
÷2
÷2
÷2
÷2
÷2
TACK
÷2
TBR0
÷2
TBR1
÷2
TBR2
TBMINT
TBIF
000
TBIE
R
001
010
100
SEL
011
101
110
111
Figure 16-1. Timebase Block Diagram
16.4 Interrupts
The timebase module can periodically interrupt the CPU with a rate defined by the selected TBMCLK and
the select bits TBR2–TBR0. When the timebase counter chain rolls over, the TBIF flag is set. If the TBIE
bit is set, enabling the timebase interrupt, the counter chain overflow will generate a CPU interrupt
request.
Interrupts must be acknowledged by writing a 1 to the TACK bit.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
TBM Interrupt Rate
16.5 TBM Interrupt Rate
The interrupt rate is determined by the equation:
Divider
1
t TBMRATE = ------------------------ = --------------------f TBMCLK
f TBMRATE
where:
fTBMCLK =Frequency supplied from the internal clock generator (ICG) module
Divider = Divider value as determined by TBR2–TBR0 settings.
See Table 16-1
As an example, a clock source of 4.9152 MHz and the TBR2–TBR0 set to {011}, the divider tap is 128
and the interrupt rate calculates to 128/4.9152 x 106 = 26 µs.
Table 16-1. Timebase Divider Selection
TBR2(1)
TBR1(1)
Divider Tap
TMBCLKSEL
TBR0(1)
0
1
0
0
0
32,768
4,194,304
0
0
1
8192
1,048,576
0
1
0
2048
262144
0
1
1
128
16,384
1
0
0
64
8192
1
0
1
32
4096
1
1
0
16
2048
1
1
1
8
1024
1. Do not change TBR2–TBR0 bits while the timebase is enabled (TBON = 1).
16.6 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
16.6.1 Wait Mode
The timebase module remains active after execution of the WAIT instruction. In wait mode the timebase
register is not accessible by the CPU.
If the timebase functions are not required during wait mode, reduce the power consumption by stopping
the timebase before executing the WAIT instruction.
16.6.2 Stop Mode
The timebase module may remain active after execution of the STOP instruction if the internal clock
generator has been enabled to operate during stop mode through the OSCENINSTOP bit in the
configuration register. The timebase module can be used in this mode to generate a periodic wake up
from stop mode.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
191
Timebase Module (TBM)
If the internal clock generator has not been enabled to operate in stop mode, the timebase module will
not be active during stop mode. In stop mode, the timebase register is not accessible by the CPU.
If the timebase functions are not required during stop mode, reduce power consumption by disabling the
timebase module before executing the STOP instruction.
16.7 Timebase Control Register
The timebase has one register, the timebase control register (TBCR), which is used to enable the
timebase interrupts and set the rate.
Address: $001C
Bit 7
Read:
TBIF
Write:
Reset:
0
6
5
4
TBR2
TBR1
TBR0
0
0
0
= Unimplemented
3
2
1
Bit 0
TBIE
TBON
R
0
0
0
0
R
= Reserved
0
TACK
Figure 16-2. Timebase Control Register (TBCR)
TBIF — Timebase Interrupt Flag
This read-only flag bit is set when the timebase counter has rolled over.
1 = Timebase interrupt pending
0 = Timebase interrupt not pending
TBR2–TBR0 — Timebase Divider Selection Bits
These read/write bits select the tap in the counter to be used for timebase interrupts as shown in
Table 16-1.
NOTE
Do not change TBR2–TBR0 bits while the timebase is enabled (TBON = 1).
TACK— Timebase ACKnowledge Bit
The TACK bit is a write-only bit and always reads as 0. Writing a 1 to this bit clears TBIF, the timebase
interrupt flag bit. Writing a 0 to this bit has no effect.
1 = Clear timebase interrupt flag
0 = No effect
TBIE — Timebase Interrupt Enabled Bit
This read/write bit enables the timebase interrupt when the TBIF bit becomes set. Reset clears the
TBIE bit.
1 = Timebase interrupt is enabled.
0 = Timebase interrupt is disabled.
TBON — Timebase Enabled Bit
This read/write bit enables the timebase. Timebase may be turned off to reduce power consumption
when its function is not necessary. The counter can be initialized by clearing and then setting this bit.
Reset clears the TBON bit.
1 = Timebase is enabled.
0 = Timebase is disabled and the counter initialized to 0s.
NOTE
Clearing TBON has no effect on the TBIF flag.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Chapter 17
Timer Interface A (TIMA) Module
17.1 Introduction
This section describes the timer interface A module (TIMA). The TIMA is a 2-channel timer that provides
a timing reference with input capture, output compare, and pulse width modulation (PWM) functions.
Figure 17-2 is a block diagram of the TIMA.
For further information regarding timers on M68HC08 family devices, please consult the HC08 Timer
Reference Manual, Freescale document order number TIM08RM/AD.
17.2 Features
Features 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 PWM signal generation
• Programmable TIMA clock input
– 7-frequency internal bus clock prescaler selection
• Free-running or modulo up-count operation
• Toggle any channel pin on overflow
• TIMA counter stop and reset bits
17.3 Functional Description
Figure 17-2 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 two TIMA channels are programmable independently as input capture or output compare channels.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
193
Timer Interface A (TIMA) Module
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 17-1. Block Diagram Highlighting TIMA Block and Pins
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
194
Freescale Semiconductor
Functional Description
INTERNAL
BUS CLOCK
PRESCALER SELECT
PRESCALER
TSTOP
PS2
TRST
PS1
PS0
16-BIT COUNTER
TOF
TOIE
INTERRUPT
LOGIC
16-BIT COMPARATOR
TAMODH:TAMODL
ELS0B
CHANNEL 0
ELS0A
TOV0
CH0MAX
16-BIT COMPARATOR
TACH0H:TACH0L
CH0F
16-BIT LATCH
MS0A
ELS1B
CHANNEL 1
MS0B
ELS1A
TOV1
CH1MAX
16-BIT COMPARATOR
TACH1H:TACH1L
CH0IE
CH1F
16-BIT LATCH
MS1A
CH1IE
PTD0
LOGIC
PTD0/TACH0
INTERRUPT
LOGIC
PTD1
LOGIC
PTD1/TACH1
INTERRUPT
LOGIC
Figure 17-2. TIMA Block Diagram
17.3.1 TIMA Counter Prescaler
The TIMA 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, PS[2:0], in the TIMA status and control register
select the TIMA clock source.
17.3.2 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 TASC1
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 free-running counter contents are transferred to the TIMA channel status and control register
(TACHxH–TACHxL, see 17.8.5 TIMA Channel Registers) on each proper signal transition regardless of
whether the TIMA channel flag (CH0F–CH1F in TASC0–TASC1 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
195
Timer Interface A (TIMA) Module
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 17.8.5 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 input capture channel register (TACHxH–TACHxL).
17.3.3 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.
17.3.3.1 Unbuffered Output Compare
Any output compare channel can generate unbuffered output compare pulses as described in 17.3.3
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 these 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
196
Freescale Semiconductor
Functional Description
17.3.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare channel whose output appears on the
PTD0/TACH0 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
PTD0/TACH0 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. TSC0 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, PTD1/TACH1, 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. User software should track
the currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as generating
unbuffered output compares.
17.3.4 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 17-3 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
PTDx/TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 17-3. PWM Period and Pulse Width
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
197
Timer Interface A (TIMA) Module
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 17.8.1 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%.
17.3.4.1 Unbuffered PWM Signal Generation
Any output compare channel can generate unbuffered PWM pulses as described in 17.3.4 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.
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 these 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.
17.3.4.2 Buffered PWM Signal Generation
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the
PTD0/TACH0 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 PTD0/TACH0 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Functional Description
PWM function, and TIMA channel 1 status and control register (TASC1) is unused. While the MS0B bit is
set, the channel 1 pin, PTD1/TACH1, 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. User software should track the
currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as generating
unbuffered PWM signals.
17.3.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use this 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 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 17-2.
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 17-2.
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.
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.
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 17.8.4 TIMA Channel Status and Control Registers.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Timer Interface A (TIMA) Module
17.4 Interrupts
These TIMA sources can generate interrupt requests:
• TIMA overflow flag (TOF) — The TOF bit is set when the TIM 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 (CH1F–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.
17.5 Low-Power Modes
The WAIT and STOP instructions put the microcontroller unit (MCU) in low power-consumption standby
modes.
17.5.1 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.
17.5.2 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.
17.6 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.
To allow software to clear status bits during a break interrupt, write a 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 0 to the BCFE bit. With BCFE at 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 0. After the break, doing the
second step clears the status bit.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Signals
17.7 I/O Signals
Port D shares two of its pins with the TIMA. There is no external clock input to the TIMA prescaler. The
two TIMA channel I/O pins are PTD0/TACH0 and PTD1/TACH1. See Chapter 12 Input/Output (I/O) Ports
(PORTS)
17.7.1 TIMA Channel I/O Pins (PTD0/TACH0, PTD1/TACH1)
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.
PTD0/TACH0 and PTD1/TACH1 can be configured as buffered output compare or buffered PWM pins.
17.8 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 and TASC1
• TIMA channel registers, TACH0H–TACH0L and TACH1H–TACH1L
17.8.1 TIMA Status and Control Register
The TIMA status and control register (TASC):
• 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:
TOF
Write:
0
Reset:
6
5
TOIE
TSTOP
0
0
1
R
= Reserved
4
0
TRST
0
3
2
1
Bit 0
R
PS2
PS1
PS0
0
0
0
0
Figure 17-4. 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 0 to TOF. If another TIMA overflow occurs before the clearing sequence is complete,
then writing 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 1 to TOF has no effect.
1 = TIMA counter has reached modulo value
0 = TIMA counter has not reached modulo value
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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201
Timer Interface A (TIMA) Module
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
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 the timer is
configured for input capture operation, input captures are inhibited until
TSTOP is cleared.
When using TSTOP to stop the timer counter, check for any timer flags
being 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 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 one of the seven prescaler outputs as the input to the TIMA counter as
Table 17-1 shows. Reset clears the PS[2:0] bits.
Table 17-1. Prescaler Selection
PS[2:0]
TIMA Clock Source
0 0 0
Internal bus clock ÷ 1
0 0 1
Internal bus clock ÷ 2
0 1 0
Internal bus clock ÷ 4
0 1 1
Internal bus clock ÷ 8
1 0 0
Internal bus clock ÷ 16
1 0 1
Internal bus clock ÷ 32
1 1 0
Internal bus clock ÷ 64
1 1 1
Unused
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Registers
17.8.2 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 — $0021
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 — $0022
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 17-5. TIMA Counter Registers (TACNTH and TACNTL)
17.8.3 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 timer clock. Writing to the high byte (TMODH) inhibits the TOF bit and
overflow interrupts until the low byte (TMODL) is written. Reset sets the TIMA counter modulo registers.
Register Name and Address
Read:
Write:
Reset:
TAMODH — $0023
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 — $0024
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 17-6. TIMA Counter Modulo Registers (TMODH and TMODL)
NOTE
Reset the TIMA counter before writing to the TIMA counter modulo registers.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Timer Interface A (TIMA) Module
17.8.4 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
6
Read:
CH0F
CH0IE
Write:
0
Reset:
0
0
TASC0 — $0025
5
4
3
2
1
Bit 0
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
3
2
1
Bit 0
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
Register Name and Address
TASC1 — $0028
Bit 7
6
5
4
Read:
CH1F
0
CH1IE
MS1A
Write:
0
R
Reset:
0
0
0
0
R
R = Reserved
Figure 17-7. TIMA Channel Status and Control Register
(TASC0–TASC1)
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 0 to CHxF. If another interrupt request occurs before the clearing sequence is
complete, then writing 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 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.
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I/O Registers
Setting MS0B disables the channel 1 status and control register and reverts TACH1 to
general-purpose I/O.
Reset clears the MSxB bit.
1 = Buffered output compare/PWM operation enabled
0 = Buffered output compare/PWM operation disabled
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 17-2.
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 TCHx pin once PWM, input
capture, or output compare operation is enabled (see Table 17-2). 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 D, and pin PTD0/TACH0
or pin PTD1/TACH1 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 17-2 shows how ELSxB and ELSxA work. Reset clears the
ELSxB and ELSxA bits.
Table 17-2. Mode, Edge, and Level Selection
MSxB
MSxA
ELSxB
ELSxA
Mode
X
0
0
0
X
1
0
0
0
0
0
1
0
0
1
0
0
0
1
1
Capture on rising or falling edge
0
1
0
0
Software compare only
0
1
0
1
0
1
1
0
0
1
1
1
X
0
1
X
1
0
1
X
1
1
Output preset
Configuration
Pin under port control; initial output level high
Pin under port control; initial output level low
Capture on rising edge only
Input capture
Capture on falling edge only
Output compare
or PWM
Toggle output on compare
1
Set output on compare
1
Buffered output
compare or
buffered PWM
Toggle output on compare
Clear 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 PTDx/TACHx pin is stable for at least two bus clocks.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
205
Timer Interface A (TIMA) Module
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 1 and clear output on compare is selected, setting the CHxMAX bit forces the
duty cycle of buffered and unbuffered PWM signals to 100 percent. As Figure 17-8 shows, the
CHxMAX bit takes effect in the cycle after it is set or cleared. The output stays at 100 percent duty
cycle level until the cycle after CHxMAX is cleared.
NOTE
The PWM 100 percent duty cycle is defined as output high all of the time.
To generate the 100 percent duty cycle, use the CHxMAX bit in the TSCx
register. The PWM 0 percent duty cycle is defined as output low all of the
time. To generate the 0 percent duty cycle, select clear output on compare
and then clear the TOVx bit (CHxMAX = 0).
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PTEx/TCHx
TOV = 1
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
TOV = 0
Figure 17-8. CHxMAX Latency
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Registers
17.8.5 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:
TACH0H — $0026
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:
TACH0L — $0027
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 — $0029
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:
TACH1L — $002A
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 17-9. TIMA Channel Registers (TACH0H/L–TACH1H/L)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Timer Interface A (TIMA) Module
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
208
Freescale Semiconductor
Chapter 18
Timer Interface B (TIMB) Module
18.1 Introduction
This section describes the timer interface B module (TIMB). The TIMB is a 2-channel timer that provides
a timing reference with input capture, output compare, and pulse width modulation (PWM) functions.
Figure 18-2 is a block diagram of the TIMB.
For further information regarding timers on M68HC08 family devices, please consult the HC08 Timer
Reference Manual, Freescale document order number TIM08RM/AD.
18.2 Features
Features 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 PWM signal generation
• Programmable TIMB clock input
– 7-frequency internal bus clock prescaler selection
• Free-running or modulo up-count operation
• Toggle any channel pin on overflow
• TIMB counter stop and reset bits
18.3 Functional Description
Figure 18-2 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
209
Timer Interface B (TIMB) Module
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 18-1. Block Diagram Highlighting TIMB Block and Pin
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Functional Description
INTERNAL
BUS CLOCK
PRESCALER SELECT
PRESCALER
TSTOP
PS2
TRST
PS1
PS0
16-BIT COUNTER
TOF
TOIE
INTERRUPT
LOGIC
16-BIT COMPARATOR
TBMODH:TBMODL
CHANNEL 0
ELS0B
ELS0A
TOV0
CH0MAX
16-BIT COMPARATOR
TBCH0H:TBCH0L
PTB6/TBCH0
CH0F
16-BIT LATCH
MS0A
CHANNEL 1
PTB6
LOGIC
ELS1B
MS0B
ELS1A
TOV1
CH1MAX
16-BIT COMPARATOR
TBCH1H:TBCH1L
CH0IE
INTERRUPT
LOGIC
PTB7
LOGIC
PTB7/TBCH1
CH1F
16-BIT LATCH
MS1A
CH1IE
INTERRUPT
LOGIC
Figure 18-2. TIMB Block Diagram
18.3.1 TIMB Counter Prescaler
The TIMB 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, PS[2:0], in the TIMB status and control register
select the TIMB 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 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 free-running counter contents are transferred to the TIMB channel status and control register
(TBCHxH–TBCHxL, see 18.8.5 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Timer Interface B (TIMB) Module
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 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).
18.3.3 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.
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 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 these 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Functional Description
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
PTB6/TBCH0 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
PTB6/TBCH0 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. TSC0 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, PTB7/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. User software should track
the currently active channel to prevent writing a new value to the active
channel. 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 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 18-3 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 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
PTBx/TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 18-3. 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 (see 18.8.1 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%.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
213
Timer Interface B (TIMB) Module
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 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 these 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
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
PTB6/TBCH0 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 PTB6/TBCH0 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, PTB7/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. User software should track the
currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as generating
unbuffered PWM signals.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
Interrupts
18.3.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use this 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 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 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 TIMB status control register (TBSC), clear the TIMB stop bit, TSTOP.
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 18.8.4 TIMB Channel Status and Control Registers.
18.4 Interrupts
These TIMB sources can generate interrupt requests:
• TIMB overflow flag (TOF) — The TOF bit is set when the TIMB counter reaches the modulo value
programmed 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
215
Timer Interface B (TIMB) Module
18.5 Low-Power Modes
The WAIT and STOP instructions put the microcontroller unit (MCU) in low power-consumption standby
modes.
18.5.1 Wait Mode
The TIMB remains active after the execution of a WAIT instruction. In wait mode, the TIMB registers are
not accessible by the central processor unit (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.
18.5.2 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.
18.6 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.
To allow software to clear status bits during a break interrupt, write a 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 0 to the BCFE bit. With BCFE at 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 0. After the break, doing the
second step clears the status bit.
18.7 I/O Signals
Port B shares two of its pins with the TIMB. There is no external clock input to the TIMB prescaler. The
two TIMB channel I/O pins are PTB6/TBCH0 and PTB7/TBCH1. See Chapter 12 Input/Output (I/O) Ports
(PORTS).
18.7.1 TIMB Channel I/O Pins (PTB7/TBCH1–PTB6/TBCH0)
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.
PTB6/TBCH0 and PTB7/TBCH1 can be configured as buffered output compare or buffered PWM pins.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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I/O Registers
18.8 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 and TBCH1H–TBCH1L
18.8.1 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
Address:
$002B
Bit 7
Read:
TOF
Write:
0
Reset:
6
5
TOIE
TSTOP
0
0
1
R
= Reserved
4
0
TRST
0
3
2
1
Bit 0
R
PS2
PS1
PS0
0
0
0
0
Figure 18-4. TIMB Status and Control Register (TBSC)
TOF — TIMB Overflow Flag Bit
This read/write flag is set when the TIMB counter reaches 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 0 to TOF. If another TIMB overflow occurs before the clearing sequence is complete,
then writing 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 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
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
217
Timer Interface B (TIMB) Module
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 TIMB is required
to exit wait mode. Also, when the TSTOP bit is set and the timer is
configured for input capture operation, input captures are inhibited until
TSTOP is cleared.
When using TSTOP to stop the timer counter, check for any timer flags
being 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 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.
PS[2:0] — Prescaler Select Bits
These read/write bits select one of the seven prescaler outputs as the input to the TIMB counter as
Table 18-1 shows. Reset clears the PS[2:0] bits.
Table 18-1. Prescaler Selection
PS[2:0]
TIMB Clock Source
0 0 0
Internal bus clock ÷ 1
0 0 1
Internal bus clock ÷ 2
0 1 0
Internal bus clock ÷ 4
0 1 1
Internal bus clock ÷ 8
1 0 0
Internal bus clock ÷ 16
1 0 1
Internal bus clock ÷ 32
1 1 0
Internal bus clock ÷ 64
1 1 1
Unused
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Registers
18.8.2 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 — $002C
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 — $002D
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. TIMB Counter Registers (TBCNTH and TBCNTL)
18.8.3 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 timer clock. Writing to the high byte (TMODH) inhibits the TOF bit and
overflow interrupts until the low byte (TMODL) is written. Reset sets the TIMB counter modulo registers.
Register Name and Address
Read:
Write:
Reset:
TBMODH — $002E
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 — $002F
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. TIMB Counter Modulo Registers (TMODH and TMODL)
NOTE
Reset the TIMB counter before writing to the TIMB counter modulo registers.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
219
Timer Interface B (TIMB) Module
18.8.4 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
Register Name and Address
Bit 7
Read:
CH0F
Write:
0
Reset:
0
TBSC0 — $0030
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 — $0033
6
Read:
CH1F
Write:
0
Reset:
0
0
R
= Reserved
CH1IE
5
0
R
0
Figure 18-7. 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 0 to CHxF. If another interrupt request occurs before the clearing sequence is
complete, then writing 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 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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Freescale Semiconductor
I/O Registers
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
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 TCHx pin once PWM, input
capture, or output compare operation 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 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 B, and pin PTBx/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 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
X
0
0
0
X
1
0
0
0
0
0
1
Mode
Output preset
Configuration
Pin under port control; initial output level high
Pin under port control; initial output level low
Capture on rising edge only
0
0
1
0
0
0
1
1
Capture on rising or falling edge
0
1
0
0
Software compare only
0
1
0
1
0
1
1
0
0
1
1
1
1
X
0
1
1
X
1
0
1
X
1
1
Input capture
Output compare
or PWM
Capture on falling edge only
Toggle output on compare
Clear output on compare
Set output on compare
Buffered output
compare or
buffered PWM
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 PTBx/TBCHx pin is stable for at least two bus clocks.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
221
Timer Interface B (TIMB) Module
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 1 and clear output on compare is selected, setting the CHxMAX bit forces the
duty cycle of buffered and unbuffered PWM signals to 100 percent. As Figure 18-8 shows, the
CHxMAX bit takes effect in the cycle after it is set or cleared. The output stays at 100 percent duty
cycle level until the cycle after CHxMAX is cleared.
NOTE
The PWM 100 percent duty cycle is defined as output high all of the time.
To generate the 100 percent duty cycle, use the CHxMAX bit in the TSCx
register. The PWM 0 percent duty cycle is defined as output low all of the
time. To generate the 0 percent duty cycle, select clear output on compare
and then clear the TOVx bit (CHxMAX = 0).
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PTEx/TCHx
TOV = 1
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
TOV = 0
Figure 18-8. CHxMAX Latency
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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I/O Registers
18.8.5 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:
TBCH0H — $0031
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:
TBCH0L — $0032
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 — $0034
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 — $0035
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. TIMB Channel Registers (TBCH0H/L–TBCH1H/L)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
223
Timer Interface B (TIMB) Module
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
224
Freescale Semiconductor
Chapter 19
Development Support
19.1 Introduction
This section describes the break module, the monitor module (MON), and the monitor mode entry
methods.
19.2 Break Module (BRK)
The break module can generate a break interrupt that stops normal program flow at a defined address to
enter a background program.
Features of the break module include:
• Accessible input/output (I/O) registers during the break Interrupt
• Central processor unit (CPU) generated break interrupts
• Software-generated break interrupts
• Computer operating properly (COP) disabling during break interrupts
19.2.1 Functional Description
When the internal address bus matches the value written in the break address registers, the break module
issues a breakpoint signal (BKPT) to the system integration module (SIM). The SIM then causes the CPU
to load the instruction register with a software interrupt instruction (SWI). 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 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
is generated. A return-from-interrupt instruction (RTI) in the break routine ends the break interrupt and
returns the microcontroller unit (MCU) to normal operation.
Figure 19-2 shows the structure of the break module.
When the internal address bus matches the value written in the break address registers or when software
writes a 1 to the BRKA bit in the break status and control register, the CPU starts a break interrupt by:
• Loading the instruction register with the SWI instruction
• Loading the program counter with $FFFC and $FFFD ($FEFC and $FEFD in monitor mode)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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225
Development Support
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure 19-1. Block Diagram Highlighting BRK and MON Blocks
The break interrupt timing is:
• When a break address is placed at the address of the instruction opcode, the instruction is not
executed until after completion of the break interrupt routine.
• When a break address is placed at an address of an instruction operand, the instruction is executed
before the break interrupt.
• When software writes a 1 to the BRKA bit, the break interrupt occurs just before the next instruction
is executed.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
226
Freescale Semiconductor
Break Module (BRK)
ADDRESS BUS[15:8]
BREAK ADDRESS REGISTER HIGH
8-BIT COMPARATOR
ADDRESS BUS[15:0]
CONTROL
BKPT
(TO SIM)
8-BIT COMPARATOR
BREAK ADDRESS REGISTER LOW
ADDRESS BUS[7:0]
Figure 19-2. Break Module Block Diagram
By updating a break address and clearing the BRKA bit in a break interrupt routine, a break interrupt can
be generated continuously.
CAUTION
A break address should be placed at the address of the instruction opcode.
When software does not change the break address and clears the BRKA
bit in the first break interrupt routine, the next break interrupt will not be
generated after exiting the interrupt routine even when the internal address
bus matches the value written in the break address registers.
19.2.1.1 Flag Protection During Break Interrupts
The system integration module (SIM) controls whether or not module status bits can be cleared during
the break state. The BCFE bit in the break flag control register (SBFCR) enables software to clear status
bits during the break state. See 14.7.3 SIM Break Flag Control Register and the Break Interrupts
subsection for each module.
19.2.1.2 TIM During Break Interrupts
A break interrupt stops the timer counter.
19.2.1.3 COP During Break Interrupts
The COP is disabled during a break interrupt when VTST is present on the RST pin.
19.2.2 Break Module Registers
These registers control and monitor operation of the break module:
• Break status and control register (BSCR)
• Break address register high (BRKH)
• Break address register low (BRKL)
• Break status register (SBSR)
• Break flag control register (SBFCR)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
227
Development Support
19.2.2.1 Break Status and Control Register
The break status and control register (BSCR) contains break module enable and status bits.
Address: $FE0B
Read:
Write:
Reset:
Bit 7
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 19-3. 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 0 to bit
7. Reset clears the BRKE bit.
1 = Breaks enabled on 16-bit address match
0 = Breaks disabled
BRKA — Break Active Bit
This read/write status and control bit is set when a break address match occurs. Writing a 1 to BRKA
generates a break interrupt. Clear BRKA by writing a 0 to it before exiting the break routine. Reset
clears the BRKA bit.
1 = Break address match
0 = No break address match
19.2.2.2 Break Address Registers
The break address registers (BRKH and BRKL) contain the high and low bytes of the desired breakpoint
address. Reset clears the break address registers.
Address: $FE09
Read:
Write:
Reset:
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
0
0
0
0
0
0
0
0
Figure 19-4. Break Address Register High (BRKH)
Address: $FE0A
Read:
Write:
Reset:
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
0
0
0
0
0
0
0
0
Figure 19-5. Break Address Register Low (BRKL)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
228
Freescale Semiconductor
Break Module (BRK)
19.2.2.3 Break Status Register
The break status register (SBSR) contains a flag to indicate that a break caused an exit from wait mode.
This register is only used in emulation mode.
Address: $FE00
Bit 7
Read:
Write:
6
R
R
5
R
4
R
3
R
2
R
Reset:
1
SBSW
Note(1)
Bit 0
R
0
R
= Reserved
1. Writing a 0 clears SBSW.
Figure 19-6. Break Status Register (SBSR)
SBSW — SIM Break Stop/Wait
SBSW can be read within the break state SWI routine. The user can modify the return address on the
stack by subtracting one from it.
1 = Wait mode was exited by break interrupt
0 = Wait mode was not exited by break interrupt
19.2.2.4 Break Flag Control Register
The break control register (SBFCR) contains a bit that enables software to clear status bits while the MCU
is in a break state.
Address: $FE03
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
BCFE
R
R
R
R
R
R
R
0
= Reserved
R
Figure 19-7. 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
19.2.3 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power- consumption standby modes. If enabled,
the break module will remain enabled in wait and stop modes. However, since the internal address bus
does not increment in these modes, a break interrupt will never be triggered.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
229
Development Support
19.3 Monitor Module (MON)
The monitor module allows debugging and programming of the microcontroller unit (MCU) through a
single-wire interface with a host computer. Monitor mode entry can be achieved without use of the higher
test voltage, VTST, as long as vector addresses $FFFE and $FFFF are blank, thus reducing the hardware
requirements for in-circuit programming.
Features of the monitor module include:
• Normal user-mode pin functionality
• One pin dedicated to serial communication between MCU and host computer
• Standard non-return-to-zero (NRZ) communication with host computer
• Standard communication baud rate (9600 @ 2.4576-MHz bus frequency)
• Execution of code in random-access memory (RAM) or FLASH
• FLASH memory security feature(1)
• FLASH memory programming interface
• Monitor mode entry without high voltage, VTST, if reset vector is blank ($FFFE and $FFFF contain
$FF)
• Normal monitor mode entry if VTST is applied to IRQ
19.3.1 Functional Description
Figure 19-8 shows a simplified diagram of the monitor mode.
The monitor module receives and executes commands from a host computer.
Figure 19-9 and Figure 19-11 show example circuits used to enter monitor mode and communicate with
a host computer via a standard RS-232 interface.
Simple monitor commands can access any memory address. In monitor mode, the MCU can execute
code downloaded into RAM by a host computer while most MCU pins 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.
Table 19-1 shows the pin conditions for entering monitor mode. As specified in the table, monitor mode
may be entered after a power-on reset (POR) and will allow communication at 9600 baud provided one
of the following sets of conditions is met:
• If $FFFE and $FFFF do not contain $FF (programmed state):
– The external clock is 9.8304 MHz (9600 baud)
– IRQ = VTST
• If $FFFE and $FFFF contain $FF (erased state):
– The external clock is 9.8304 MHz (9600 baud)
– IRQ = VDD (this can be implemented through the internal IRQ pullup)
• If $FFFE and $FFFF contain $FF (erased state):
– The ICG clock is nominal 1.6 MHz (nominal 6300 baud)
– IRQ = VSS
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
230
Freescale Semiconductor
Monitor Module (MON)
POR RESET
NO
CONDITIONS
FROM Table 19-1
PTA0 = 1,
PTA1 = 0, RESET
VECTOR BLANK?
IRQ = VTST?
YES
PTA0 = 1, PTA1 = 0,
PTB4 = 1, AND
PTB3 = 0?
NO
NO
YES
YES
FORCED
MONITOR MODE
NORMAL
USER MODE
NORMAL
MONITOR MODE
INVALID
USER MODE
HOST SENDS
8 SECURITY BYTES
IS RESET
POR?
YES
NO
YES
ARE ALL
SECURITY BYTES
CORRECT?
ENABLE FLASH
NO
DISABLE FLASH
MONITOR MODE ENTRY
DEBUGGING
AND FLASH
PROGRAMMING
(IF FLASH
IS ENABLED)
EXECUTE
MONITOR CODE
YES
DOES RESET
OCCUR?
NO
Figure 19-8. Simplified Monitor Mode Entry Flowchart
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
231
Development Support
MC68HC908EY16
N.C.
VDD
VDD
RST
VDDA
MAX232
1
1 µF
+
4
1 µF
C1–
GND 15
C2+
V+ 2
+
VDD
1 µF
+
IRQ
7
10
8
9
10 k
VDD
9.1 V
PTB3
10 k
1 µF
74HC125
5
6
DB9
3
PTB4
1 kΩ
+
2
10 k
1 µF
V– 6
5 C2–
0.1 µF
OSC1
VCC 16
C1+
+
3
9.8304-MHz CLOCK
VDD
74HC125
3
2
PTA1
10 kΩ
PTA0
VSSA
VSS
4
1
5
Figure 19-9. Normal Monitor Mode Circuit
MC68HC908EY16
N.C.
RST
VDD
VDD
VDDA
9.8304-MHz CLOCK
MAX232
1
1 µF
+
OSC1
VCC 16
+
3
4
1 µF
C1+
C1–
GND 15
C2+
V+ 2
+
5 C2–
1 µF
+
1 µF
N.C.
3
5
8
74HC125
5
6
10
9
PTB4
N.C.
PTB3
N.C.
10 k
1 µF
DB9
7
IRQ
VDD
V– 6
+
2
0.1 µF
VDD
74HC125
3
2
PTA1
10 kΩ
PTA0
4
VSSA
VSS
1
Figure 19-10. Forced Monitor Mode (IRQ = VDD)
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
232
Freescale Semiconductor
Monitor Module (MON)
MC68HC908EY16
N.C.
RST
VDD
VDD
VDDA
MAX232
1
1 µF
+
N.C.
VCC 16
+
3
4
1 µF
C1+
C1–
GND 15
C2+
V+ 2
+
5 C2–
0.1 µF
VDD
1 µF
+
1 µF
IRQ
VDD
V– 6
+
3
7
8
74HC125
5
6
10
9
PTB4
N.C.
PTB3
N.C.
10 k*
1 µF
DB9
2
OSC1
74HC125
3
2
10 k
PTA1
10 kΩ
PTA0
VSSA
VSS
4
1
5
* Value not critical
Figure 19-11. Forced Monitor Mode (IRQ = VSS)
Enter monitor mode with pin configuration shown in Table 19-1 by pulling RST low and then high. The
rising edge of RST latches monitor mode. Once monitor mode is latched, the levels on the port pins
except PTA0 can change.
Once out of reset, the MCU waits for the host to send eight security bytes (see 19.3.2 Security). After the
security bytes, the MCU sends a break signal (10 consecutive 0s) to the host, indicating that it is ready to
receive a command.
19.3.1.1 Normal Monitor Mode
If VTST is applied to IRQ upon monitor mode entry, the bus frequency is a divide-by-four of the input clock.
When monitor mode was entered with VTST on IRQ, the computer operating properly (COP) is disabled
as long as VTST is applied to either IRQ or RST.
This condition states that as long as VTST is maintained on the IRQ pin after entering monitor mode, or if
VTST is applied to RST after the initial reset to get into monitor mode (when VTST was applied to IRQ),
then the COP will be disabled. In the latter situation, after VTST is applied to the RST pin, VTST can be
removed from the IRQ pin in the interest of freeing the IRQ for normal functionality in monitor mode.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
233
Development Support
Table 19-1. Monitor Mode Signal Requirements and Options
Mode
IRQ
RST
VTST
VDD
or
VTST
VDD
VDD
VSS
VDD
User
VDD
or
VSS
VDD
or
VTST
MON08
Function
[Pin No.]
VTST
[6]
RST
[4]
Normal
Monitor
Forced
Monitor
Reset
Vector
Serial
Communication
Communication
Speed
ICG
COP
0
OFF
Disabled
9.8304
MHz
2.4576
MHz
9600
X
X
OFF
Disabled
9.8304
MHz
2.4576
MHz
9600
0
X
X
ON
Disabled
—
Nominal
1.6 MHz
Nominal
6300
X
X
X
X
CN
Enabled
—
Nominal
1.6 MHz
X
COM
[8]
SSEL
[10]
—
—
OSC1
[13]
—
—
PTA0
PTA1
PTB4
PTB3
1
0
1
1
0
1
X
$FF
(blank)
Not
$FF
—
Mode
Selection
MOD0 MOD1
[12]
[14]
External
Bus
Clock
Frequency
Baud
Rate
1. PTA0 must have a pullup resistor to VDD in monitor mode.
2. Communication speed in the table is an example to obtain a baud rate of 9600 except the forced monitor IRQ = VSS case.
Baud rate using external oscillator is bus frequency / 256.
3. External clock is a 9.8304 MHz canned oscillator on OSC1.
4. X = don’t care
5. MON08 pin refers to P&E Microcomputer Systems’ MON08-Cyclone 2 by 8-pin connector.
NC
1
2
GND
NC
3
4
RST
NC
5
6
IRQ
NC
7
8
PTA0
NC
9
10
PTA1
NC
11
12
PTB3
OSC1
13
14
PTB4
VDD
15
16
N.C.
19.3.1.2 Forced Monitor Mode
If entering monitor mode without high voltage on IRQ, then all port B pin requirements and conditions are
not in effect. This is to reduce circuit requirements when performing in-circuit programming.
NOTE
If the reset vector is blank and monitor mode is entered, the chip will see an
additional reset cycle after the initial power-on reset (POR). Once the reset
vector has been programmed, the traditional method of applying a voltage,
VTST, to IRQ must be used to enter monitor mode.
With VDD on IRQ, an external oscillator of 9.8034 MHz is required for a baud rate of 9600, as the internal
bus frequency is automatically set to the external frequency divided by four.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
234
Freescale Semiconductor
Monitor Module (MON)
With VSS on IRQ at the monitor entry, the ICG is on. In this case, the bus frequency is a nominal 1.6 MHz
and the baud rate is a nominal 6300.
When the forced monitor mode is entered the COP is always disabled regardless of the state of IRQ or
RST.
19.3.1.3 Monitor Vectors
In monitor mode, the MCU uses different vectors for reset, SWI (software interrupt), and break interrupt
than those for user mode. 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.
Table 19-2 summarizes the differences between user mode and monitor mode.
Table 19-2. Mode Differences
Functions
Modes
Reset
Vector High
Reset
Vector Low
Break
Vector High
Break
Vector Low
SWI
Vector High
SWI
Vector Low
User
$FFFE
$FFFF
$FFFC
$FFFD
$FFFC
$FFFD
Monitor
$FEFE
$FEFF
$FEFC
$FEFD
$FEFC
$FEFD
19.3.1.4 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.
Transmit and receive baud rates must be identical.
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
STOP
BIT
NEXT
START
BIT
Figure 19-12. Monitor Data Format
19.3.1.5 Break Signal
A start bit (0) followed by nine 0 bits is a break signal. When the monitor receives a break signal, it drives
the PTA0 pin high for the duration of approximately two bits and then echoes back the break signal.
MISSING STOP BIT
0
1
2
3
4
5
6
APPROXIMATELY 2 BITS DELAY
BEFORE ZERO ECHO
7
0
1
2
3
4
5
6
7
Figure 19-13. Break Transaction
19.3.1.6 Baud Rate
The communication baud rate is controlled by the crystal frequency or external clock and the state of the
PTB5 pin (when IRQ is set to VTST) upon entry into monitor mode. If monitor mode was entered with VDD
on IRQ and the reset vector blank, then the baud rate is independent of PTB5.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
235
Development Support
Table 19-1 also lists external frequencies required to achieve a standard baud rate of 7200 bps. The
effective baud rate is the bus frequency divided by 278. If using a crystal as the clock source, be aware
of the upper frequency limit that the internal clock module can handle. See 20.6 Control Timing for this
limit.
19.3.1.7 Commands
The monitor ROM firmware uses these commands:
• READ (read memory)
• WRITE (write memory)
• IREAD (indexed read)
• IWRITE (indexed write)
• READSP (read stack pointer)
• RUN (run user program)
The monitor ROM firmware echoes each received byte back to the PTA0 pin for error checking. An 11-bit
delay at the end of each command allows the host to send a break character to cancel the command. A
delay of two bit times occurs before each echo and before READ, IREAD, or READSP data is returned.
The data returned by a read command appears after the echo of the last byte of the command.
NOTE
Wait one bit time after each echo before sending the next byte.
FROM
HOST
READ
4
ADDRESS
HIGH
READ
4
1
ADDRESS
HIGH
ADDRESS
LOW
1
4
ADDRESS
LOW
DATA
1
3, 2
4
ECHO
RETURN
Notes:
1 = Echo delay, approximately 2 bit times
2 = Data return delay, approximately 2 bit times
3 = Cancel command delay, 11 bit times
4 = Wait 1 bit time before sending next byte.
Figure 19-14. Read Transaction
FROM
HOST
3
ADDRESS
HIGH
WRITE
WRITE
1
3
ADDRESS
HIGH
1
ADDRESS
LOW
3
ADDRESS
LOW
1
DATA
3
DATA
1
2, 3
ECHO
Notes:
1 = Echo delay, approximately 2 bit times
2 = Cancel command delay, 11 bit times
3 = Wait 1 bit time before sending next byte.
Figure 19-15. Write Transaction
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
236
Freescale Semiconductor
Monitor Module (MON)
A brief description of each monitor mode command is given in Table 19-3 through Table 19-8.
Table 19-3. READ (Read Memory) Command
Description
Read byte from memory
Operand
2-byte address in high-byte:low-byte order
Data Returned
Returns contents of specified address
Opcode
$4A
Command Sequence
SENT TO MONITOR
READ
ADDRESS
HIGH
READ
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
ECHO
RETURN
Table 19-4. WRITE (Write Memory) Command
Description
Operand
Data Returned
Opcode
Write byte to memory
2-byte address in high-byte:low-byte order; low byte followed by data byte
None
$49
Command Sequence
FROM HOST
WRITE
ADDRESS
HIGH
WRITE
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
DATA
ECHO
Table 19-5. IREAD (Indexed Read) Command
Description
Operand
Data Returned
Opcode
Read next 2 bytes in memory from last address accessed
None
Returns contents of next two addresses
$1A
Command Sequence
FROM HOST
IREAD
ECHO
IREAD
DATA
DATA
RETURN
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
237
Development Support
Table 19-6. IWRITE (Indexed Write) Command
Description
Operand
Data Returned
Opcode
Write to last address accessed + 1
Single data byte
None
$19
Command Sequence
FROM HOST
IWRITE
IWRITE
DATA
DATA
ECHO
A sequence of IREAD or IWRITE commands can access a block of memory sequentially over the full
64-Kbyte memory map.
Table 19-7. READSP (Read Stack Pointer) Command
Description
Operand
Data Returned
Opcode
Reads stack pointer
None
Returns incremented stack pointer value (SP + 1) in high-byte:low-byte order
$0C
Command Sequence
FROM HOST
READSP
SP
HIGH
READSP
ECHO
SP
LOW
RETURN
Table 19-8. RUN (Run User Program) Command
Description
Executes PULH and RTI instructions
Operand
None
Data Returned
None
Opcode
$28
Command Sequence
FROM HOST
RUN
RUN
ECHO
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
238
Freescale Semiconductor
Monitor Module (MON)
The MCU executes the SWI and PSHH instructions when it enters monitor mode. The RUN command
tells the MCU to execute the PULH and RTI instructions. Before sending the RUN command, the host can
modify the stacked CPU registers to prepare to run the host program. The READSP command returns
the incremented stack pointer value, SP + 1. The high and low bytes of the program counter are at
addresses SP + 5 and SP + 6.
SP
HIGH BYTE OF INDEX REGISTER
SP + 1
CONDITION CODE REGISTER
SP + 2
ACCUMULATOR
SP + 3
LOW BYTE OF INDEX REGISTER
SP + 4
HIGH BYTE OF PROGRAM COUNTER
SP + 5
LOW BYTE OF PROGRAM COUNTER
SP + 6
SP + 7
Figure 19-16. Stack Pointer at Monitor Mode Entry
19.3.2 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.
During monitor mode entry, the MCU waits after the power-on reset for the host to send the eight security
bytes on pin PTA0. 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. If the reset was not a power-on reset, security remains bypassed
and security code entry is not required. See Figure 19-17.
Upon power-on reset, if the received bytes of the security code 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 a FLASH location returns an invalid value and trying to execute code from FLASH causes an
illegal address reset. After receiving the eight security bytes from the host, the MCU transmits a break
character, signifying 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.
To determine whether the security code entered is correct, check to see if bit 6 of RAM address $40 is
set. If it is, then the correct security code has been entered and FLASH can be accessed.
If the security sequence fails, the device should be reset by a power-on reset and brought up in monitor
mode to attempt another entry. After failing the security sequence, the FLASH module can also be mass
erased by executing an erase routine that was downloaded into internal RAM. The mass erase operation
clears the security code locations so that all eight security bytes become $FF (blank).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
239
Development Support
VDD
4096 + 32 CGMXCLK CYCLES
COMMAND
BYTE 8
BYTE 2
BYTE 1
RST
FROM HOST
PA0
4
BYTE 8 ECHO
2
Notes:
1 = Echo delay, approximately 2 bit times
2 = Data return delay, approximately 2 bit times
4 = Wait 1 bit time before sending next byte
5 = Wait until the monitor ROM runs
1
COMMAND ECHO
1
BREAK
1
BYTE 2 ECHO
FROM MCU
4
1
BYTE 1 ECHO
5
Figure 19-17. Monitor Mode Entry Timing
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
240
Freescale Semiconductor
Chapter 20
Electrical Specifications
20.1 Introduction
This section contains preliminary electrical and timing specifications.
20.2 Absolute 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 20.5 DC Electrical Characteristics for guaranteed operating
conditions.
Characteristic(1)
Symbol
Value
Unit
Supply voltage
VDD
–0.3 to +6.0
V
Input voltage
VIn
VSS –0.3 to VDD +0.3
V
I
±15
mA
IPTA0–IPTA6,
IPTC0–IPTC1
±25
mA
Maximum current out of VSS
IMVSS
100
mA
Maximum current into VDD
IMVDD
100
mA
Storage temperature
TSTG
–55 to +150
°C
Maximum current per pin
excluding VDD, VSS,
and PTA0–PTA6 and PTC0-PTC1
Maximum current for pins
PTA0–PTA6 and PTC0-PTC1
1. Voltages 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).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
241
Electrical Specifications
20.3 Functional Operating Range
Characteristic
Symbol
Value
Unit
TA
–40 to 135
°C
VDD
5.0 ± 10%
V
Symbol
Value
Unit
Thermal resistance
QFP (32 pins)
θJA
100
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
Operating temperature range
Operating voltage range
20.4 Thermal Characteristics
Characteristic
PD x (TA + 273°C)
+ PD2 x θJA
W/C
TA + (PD x θJA)
°C
1. Power dissipation is a function of temperature.
2. K is a constant unique to the device. K can be determined for a known TA and measured PD. With this value of K, PD and
TJ can be determined for any value of TA.
20.5 DC Electrical Characteristics
Characteristic(1)
Symbol
Min
Typ(2)
Max
VDD –0.7
VDD –1.1
VDD –1.7
VDD –1.5
VDD –0.54
VDD –0.91
VDD –1.51
VDD –0.81
—
—
—
—
—
—
—
—
0.31
0.56
0.99
1.44
0.4
1
1.5
1.8
Unit
Output high voltage
ILoad = –2.0 mA, all I/O pins
ILoad = –5.0 mA, all I/O pins
ILoad = –10.0 mA, all I/O pins
ILoad = –15.0 mA, PTA0–PTA6/SS and PTC0–PTC1 only
VOH
Output low voltage
ILoad = 1.6 mA, all I/O pins
ILoad = 5.0 mA, all I/O pins
ILoad = 10.0 mA, all I/O pins
ILoad = 15.0 mA, PTA0–PTA6/SS and PTC0–PTC1 only
VOL
Input high voltage — all ports, IRQ, RST
VIH
0.7 x VDD
—
VDD + 0.3
V
Input low voltage — all ports, IRQ, RST
VIL
VSS
—
0.3 x VDD
V
DC injection current, all ports(3)
IINJ
– 2.0
—
+ 2.0
mA
IINJTOT
– 25
+ 25
mA
Total DC current injection (sum of all I/O)
V
V
— Continued on next page
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
242
Freescale Semiconductor
DC Electrical Characteristics
Characteristic(1)
Symbol
Min
Typ(2)
Max
Unit
—
—
—
—
—
—
18
5.2
0.83
0.19
3.0
0.19
25
7.0
2.00
0.24
30
0.30
mA
mA
µA
mA
µA
mA
VDD + VDDA supply current
Run(4),(5)
Wait(5), (6)
Stop (LVI off) @ 25°C(7)
Stop (LVI on) @ 25°C
Stop (LVI off), –40°C to 135°C
Stop (LVI on), –40°C to 135°C
IDD
I/O ports Hi-Z leakage current(8)
IIL
–1
—
+1
µA
Input current – RST, OSC1
IIn
–1
—
+1
µA
Capacitance
Ports (as input or output)
COut
CIn
—
—
—
—
12
8
pF
POR rearm voltage(9)
VPOR
0
—
100
mV
POR reset voltage(10)
VPOR
0
700
800
mV
POR rise time ramp rate
RPOR
0.035
—
—
V/ms
Monitor mode entry voltage
VTST
VDD+ 3.5
VDD+ 4.5
V
Low-voltage inhibit reset, trip falling voltage(11)
VTRIPF
3.90
4.30
4.50
V
Low-voltage inhibit reset, trip rising voltage(12)
VTRIPR
4.00
4.40
4.60
V
Low-voltage inhibit reset/recover hysteresis(13)
VHYS
—
0.09
—
V
Pullup resistor — PTA0–PTA6/SS(14), IRQ, RST
RPU
24
—
48
kΩ
1. VDD = 5.5 Vdc to 4.5 Vdc, VSS = 0 Vdc, TA = –40°C to +135°C, unless otherwise noted
2. Typical values reflect average measurements at midpoint of voltage range, 25°C only.
3. Some disturbance of the ADC accuracy is possible during any injection event and is dependent on board layout and power
supply decoupling.
4. Run (operating) IDD measured using internal oscillator at its 32-MHz rate. VDD = 5.5 Vdc. All inputs 0.2 V from rail. No dc
loads. Less than 100 pF on all outputs. All ports configured as inputs. Measured with all modules enabled.
5. All measurements taken with LVI enabled.
6. Wait IDD measured using internal oscillator at its 1-MHz rate. All inputs 0.2 V from rail; no dc loads; less than 100 pF on all
outputs. All ports configured as inputs.
7. Stop IDD is measured with no port pin sourcing current; all modules are disabled. OSCSTOPEN option is not selected.
8. Pullups and pulldowns are disabled.
9. Maximum is highest voltage that power-on reset (POR) is guaranteed.
10. Maximum is highest voltage that POR is possible.
11. These values assume the LVI is operating in 5-V mode (i.e. LVI5OR3 bit is set to 1).
For 3-V mode (LVI5OR3 = 0), values become Min: 2.45, Typ: 2.60, Max: 2.80
12. These values assume the LVI is operating in 5-V mode (i.e. LVI5OR3 bit is set to 1).
For 3-V mode (LVI5OR3 = 0), values become Min: 2.55, Typ: 2.66, Max: 2.80
13. These values assume the LVI is operating in 5-V mode (i.e. LVI5OR3 bit is set to 1).
For 3-V mode (LVI5OR3 = 0), values become Typ: 60
14. PTA0–PTA4 pullup resistors are for interrupts only and are only enabled when the keyboard is in use.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
243
Electrical Specifications
20.6 Control Timing
Symbol
Characteristic(1)
Min
Max
Unit
32
1
dc(4)
100
8
32
kHz
MHz
MHz
Frequency of operation(2)
Crystal option (EXTSLOW = 1)
Crystal option (EXTSLOW = 0)
External clock option(3)
fosc
Internal operating frequency
fop
—
8
MHz
Internal clock period (1/fOP)
tcyc
125
—
ns
RST input pulse width low(5)
tIRL
50
—
ns
IRQ interrupt pulse width low(6)
(edge-triggered)
tILIH
50
—
ns
IRQ interrupt pulse period
tILIL
Note 8
—
tcyc
16-bit timer(7)
Input capture pulse width
Input capture period
tTH,tTL
tTLTL
Note 8
—
—
ns
tcyc
1. VSS = 0 Vdc; timing shown with respect to 20% VDD and 70% VSS unless otherwise noted.
2. See Chapter 8 Internal Clock Generator (ICG) Module for more information.
3. No more than 10% duty cycle deviation from 50%
4. Some modules may require a minimum frequency greater than dc for proper operation. See appropriate table for this
information.
5. Minimum pulse width reset is guaranteed to be recognized. It is possible for a smaller pulse width to cause a reset.
6. Minimum pulse width is for guaranteed interrupt. It is possible for a smaller pulse width to be recognized.
7. Minimum pulse width is for guaranteed interrupt. It is possible for a smaller pulse width to be recognized.
8. The minimum period, tILIL or tTLTL, should not be less than the number of cycles it takes to execute the interrupt service
routine plus tcyc.
20.7 Internal Oscillator Characteristics
Characteristic(1)
Symbol
Min
Typ
Max
Unit
Internal oscillator base frequency(2), (3)
fINTOSC
230.4
307.2
384
kHz
fOSC_TOL
–25
—
+25
%
N
1
—
127
—
Internal oscillator tolerance
Internal oscillator multiplier(4)
1. VDD = 4.5 to 5.5 Vdc, VSS = 0 Vdc, TA = –40°C to +135°C, unless otherwise noted
2. Internal oscillator is selectable through software for a maximum frequency. Actual frequency will be multiplier (N) x base
frequency.
3. fBus = (fINTOSC / 4) x N when internal clock source selected
4. Multiplier must be chosen to limit the maximum bus frequency of 8 MHz for 4.5-V operation.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
244
Freescale Semiconductor
External Oscillator Characteristics
20.8 External Oscillator Characteristics
Characteristic(1)
Symbol
Min
Typ
Max
dc(5)
—
32 M(6)
60
307.2 k
—
—
307.2 k
32 M(6)
Unit
External clock option(2)(3)
With ICG clock disabled
With ICG clock enabled
EXTSLOW = 1(4)
EXTSLOW = 0(4)
fEXTOSC
External crystal options(7)(8)
EXTSLOW = 1(4)
EXTSLOW = 0(4)
fEXTOSC
30 k
1M
—
—
100 k
8M
Hz
Crystal load capacitance(9)
CL
—
12.5
—
pF
Crystal fixed capacitance(9)
C1
—
15
—
pF
Crystal tuning capacitance(9)
C2
—
15
—
pF
EXTSLOW = 1
Feedback bias resistor(9)
Series resistor (9)
RB
Rs
—
100
10
330
—
470
MΩ
kΩ
RB
—
1
—
MΩ
Rs
Rs
Rs
—
—
—
20
10
0
—
—
—
kΩ
kΩ
kΩ
EXTSLOW = 0
Feedback bias resistor(9)
Series resistor (9)(10)
fEXTOSC = 1 MHz
fEXTOSC = 4 MHz
fEXTOSC = 8 MHz
Hz
1. VDD = 4.5 to 5.5 Vdc, VSS = 0 Vdc, TA = –40°C to +135°C, unless otherwise noted
2. Setting EXTCLKEN configuration option enables OSC1 pin for external clock square-wave input.
3. No more than 10% duty cycle deviation from 50%
4. EXTSLOW configuration option configures external oscillator for a slow speed crystal and sets the clock monitor circuits
of the ICG module to expect an external clock frequency that is higher/lower than the internal oscillator base frequency,
fINTOSC.
5. Some modules may require a minimum frequency greater than dc for proper operation. See appropriate table for this
information.
6. MCU speed derates from 32 MHz at VDD = 4.5 Vdc
7. Setting EXTCLKEN and EXTXTALEN configuration options enables OSC1 and OSC2 pins for external crystal option.
8. fBus = (fEXTOSC / 4) when external clock source is selected.
9. Crystal manufacturer’s value, see Figure 8-3. Internal Clock Generator Block Diagram.
10. Not required for high-frequency crystals
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
245
Electrical Specifications
20.9 Trimmed Accuracy of the Internal Clock Generator
The unadjusted frequency of the low-frequency base clock (IBASE), when the comparators in the
frequency comparator indicate zero error, can vary as much as ±25% due to process, temperature, and
voltage. The trimming capability exists to compensate for process affects. The remaining variation in
frequency is due to temperature, voltage, and change in target frequency (multiply register setting). These
affects are designed to be minimal, however variation does occur. Better performance is seen with lower
settings of N.
20.9.1 Trimmed Internal Clock Generator Characteristics
Characteristic(1)
Symbol
Min
Typ
Max
Unit
Absolute trimmed internal oscillator tolerance(2),(3)
–40°C to 85°C
–40°C to 135°C
Fabs_tol
—
—
±2.0
±2.5
±3.5
±5.0
%
Variation over temperature(3), (4)
Var_temp
—
0.05
0.08
%/°C
Variation over voltage(3), (5)
25°C
–40°C to 85°C
–40°C to 135°C
Var_volt
—
—
—
1.0
1.0
1.0
2.0
2.0
2.0
%/V
1. These specifications concern long-term frequency variation. Each measurement is taken over a 1-ms period.
2. Absolute value of variation in ICG output frequency, trimmed at nominal VDD and temperature, as temperature and VDD
are allowed to vary for a single given setting of N.
3. Specification is characterized but not tested.
4. Variation in ICG output frequency for a fixed N and voltage
5. Variation in ICG output frequency for a fixed N
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
246
Freescale Semiconductor
Analog-to-Digital Converter (ADC) Characteristics
20.10 Analog-to-Digital Converter (ADC) Characteristics
Characteristic
Symbol
Min
Typ
Max
Unit
Notes
Supply voltage
VDDA
4.5
—
5.5
V
VDDA should be tied to
the same potential as
VDD via separate traces
Input voltages
VADIN
0
—
VDDA
V
VADIN <= VDDA
Resolution
BAD
10
—
10
Bits
Absolute accuracy
AAD
–4
—
+4
LSB
Includes quantization
ADC internal clock
fADIC
500 k
—
1.048 M
Hz
tAIC = 1/fADIC
Conversion range
RAD
VSSA
—
VDDA
V
Power-up time
tADPU
16
—
—
tAIC cycles
Conversion time
tADC
16
—
17
tAIC cycles
Sample time
tADS
5
—
—
tAIC cycles
Monotonicity
MAD
Zero input reading
ZADI
000
—
003
Hex
Full-scale reading
FADI
3FC
—
3FF
Hex
Input capacitance
CADI
—
—
30
pF
VREFH/VREFL current
IVREF
—
1.6
—
mA
Absolute accuracy
(8-bit truncated mode)
AAD
–1
—
+1
LSB
Zero input reading
(8-bit truncated mode)
ZADI
00
—
01
Hex
Full-scale reading
(8-bit truncated mode)
FADI
FE
—
FF
Hex
Quantization error
(8-bit truncated mode)
—
—
—
+7/8
–1/8
LSB
Guaranteed
Not tested
Includes quantization
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
247
Electrical Specifications
20.11 SPI Characteristics
Diagram
Number(1)
Characteristic(2)
Symbol
Min
Max
Unit
Operating frequency
Master
Slave
fOP(M)
fOP(S)
fOP/128
DC
fOP/2
fOP
MHz
MHz
1
Cycle time
Master
Slave
tCYC(M)
tCYC(S)
2
1
128
—
tcyc
tcyc
2
Enable lead time
tLead(S)
1
—
tcyc
3
Enable lag time
tLag(S)
1
—
tcyc
4
Clock (SPSCK) high time
Master
Slave
tSCKH(M)
tSCKH(S)
tcyc –25
1/2 tcyc –25
64 tcyc
—
ns
ns
5
Clock (SPSCK) low time
Master
Slave
tSCKL(M)
tSCKL(S)
tcyc –25
1/2 tcyc –25
64 tcyc
—
ns
ns
6
Data setup time (inputs)
Master
Slave
tSU(M)
tSU(S)
30
30
—
—
ns
ns
7
Data hold time (inputs)
Master
Slave
tH(M)
tH(S)
30
30
—
—
ns
ns
8
Access time, slave(3)
CPHA = 0
CPHA = 1
tA(CP0)
tA(CP1)
0
0
40
40
ns
ns
9
Disable time, slave(4)
tDIS(S)
—
40
ns
10
Data valid time, after enable edge
Master
Slave(5)
tV(M)
tV(S)
—
—
50
50
ns
ns
11
Data hold time, outputs, after enable edge
Master
Slave
tHO(M)
tHO(S)
0
0
—
—
ns
ns
1. Numbers refer to dimensions in Figure 20-1 and Figure 20-2.
2. All timing is shown with respect to 20% VDD and 70% VDD, unless noted; 100 pF load on all SPI pins.
3. Time to data active from high-impedance state
4. Hold time to high-impedance state
5. With 100 pF on all SPI pins
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
248
Freescale Semiconductor
SPI Characteristics
SS
INPUT
SS PIN OF MASTER HELD HIGH
1
SPSCK OUTPUT
CPOL = 0
NOTE
SPSCK OUTPUT
CPOL = 1
NOTE
5
4
5
4
6
MISO
INPUT
MSB IN
BITS 6–1
11
MOSI
OUTPUT
MASTER MSB OUT
7
LSB IN
10
11
BITS 6–1
MASTER LSB OUT
Note: This first clock edge is generated internally, but is not seen at the SPSCK pin.
a) SPI Master Timing (CPHA = 0)
SS
INPUT
SS PIN OF MASTER HELD HIGH
1
SPSCK OUTPUT
CPOL = 0
5
NOTE
4
SPSCK OUTPUT
CPOL = 1
5
NOTE
4
6
MISO
INPUT
MSB IN
10
MOSI
OUTPUT
BITS 6–1
11
MASTER MSB OUT
7
LSB IN
10
BITS 6–1
MASTER LSB OUT
Note: This last clock edge is generated internally, but is not seen at the SPSCK pin.
b) SPI Master Timing (CPHA = 1)
Figure 20-1. SPI Master Timing
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
249
Electrical Specifications
SS
INPUT
3
1
SPSCK INPUT
CPOL = 0
5
4
2
SPSCK INPUT
CPOL = 1
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
SPSCK INPUT
CPOL = 0
5
4
2
3
SPSCK INPUT
CPOL = 1
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 20-2. SPI Slave Timing
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
250
Freescale Semiconductor
Memory Characteristics
20.12 Memory Characteristics
Characteristic
Symbol
Min
Typ
Max
Unit
VRDR
1.3
—
—
V
—
1
—
—
MHz
fRead(1)
0
—
8M
Hz
FLASH page erase time
<1 K cycles
>1 K cycles
tErase
0.9
3.6
1
4
1.1
5.5
ms
FLASH mass erase time
tMErase
4
—
—
ms
FLASH PGM/ERASE to HVEN setup time
tNVS
10
—
—
µs
FLASH high-voltage hold time
tNVH
5
—
—
µs
FLASH high-voltage hold time (mass erase)
tNVHL
100
—
—
µs
FLASH program hold time
tPGS
5
—
—
µs
FLASH program time
tPROG
30
—
40
µs
FLASH return to read time
tRCV(2)
1
—
—
µs
FLASH cumulative program hv period
tHV(3)
—
—
4
ms
FLASH endurance(4)
—
10 k
100 k
—
Cycles
FLASH data retention time(5)
—
15
100
—
Years
RAM data retention voltage
FLASH program bus clock frequency
FLASH read bus clock frequency
1. fRead is defined as the frequency range for which the FLASH memory can be read.
2. 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 0.
3. 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 + (tPROG x 64) ≤ tHV maximum.
4. Typical endurance was evaluated for this product family. For additional information on how Freescale defines Typical
Endurance, please refer to Engineering Bulletin EB619.
5. Typical data retention values are based on intrinsic capability of the technology measured at high temperature and de-rated
to 25°C using the Arrhenius equation. For additional information on how Freescale defines Typical Data Retention, please
refer to Engineering Bulletin EB618.
6. In the 125°C to 135°C temperature range, the FLASH is guaranteed as read only.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
251
Electrical Specifications
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
252
Freescale Semiconductor
Chapter 21
Ordering Information and Mechanical Specifications
21.1 Introduction
This section contains ordering numbers for MC68HC908EY16. An example of the device numbering
system is given in Figure 21-1. In addition, this section gives the package dimensions for the 32-pin quad
flat pack (QFP).
21.2 MC Order Numbers
Table 21-1. MC Order Numbers
Operating
Temperature Range
MC Order Number(1)
MC68HC908EY16KFA
–40°C to +135°C
MC68HC908EY16MFA
–40°C to +125°C
MC68HC908EY16VFA
–40°C to +105°C
MC68HC908EY16CFA
–40°C to +85°C
1. FA = Quad flat pack
MC68HC908EY16 XX X E
FAMILY
Pb FREE
PACKAGE DESIGNATOR
TEMPERATURE RANGE
Figure 21-1. Device Numbering System
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
253
Ordering Information and Mechanical Specifications
21.3 32-Pin QFP (Case Number 873)
L
D
S
H A–B
V
M
C A–B
0.20 (0.008)
B
0.20 (0.008)
L
M
–B–
–A–
0.05 (0.002) A–B
S
D
S
16
S
17
24
25
B
32
P
B
DETAIL A
9
1
8
–A–, –B–, –D–
–D–
DETAIL A
A
0.20 (0.008)
M
C A–B
D
S
S
0.05 (0.002) A–B
S
0.20 (0.008)
M
H A–B
S
D
F
BASE
METAL
S
M
DETAIL C
N
J
C E
–H–
–C–
SEATING
PLANE
H
M
G
DATUM
PLANE
0.01 (0.004)
D
0.20 (0.008)
M
C A–B
S
D
S
SECTION B–B
VIEW ROTATED 90 _CLOCKWISE
U
T
R
–H–
DATUM
PLANE
K
X
DETAIL C
Q
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DATUM PLANE –H– IS LOCATED AT BOTTOM OF
LEAD AND IS COINCIDENT WITH THE LEAD WHERE
THE LEAD EXITS THE PLASTIC BODY AT THE
BOTTOM OF THE PARTING LINE.
4. DATUMS –A–, –B– AND –D– TO BE DETERMINED AT
DATUM PLANE –H–.
5. DIMENSIONS S AND V TO BE DETERMINED AT
SEATING PLANE –C–.
6. DIMENSIONS A AND B DO NOT INCLUDE MOLD
PROTRUSION. ALLOWABLE PROTRUSION IS 0.25
(0.010) PER SIDE. DIMENSIONS A AND B DO
INCLUDE MOLD MISMATCH AND ARE DETERMINED
AT DATUM PLANE –H–.
7. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR PROTRUSION
SHALL BE 0.08 (0.003) TOTAL IN EXCESS OF THE D
DIMENSION AT MAXIMUM MATERIAL CONDITION.
DAMBAR CANNOT BE LOCATED ON THE LOWER
RADIUS OR THE FOOT.
DIM
A
B
C
D
E
F
G
H
J
K
L
M
N
P
Q
R
S
T
U
V
X
MILLIMETERS
MIN
MAX
6.95
7.10
6.95
7.10
1.40
1.60
0.273
0.373
1.30
1.50
0.273
–––
0.80 BSC
–––
0.20
0.119
0.197
0.33
0.57
5.6 REF
6_
8_
0.119
0.135
0.40 BSC
5_
10_
0.15
0.25
8.85
9.15
0.15
0.25
5_
11_
8.85
9.15
1.00 REF
INCHES
MIN
MAX
0.274
0.280
0.274
0.280
0.055
0.063
0.010
0.015
0.051
0.059
0.010
–––
0.031 BSC
–––
0.008
0.005
0.008
0.013
0.022
0.220 REF
6_
8_
0.005
0.005
0.016 BSC
5_
10_
0.006
0.010
0.348
0.360
0.006
0.010
5_
11_
0.348
0.360
0.039 REF
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
254
Freescale Semiconductor
Appendix A
MC68HC908EY8
A.1 Introduction
The MC68HC908EY8 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.
The information contained in this document pertains to the MC68HC908EY8 with the exceptions shown
in this appendix.
A.2 Block Diagram
See Figure A-1.
A.3 Memory
The memory map, shown in Figure A-2, includes:
• 8 Kbytes of FLASH memory, 7680 bytes of user space
• 512 bytes of random-access memory (RAM)
• 36 bytes of user-defined vectors
• 310 bytes of monitor routines in read-only memory (ROM)
• 1024 bytes of integrated FLASH burn-in routines in ROM
The FLASH memory is an array of 7680 bytes with an additional 36 bytes of user vectors and one byte
used for block protection. The FLASH is organized internally as an 8192-word by 8-bit complementary
metal-oxide semiconductor (CMOS) page erase, byte (8-bit) program embedded FLASH memory. Each
page consists of 64 bytes. The page erase operation erases all words within a page. A page is composed
of two adjacent rows.
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
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255
INTERNAL BUS
M68HC08 CPU
USER FLASH
7680 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA0/KBD0
PTB7/AD7/TBCH1
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
VREFH
VDDA
VREFL
VSSA
VDD
VSS
DDRC
PORT C
PORT D
PORT E
10-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
ARBITER
MODULE
POWER
PRESCALER
MODULE
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK
PTC1/MOSI
PTC0/MISO
DDRD
SINGLE EXTERNAL IRQ
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
PTE1/RxD
DDRE
24 INTERNAL SYSTEM
INTEGRATION MODULE
PTB3/AD3
PTD1/TACH1
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PTB5/AD5
PTB4/AD4
PTB2/AD2
PTB1/AD1
PTB0/AD0
COMPUTER OPERATING
PROPERLY MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
1024 BYTES
IRQ
PTA3/KBD3
PTA1/KBD1
MONITOR ROM
310 BYTES
RST
PTA4/KBD4
PTA2/KBD2
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
384 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
PTA5/SPSCK
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTD0/TACH0
PTE0/TxD
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
Figure A-1. MC68HC908EY8 Block Diagram
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
256
Freescale Semiconductor
$0000
I/O Registers
64 Bytes
↓
$003F
$0040
RAM
384 Bytes
↓
$FE08
FLASH Control Register (FLCR)
$FE09
Break Address Register High (BRKH)
$FE0A
Break Address Register Low (BRKL)
$FE0B
Break Status and Control Register (BRKSCR)
$FE0C
LVI Status Register (LVISR)
$01BF
$FE0D
$01C00
↓
Unimplemented
3648 Bytes
↓
$0FFF
↓
$FE0F
$FE10
↓
$1000
Reserved for Integrated FLASH Burn-in Routines
1024 Bytes
$13FF
Reserved
3 Bytes
$FE1F
Reserved
16 Bytes
Reserved for Compatibility with Monitor Code
for A-Family Parts
$FE20
↓
$1400
Unimplemented
53,334 Bytes
↓
FF55
$DFFF
FF56
$E000
↓
FLASH Memory
7680 Bytes
↓
$FDFF
Monitor ROM 310 Bytes
Unimplemented
40 Bytes
FF7D
$FF7E
$FE00
SIM Break Status Register (SBSR)
$FF7F
$FE01
SIM Reset Status Register (SRSR)
↓
$FE02
Reserved
$FFDB
$FE03
SIM Break Flag Control Register (SBFCR)
$FFDC
$FE04
RESERVED
↓
$FE05
RESERVED
$FFFF
$FE06
RESERVED
$FE07
Reserved for FLASH Test Control Register (FLTCR)
FLASH Block Protect Register (FLBPR)
Unimplemented
93 Bytes
FLASH Vectors
36 Bytes
Note:
Locations $FFF6–$FFFD are reserved for eight
security bytes.
Figure A-2. MC68HC908EY8 Memory Map
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
257
A.4 MC Order Numbers
Table A-1. MC Order Numbers
Operating
Temperature Range
MC Order Number(1)
MC68HC908EY8KFA
–40°C to +135°C
MC68HC908EY8MFA
–40°C to +125°C
MC68HC908EY8VFA
–40°C to +105°C
MC68HC908EY8CFA
–40°C to +85°C
1. FA = Quad flat pack
MC68HC908EY8 XX X E
FAMILY
Pb FREE
PACKAGE DESIGNATOR
TEMPERATURE RANGE
Figure A-3. Device Numbering System
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
258
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 0 or 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).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
259
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 1 to 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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
260
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
261
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).
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
262
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
263
Glossary
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
264
Freescale Semiconductor
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.
software interrupt (SWI) — An instruction that causes an interrupt and its associated vector fetch.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
265
Glossary
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.
VCO — See "voltage-controlled oscillator."
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
266
Freescale Semiconductor
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.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
267
Glossary
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
268
Freescale Semiconductor
Revision History
Changes from Rev 9.0 published in August 2005 to Rev 10 published in October 2005
Section
Page (in Rev 10)
Description of change
Configuration
Registers (CONFIG1
and CONFIG2)
57
Figure 5-1. Configuration Register 2 (CONFIG2) — Corrected name for bit 6
to ESCIBDSRC.
System Integration
Module (SIM)
159
14.3.2.5 Forced Monitor Mode Entry Reset (MENRST) — Corrected erased
value from $00 to $FF.
Timebase Module
(TBM)
189
Figure 16-1. Timebase Block Diagram — Corrected label from
TBMCLKSEL to TMBCLKSEL.
Changes from Rev 8.0 published in July 2005 to Rev 9 published in August 2005
Section
Page (in Rev 9)
Throughout
N/A
Updated to meet Freescale identity guidelines.
Memory
32
Changed ADRH register bit names at address location $003D from ADCH9
and ADCH8 to AD9 and AD8 respectively.
Analog-to-Digital
Converter (ADC)
Module
53
Table 3-2. ADC Clock Divide Ratio — Changed last table entry under ADC
Clock Rate from ADC input clock ÷ 6 to ADC input clock ÷ 16.
Computer Operating
Properly (COP)
Module
63
6.6 Monitor Mode — changed VDD = VTST is present to VTST is present.
Keyboard Interrupt
(KBD) Module
110
10.7.2 Keyboard Interrupt Enable Register — In bit definition changed PDx
to KBDx.
112
11.3.1 Polled LVI Operation — Changed LVIRSTD bit must be at 0 to enable
LVI resets to LVIRSTD bit must be at 1 to disable LVI resets
113
11.5.2 Stop Mode — Changed LVIPWRD bit in the configuration register
programmed to 0 to LVIPWRD bit in the configuration register programmed
to 1
117
Figure 12-4. Port B Data Register (PTB) — Changed ATD7–ATD0 to
AD7–AD0 in both the bit descriptions and alternative function blocks.
142
13.8.3 ESCI Control Register 3 — In the bit description for PEIE, changed
ESCI receiver CPU interrupt request to ESCI error CPU interrupt request
143
13.8.4 ESCI Status Register 1 — In the bit description for IDLE, changed
ESCI error CPU interrupt request to ESCI receiver CPU interrupt request.
Low-Voltage Inhibit
(LVI) Module
Input/Output (I/O)
Ports (PORTS)
Enhanced Serial
Communications
Interface (ESCI)
Module
Description of change
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
269
Revision History
Changes from Rev 7.0 published in March 2004 to Rev 8 published in July 2005
Section
Page (in Rev 8)
Memory
26 on
Internal Clock
Generator (ICG)
Module
80
Removed overbars from OSC1 and OSC2 in Figure 8-1.
103
Added 8.7.4 ICG Trim Value.
117
New introductory paragraph in 11.3 Functional Description. Modified
sections 11.3.1, 11.3.2, 11.5.1, 11.5.2.
118
Changed “to disable LVI resets” to “to enable LVI resets” in 11.3.1 Polled LVI
Operation.
Deleted “for 32 to 40 CGMXCLK cycles” from last sentence in 11.3.4 LVI
Status Register.
129
Modified Figure 12-13.
158
Changed “11-bit” to “13-bit” and “12-bit” to “14-bit” in Table 13-6.
Low-Voltage Inhibit
(LVI) Module
Input/Output (I/O)
Ports (PORTS)
Enhanced Serial
Communications
Interface (ESCI)
Module
System Integration
Module (SIM)
Serial Peripheral
Interface (SPI)
Module
Timer Interface A
(TIMA) Module
Timer Interface B
(TIMB) Module
Development Support
Electrical
Specifications
Appendix A
MC68HC908EY8
163, 164
Description of change
Added ICGT at $FF80 in Figure 2-1 and Figure 2-2.
Changed “...is clocked with one half...” to “...is clocked with one quarter...”
170
New introductory paragraph in 14.3.1 External Pin Reset.
170
Updated and moved Table 14-2.
186
Changed SS pin to from input/output to input only in Figure 15-2.
216
Changed PTEx/TCHx to PTDx/TCHx in Figure 17-3.
221
Added para to note after TSTOP — TIMA Stop Bit
225
New Table 17-2.
232
Changed “TCHxH–TCHxL” to ”TBCHxH–TBCHxL” in 18.3.2 Input Capture.
234
Changed PTEx/TCHx to PTBx/TCHx in Figure 18-3.
239
Added para to note after TSTOP — TIMB Stop Bit
243
New Table 18-2.
247
Whole chapter replaced with new version.
267
Changed values of Hi-Z leakage current in 20.5 DC Electrical
Characteristics.
269
Changed specification for resistance and capacitance values for
EXTSLOW = 1 and EXTSLOW = 0, in 20.8 External Oscillator
Characteristics.
279
Added appendix describing the MC68HC908EY8
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
270
Freescale Semiconductor
Changes from Rev 6.0 published in January 2004 to Rev 7.0 published in March 2004
Section
Page (in Rev 7.0)
Description of change
General Description
19
Changed “25 percent accuracy with trim capability to 2 percent” to “25
percent accuracy with a trimming capability of better than 1 percent” (two
instances).
Memory
35
Changed “BRKSCR” to “BSCR”.
Memory
37
Added sentence about 125°C to 135°C temperature range.
Analog-to-Digital
Converter (ADC)
Module
50
Changed “ms” to “µs” (two instances).
Computer Operating
Properly (COP) Module
72
Changed “COPRS = 1” to “COPRS = 0”.
Internal Clock
Generator (ICG)
Module
89
Changed “7 percent” to “3.5 percent” (two instances).
Internal Clock
Generator (ICG)
Module
116
Replaced “to +/-2%” with a cross-reference.
Input/Output (I/O) Ports
(PORTS)
141
Added note.
Enhanced Serial
Communications
Interface (ESCI)
Module
177
Modified note to include reference to Prescaler Divisor Fine Adjust (PDFA).
Timer Interface A
(TIMA) Module
244
Deleted “port B or”.
Development Support
265 on
Whole section on Development Support replaced.
Electrical Specifications
284 on
Changed “125°C” to “135°C” on pages 282, 283 (3), 285 (2), 286 (2).
Added note 6 on page 291.
Electrical Specifications
286
Modified the first row of the table to show two crystal options, instead of one..
Electrical Specifications
288
Modified the typical and maximum values in the first row of the table.
Ordering Information
and Mechanical
Specifications
295
Appended row to Table 21-1.
Appendix A.
MC68HC908EY8
297
Appended row to Table A-1.
Appendix A.
MC68HC908EY8
298, 299
Change RAM size from 512 to 384 and adjusted addresses accordingly.
Changes from Rev 5.0 published in September 2003 to Rev 6.0 published in January 2004
Section
Page (in Rev 6.0)
Description of change
Memory
40
Removed erroneous Caution note to 2.6.3 FLASH Mass Erase Operation
Updated 2.6.5 FLASH Block Protection and 2.6.6 FLASH Block Protect
Register
Appendix A.
MC68HC908EY8
295
Added appendix describing the MC68HC908EY8
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
271
Revision History
Changes from Rev 4.0 published in February 2003 to Rev 5.0 published in September 2003
Section
Page (in Rev 5.0)
Throughout
N/A
Reformatted document to current publications standards
39
Updated procedures for FLASH page erase operation
40
Updated procedures for FLASH mass erase operation
Computer Operating
Properly (COP) Module
69
Updated block diagram
System Integration
Module (SIM)
196
Updated definition for SBSW bit of SIM break status register (SBSR)
Development Support
263
Updated definition for SBSW bit of SIM break status register (SBSR)
Electrical Specifications
289
Updated memory characteristics table with new information
Corrected notes to supply currents in 20.5 DC Electrical Characteristics.
Memory
Description of change
Changes from Rev 3.0 published in November 2002 to Rev 4.0 published in February 2003
Section
Electrical
Specifications
Page (in Rev 4.0)
Description of change
280
Updated parameters for output high voltage (VOH), output low voltage (VOL)
and supply current (IDD)
Updated parameters for low voltage inhibit reset: VTRIPF, VTRIPR and VHYS.
Updated parameters for ADC absolute accuracy, zero input reading, full-scale
reading, zero input reading (8-bit truncated mode) and full-scale reading
(8-bit truncated mode).
281
285
Changes from Rev 2.0 published in May 2002 to Rev 3.0 published in November 2002
Section
Page (in Rev 3.0)
Description of change
50
LVI5OR3 bit added to CONFIG1
56
ESCI vectors re-ordered
FLASH Memory
62
Minimum changed to 4ms in step 6.
System Integration
Module (SIM)
93
94
106
Figure 6-5 updated
Figure 6-6 updated
Code example removed from SBSW description
Internal Clock
Generator (ICG)
Module
118
137
PTB6/OSC1 and PTB7/OSC2 corrected to PTC4/OSC1 and PTC3/OSC2
respectively
151
COPD corrected to COPRS in COPRS bit description
148
152
LVI5OR3 bit added to CONFIG1 and default reset state changed to 0
LVI5OR3 description added
Memory Map
Configuration Registers
(CONFIG1 &
CONFIG2)
Break Module (BRK)
Computer Operating
Properly (COP) Module
162
Code example removed from SBSW description
178
COPL corrected to COPRS in Figure 11-1
179
COPL corrected to COPRS in top paragraph
180
COPL corrected to COPRS in Section 11.4.8
181
IRQ1 corrected to IRQ
Low-Voltage Inhibit
(LVI) Module
183
3rd bullet added to features
External Interrupt (IRQ)
190
191
IRQ1 corrected to IRQ
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
272
Freescale Semiconductor
Section
Page (in Rev 3.0)
Enhanced Serial
Communications
Interface (ESCI)
Module
233
237
382
Electrical Specifications
383
Description of change
Extra paragraph added describing LINR bit functionality in LIN version 1.2
systems
‘SCI clock source’ changed to ‘Frequency of the SCI clock source’ in baud
rate equation and description
Output high voltage, ILOAD=–10.0mA changed to –5.0mA
Output low voltage, ILOAD=10.0mA changed to 5.0mA
Footnotes 11, 12 and 13 added
Changes from Rev 1.0 published on 17 April 2002 to Rev 2.0 published in May 2002
3V option removed.
PTB5 frequency divider function removed.
BEMF section moved from appendix to Section 18
.
Section
Page (in Rev 2.0)
Description of change
Memory Map
50
ESCIBDSRC bit added to CONFIG2
Configuration Registers
(CONFIG1 &
CONFIG2)
148
ESCIBDSRC bit added to CONFIG2 with bit description
Enhanced Serial
Communications
Interface (ESCI)
Module
200
Baud rate selection sentence added to sections 14.5 and 14.5.2 and after
Table 14-10.
Changes from Rev 0.4 published internally on 9 April 2002 to Rev 1.0 published
on 17 April 2002
Change in revision number only to denote external release version.
Changes from Rev 0.3 published on 6 September 2001 to Rev 0.4 published internally
on 9 April 2002
Section
Page (in Rev 0.4)
Memory Map
43
Reserved port register bits redefined as unimplemented
62
Note added about erasing last FLASH page
65
Removed last two sentences of FLASH Block Protection description
System Integration
Module (SIM)
92
RST description added
Configuration Registers
(CONFIG1 &
CONFIG2)
149
PTB7 changed to PTC3
169
Table 10-1. Mode Selection added
170
Added sentence about forced monitor mode
Updated first note in section 10.5.1
170
PTB5 column added to Table 10-2
171
PTB5 pin added to Figure 10-1
FLASH Memory
Monitor ROM (MON)
Description of change
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
273
Revision History
Section
Page (in Rev 0.4)
Enhanced Serial
Communications
Interface (ESCI)
Module
210
238
243 and 244
Description of change
Note added regarding length of break character when followed by an idle.
Prescale bits renamed
ACLK = 0 description changed
Timer Interface A
(TIMA) Module
279 – 301
Several updates for clarification
Timer Interface B
(TIMB) Module
303 – 326
Several updates for clarification
Analog-to-Digital
Converter (ADC)
Module
345
354
355
Input/Output (I/O) Ports
361 – 376
366
Preliminary Electrical
Specifications
382 and 384
382 and 384
382 and 384
386
391
Reserved register bits redefined as unimplemented
Table 20-1 updated to show all unused combinations
Left Justified Mode description corrected
Reserved register bits redefined as unimplemented
Port B description updated
Changes to:
Hi-Z leakage current
Input current
Monitor mode entry voltage
External clock frequency of operation
FLASH page erase time
Changes from Rev 0.2 published on 1 August 2001 to Rev 0.3 published
on 6 September 2001
Section
Page (in Rev 0.3)
Description of change
Memory Map
50
$001E TMBCLKSEL and SSBPUENB bits added
Configuration Registers
(CONFIG1 &
CONFIG2)
150
$001E TMBCLKSEL and SSBPUENB bits added
152
Corrections to Table 8-1: PTB6 to PTC4 and PTB7 to PTC3
188
Figure 12-1 updated, digital filter removed
189
False reset protection text updated
190
Table 12-1 updated
191
References to digital filter removed
Timer Interface A
(TIMA) Module
280
External clock input removed from features
Timer Interface B
(TIMB) Module
304
External clock input removed from features
Low-Voltage Inhibit
(LVI) Module
Timebase Module
(TBM)
Analog-to-Digital
Converter (ADC)
Module
Preliminary Electrical
Specifications
336
Divide-by-128 replaced by divide-by-1024
337
Figure 19-1 updated
338
Note added after Table 19-1
345
PTC and Cx removed from Figure 20-1
347
ADCR changed to ADCLK
384 and 386
Control Timing specifications added
388 and 392
SPI characteristics added
391
FLASH read bus clock frequency changed to 8 MHz
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
274
Freescale Semiconductor
Changes from Rev 0.0 published on 17 July 2001 to Rev 0.2 published on 1 August 2001
Section
General Description
Memory Map
Page (in Rev 0.2)
Description of change
34
Third bullet in standard features list changes to:
8-MHz internal bus frequency at 5V, 4MHZ at 3V
37
BEMF module added to block diagram
48
BEMF register added
53
Register addresses changed for ADC:
$003B is now reserved
ADSCR is now $003C
ADRH is now $003D
ADRL is now $003E
54
Reset value of $003F corrected to $04
FLASH Memory
68
Several corrections made to Table 4-1
Monitor ROM (MON)
168, 172
Keyboard Interrupt
(KBD) Module
330
Keyboard interrupt vector corrected to $FFE4 and $FFE5
352
Address of ADSCR is now $003C
355
Address of ADRH is now $003D
Register description now includes left justified mode
358
Address of ADRL is now $003E for right justified mode as well as 8-bit mode
Register description now includes left justified mode
359
Reset value of $003F corrected to $04
Input/Output (I/O) Ports
361
BEMF register added to Figure 21-1
Preliminary Electrical
Specifications
383
dc injection current specifications corrected
BEMF Module
401
New appendix
Analog-to-Digital
Converter (ADC)
Module
Erased Flash locations corrected to $FF
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
275
Revision History
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
276
Freescale Semiconductor
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MC68HC908EY16
Rev. 10, 10/2005
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