Freescale MC68HC908EY16A A member of the low-cost, high-performance m68hc08 family of 8-bit Datasheet

MC68HC908EY16A
MC68HC908EY8A
Data Sheet
M68HC08
Microcontrollers
MC68HC908EY16A
Rev. 2
09/2010
freescale.com
Blank
MC68HC908EY16A
MC68HC908EY8A
Data Sheet
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available, refer to:
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The following revision history table summarizes changes contained in this document. For your
convenience, the page number designators have been linked to the appropriate location.
Revision History
Date
Revision
Level
April,
2006
0
September,
2006
Description
Page
Number(s)
Initial release
N/A
21.2 Ordering Information — Separated automotive and consumer/industrial
part numbers.
279
A.4 Ordering Information — Separated automotive and consumer/industrial
part numbers.
286
1
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This product incorporates SuperFlash® technology licensed from SST.
© Freescale Semiconductor, Inc., 2006, 2010. All rights reserved.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
3
Revision History (Continued)
Date
September
2010
Revision
Level
2
Page
Number(s)
Description
20.3 Functional Operating Range — Changed maximum temperature
specification from 135 C to 125 C.
262
20.5 5V DC Electrical Characteristics — Changed maximum temperature
specification from 135 C to 125 C.
262
20.7 3V DC Electrical Characteristics — Changed maximum temperature
specification from 135 C to 125 C.
265
20.9 Internal Oscillator Characteristics — Changed maximum temperature
specification from 135 C to 125 C.
266
20.10 External Oscillator Characteristics — Changed maximum temperature
specification from 135 C to 125 C.
267
20.11 Trimmed Accuracy of the Internal Clock Generator — Changed
maximum temperature specification from 135 C to 125 C.
268
20.16 Memory Characteristics — Removed note referring to flash memory
behavior between 125 C to 135 C.
275
21.2 Ordering Information — Removed S908EY16AKFJE and
MC908EY16AKFJE part numbers.
279
A.4 Ordering Information — Removed S908EY16AKFJE and
MC908EY16AKFJE part numbers.
286
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
List of Chapters
Chapter 1
General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Chapter 2
Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter 3
Analog-to-Digital Converter (ADC10) Module. . . . . . . . . . . . . . . . . . . . . . . . . . 47
Chapter 4
BEMF Counter Module (BEMF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Chapter 5
Configuration Registers (CONFIG1, CONFIG2, CONFIG3) . . . . . . . . . . . . . . . 63
Chapter 6
Computer Operating Properly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Chapter 7
Central Processor Unit (CPU). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Chapter 8
Internal Clock Generator (ICG) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Chapter 9
External Interrupt (IRQ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Chapter 10
Keyboard Interrupt (KBI) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Chapter 11
Low-Voltage Inhibit (LVI) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Chapter 12
Input/Output (I/O) Ports (PORTS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
Chapter 13
Enhanced Serial Communications Interface (ESCI) Module . . . . . . . . . . . . . 133
Chapter 14
System Integration Module (SIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
Chapter 15
Serial Peripheral Interface (SPI) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Chapter 16
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Timebase Module (TBM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Chapter 17
Timer Interface A (TIMA) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
Chapter 18
Timer Interface B (TIMB) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Chapter 19
Development Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Chapter 20
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
Chapter 21
Ordering Information and Mechanical Specifications . . . . . . . . . . . . . . . . . . . 279
Appendix A
MC68HC908EY8A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
Appendix B
Differences Between 908EY16A and 908EY16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
Table of Contents
Chapter 1
General Description
1.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.2
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.3
MCU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.4
Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.5
Pin Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.5.1
Power Supply Pins (VDD and VSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.5.2
Oscillator Pins (PTC4/OSC1 and PTC3/OSC2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.5.3
External Reset Pin (RST). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.5.4
External Interrupt Pin (IRQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.5.5
Analog Power Supply/Reference Pins (VDDA, VREFH, VSSA, and VREFL) . . . . . . . . . . . . . . 23
1.5.6
Port A I/O Pins (PTA6/SS, PTA5/SPSCK, PTA4/KBD4, PTA3/KBD3/RxD, PTA2/KBD2/TxD,
PTA1/KBD1, and PTA0/KBD0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.5.7
Port B I/O Pins (PTB7/AD7/TBCH1, PTB6/AD6/TBCH0, PTB5/AD5/SPSCK, PTB4/AD4/MOSI, PTB3/AD3/MISO, PTB2/AD2–PTB0/AD0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.5.8
Port C I/O Pins (PTC4/OSC1, PTC3/OSC2, PTC2/MCLK/SS, PTC1/MOSI, PTC0/MISO) . 24
1.5.9
Port D I/O Pins (PTD1/TACH1–PTD0/TACH0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.5.10
Port E I/O Pins (PTE1/RxD–PTE0/TxD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.6
Pin Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.7
Priority of Shared Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
29
29
29
39
39
40
41
42
43
45
45
46
46
Chapter 3
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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7
Analog-to-Digital Converter (ADC10) Module
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.1
Clock Select and Divide Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.2
Input Select and Pin Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3
Conversion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3.1
Initiating Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3.2
Completing Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3.3
Aborting Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3.4
Total Conversion Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4
Sources of Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.1
Sampling Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.2
Pin Leakage Error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.3
Noise-Induced Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.4
Code Width and Quantization Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.5
Linearity Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4.6
Code Jitter, Non-Monotonicity and Missing Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6
ADC10 During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.1
ADC10 Analog Power Pin (VDDA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.2
ADC10 Analog Ground Pin (VSSA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.3
ADC10 Voltage Reference High Pin (VREFH). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.4
ADC10 Voltage Reference Low Pin (VREFL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.5
ADC10 Channel Pins (ADn). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8
Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8.1
ADC10 Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8.2
ADC10 Result High Register (ADRH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8.3
ADC10 Result Low Register (ADRL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8.4
ADC10 Clock Register (ADCLK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
47
47
49
50
50
50
50
50
51
52
52
52
52
53
53
53
54
54
54
54
54
55
55
55
55
55
56
56
56
58
58
59
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61
61
61
61
61
61
62
Chapter 5
Configuration Registers (CONFIG1, CONFIG2, CONFIG3)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
8
Freescale Semiconductor
5.1
5.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Chapter 6
Computer Operating Properly
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69
69
70
70
70
70
70
70
70
70
71
71
71
71
71
71
71
71
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
73
73
74
74
75
75
76
77
77
77
77
77
78
83
Chapter 8
Internal Clock Generator (ICG) Module
8.1
8.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
9
8.3
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.3.1
Clock Enable Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.3.2
Internal Clock Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.3.2.1
Digitally Controlled Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
8.3.2.2
Modulo N Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
8.3.2.3
Frequency Comparator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
8.3.2.4
Digital Loop Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
8.3.3
External Clock Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
8.3.3.1
External Oscillator Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
8.3.3.2
External Clock Input Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
8.3.4
Clock Monitor Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
8.3.4.1
Clock Monitor Reference Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.3.4.2
Internal Clock Activity Detector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.3.4.3
External Clock Activity Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.3.5
Clock Selection Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
8.3.5.1
Clock Selection Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
8.3.5.2
Clock Switching Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
8.4
Usage Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.4.1
Switching Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.4.2
Enabling the Clock Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.4.3
Using Clock Monitor Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
8.4.4
Quantization Error in DCO Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
8.4.4.1
Digitally Controlled Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
8.4.4.2
Binary Weighted Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
8.4.4.3
Variable-Delay Ring Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
8.4.4.4
Ring Oscillator Fine-Adjust Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
8.4.5
Switching Internal Clock Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
8.4.6
Nominal Frequency Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
8.4.6.1
Settling to Within 15 Percent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
8.4.6.2
Settling to Within 5 Percent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
8.4.6.3
Total Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
8.4.7
Trimming Frequency on the Internal Clock Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
8.5
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
8.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
8.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
8.6
CONFIG Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
8.6.1
External Clock Enable (EXTCLKEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
8.6.2
External Crystal Enable (EXTXTALEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
8.6.3
Slow External Clock (EXTSLOW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.6.4
Oscillator Enable In Stop (OSCENINSTOP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.7
Input/Output (I/O) Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.7.1
ICG Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
8.7.2
ICG Multiplier Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
8.7.3
ICG Trim Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
8.7.4
ICG 5-Volt Trim Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8.7.5
ICG 3-Volt Trim Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8.7.6
ICG DCO Divider Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8.7.7
ICG DCO Stage Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
10
Freescale Semiconductor
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
109
109
109
110
112
112
Chapter 10
Keyboard Interrupt (KBI) Module
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3.1
Keyboard Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3.1.1
MODEK = 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3.1.2
MODEK = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.3.2
Keyboard Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.6 KBI During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7.1
KBI Input Pins (KBI7:KBI0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.1
Keyboard Status and Control Register (KBSCR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.2
Keyboard Interrupt Enable Register (KBIER). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8.3
Keyboard Interrupt Polarity Register (KBIPR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
113
113
113
113
115
115
116
116
116
116
116
116
117
117
117
117
118
118
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
119
119
119
120
120
120
120
121
121
121
121
Chapter 12
Input/Output (I/O) Ports (PORTS)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
11
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
123
123
123
123
125
125
125
126
126
127
128
128
128
130
130
130
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.6 ESCI During Break Module Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.7 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.7.1
PTE0/TxD (Transmit Data). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.7.2
PTE1/RxD (Receive Data) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
133
133
133
135
136
136
137
137
137
138
138
138
138
138
139
140
141
141
143
144
144
144
144
145
145
145
145
145
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Freescale Semiconductor
13.8 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
13.8.1
ESCI Control Register 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
13.8.2
ESCI Control Register 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
13.8.3
ESCI Control Register 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
13.8.4
ESCI Status Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
13.8.5
ESCI Status Register 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
13.8.6
ESCI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
13.8.7
ESCI Baud Rate Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
13.8.8
ESCI Prescaler Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
13.9 ESCI Arbiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
13.9.1
ESCI Arbiter Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
13.9.2
ESCI Arbiter Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
13.9.3
Bit Time Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
13.9.4
Arbitration Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6 Interrupt Status Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.1
Interrupt Status Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.2
Interrupt Status Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.3
Interrupt Status Register 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.4
Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.5
Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.6.6
Status Flag Protection in Break Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.7 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
163
163
165
165
165
165
165
166
166
167
167
167
167
168
168
168
168
168
168
169
170
171
172
172
173
173
173
173
174
174
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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14.7.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.7.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.8 SIM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.8.1
SIM Break Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.8.2
SIM Reset Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.8.3
SIM Break Flag Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
174
175
176
176
177
178
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 SPI 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
179
179
179
181
182
182
183
183
183
184
185
185
186
187
189
190
191
191
191
191
191
192
192
192
193
193
193
194
194
195
197
Chapter 16
Timebase Module (TBM)
16.1
16.2
16.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
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16.4
16.5
16.6
16.6.1
16.6.2
16.7
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TBM Interrupt Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timebase Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
199
200
201
201
201
202
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
203
203
203
203
205
206
206
206
207
208
208
209
209
210
210
210
210
210
210
211
211
213
213
214
217
Chapter 18
Timer Interface B (TIMB) Module
18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
219
219
219
219
221
222
222
223
223
224
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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/AD7/TBCH1–PTB6/AD6/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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
224
225
225
226
226
226
226
226
226
227
227
229
229
230
233
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.3
Extended Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4 Routines Supported in ROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4.1
Variables Used in the Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4.2
How to Use the Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4.2.1
GetByte. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4.2.2
PutByte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.4.2.3
Verify . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
235
235
235
237
237
237
237
238
238
239
239
239
240
240
243
244
245
245
245
246
246
249
250
250
251
251
253
254
254
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19.4.2.4
19.4.2.5
fProgram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
fErase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Chapter 20
Electrical Specifications
20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.2 Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.3 Functional Operating Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.4 Thermal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.5 5V DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.6 5V Control Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.7 3V DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.8 3V Control Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.9 Internal Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.10 External Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.11 Trimmed Accuracy of the Internal Clock Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.11.1
Trimmed Internal Clock Generator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.12 ADC10 Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.13 5V SPI Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.14 3V SPI Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.15 Timer Interface Module Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.16 Memory Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.17 EMC Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.17.1
Radiated Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.17.2
Conducted Transient Susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
261
261
262
262
262
264
265
266
266
267
268
268
268
270
271
274
275
276
276
277
Chapter 21
Ordering Information and Mechanical Specifications
21.1
21.2
21.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Package Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Appendix A
MC68HC908EY8A
A.1
A.2
A.3
A.4
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
283
283
283
286
Appendix B
Differences Between 908EY16A and 908EY16
B.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.2
Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.2.1
Enhanced Serial Communications Interface Module (ESCI). . . . . . . . . . . . . . . . . . . . . . . .
B.2.2
Serial Peripheral Interface Module (SPI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
287
287
287
288
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
17
B.2.3
Internal Clock Generator Module (ICG). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.2.4
Keyboard Interface Module (KBI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.2.5
Analog-to-Digital Converter Module (ADC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.3
Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.3.1
Monitor Extended Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.3.2
Zeroes in Security Bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.3.3
Forced Monitor Mode Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.4
Monitor ROM FLASH Programming Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.4.1
Erase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.4.2
Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
288
288
288
289
289
289
289
289
289
290
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
18
Freescale Semiconductor
Chapter 1
General Description
1.1 Introduction
The MC68HC908EY16A 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 MC68HC908EY8A with the exceptions noted
in Appendix A MC68HC908EY8A.
1.2 Features
For convenience, features have been organized to reflect:
• Standard features of the MC68HC908EY16A
• Features of the CPU08
Standard features of the MC68HC908EY16A 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
19
•
•
•
•
•
•
•
•
•
•
•
•
Timebase Module (TBM)
5-bit keyboard wakeup port with software selectable rising or falling edge detect, as well as highor low-level detection
– Programmable for rising/falling edge or high/low level detection
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/RxD, PTA2/KBD2/TxD, 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
1.3 MCU Block Diagram
Figure 1-1 shows the structure of the MC68HC908EY16A.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
20
Freescale Semiconductor
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 1-1. MCU Block Diagram
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
21
1.4 Pin Assignments
PTA4/KBD4
VREFH
VDDA
VDD
VSS
VSSA
VREFL
30
29
28
27
26
25
PTA2/KBD2/TxD 1
31
32 PTA3/KBD3/RxD
Figure 1-2 shows the pin assignments for the MC68HC908EY16A.
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/SS
8
17
IRQ
PTD1/TACH1
PTD0/TACH0
PTB1/AD1
RST
PTB2/AD2
PTB3/AD3/MISO
PTB4/AD4/MOSI
PTB5/AD5/SPSCK
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
22
Freescale Semiconductor
MCU
VSS
VDD
C1
0.1F
+
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 (ADC10) Module.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
23
1.5.6 Port A I/O Pins (PTA6/SS, PTA5/SPSCK, PTA4/KBD4, PTA3/KBD3/RxD,
PTA2/KBD2/TxD, PTA1/KBD1, and PTA0/KBD0)
Port A input/output (I/O) pins (PTA6/SS, PTA5/SPSCK, PTA4/KBD4, PTA3/KBD3/RxD,
PTA2/KBD2/TxD, 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. PTA2 and PTA3 can be programmed to serve as the ESCI transmit and
receive data pins.
See Chapter 12 Input/Output (I/O) Ports (PORTS), Chapter 15 Serial Peripheral Interface (SPI) Module,
Chapter 10 Keyboard Interrupt (KBI) Module, and Chapter 13 Enhanced Serial Communications Interface
(ESCI) Module.
1.5.7 Port B I/O Pins (PTB7/AD7/TBCH1, PTB6/AD6/TBCH0, PTB5/AD5/SPSCK,
PTB4/AD4/MOSI, PTB3/AD3/MISO, PTB2/AD2–PTB0/AD0)
PTB7/AD7/TBCH1, PTB6/AD6/TBCH0, PTB5/AD5/SPSCK, PTB4/AD4/MOSI, PTB3/AD3/MISO,
PTB2/AD2–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. PTB5/AD5/SPSCK, PTB4/AD4/MOSI, and PTB3/AD3/MISO can be
programmed to serve as SPI clock and data pins.
See Chapter 12 Input/Output (I/O) Ports (PORTS), Chapter 3 Analog-to-Digital Converter (ADC10)
Module, Chapter 18 Timer Interface B (TIMB) Module, and Chapter 15 Serial Peripheral Interface (SPI)
Module.
1.5.8 Port C I/O Pins (PTC4/OSC1, PTC3/OSC2, PTC2/MCLK/SS, PTC1/MOSI, PTC0/MISO)
PTC4/OSC1, PTC3/OSC2, PTC2/MCLK/SS, PTC1/MOSI, 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/SS 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.
See Chapter 15 Serial Peripheral Interface (SPI) Module.
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 12 Input/Output (I/O) Ports (PORTS) and Chapter 17 Timer Interface A (TIMA) Module.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
24
Freescale Semiconductor
See Chapter 12 Input/Output (I/O) Ports (PORTS) and Chapter 13 Enhanced Serial Communications
Interface (ESCI) Module.
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 MC68HC908EY16A do
not require termination, termination is recommended to reduce the
possibility of electro-static discharge damage.
1.6 Pin Summary
Table 1-1. External Pin Summary
Pin Name
Function
Driver Type
Hysteresis(1)
Reset State
PTA6/SS
General-Purpose I/O
SPI Slave Select
Dual State
Yes
Input Hi-Z
PTA5/SPSCK
General-Purpose I/O
SPI Clock
Dual State
Yes
Input Hi-Z
PTA4/KBD4
General-Purpose I/O
Keyboard Wakeup Pin
Dual State
Yes
Input Hi-Z
PTA3/KBD3/RxD
General-Purpose I/O
Keyboard Wakeup Pin
SCI Receive Data
Dual State
Yes
Input Hi-Z
PTA2/KBD2/TxD
General-Purpose I/O
Keyboard Wakeup Pin
SCI Transmit Data
Dual State
Yes
Input Hi-Z
PTA1/KBD1
General-Purpose I/O
Keyboard Wakeup Pin
Dual State
Yes
Input Hi-Z
PTA0/KBD0
General-Purpose I/O
Keyboard Wakeup Pin
Dual State
Yes
Input Hi-Z
PTB7/ATD7/TBCH1
General-Purpose I/O
ADC Channel
Timer B Channel 1
Dual State
Yes
Input Hi-Z
PTB6/ATD6/TBCH0
General-Purpose I/O
ADC Channel
Timer B Channel 0
Dual State
Yes
Input Hi-Z
PTB5/ATD5/SPSCK
General-Purpose I/O
ADC Channel
SPI Clock
Dual State
Yes
Input Hi-Z
PTB4/ATD4/MOSI
General-Purpose I/O
ADC Channel
SPI Data Path
Dual State
Yes
Input Hi-Z
PTB3/ATD3/MISO
General-Purpose I/O
ADC Channel
SPI Data Path
Dual State
Yes
Input Hi-Z
PTB2/ATD2
General-Purpose I/O
ADC Channel
Dual State
Yes
Input Hi-Z
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
25
Table 1-1. External Pin Summary (Continued)
Pin Name
Function
Driver Type
Hysteresis(1)
Reset State
PTB1/ATD1
General-Purpose I/O
ADC Channel
Dual State
Yes
Input Hi-Z
PTB0/ATD0
General-Purpose I/O
ADC Channel
Dual State
Yes
Input Hi-Z
PTC4/OSC1
General-Purpose I/O
External Clock In
Dual State
Yes
Input Hi-Z
PTC3/OSC2
General-Purpose I/O
Dual State
Yes
Input Hi-Z
PTC2/MCLK/SS
General-Purpose I/O
MCLK output
SPI Slave Select
Dual State
Yes
Input Hi-Z
PTC1/MOSI
General-Purpose I/O
SPI Data Path
Dual State
Yes
Input Hi-Z
PTC0/MISO
General-Purpose I/O
SPI Data Path
Dual State
Yes
Input Hi-Z
PTD1/TACH1
General Purpose I/O
Timer A Channel 1
Dual State
Yes
Input Hi-Z
PTD0/TACH0
General Purpose I/O
Timer A Channel 0
Dual State
Yes
Input Hi-Z
PTE1/RxD
General-Purpose I/O
SCI Receive Data
Dual State
Yes
Input Hi-Z
PTE0/TxD
General-Purpose I/O
SCI Transmit Data
Dual State
Yes
Input Hi-Z
VDD
Chip Power Supply
N/A
N/A
N/A
VSS
Chip Ground
N/A
N/A
N/A
VDDA
CGM Analog Power Supply
N/A
N/A
N/A
VSSA
CGM Analog Ground
N/A
N/A
N/A
VREFH
ADC Reference High
Voltage
N/A
N/A
N/A
VREFL
ADC Reference Low
Voltage
N/A
N/A
N/A
IRQ
External Interrupt Request
N/A
Yes
Input Hi-Z
RST
External Reset
Open Drain
Yes
Output Low
1. Hysteresis is not 100% tested but is typically a minimum of 300mV.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
26
Freescale Semiconductor
1.7 Priority of Shared Pins
Table 1-2. Priority of Shared Pins
Port Number
Priority 1
Priority 2
Priority 3
PTA6
SSB(1) (in)
PTA6 (in/out)
PTA5
SPSCK(1) (in/out)
PTA5 (in/out)
PTA4
KBD4 (in)
PTA4 (in/out)
PTA3
RX(1) (in)
KBD3 (in)
PTA3 (in/out)
PTA2
TX(1) (out)
KBD2 (in)
PTA2 (in/out)
PTA1
KBD1 (in)
PTA1 (in/out)
PTA0
KBD0 (in)
PTA0 (in/out)
PTB7
AD7 (in)
TBCH1 (in/out)
PTB7 (in/out)
PTB6
AD6 (in)
TBCH0 (in/out)
PTB6 (in/out)
PTB5
AD5 (in)
SPSCK(1) (in/out)
PTB5 (in/out)
PTB4
AD4 (in)
MOSI(1) (in/out)
PTB4 (in/out)
PTB3
AD3 (in)
MISO(1) (in/out)
PTB3 (in/out)
PTB2
AD2 (in)
PTB2 (in/out)
PTB1
AD1 (in)
PTB1 (in/out)
PTB0
AD0 (in)
PTB0 (in/out)
PTC4
OSC1 (in)
PTC4 (in/out)
PTC3
OSC2 (out)
PTC3 (in/out)
PTC2
MCLK (out)
SSB(1) (in)
PTC1
MOSI(1) (in/out)
PTC1 (in/out)
PTC0
MISO(1) (in/out)
PTC0 (in/out)
PTD1
TACH1 (in/out)
PTD1 (in/out)
PTD0
TACH0 (in/out)
PTD0 (in/out)
PTE1
RX(1) (in)
PTE1 (in/out)
PTE0
TX(1) (out)
PTE0 (in/out)
PTC2 (in/out)
1. Pin location can be changed using CONFIG3 register bits.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
27
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
28
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
• 350 bytes of monitor routines in read-only memory (ROM)
• 674 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
• $FE04; interrupt status register 1, INT1
• $FE05; interrupt status register 2, INT2
• $FE06; interrupt status register 3, INT3
• $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; 5V internal oscillator trim value (optional), ICGT5V
• $FF81; 3V internal oscillator trim value (optional), ICGT3V
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
29
Data registers are shown in Figure 2-2. and Table 2-1 is a list of vector locations.
$0000

I/O Registers
64 Bytes
$003F
$0040

RAM
512 Bytes
$023F
$0240

Unimplemented
3520 Bytes
$0FFF
$1000

Jump Table for FLASH Routines
32 Bytes
$101F
$1020

$121F
Integrated FLASH Program
and Erase Routines
512 Bytes

$13FF
Integrated FLASH Program
and Erase Routines
130 Bytes
$FE04
Interrupt Status Register 1 (INT1)
$FE05
Interrupt Status Register 2 (INT2)
$FE06
Interrupt Status Register 3 (INT3)
$FE07
Reserved
$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)
Reserved
19 Bytes

$FE1F
$FE20
Monitor ROM 350 Bytes
$FF7E
FLASH Block Protect Register (FLBPR)
$FF7F
Unimplemented
$FF80
5V ICG Trim Value (Optional) (ICGT5V)
$FF81
3V ICG Trim Value (Optional) (ICGT3V)
$FF82
Unimplemented
44,032 Bytes

$BFFF
$C000
SIM Break Flag Control Register (SBFCR)
FF7D
$1400

$FE03

Unimplemented
350 Bytes
$137D
$137E
Reserved
$FE0D
$1220

$FE02
Unimplemented
90 Bytes
$FFDB
$FFDC

FLASH Memory
15,872 Bytes
$FDFF
Extended Security Byte
$FFFF
$FE00
SIM Break Status Register (SBSR)
$FE01
SIM Reset Status Register (SRSR)

FLASH Vectors
36 Bytes
Note:
Locations $FFF6–$FFFD are used for the eight
security bytes.
Figure 2-1. Memory Map
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
30
Freescale Semiconductor
Addr.
$0000
$0001
Register Name
Bit 7
Port A Data Register Read:
(PTA) Write:
See page 123. Reset:
Port B Data Register Read:
(PTB) Write:
See page 125. Reset:
0
PTB7
Port D Data Register Read:
(PTD) Write:
See page 128.
Reset:
0
0
$0004
Data Direction Read:
Register A (DDRA) Write:
See page 123. Reset:
$0005
Data Direction Read:
Register B (DDRB) Write:
See page 125. Reset:
$0006
$0007
$0008
3
2
1
Bit 0
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
PTB2
PTB1
PTB0
PTC2
PTC1
PTC0
PTD1
PTD0
PTB6
PTB5
PTB4
PTB3
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
Data Direction Read: MCLKEN
Register C (DDRC) Write:
See page 127. 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 128.
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
PORTSRE
ESCISEL
SPISEL
0
0
DDRE1
DDRE0
Port E Data Register Read:
(PTE) Write:
See page 130. Reset:
$0009
Configuration Register 3 Read:
(CONFIG3) Write:
See page 67. Reset:
$000A
Data Direction Read:
Register E (DDRE) Write:
See page 130. Reset:
$000B
4
Unaffected by reset
0
$0003
5
Unaffected by reset
Port C Data Register Read:
(PTC) Write:
See page 126. Reset:
$0002
6
BEMF Register Read:
(BEMF) Write:
See page 61. Reset:
Unaffected by reset
RNGSEL
ESCISRE
SPISRE
MCLKSRE
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
BEMF7
BEMF6
BEMF5
BEMF4
BEMF3
BEMF2
BEMF1
BEMF0
0
0
0
0
0
0
0
0
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 1 of 7)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
31
Addr.
$000C
$000D
$000E
Register Name
KBI Polarity Read:
Register (KBIPR) Write:
See page 118. Reset:
SPI Control Register Read:
(SPCR) Write:
See page 194. Reset:
SPI Status and Control Read:
Register (SPSCR) Write:
See page 195. Reset:
$000F
SPI Data Register Read:
(SPDR) Write:
See page 197. Reset:
$0010
ESCI Control Register 1 Read:
(SCC1) Write:
See page 146. Reset:
$0011
ESCI Control Register 2 Read:
(SCC2) Write:
See page 148. Reset:
Bit 7
6
5
0
0
0
0
0
SPRIE
0
SPRF
4
3
2
1
Bit 0
KBIP4
KBIP3
KBIP2
KBIP1
KBIP0
0
0
0
0
0
0
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
0
1
0
1
0
0
0
OVRF
MODF
SPTE
MODFEN
SPR1
SPR0
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
ESCI Control Register 3 Read:
(SCC3) Write:
See page 150. Reset:
R8
U
0
0
0
0
0
0
0
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
$0013
ESCI Status Register 1 Read:
(SCS1) Write:
See page 151. Reset:
1
1
0
0
0
0
0
0
0
0
0
0
0
0
BKF
RPF
$0014
ESCI Status Register 2 Read:
(SCS2) Write:
See page 153. Reset:
0
0
0
0
0
0
0
0
ESCI Data Register Read:
(SCDR) Write:
See page 154. Reset:
R7
R6
R5
R4
R3
R2
R1
R0
T7
T6
T5
T4
T3
T2
T1
T0
$0012
$0015
$0016
$0017
ESCI Baud Rate Register Read:
(SCBR) Write:
See page 154. Reset:
ESCI Prescale Register Read:
(SCPSC) Write:
See page 156. Reset:
Unaffected by reset
LINT
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
32
Freescale Semiconductor
Addr.
$0018
$0019
$001A
$001B
$001C
$001D
Register Name
Bit 7
ESCII Arbiter Control Read:
Register Write:
(SCIACTL)
See page 159. Reset:
ESCI Arbiter Data Register Read:
(SCIACTL) Write:
See page 160. Reset:
Keyboard Status Read:
and Control Register Write:
(KBSCR)
See page 117. Reset:
AM1
6
ALOST
5
AM0
ACLK
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
IMASKK
MODEK
0
ACKK
0
0
0
0
0
Read:
Timebase Control Register Write:
(TBCR)
See page 202. Reset:
TBIF
$001F
Bit 0
ARD8
0
Keyboard Interrupt Enable Read:
Register (KBIER) Write:
See page 118. Reset:
Configuration Register 1 Read:
(CONFIG1) Write:
See page 64. Reset:
1
AROVFL
0
0
$001E
2
ARUN
0
0
Configuration Register 2 Read:
(CONFIG2) Write:
See page 65. Reset:
3
AFIN
0
0
IRQ Status and Control Read:
Register (INTSCR) Write:
See page 112. Reset:
4
0
0
0
0
0
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
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
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
R
PS2
PS1
PS0
1. The LVI5OR3 bit is cleared only by a power-on reset (POR).
Timer A Status and Control Read:
$0020
Register (TASC) Write:
See page 211. Reset:
$0021
$0022
$0023
TOF
0
TOIE
TSTOP
0
0
1
0
0
0
0
0
Timer A Counter Register Read:
High (TACNTH) Write:
See page 213. 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
Timer A Counter Register Read:
Low (TACNTL) Write:
See page 213. 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
Timer A Counter Modulo Read:
Register High (TAMODH) Write:
See page 213. Reset:
0
1
= Unimplemented
TRST
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 3 of 7)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
33
Addr.
$0024
$0025
$0026
$0027
$0028
Register Name
Timer A Counter Modulo Read:
Register Low (TAMODL) Write:
See page 213. Reset:
Timer A Channel 0 Status Read:
and Control Register Write:
(TASC0)
See page 214. Reset:
Timer A Channel 0 Read:
Register High (TACH0H) Write:
See page 217. Reset:
Timer A Channel 0 Read:
Register Low (TACH0L) Write:
See page 217. Reset:
Timer A Channel 1 Status Read:
and Control Register Write:
(TASC1)
See page 214. Reset:
$0029
Timer A Channel 1 Read:
Register High (TACH1H) Write:
See page 217. Reset:
$002A
Timer A Channel 1 Read:
Register Low (TACH1L) Write:
See page 217. 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
R
PS2
PS1
PS0
Indeterminate after reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Indeterminate after reset
Timer B Status and Control Read:
Register (TBSC) Write:
See page 227. Reset:
TOF
0
TOIE
TSTOP
0
0
1
0
0
0
0
0
Timer B Counter Register Read:
High (TBCNTH) Write:
See page 229. 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
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
$002D
Timer B Counter Register Read:
Low (TBCNTL) Write:
See page 229. Reset:
0
0
0
0
0
0
0
0
$002E
Timer B Counter Modulo Read:
Register High (TBMODH) Write:
See page 229. Reset:
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
$002B
$002C
$002F
Timer B Counter Modulo Read:
Register Low (TBMODL) Write:
See page 229. Reset:
0
= Unimplemented
TRST
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 4 of 7)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
34
Freescale Semiconductor
Addr.
$0030
$0031
$0032
$0033
$0034
Register Name
Bit 7
Timer B Channel 0 Status Read:
and Control Register Write:
(TBSC0)
See page 230. Reset:
Timer B Channel 0 Read:
Register High (TBCH0H) Write:
See page 233. Reset:
Timer B Channel 0 Read:
Register Low (TBCH0L) Write:
See page 233. Reset:
Timer B Channel 1 Status Read:
and Control Register Write:
(TBSC1)
See page 230. Reset:
Timer B Channel 1 Read:
Register High (TBCH1H) Write:
See page 233. Reset:
$0035
Timer B Channel 1 Read:
Register Low (TBCH1L) Write:
See page 233. Reset:
$0036
ICG Control Register Read:
(ICGCR) Write:
See page 104. Reset:
$0037
$0038
ICG Multiplier Register Read:
(ICGMR) Write:
See page 106. Reset:
Read:
ICG Trim Register (ICGTR)
Write:
See page 106.
Reset:
$0039
ICG Divider Control Read:
Register (ICGDVR) Write:
See page 107. Reset:
$003A
ICG DCO Stage Control Read:
Register (ICGDSR) Write:
See page 108. Reset:
$003B
$003C
Reserved
ADC10 Status and Control Read:
Register Write:
(ADSCR)
See page 56. Reset:
6
5
4
3
2
1
Bit 0
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
R
R
R
R
R
R
R
R
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
0
0
1
1
1
1
1
COCO
0
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 5 of 7)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
35
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
ADC10 Data Register High Read:
$003D
(ADRH) Write:
See page 58. Reset:
0
0
0
0
0
0
AD9
AD8
AD2
AD1
AD0
$003E
$003F
$FE00
Analog-to-Digital Data Read:
Register Low (ADRL) Write:
See page 58. Reset:
Analog-to-Digital Clock Read:
Register (ADCLK) Write:
See page 59. Reset:
Unaffected by reset
AD7
AD6
AD5
AD4
AD3
Unaffected by reset
ADLPC
ADIV1
ADIV0
ADICLK
MODE1
MODE0
ADLSMP
ACLKEN
0
0
0
0
0
1
0
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
Interrupt Status
Register 1 (INT1)
See See page 172.
IF6
IF5
IF4
IF3
IF2
IF1
0
0
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
Interrupt Status
Register 2 (INT2)
See See page 173.
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
Interrupt Status
Register 3 (INT3)
See See page 173.
0
0
0
0
0
0
IF16
IF15
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
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
SIM Break Status Register Read:
(SBSR) Write:
See page 176. Reset:
SBSW
NOTE
R
Note: Writing a 0 clears SBSW.
$FE01
SIM Reset Status Register Read:
(SRSR) Write:
See page 177. POR:
$FE02
Reserved
$FE03
SIM Break Flag Control
Register (SBFCR)
$FE04
$FE05
$FE06
$FE07
$FE08
$FE09
Reserved
FLASH Control Register Read:
(FLCR) Write:
See page 40. Reset:
Break Address Register Read:
High (BRKH) Write:
See page 238. Reset:
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 6 of 7)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
36
Freescale Semiconductor
Addr.
Register Name
$FE0A
Break Address Register Read:
Low (BRKL) Write:
See page 238. Reset:
$FE0B
$FE0C
Break Status and Control Read:
Register (BSCR) Write:
See page 239. Reset:
LVI Status Register Read:
(LVISR) Write:
See page 120. Reset:
$FF7E
FLASH Block Protect Read:
Register (FLBPR)(1) Write:
See page 45. Reset:
$FF80
5V Internal Oscillator Trim Read:
Value (Optional) Write:
(ICGT5V)(1)
Reset:
$FF81
3V Internal Oscillator Trim Read:
Value (Optional) Write:
(ICGT3V)(1)
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
BIT 2
BIT 1
BIT 0
BIT 2
BIT 1
BIT 0
Unaffected by reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Unaffected by reset
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
Unaffected by reset
1. Non-volatile FLASH register
$FFFF
COP Control Register Read:
(COPCTL) Write:
See page 71. 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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
37
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
38
Freescale Semiconductor
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)
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
39
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
40
Freescale Semiconductor
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 s).
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 s).
9. Clear the HVEN bit.
10. After time, tRCV (typical 1 s), 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
41
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 s).
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 s).
9. Clear the HVEN bit.
10. After time, tRCV (typical 1s), 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
42
Freescale Semiconductor
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 s).
5. Set the HVEN bit.
6. Wait for a time, tPGS (minimum of 5 s).
7. Write data to the FLASH address(1) to be programmed.
8. Wait for a time, tPROG (minimum of 30 s).
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 s).
12. Clear the HVEN bit.
13. After a time, tRCV (minimum of 1 s), 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
43
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
44
Freescale Semiconductor
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
45
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
46
Freescale Semiconductor
Chapter 3
Analog-to-Digital Converter (ADC10) Module
3.1 Introduction
This section describes the 10-bit successive approximation analog-to-digital converter (ADC10).
The ADC10 module shares its pins with general-purpose input/output (I/O) port pins. See Figure 3-1 for
port location of these shared pins. The ADC10 on this MCU uses VDDA and VSSA as its supply pins and
VREFH and VREFL as its reference pins. This MCU uses CGMXCLK as its alternate clock source for the
ADC. This MCU does not have a hardware conversion trigger.
3.2 Features
Features of the ADC10 module include:
• Linear successive approximation algorithm with 10-bit resolution
• Output formatted in 10- or 8-bit right-justified format
• Single or continuous conversion (automatic power-down in single conversion mode)
• Configurable sample time and conversion speed (to save power)
• Conversion complete flag and interrupt
• Input clock selectable from up to three sources
• Operation in wait and stop modes for lower noise operation
3.3 Functional Description
The ADC10 uses successive approximation to convert the input sample taken from ADVIN to a digital
representation. The approximation is taken and then rounded to the nearest 10- or 8-bit value to provide
greater accuracy and to provide a more robust mechanism for achieving the ideal code-transition voltage.
Figure 3-2 shows a block diagram of the ADC10.
For proper conversion, the voltage on ADVIN must fall between VREFH and VREFL. If ADVIN is equal to
or exceeds VREFH, the converter circuit converts the signal to $3FF for a 10-bit representation or $FF for
a 8-bit representation. If ADVIN is equal to or less than VREFL, the converter circuit converts it to $000.
Input voltages between VREFH and VREFL are straight-line linear conversions.
NOTE
Input voltage must not exceed the analog supply voltages.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
47
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 3-1. Block Diagram Highlighting ADC10 Block and Pins
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
48
Freescale Semiconductor
ADCK
MCU STOP
CONTROL SEQUENCER
ADHWT
ADICLK
ADIV
ADLPC
ADLSMP
MODE
COMPLETE
2
ADCLK
ADCO
AIEN
ADCH
1
COCO
ADCSC
ACLKEN
ASYNC
CLOCK
GENERATOR
ACLK
CLOCK
DIVIDE
BUS CLOCK
•••
ADVIN
ABORT
CONVERT
TRANSFER
AD0
SAMPLE
INITIALIZE
ALTERNATE CLOCK SOURCE
SAR CONVERTER
AIEN 1
COCO 2
INTERRUPT
ADn
VREFH
VREFL
DATA REGISTERS ADRH:ADRL
Figure 3-2. ADC10 Block Diagram
The ADC10 can perform an analog-to-digital conversion on one of the software selectable channels. The
output of the input multiplexer (ADVIN) is converted by a successive approximation algorithm into a 10-bit
digital result. When the conversion is completed, the result is placed in the data registers (ADRH and
ADRL). In 8-bit mode, the result is rounded to 8 bits and placed in ADRL. The conversion complete flag
is then set and an interrupt is generated if the interrupt has been enabled.
3.3.1 Clock Select and Divide Circuit
The clock select and divide circuit selects one of three clock sources and divides it by a configurable value
to generate the input clock to the converter (ADCK). The clock can be selected from one of the following
sources:
• The asynchronous clock source (ACLK) — This clock source is generated from a dedicated clock
source which is enabled when the ADC10 is converting and the clock source is selected by setting
the ACLKEN bit. When the ADLPC bit is clear, this clock operates from 1–2 MHz; when ADLPC is
set it operates at 0.5–1 MHz. This clock is not disabled in STOP and allows conversions in stop
mode for lower noise operation.
• Alternate clock source — This clock source is equal to the external oscillator clock or a four times
the bus clock. The alternate clock source is MCU specific, see 3.1 Introduction to determine source
and availability of this clock source option. This clock is selected when ADICLK and ACLKEN are
both low.
• The bus clock — This clock source is equal to the bus frequency. This clock is selected when
ADICLK is high and ACLKEN is low.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
49
Whichever clock is selected, its frequency must fall within the acceptable frequency range for ADCK. If
the available clocks are too slow, the ADC10 will not perform according to specifications. If the available
clocks are too fast, then the clock must be divided to the appropriate frequency. This divider is specified
by the ADIV[1:0] bits and can be divide-by 1, 2, 4, or 8.
3.3.2 Input Select and Pin Control
Only one analog input may be used for conversion at any given time. The channel select bits in ADCSC
are used to select the input signal for conversion.
3.3.3 Conversion Control
Conversions can be performed in either 10-bit mode or 8-bit mode as determined by the MODE bits.
Conversions can be initiated by either a software or hardware trigger. In addition, the ADC10 module can
be configured for low power operation, long sample time, and continuous conversion.
3.3.3.1 Initiating Conversions
A conversion is initiated:
• Following a write to ADCSC (with ADCH bits not all 1s) if software triggered operation is selected.
• Following a hardware trigger event if hardware triggered operation is selected.
• Following the transfer of the result to the data registers when continuous conversion is enabled.
If continuous conversions are enabled a new conversion is automatically initiated after the completion of
the current conversion. In software triggered operation, continuous conversions begin after ADCSC is
written and continue until aborted. In hardware triggered operation, continuous conversions begin after a
hardware trigger event and continue until aborted.
3.3.3.2 Completing Conversions
A conversion is completed when the result of the conversion is transferred into the data result registers,
ADRH and ADRL. This is indicated by the setting of the COCO bit. An interrupt is generated if AIEN is
high at the time that COCO is set.
A blocking mechanism prevents a new result from overwriting previous data in ADRH and ADRL if the
previous data is in the process of being read while in 10-bit mode (ADRH has been read but ADRL has
not). In this case the data transfer is blocked, COCO is not set, and the new result is lost. When a data
transfer is blocked, another conversion is initiated regardless of the state of ADCO (single or continuous
conversions enabled). If single conversions are enabled, this could result in several discarded
conversions and excess power consumption. To avoid this issue, the data registers must not be read after
initiating a single conversion until the conversion completes.
3.3.3.3 Aborting Conversions
Any conversion in progress will be aborted when:
• A write to ADCSC occurs (the current conversion will be aborted and a new conversion will be
initiated, if ADCH are not all 1s).
• A write to ADCLK occurs.
• The MCU is reset.
• The MCU enters stop mode with ACLK not enabled.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
50
Freescale Semiconductor
When a conversion is aborted, the contents of the data registers, ADRH and ADRL, are not altered but
continue to be the values transferred after the completion of the last successful conversion. In the case
that the conversion was aborted by a reset, ADRH and ADRL return to their reset states.
Upon reset or when a conversion is otherwise aborted, the ADC10 module will enter a low power, inactive
state. In this state, all internal clocks and references are disabled. This state is entered asynchronously
and immediately upon aborting of a conversion.
3.3.3.4 Total Conversion Time
The total conversion time depends on many factors such as sample time, bus frequency, whether
ACLKEN is set, and synchronization time. The total conversion time is summarized in Table 3-1.
Table 3-1. Total Conversion Time versus Control Conditions
Conversion Mode
ACLKEN
Maximum Conversion Time
8-Bit Mode (short sample — ADLSMP = 0):
Single or 1st continuous
Single or 1st continuous
Subsequent continuous (fBus fADCK)
0
1
x
18 ADCK + 3 bus clock
18 ADCK + 3 bus clock + 5s
16 ADCK
8-Bit Mode (long sample — ADLSMP = 1):
Single or 1st continuous
Single or 1st continuous
Subsequent continuous (fBus fADCK)
0
1
x
38 ADCK + 3 bus clock
38 ADCK + 3 bus clock + 5 s
36 ADCK
10-Bit Mode (short sample — ADLSMP = 0):
Single or 1st continuous
Single or 1st continuous
Subsequent continuous (fBus fADCK)
0
1
x
21 ADCK + 3 bus clock
21 ADCK + 3 bus clock + 5 s
19 ADCK
10-Bit Mode (long sample — ADLSMP = 1):
Single or 1st continuous
Single or 1st continuous
Subsequent continuous (fBus fADCK)
0
1
x
41 ADCK + 3 bus clock
41 ADCK + 3 bus clock + 5 s
39 ADCK
The maximum total conversion time for a single conversion or the first conversion in continuous
conversion mode is determined by the clock source chosen and the divide ratio selected. The clock
source is selectable by the ADICLK and ACLKEN bits, and the divide ratio is specified by the ADIV bits.
For example, if the alternate clock source is 16 MHz and is selected as the input clock source, the input
clock divide-by-8 ratio is selected and the bus frequency is 4 MHz, then the conversion time for a single
10-bit conversion is:
Maximum Conversion time =
21 ADCK cycles
16 MHz/8
+
3 bus cycles
4 MHz
= 11.25 s
Number of bus cycles = 11.25 s x 4 MHz = 45 cycles
NOTE
The ADCK frequency must be between fADCK minimum and fADCK
maximum to meet A/D specifications.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
51
3.3.4 Sources of Error
Several sources of error exist for ADC conversions. These are discussed in the following sections.
3.3.4.1 Sampling Error
For proper conversions, the input must be sampled long enough to achieve the proper accuracy. Given
the maximum input resistance of approximately 15 k and input capacitance of approximately 10 pF,
sampling to within 1/4LSB (at 10-bit resolution) can be achieved within the minimum sample window
(3.5 cycles / 2 MHz maximum ADCK frequency) provided the resistance of the external analog source
(RAS) is kept below 10 k. Higher source resistances or higher-accuracy sampling is possible by setting
ADLSMP (to increase the sample window to 23.5 cycles) or decreasing ADCK frequency to increase
sample time.
3.3.4.2 Pin Leakage Error
Leakage on the I/O pins can cause conversion error if the external analog source resistance (RAS) is high.
If this error cannot be tolerated by the application, keep RAS lower than VADVIN / (4096*ILeak) for less than
1/4LSB leakage error (at 10-bit resolution).
3.3.4.3 Noise-Induced Errors
System noise which occurs during the sample or conversion process can affect the accuracy of the
conversion. The ADC10 accuracy numbers are guaranteed as specified only if the following conditions
are met:
• There is a 0.1F low-ESR capacitor from VREFH to VREFL (if available).
• There is a 0.1F low-ESR capacitor from VDDA to VSSA (if available).
• If inductive isolation is used from the primary supply, an additional 1F capacitor is placed from
VDDA to VSSA (if available).
• VSSA and VREFL (if available) is connected to VSS at a quiet point in the ground plane.
• The MCU is placed in wait mode immediately after initiating the conversion (next instruction after
write to ADCSC).
• There is no I/O switching, input or output, on the MCU during the conversion.
There are some situations where external system activity causes radiated or conducted noise emissions
or excessive VDD noise is coupled into the ADC10. In these cases, or when the MCU cannot be placed
in wait or I/O activity cannot be halted, the following recommendations may reduce the effect of noise on
the accuracy:
• Place a 0.01 F capacitor on the selected input channel to VREFL or VSSA (if available). This will
improve noise issues but will affect sample rate based on the external analog source resistance.
• Operate the ADC10 in stop mode by setting ACLKEN, selecting the channel in ADCSC, and
executing a STOP instruction. This will reduce VDD noise but will increase effective conversion time
due to stop recovery.
• Average the input by converting the output many times in succession and dividing the sum of the
results. Four samples are required to eliminate the effect of a 1LSB, one-time error.
• Reduce the effect of synchronous noise by operating off the asynchronous clock (ACLKEN=1) and
averaging. Noise that is synchronous to the ADCK cannot be averaged out.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
52
Freescale Semiconductor
3.3.4.4 Code Width and Quantization Error
The ADC10 quantizes the ideal straight-line transfer function into 1024 steps (in 10-bit mode). Each step
ideally has the same height (1 code) and width. The width is defined as the delta between the transition
points from one code to the next. The ideal code width for an N bit converter (in this case N can be 8 or
10), defined as 1LSB, is:
1LSB = (VREFH–VREFL) / 2N
Because of this quantization, there is an inherent quantization error. Because the converter performs a
conversion and then rounds to 8 or 10 bits, the code will transition when the voltage is at the midpoint
between the points where the straight line transfer function is exactly represented by the actual transfer
function. Therefore, the quantization error will be ± 1/2LSB in 8- or 10-bit mode. As a consequence,
however, the code width of the first ($000) conversion is only 1/2LSB and the code width of the last ($FF
or $3FF) is 1.5LSB.
3.3.4.5 Linearity Errors
The ADC10 may also exhibit non-linearity of several forms. Every effort has been made to reduce these
errors but the user should be aware of them because they affect overall accuracy. These errors are:
• Zero-Scale Error (EZS) (sometimes called offset) — This error is defined as the difference between
the actual code width of the first conversion and the ideal code width (1/2LSB). Note, if the first
conversion is $001, then the difference between the actual $001 code width and its ideal (1LSB) is
used.
• Full-Scale Error (EFS) — This error is defined as the difference between the actual code width of
the last conversion and the ideal code width (1.5LSB). Note, if the last conversion is $3FE, then the
difference between the actual $3FE code width and its ideal (1LSB) is used.
• Differential Non-Linearity (DNL) — This error is defined as the worst-case difference between the
actual code width and the ideal code width for all conversions.
• Integral Non-Linearity (INL) — This error is defined as the highest-value the (absolute value of the)
running sum of DNL achieves. More simply, this is the worst-case difference of the actual transition
voltage to a given code and its corresponding ideal transition voltage, for all codes.
• Total Unadjusted Error (TUE) — This error is defined as the difference between the actual transfer
function and the ideal straight-line transfer function, and therefore includes all forms of error.
3.3.4.6 Code Jitter, Non-Monotonicity and Missing Codes
Analog-to-digital converters are susceptible to three special forms of error. These are code jitter,
non-monotonicity, and missing codes.
• Code jitter is when, at certain points, a given input voltage converts to one of two values when
sampled repeatedly. Ideally, when the input voltage is infinitesimally smaller than the transition
voltage, the converter yields the lower code (and vice-versa). However, even very small amounts
of system noise can cause the converter to be indeterminate (between two codes) for a range of
input voltages around the transition voltage. This range is normally around ±1/2 LSB but will
increase with noise.
• Non-monotonicity is defined as when, except for code jitter, the converter converts to a lower code
for a higher input voltage.
• Missing codes are those which are never converted for any input value. In 8-bit or 10-bit mode, the
ADC10 is guaranteed to be monotonic and to have no missing codes.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
53
3.4 Interrupts
When AIEN is set, the ADC10 is capable of generating a CPU interrupt after each conversion. A CPU
interrupt is generated when the conversion completes (indicated by COCO being set). COCO will set at
the end of a conversion regardless of the state of AIEN.
3.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
3.5.1 Wait Mode
The ADC10 will continue the conversion process and will generate an interrupt following a conversion if
AIEN is set. If the ADC10 is not required to bring the MCU out of wait mode, ensure that the ADC10 is not
in continuous conversion mode by clearing ADCO in the ADC10 status and control register before
executing the WAIT instruction. In single conversion mode the ADC10 automatically enters a low-power
state when the conversion is complete. It is not necessary to set the channel select bits (ADCH[4:0]) to
all 1s to enter a low power state.
3.5.2 Stop Mode
If ACLKEN is clear, executing a STOP instruction will abort the current conversion and place the ADC10
in a low-power state. Upon return from stop mode, a write to ADCSC is required to resume conversions,
and the result stored in ADRH and ADRL will represent the last completed conversion until the new
conversion completes.
If ACLKEN is set, the ADC10 continues normal operation during stop mode. The ADC10 will continue the
conversion process and will generate an interrupt following a conversion if AIEN is set. If the ADC10 is
not required to bring the MCU out of stop mode, ensure that the ADC10 is not in continuous conversion
mode by clearing ADCO in the ADC10 status and control register before executing the STOP instruction.
In single conversion mode the ADC10 automatically enters a low-power state when the conversion is
complete. It is not necessary to set the channel select bits (ADCH[4:0]) to all 1s to enter a low-power state.
If ACLKEN is set, a conversion can be initiated while in stop using the external hardware trigger
ADEXTCO when in external convert mode. The ADC10 will operate in a low-power mode until the trigger
is asserted, at which point it will perform a conversion and assert the interrupt when complete (if AIEN is
set).
3.6 ADC10 During Break Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. BCFE in the break flag control register (BFCR) enables software to clear status bits during
the break state. See BFCR in the SIM section of this data sheet.
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. 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 BCFE. With BCFE cleared (its default state),
software can read and write 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
54
Freescale Semiconductor
break, the bit cannot change during the break state as long as BCFE is cleared. After the break, doing the
second step clears the status bit.
3.7 I/O Signals
The ADC10 module shares its pins with general-purpose input/output (I/O) port pins. See Figure 3-1 for
port location of these shared pins. The ADC10 on this MCU uses VDD and VSS as its supply and reference
pins. This MCU does not have an external trigger source.
3.7.1 ADC10 Analog Power Pin (VDDA)
The ADC10 analog portion uses VDDA as its power pin. In some packages, VDDA is connected internally
to VDD. If externally available, connect the VDDA pin to the same voltage potential as VDD. External filtering
may be necessary to ensure clean VDDA for good results.
NOTE
If externally available, route VDDA carefully for maximum noise immunity
and place bypass capacitors as near as possible to the package.
3.7.2 ADC10 Analog Ground Pin (VSSA)
The ADC10 analog portion uses VSSA as its ground pin. In some packages, VSSA is connected internally
to VSS. If externally available, connect the VSSA pin to the same voltage potential as VSS.
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.
3.7.3 ADC10 Voltage Reference High Pin (VREFH)
VREFH is the power supply for setting the high-reference voltage for the converter. In some packages,
VREFH is connected internally to VDDA. If externally available, VREFH may be connected to the same
potential as VDDA, or may be driven by an external source that is between the minimum VDDA spec and
the VDDA potential (VREFH must never exceed VDDA).
NOTE
Route VREFH carefully for maximum noise immunity and place bypass
capacitors as near as possible to the package.
AC current in the form of current spikes required to supply charge to the capacitor array at each
successive approximation step is drawn through the VREFH and VREFL loop. The best external component
to meet this current demand is a 0.1 F capacitor 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 current will cause a voltage drop which could
result in conversion errors. Inductance in this path must be minimum (parasitic only).
3.7.4 ADC10 Voltage Reference Low Pin (VREFL)
VREFL is the power supply for setting the low-reference voltage for the converter. In some packages,
VREFL is connected internally to VSSA. If externally available, connect the VREFL pin to the same voltage
potential as VSSA. There will be a brief current associated with VREFL when the sampling capacitor is
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
55
charging. If externally available, connect the VREFL pin to the same potential as VSSA at the single point
ground location.
3.7.5 ADC10 Channel Pins (ADn)
The ADC10 has multiple input channels. Empirical data shows that capacitors on the analog inputs
improve performance in the presence of noise or when the source impedance is high. 0.01 F capacitors
with good high-frequency characteristics are sufficient. These capacitors are not necessary in all cases,
but when used they must be placed as close as possible to the package pins and be referenced to VSSA.
3.8 Registers
These registers control and monitor operation of the ADC10:
• ADC10 status and control register, ADCSC
• ADC10 data registers, ADRH and ADRL
• ADC10 clock register, ADCLK
3.8.1 ADC10 Status and Control Register
This section describes the function of the ADC10 status and control register (ADCSC). Writing ADCSC
aborts the current conversion and initiates a new conversion (if the ADCH[4:0] bits are equal to a value
other than all 1s).
Address:
$003C
Read:
COCO
Bit 7
Write:
Reset:
0
6
5
4
3
2
1
Bit 0
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
0
0
1
1
1
1
1
= Unimplemented
Figure 3-3. ADC10 Status and Control Register (ADCSC)
COCO — Conversion Complete Bit
COCO is a read-only bit which is set each time a conversion is completed. This bit is cleared whenever
the status and control register is written or whenever the data register (low) is read.
1 = Conversion completed
0 = Conversion not completed
AIEN — ADC10 Interrupt Enable Bit
When this bit is set, an interrupt is generated at the end of a conversion. The interrupt signal is cleared
when the data register is read or the status/control register is written.
1 = ADC10 interrupt enabled
0 = ADC10 interrupt disabled
ADCO — ADC10 Continuous Conversion Bit
When this bit is set, the ADC10 will begin to convert samples continuously (continuous conversion
mode) and update the result registers at the end of each conversion, provided the ADCH[4:0] bits do
not decode to all 1s. The ADC10 will continue to convert until the MCU enters reset, the MCU enters
stop mode (if ACLKEN is clear), ADCLK is written, or until ADCSC is written again. If stop is entered
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
56
Freescale Semiconductor
(with ACLKEN low), continuous conversions will cease and can be restarted only with a write to
ADCSC. Any write to ADCSC with ADCO set and the ADCH bits not all 1s will abort the current
conversion and begin continuous conversions.
If the bus frequency is less than the ADCK frequency, precise sample time for continuous conversions
cannot be guaranteed in short-sample mode (ADLSMP = 0). If the bus frequency is less than 1/11th
of the ADCK frequency, precise sample time for continuous conversions cannot be guaranteed in
long-sample mode (ADLSMP = 1).
When clear, the ADC10 will perform a single conversion (single conversion mode) each time ADCSC
is written (assuming the ADCH[4:0] bits do not decode all 1s).
1 = Continuous conversion following a write to ADCSC
0 = One conversion following a write to ADCSC
ADCH[4:0] — Channel Select Bits
The ADCH[4:0] bits form a 5-bit field that is used to select one of the input channels. The input
channels are detailed in Table 3-2. The successive approximation converter subsystem is turned off
when the channel select bits are all set to 1. This feature allows explicit disabling of the ADC10 and
isolation of the input channel from the I/O pad. Terminating continuous conversion mode this way will
prevent an additional, single conversion from being performed. It is not necessary to set the channel
select bits to all 1s to place the ADC10 in a low-power state, however, because the module is
automatically placed in a low-power state when a conversion completes.
Table 3-2. Input Channel Select
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
Input Select(1)
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
Unused
1
1
0
1
0
Unused
1
1
0
1
1
Reserved
1
1
1
0
0
Reserved
1
1
1
0
1
VREFH
1
1
1
1
0
VREFL
1
1
1
1
1
Low-power state
Continuing through
Unused
1. If any unused or reserved channels are selected, the resulting conversion will
be unknown.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
57
3.8.2 ADC10 Result High Register (ADRH)
This register holds the MSBs of the result and is updated each time a conversion completes. All other bits
read as 0s. Reading ADRH prevents the ADC10 from transferring subsequent conversion results into the
result registers until ADRL is read. If ADRL is not read until the after next conversion is completed, then
the intermediate conversion result will be lost. In 8-bit mode, this register contains no interlocking with
ADRL.
Address:
Read:
$003D
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 3-4. ADC10 Data Register High (ADRH), 8-Bit Mode
Address:
Read:
$003D
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
AD9
AD8
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 3-5. ADC10 Data Register High (ADRH), 10-Bit Mode
3.8.3 ADC10 Result Low Register (ADRL)
This register holds the LSBs of the result. This register is updated each time a conversion completes.
Reading ADRH prevents the ADC10 from transferring subsequent conversion results into the result
registers until ADRL is read. If ADRL is not read until the after next conversion is completed, then the
intermediate conversion result will be lost. In 8-bit mode, there is no interlocking with ADRH.
Address:
Read:
$003E
Bit 7
6
5
4
3
2
1
Bit 0
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 3-6. ADC10 Data Register Low (ADRL)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
58
Freescale Semiconductor
3.8.4 ADC10 Clock Register (ADCLK)
This register selects the clock frequency for the ADC10 and the modes of operation.
Address:
Read:
Write:
Reset:
$003F
Bit 7
6
5
4
3
2
1
Bit 0
ADLPC
ADIV1
ADIV0
ADICLK
MODE1
MODE0
ADLSMP
ACLKEN
0
0
0
0
0
0
0
0
Figure 3-7. ADC10 Clock Register (ADCLK)
ADLPC — ADC10 Low-Power Configuration Bit
ADLPC controls the speed and power configuration of the successive approximation converter. This
is used to optimize power consumption when higher sample rates are not required.
1 = Low-power configuration: The power is reduced at the expense of maximum clock speed.
0 = High-speed configuration
ADIV[1:0] — ADC10 Clock Divider Bits
ADIV1 and ADIV0 select the divide ratio used by the ADC10 to generate the internal clock ADCK.
Table 3-3 shows the available clock configurations.
Table 3-3. ADC10 Clock Divide Ratio
ADIV1
ADIV0
Divide Ratio (ADIV)
Clock Rate
0
0
1
Input clock1
0
1
2
Input clock2
1
0
4
Input clock4
1
1
8
Input clock8
ADICLK — Input Clock Select Bit
If ACLKEN is clear, ADICLK selects either the bus clock or an alternate clock source as the input clock
source to generate the internal clock ADCK. If the alternate clock source is less than the minimum
clock speed, use the internally-generated bus clock as the clock source. As long as the internal clock
ADCK, which is equal to the selected input clock divided by ADIV, is at a frequency (fADCK) between
the minimum and maximum clock speeds (considering ALPC), correct operation can be guaranteed.
1 = The internal bus clock is selected as the input clock source
0 = The alternate clock source IS SELECTED
MODE[1:0] — 10- or 8-Bit Mode Selection
These bits select 10- or 8-bit operation. The successive approximation converter generates a result
that is rounded to 8- or 10-bit value based on the mode selection. This rounding process sets the
transfer function to transition at the midpoint between the ideal code voltages, causing a quantization
error of ± 1/2LSB.
Reset returns 8-bit mode.
00 = 8-bit, right-justified, ADCSC software triggered mode enabled
01 = 10-bit, right-justified, ADCSC software triggered mode enabled
10 = Reserved
11 = Reserved
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
59
ADLSMP — Long Sample Time Configuration
This bit configures the sample time of the ADC10 to either 3.5 or 23.5 ADCK clock cycles. This adjusts
the sample period to allow higher impedance inputs to be accurately sampled or to maximize
conversion speed for lower impedance inputs. Longer sample times can also be used to lower overall
power consumption in continuous conversion mode if high conversion rates are not required.
1 = Long sample time (23.5 cycles)
0 = Short sample time (3.5 cycles)
ACLKEN — Asynchronous Clock Source Enable
This bit enables the asynchronous clock source as the input clock to generate the internal clock ADCK,
and allows operation in stop mode. The asynchronous clock source will operate between 1 MHz and
2 MHz if ADLPC is clear, and between 0.5 MHz and 1 MHz if ADLPC is set.
1 = The asynchronous clock is selected as the input clock source (the clock generator is only
enabled during the conversion)
0 = ADICLK specifies the input clock source and conversions will not continue in stop mode
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
60
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
61
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 4-2. Block Diagram Highlighting BEMF Block and Pins
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
62
Freescale Semiconductor
Chapter 5
Configuration Registers (CONFIG1, CONFIG2, CONFIG3)
5.1 Introduction
This section describes the configuration registers, CONFIG1, CONFIG2, and CONFIG3.
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
• SPI pin selection
• ESCI pin selection
• External oscillator frequency range selection
• Slew rate control for the ports, SPI, ESCI, and MCLK outputs
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 $0009, $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
On a ROM device, the CONFIG module is known as an MOR (mask option
register). 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,
Figure 5-2, and Figure 5-3.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Address:
Read:
Write:
Reset:
$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
1. The LVI5OR3 bit is cleared only by a power-on reset (POR).
Figure 5-1. Configuration Register 1 (CONFIG1)
COPRS — COP Rate Select Bit
COPRS selects the COP timeout period. Reset clears COPRS. See Chapter 6 Computer Operating
Properly.
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
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.
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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.
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.
1 = COP module disabled
0 = COP module enabled
Address:
$001E
Bit 7
Read:
Write:
Reset:
R
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 5-2. Configuration Register 2 (CONFIG2)
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.
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).
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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).
EXTSLOW — Slow External Crystal Enable Bit
The EXTSLOW bit has two functions. It configures the ICG module for a fast (1 MHz to 32 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
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
OSC2
External oscillator configured for
an external crystal configuration
on OSC1 and OSC2. System will
also operate with square-wave
clock source in OSC1.
1
1
OSC1
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.
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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)
SSBPUENB — SS Pullup Enable Bit
Clearing SSBPUENB enables the SS pullup resistor.
1 = Disables SS pullup resistor.
0 = Enables SS pullup resistor.
Address:
$0009
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
1
Bit 0
RNGSEL
ESCISRE
SPISRE
MCLKSRE
PORTSRE
ESCISEL
SPISEL
1
0
0
0
0
0
0
0
= Unimplemented
Figure 5-3. Configuration Register 3 (CONFIG3)
RNGSEL — External Oscillator Frequency Range Select
RNGSEL works in conjunction with EXTSLOW to enable the amplifiers for the crystal oscillator.
Table 5-2. External Crystal Frequency Range Selection
EXTSLOW
RNGSEL
Frequency Range
0
0
8–32 MHz
0
1
1–8 MHz
1
0
32–100 kHz
1
1
Reserved
Setting EXTSLOW will force RNGSEL to a 0. RNGSEL cannot be written if EXTSLOW = 1.
ESCISRE — Slew Rate Enable for ESCI
1 = Slew rate controlled output for TxD
0 = Normal output
SPISRE — Slew Rate Enable for SPI
1 = Slew rate controlled output for MISO, MOSI, and SCK
0 = Normal outputs
MCLKSRE — Slew Rate Enable for MCLK
1 = Slew rate controlled output for MCLK
0 = Normal output
PORTSRE — Slew Rate Enable for Ports
1 = Slew rate controlled output for all ports
0 = Normal output
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ESCISEL — ESCI Pin Selection Bit
ESCISEL is used to select the pins to be used as ESCI pins when the ESCI is enabled. For more
information on the ESCI, see Chapter 13 Enhanced Serial Communications Interface (ESCI) Module.
1 = TxD on PTA2 — RxD on PTA3
0 = TxD on PTE0 — RxD on PTE1
SPISEL — SPI Pin Selection Bit
SPISEL is used to select the pins to be used as SPI pins when the SPI is enabled. For more information
on the SPI, see Chapter 15 Serial Peripheral Interface (SPI) Module.
1 = MISO on PTB3 — MOSI on PTB4 — SPSCK on PTB5 — SS on PTC2
0 = MISO on PTC0 — MOSI on PTC1 — SPSCK on PTA5 — SS on PTA6
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Chapter 6
Computer Operating Properly
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 CONFIG1. When COPRS = 0,
a 4.9152-MHz crystal gives a COP timeout period of 53.3 ms. Writing any value to location $FFFF before
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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, CONFIG2, CONFIG3).
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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, CONFIG2, CONFIG3).
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.
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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.
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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)
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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)
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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.
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
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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.
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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
ADD #opr
ADD opr
ADD opr
ADD opr,X
ADD opr,X
ADD ,X
ADD opr,SP
ADD opr,SP
V H I N Z C
A  (A) + (M) + (C)
Add with Carry
A  (A) + (M)
Add without Carry
IMM
DIR
EXT
IX2
  –   
IX1
IX
SP1
SP2
A9
B9
C9
D9
E9
F9
9EE9
9ED9
ii
dd
hh ll
ee ff
ff
IMM
DIR
EXT
  –    IX2
IX1
IX
SP1
SP2
AB
BB
CB
DB
EB
FB
9EEB
9EDB
ii
dd
hh ll
ee ff
ff
ff
ee ff
ff
ee ff
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 7-1. Instruction Set Summary (Sheet 1 of 6)
2
3
4
4
3
2
4
5
2
3
4
4
3
2
4
5
AIS #opr
Add Immediate Value (Signed) to SP
SP  (SP) + (16 « M)
– – – – – – IMM
A7
ii
2
AIX #opr
Add Immediate Value (Signed) to H:X
H:X  (H:X) + (16 « M)
– – – – – – IMM
AF
ii
2
A  (A) & (M)
IMM
DIR
EXT
IX2
0 – –   – IX1
IX
SP1
SP2
A4
B4
C4
D4
E4
F4
9EE4
9ED4
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
DIR
INH
INH
 – –    IX1
IX
SP1
38 dd
48
58
68 ff
78
9E68 ff
4
1
1
4
3
5
DIR
INH
 – –    INH
IX1
IX
SP1
– – – – – – REL
37
47
57
67
77
9E67
24
ff
rr
4
1
1
4
3
5
3
11
13
15
17
19
1B
1D
1F
dd
dd
dd
dd
dd
dd
dd
dd
4
4
4
4
4
4
4
4
AND #opr
AND opr
AND opr
AND opr,X
AND opr,X
AND ,X
AND opr,SP
AND opr,SP
ASL opr
ASLA
ASLX
ASL opr,X
ASL ,X
ASL opr,SP
Logical AND
Arithmetic Shift Left
(Same as LSL)
ASR opr
ASRA
ASRX
ASR opr,X
ASR opr,X
ASR opr,SP
Arithmetic Shift Right
BCC rel
Branch if Carry Bit Clear
C
0
b7
b0
C
b7
b0
PC  (PC) + 2 + rel ? (C) = 0
Mn  0
DIR (b0)
DIR (b1)
DIR (b2)
– – – – – – DIR (b3)
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
ff
ee ff
dd
ff
BCLR n, opr
Clear Bit n in M
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
Branch if Greater Than or Equal To
– – – – – – REL
PC  (PC) + 2 + rel ? (N V
(Signed Operands)
Branch if Greater Than (Signed
PC  (PC) + 2 + rel ? (Z)| (N V – – – – – – REL
Operands)
90
rr
3
92
rr
3
BGE opr
BGT opr
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
78
Freescale Semiconductor
Effect
on CCR
V H I N Z C
Cycles
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 7-1. Instruction Set Summary (Sheet 2 of 6)
Branch if Higher or Same
(Same as BCC)
PC  (PC) + 2 + rel ? (C) = 0
– – – – – – REL
BIH rel
Branch if IRQ Pin High
PC  (PC) + 2 + rel ? IRQ = 1
– – – – – – REL
2F
rr
3
BIL rel
Branch if IRQ Pin Low
PC  (PC) + 2 + rel ? IRQ = 0
– – – – – – REL
2E
rr
3
(A) & (M)
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
93
rr
3
3
BHS rel
BIT #opr
BIT opr
BIT opr
BIT opr,X
BIT opr,X
BIT ,X
BIT opr,SP
BIT opr,SP
Bit Test
PC  (PC) + 2 + rel ? (Z)| (N V 1 – – – – – – REL
24
rr
3
BLO rel
Branch if Less Than or Equal To
(Signed Operands)
Branch if Lower (Same as BCS)
PC  (PC) + 2 + rel ? (C) = 1
– – – – – – REL
25
rr
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
3
BLE opr
BMC rel
Branch if Interrupt Mask Clear
PC  (PC) + 2 + rel ? (I) = 0
– – – – – – REL
2C
rr
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
BNE rel
Branch if Not Equal
PC  (PC) + 2 + rel ? (Z) = 0
– – – – – – REL
26
rr
3
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
– – – – – – REL
DIR (b0)
DIR (b1)
DIR (b2)
DIR (b3)
– – – – – 
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
21
00
02
04
06
08
0A
0C
0E
rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
3
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
C0
– – – – – 0 INH
98
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
PC  (PC) + 3 + rel ? (Mn) = 1
Mn  1
BSET n,opr
Set Bit n in M
BSR rel
Branch to Subroutine
CBEQ opr,rel
CBEQA #opr,rel
CBEQX #opr,rel
CBEQ opr,X+,rel Compare and Branch if Equal
CBEQ X+,rel
CBEQ
opr,SP,rel
CLC
Clear Carry Bit
5
5
5
5
5
5
5
5
1
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
79
CLI
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
COM opr
COMA
COMX
COM opr,X
COM ,X
COM opr,SP
CPHX #opr
CPHX opr
Clear Interrupt Mask
Clear
Compare A with M
Complement (One’s Complement)
Compare H:X with M
Compare X with M
DAA
Decimal Adjust A
DEC opr
DECA
DECX
DEC opr,X
DEC ,X
DEC opr,SP
Decrement
DIV
Divide
Exclusive OR M with A
Increment
Cycles
I0
– – 0 – – – INH
M  $00
A  $00
X  $00
H  $00
M  $00
M  $00
M  $00
DIR
INH
INH
0 – – 0 1 – INH
IX1
IX
SP1
3F dd
4F
5F
8C
6F ff
7F
9E6F ff
3
1
1
1
3
2
4
IMM
DIR
EXT
IX2
 – –   
IX1
IX
SP1
SP2
DIR
INH
INH
0 – –   1
IX1
IX
SP1
A1
B1
C1
D1
E1
F1
9EE1
9ED1
33
43
53
63
73
9E63
ff
2
3
4
4
3
2
4
5
4
1
1
4
3
5
(H:X) – (M:M + 1)
IMM
 – –   
DIR
65
75
ii ii+1
dd
3
4
(X) – (M)
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) – (M)
M  (M) = $FF – (M)
A  (A) = $FF – (M)
X  (X) = $FF – (M)
M  (M) = $FF – (M)
M  (M) = $FF – (M)
M  (M) = $FF – (M)
(A)10
DBNZ opr,rel
DBNZA rel
DBNZX rel
Decrement and Branch if Not Zero
DBNZ opr,X,rel
DBNZ X,rel
DBNZ opr,SP,rel
INC opr
INCA
INCX
INC opr,X
INC ,X
INC opr,SP
Effect
on CCR
V H I N Z C
CPX #opr
CPX opr
CPX opr
CPX ,X
CPX opr,X
CPX opr,X
CPX opr,SP
CPX 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)
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
9A
3B
4B
5B
6B
7B
9E6B
2
ii
dd
hh ll
ee ff
ff
ff
ee ff
dd
ff
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
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
80
Freescale Semiconductor
JSR opr
JSR opr
JSR opr,X
JSR opr,X
JSR ,X
LDA #opr
LDA opr
LDA opr
LDA opr,X
LDA opr,X
LDA ,X
LDA opr,SP
LDA opr,SP
LDHX #opr
LDHX opr
LDX #opr
LDX opr
LDX opr
LDX opr,X
LDX opr,X
LDX ,X
LDX opr,SP
LDX opr,SP
LSL opr
LSLA
LSLX
LSL opr,X
LSL ,X
LSL opr,SP
LSR opr
LSRA
LSRX
LSR opr,X
LSR ,X
LSR opr,SP
MOV opr,opr
MOV opr,X+
MOV #opr,opr
MOV X+,opr
MUL
NEG opr
NEGA
NEGX
NEG opr,X
NEG ,X
NEG opr,SP
BC
CC
DC
EC
FC
dd
hh ll
ee ff
ff
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
IMM
DIR
EXT
IX2
0 – –   – IX1
IX
SP1
SP2
IMM
0 – –   –
DIR
A6
B6
C6
D6
E6
F6
9EE6
9ED6
45
55
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
3
4
IMM
DIR
EXT
IX2
0 – –   – IX1
IX
SP1
SP2
AE
BE
CE
DE
EE
FE
9EEE
9EDE
DIR
INH
INH
 – –    IX1
IX
SP1
38 dd
48
58
68 ff
78
9E68 ff
H:X  (H:X) + 1 (IX+D, DIX+)
DIR
INH
 – – 0   INH
IX1
IX
SP1
DD
DIX+
0 – –   – IMD
IX+D
34
44
54
64
74
9E64
4E
5E
6E
7E
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
Jump
Jump to Subroutine
A  (M)
Load A from M
H:X M:M+ 1
Load H:X from M
X  (M)
Load X from M
Logical Shift Left
(Same as ASL)
C
0
b7
Logical Shift Right
b0
0
C
b7
(M)Destination (M)Source
Move
Unsigned multiply
Negate (Two’s Complement)
No Operation
NSA
Nibble Swap A
b0
ff
ee ff
ii jj
dd
ii
dd
hh ll
ee ff
ff
ff
ee ff
Cycles
PC  Jump Address
DIR
EXT
– – – – – – IX2
IX1
IX
Effect
on CCR
Description
V H I N Z C
NOP
ORA #opr
ORA opr
ORA opr
ORA opr,X
ORA opr,X
ORA ,X
ORA opr,SP
ORA 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)
2
3
4
4
3
2
4
5
4
1
1
4
3
5
dd
4
1
1
ff
4
3
ff
5
dd dd 5
dd
4
ii dd
4
dd
4
42
5
30 dd
40
50
60 ff
70
9E60 ff
4
1
1
4
3
5
None
– – – – – – INH
9D
1
A  (A[3:0]:A[7:4])
– – – – – – INH
62
3
AA
BA
CA
DA
EA
FA
9EEA
9EDA
87
PSHA
PSHH
Push A onto Stack
Push (A); SP (SP) – 1
IMM
DIR
EXT
IX2
0 – –   –
IX1
IX
SP1
SP2
– – – – – – INH
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
Inclusive OR A and M
A  (A) | (M)
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
2
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
81
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
C
b7
b0
SBC #opr
SBC opr
SBC opr
SBC opr,X
SBC opr,X
SBC ,X
SBC opr,SP
SBC opr,SP
Subtract with Carry
SEC
Set Carry Bit
C1
– – – – – 1 INH
99
1
SEI
Set Interrupt Mask
I1
– – 1 – – – INH
9B
2
(M:M + 1)  (H:X)
DIR
EXT
IX2
0 – –   – IX1
IX
SP1
SP2
0 – –   – DIR
B7
C7
D7
E7
F7
9EE7
9ED7
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
STHX opr
STOP
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
M (A)
Store A in M
Store H:X in M
Enable Interrupts, Stop Processing,
Refer to MCU Documentation
Store X in M
Subtract
A  (A) – (M)
ii
dd
hh ll
ee ff
ff
ff
ee ff
dd
hh ll
ee ff
ff
ff
ee ff
dd
2
3
4
4
3
2
4
5
3
4
4
3
2
4
5
4
1
ff
ee ff
ff
ee ff
3
4
4
3
2
4
5
2
3
4
4
3
2
4
5
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
82
Freescale Semiconductor
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 6 of 6)
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
TAP
Transfer A to CCR
CCR  (A)
      INH
84
2
TAX
Transfer A to X
X  (A)
– – – – – – INH
97
1
TPA
Transfer CCR to A
A  (CCR)
– – – – – – INH
85
1
(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
TST opr
TSTA
TSTX
TST opr,X
TST ,X
TST opr,SP
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
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
&
|

()
–( )
#
«

?
:

—
– – 1 – – – INH
83
9
3D dd
4D
5D
6D ff
7D
9E6D ff
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
83
84
Table 7-2. Opcode Map
Bit Manipulation
DIR
DIR
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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
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 MC68HC908EY16A, 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
85
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
MONITOR ROM
350 BYTES
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
DDRC
PORT C
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
DDRD
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORT E
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
PORT B
2-CHANNEL TIMER INTERFACE
MODULE B
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
CONFIGURATION REGISTER
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 8-1. Block Diagram Highlighting ICG Block and Pins
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
86
Freescale Semiconductor
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}
TRIM[7:0]
DSTG[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
OSC1
PTC4
OSC2
PTC3
ECLK
PTC3
LOGIC
EXTERNAL
NAME
CONFIGURATION REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 8-2. ICG Module Block Diagram
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
87
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
88
Freescale Semiconductor
ICGEN
FICGS
++
VOLTAGE AND
CURRENT
REFERENCES
DSTG[7:0]
+
DIGITAL
LOOP
FILTER
–
DDIV[3:0]
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
89
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
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
90
Freescale Semiconductor
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
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.
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.)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
91
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
CMON
CMON
FICGS
FICGS
IBASE
IBASE
ICGEN
ICGEN
IOFF
IOFF
ICLK
ACTIVITY
DETECTOR
EREF
ICGS
IBASE
EREF
ICGS
ICGON
EXTXTALEN
EXTXTALEN
REFERENCE
GENERATOR
EXTSLOW
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
92
Freescale Semiconductor
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
93
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
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
1/4
R
R
D
DFFRS
ECLK
EOFF
Q
CK
Q
S
R
D
DFFRR
CK
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
94
Freescale Semiconductor
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
95
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
96
Freescale Semiconductor
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
97
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.
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.
Table 8-2. Quantization Error in ICLK
DDIV[3:0]
ICLK Cycles
Bus Cycles
ICLK 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%
8.4.4.3 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].
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
98
Freescale Semiconductor
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.
• 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
99
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*IBASE), and since ICLK is N (the ICG multiply factor for the desired frequency) times faster than
IBASE, each correction takes 4*N*ICLK. 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*ICLKFAST.
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*ICLKFAST; from half speed to quarter speed
takes 88*N*ICLKFAST; going from quarter speed to eighth speed takes 176*N*ICLKFAST; and so on. This
series can be expressed as (2x–1)*44*N*ICLKFAST, where x is the number of times the speed needs
doubled or halved. Since 2x happens to be equal to ICLKSLOW/ICLKFAST, the equation reduces to
44*N*(ICLKSLOW–ICLKFAST).
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 (1) minus the final clock period (2) as such:
 15 = abs  44N   1 –  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*IBASE. 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:
 5 = abs  44N   1 –  2   + 32 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*IBASE. Added to the corrections for 15 percent to 5 percent,
this makes 32 corrections (128*IBASE) to get from 15 percent to the minimum error. The total time to the
minimum error is:
 tot = abs  44N   1 –  2   + 128 IBASE
The equations for 15, 5, and tot are dependent on the actual initial and final clock periods 1 and 2, 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
100
Freescale Semiconductor
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
1
2
N
15
5
tot
1/ (6.45 MHz)
1/ (25.8 MHz)
84
430 s
535 s
850 s
1/ (25.8 MHz)
1/ (6.45 MHz)
21
107 s
212 s
525 s
1/ (25.8 MHz)
1/ (307.2 kHz)
1
141 s
246 s
560 s
1/ (307.2 kHz)
1/ (25.8 MHz)
84
11.9 ms
12.0 ms
12.3 ms
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
101
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.
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,
CONFIG2, CONFIG3) 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 32 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
102
Freescale Semiconductor
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 or 8 MHz to 32 MHz depending on RNGSEL).
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
103
Table 8-4. ICG Module Register Bit Interaction Summary
Register Bit Results for Given Condition
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.
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:
Write:
Reset:
CMIE
0
6
5
4
3
(1)
CMON
CS
ICGON
0
0
0
1
CMF
0
2
ICGS
1
ECGON
0
0
Bit 0
ECGS
0
1. See CMF bit description for method of clearing CMF bit.
= Unimplemented
Figure 8-9. ICG Control Register (ICGCR)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
104
Freescale Semiconductor
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
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
105
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 8-10. 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).
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 8-11. 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 20.11.1 Trimmed Internal Clock Generator
Characteristics). Incrementing this register by one decreases the frequency by 0.195 percent of the
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
106
Freescale Semiconductor
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.
NOTE
Optional storage for 5V and 3V trim values is provided in non-volatile
memory at addresses $FF80 and $FF81. See 8.7.4 ICG 5-Volt Trim Value
and 8.7.5 ICG 3-Volt Trim Value.
8.7.4 ICG 5-Volt 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 8-12. 5V Internal Oscillator Trim Value (ICGT5V)
This register provides non-volatile storage for an optional 5V 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 3-Volt Trim Value
Address: $FF81
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. 3V Internal Oscillator Trim Value (ICGT3V)
This register provides non-volatile storage for an optional 3V 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.)
8.7.6 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 8-14. ICG DCO Divider Control Register (ICGDVR)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
107
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.
8.7.7 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 8-15. 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
108
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
LATCH
IRQ
INTERRUPT
REQUEST
IMASK
MODE
HIGH
VOLTAGE
DETECT
TO MODE
SELECT
LOGIC
Figure 9-1. IRQ Block Diagram
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
109
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
110
Freescale Semiconductor
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
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
111
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:
Read:
$001D
Bit 7
6
5
4
3
2
0
0
0
0
IRQF
0
Write:
Reset:
ACK
0
0
0
0
0
1
Bit 0
IMASK
MODE
0
0
0
= Unimplemented
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
112
Freescale Semiconductor
Chapter 10
Keyboard Interrupt (KBI) Module
10.1 Introduction
The keyboard interrupt module (KBI) provides independently maskable external interrupts.
The KBI shares its pins with general-purpose input/output (I/O) port pins. See Figure 10-1 for port location
of these shared pins.
10.2 Features
Features of the keyboard interrupt module include:
• Keyboard interrupt pins with separate keyboard interrupt enable bits and one keyboard interrupt
mask
• Programmable edge-only or edge and level interrupt sensitivity
• Edge sensitivity programmable for rising or falling edge
• Level sensitivity programmable for high or low level
• Pullup or pulldown device automatically enabled based on the polarity of edge or level detect
• Exit from low-power modes
10.3 Functional Description
The keyboard interrupt module controls the enabling/disabling of interrupt functions on the KBI pins.
These pins can be enabled/disabled independently of each other.
10.3.1 Keyboard Operation
Writing to the KBIEx bits in the keyboard interrupt enable register (KBIER) independently enables or
disables each KBI pin. The polarity of the keyboard interrupt is controlled using the KBIPx bits in the
keyboard interrupt polarity register (KBIPR). Edge-only or edge and level sensitivity is controlled using the
MODEK bit in the keyboard status and control register (KBISCR).
Enabling a keyboard interrupt pin also enables its internal pullup or pulldown device based on the polarity
enabled. On falling edge or low level detection, a pullup device is configured. On rising edge or high level
detection, a pulldown device is configured.
The keyboard interrupt latch is set when one or more enabled keyboard interrupt inputs are asserted.
• If the keyboard interrupt sensitivity is edge-only, for KBIPx = 0, a falling (for KBIPx = 1, a rising) edge
on a keyboard interrupt input does not latch an interrupt request if another enabled keyboard pin is
already asserted. To prevent losing an interrupt request on one input because another input remains
asserted, software can disable the latter input while it is asserted.
• If the keyboard interrupt is edge and level sensitive, an interrupt request is present as long as any
enabled keyboard interrupt input is asserted.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
113
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA2/KBD2/TxD(1)
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
USER FLASH VECTOR SPACE
36 BYTES
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
PTB5/AD5/SPSCK(1)
PORT E
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
VDD
VSS
PTA3/KBD3/RxD(1)
PTA0/KBD0
2-CHANNEL TIMER INTERFACE
MODULE A
MONITOR ROM
350 BYTES
RST
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
USER RAM
512 BYTES
OSC2
OSC1
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
CONFIGURATION REGISTER
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 10-1. Block Diagram Highlighting KBI Block and Pins
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
114
Freescale Semiconductor
INTERNAL BUS
VECTOR FETCH
DECODER
ACKK
RESET
1
KBD0
0 S
VDD
KBIE0
TO PULLUP/
PULLDOWN ENABLE
KBIP0
KEYF
D
CLR
Q
CK
1
KBDx
KBIPx
0
KBI LATCH
S
SYNCHRONIZER
IMASKK
KBIEx
TO PULLUP/
PULLDOWN ENABLE
MODEK
KEYBOARD
INTERRUPT
REQUEST
Figure 10-2. Keyboard Interrupt Block Diagram
10.3.1.1 MODEK = 1
If the MODEK bit is set, the keyboard interrupt inputs are both edge and level sensitive. The KBIPx bit will
determine whether a edge sensitive pin detects rising or falling edges and on level sensitive pins whether
the pin detects low or high levels. With MODEK set, both of the following actions must occur to clear a
keyboard interrupt request:
• Return of all enabled keyboard interrupt inputs to a deasserted level. As long as any enabled
keyboard interrupt pin is asserted, the keyboard interrupt remains active.
• Vector fetch or software clear. A KBI vector fetch generates an interrupt acknowledge signal to clear
the KBI latch. Software generates the interrupt acknowledge signal by writing a 1 to ACKK in KBSCR.
The ACKK bit is useful in applications that poll the keyboard interrupt inputs and require software to
clear the KBI latch. Writing to ACKK prior to leaving an interrupt service routine can also prevent
spurious interrupts due to noise. Setting ACKK does not affect subsequent transitions on the
keyboard interrupt inputs. An edge detect that occurs after writing to ACKK latches another interrupt
request. If the keyboard interrupt mask bit, IMASKK, is clear, the CPU loads the program counter with
the KBI vector address.
The KBI vector fetch or software clear and the return of all enabled keyboard interrupt pins to a deasserted
level may occur in any order.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a
keyboard interrupt input stays asserted.
10.3.1.2 MODEK = 0
If the MODEK bit is clear, the keyboard interrupt inputs are edge sensitive. The KBIPx bit will determine
whether an edge sensitive pin detects rising or falling edges. A KBI vector fetch or software clear
immediately clears the KBI latch.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
115
The keyboard flag bit (KEYF) in KBSCR can be read to check for pending interrupts. The KEYF bit is not
affected by IMASKK, which makes it useful in applications where polling is preferred.
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.
10.3.2 Keyboard Initialization
When a keyboard interrupt pin is enabled, it takes time for the internal pullup or pulldown device to pull
the pin to its deasserted level. 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 IMASKK in KBSCR.
2. Enable the KBI polarity by setting the appropriate KBIPx bits in KBIPR.
3. Enable the KBI pins by setting the appropriate KBIEx bits in KBIER.
4. Write to ACKK in KBSCR to clear any false interrupts.
5. Clear IMASKK.
An interrupt signal on an edge sensitive pin can be acknowledged immediately after enabling the pin. An
interrupt signal on an edge and level sensitive pin must be acknowledged after a delay that depends on
the external load.
10.4 Interrupts
The following KBI source can generate interrupt requests:
• Keyboard flag (KEYF) — The KEYF bit is set when any enabled KBI pin is asserted based on the KBI
mode and pin polarity. The keyboard interrupt mask bit, IMASKK, is used to enable or disable KBI
interrupt requests.
10.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
10.5.1 Wait Mode
The KBI module remains active in wait mode. Clearing IMASKK in KBSCR enables keyboard interrupt
requests to bring the MCU out of wait mode.
10.5.2 Stop Mode
The KBI module remains active in stop mode. Clearing IMASKK in KBSCR enables keyboard interrupt
requests to bring the MCU out of stop mode.
10.6 KBI 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 break flag control register (BFCR) enables software to clear status
bits during the break state. See BFCR in the SIM section of this data sheet.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
116
Freescale Semiconductor
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. 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 BCFE. With BCFE cleared (its default state),
software can read and write 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 cleared. After the break, doing the
second step clears the status bit.
10.7 I/O Signals
The KBI module can share its pins with the general-purpose I/O pins. See Figure 10-1 for the port pins
that are shared.
10.7.1 KBI Input Pins (KBI7:KBI0)
Each KBI pin is independently programmable as an external interrupt source. KBI pin polarity can be
controlled independently. Each KBI pin when enabled will automatically configure the appropriate
pullup/pulldown device based on polarity.
10.8 Registers
The following registers control and monitor operation of the KBI module:
• KBSCR (keyboard interrupt status and control register)
• KBIER (keyboard interrupt enable register)
• KBIPR (keyboard interrupt polarity register)
10.8.1 Keyboard Status and Control Register (KBSCR)
Features of the KBSCR:
• 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
ACKK
Write:
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
KEYF — Keyboard Flag Bit
This read-only bit is set when a keyboard interrupt is pending.
1 = Keyboard interrupt pending
0 = No keyboard interrupt pending
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
117
ACKK — Keyboard Acknowledge Bit
Writing a 1 to this write-only bit clears the KBI request. ACKK always reads 0.
IMASKK— Keyboard Interrupt Mask Bit
Writing a 1 to this read/write bit prevents the output of the KBI latch from generating interrupt requests.
1 = Keyboard interrupt requests disabled
0 = Keyboard interrupt requests enabled
MODEK — Keyboard Triggering Sensitivity Bit
This read/write bit controls the triggering sensitivity of the keyboard interrupt pins.
1 = Keyboard interrupt requests on edge and level
0 = Keyboard interrupt requests on edge only
10.8.2 Keyboard Interrupt Enable Register (KBIER)
KBIER enables or disables each 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 KBI interrupt
requests.
1 = KBDx pin enabled as keyboard interrupt pin
0 = KBDx pin not enabled as keyboard interrupt pin
10.8.3 Keyboard Interrupt Polarity Register (KBIPR)
KBIPR determines the polarity of the enabled keyboard interrupt pin and enables the appropriate pullup
or pulldown device.
Address: $000C
Read:
Bit 7
6
5
0
0
0
0
0
0
Write:
Reset:
4
3
2
1
Bit 0
KBIP4
KBIP3
KBIP2
KBIP1
KBIP0
0
0
0
0
0
= Unimplemented
Figure 10-5. Keyboard Interrupt Polarity Register (KBIPR)
KBIP4–KBIP0 — Keyboard Interrupt Polarity Bits
Each of these read/write bits selects the polarity of the keyboard interrupt pin. Reset clears the
keyboard interrupt polarity register.
1 = Keyboard polarity is rising edge and/or high level
0 = Keyboard polarity is falling edge and/or low level
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
118
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
119
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 5V 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
Write:
Reset:
0
= 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
120
Freescale Semiconductor
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 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 at a 0, the LVI
module will be inactive after a STOP instruction.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
121
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
122
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
SS
SPSCK
KBD3
KBD2
KBD1
KBD0
RxD
TxD
Reset:
Alternative Function:
Unaffected by reset
Alternative Function:
KBD4
= 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
123
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
WRITE PTA ($0000)
DDRAx
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
Accesses to PTA
Read/Write
Read
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
124
Freescale Semiconductor
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 disabled 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:
$0001
Bit 7
6
5
4
3
2
1
Bit 0
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
Alternative Function:
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
Alternative Function:
TBCH1
TBCH0
SPSCK
MOSI
MISO
Read:
Write:
Reset:
Unaffected by reset
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
125
Figure 12-6 shows the port B I/O logic.
READ DDRB ($0005)
INTERNAL DATA BUS
WRITE DDRB ($0005)
DDRBx
RESET
WRITE PTB ($0001)
PTBx
PTBx
READ PTB ($0001)
Figure 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.
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:
Read:
$0002
Bit 7
6
5
0
0
0
Write:
Reset:
4
3
2
1
Bit 0
PTC4
PTC3
PTC2
PTC1
PTC0
MCLK
MOSI
MISO
Unaffected by reset
Alternative Function:
OSC1
Alternative Function:
OSC2
SS
= Unimplemented
Figure 12-7. Port C Data Register (PTC)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
126
Freescale Semiconductor
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.
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, a bus clock frequency clock signal, 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
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
WRITE PTC ($0002)
DDRCx
PTCx
PTCx
READ PTC ($0002)
Figure 12-9. Port C I/O Circuit
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
127
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
Read/Write
Read
Accesses to PTC
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.
Address:
Read:
$0003
Bit 7
6
5
4
3
2
0
0
0
0
0
0
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
128
Freescale Semiconductor
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.
Figure 12-12 shows the port D I/O logic.
READ DDRD ($0007)
INTERNAL DATA BUS
WRITE DDRD ($0007)
RESET
WRITE PTD ($0003)
DDRDx
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
Read/Write
Read
Accesses to PTD
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
129
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:
$0008
Read:
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)
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].
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.
Figure 12-15 shows the port E I/O logic.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
130
Freescale Semiconductor
READ DDRE ($000A)
INTERNAL DATA BUS
WRITE DDRE ($000A)
RESET
WRITE PTE ($0008)
DDREx
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
131
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
132
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)
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
133
INTERNAL BUS
M68HC08 CPU
5-BIT KEYBOARD
INTERRUPT MODULE
USER FLASH
15,872 BYTES
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
USER FLASH VECTOR SPACE
36 BYTES
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
DDRC
PORT C
PORT D
DDRE
COMPUTER OPERATING
PROPERLY MODULE
DDRD
PRESCALER
MODULE
SYSTEM
INTEGRATION MODULE
SERIAL PERIPHERAL
INTERFACE MODULE
PTB3/AD3/MISO(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
CONFIGURATION REGISTER
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
POWER
PTB4/AD4/MOSI(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
PTB5/AD5/SPSCK(1)
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 13-1. Block Diagram Highlighting ESCI Block and Pins
Table 13-1. Pin Name Conventions
ESCI Generic Pin Name
RxD
TxD
Full Pin Name
PTE1/RxD
PTE0/TxD
Alternative Pin
PTA3
PTA2
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
134
Freescale Semiconductor
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
SCI_TxD
TRANSMIT
SHIFT REGISTER
TXINV
LINR
SCTIE
ARBITER-
TxD
BUS_CLK
R8
TCIE
RxD
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
LINT
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
135
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
T8
PSSB1
PSSB0
TRANSMITTER
CONTROL LOGIC
SCTE
SCTE
SCTIE
TC
TCIE
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
SBK
LOOPS
SCTIE
ENSCI
TC
TE
TCIE
LINT
Figure 13-4. ESCI Transmitter
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
136
Freescale Semiconductor
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
137
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.
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.
13.4.3 Receiver
Figure 13-5 shows the structure of the ESCI receiver.
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).
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
138
Freescale Semiconductor
INTERNAL BUS
SCR2
SCP0
SCR0
DATA
RECOVERY
RxD
ALL ZEROS
BKF
PDS2
RPF
PDS1
PDS0
PSSB4
PSSB3
PSSB2
M
PEN
PTY
8
7
6
5
4
WAKEUP
LOGIC
ILTY
PSSB0
H
3
SCRF
WAKE
PSSB1
11-BIT
RECEIVE SHIFT REGISTER
STOP
16
ALL ONES
BUS CLOCK
BAUD
DIVIDER
PRESCALER
PRESCALER
4
ESCI DATA REGISTER
CPU INTERRUPT
REQUEST
1
0
L
RWU
R8
IDLE
ILIE
ILIE
SCRIE
OR
ORIE
NF
ERROR CPU
INTERRUPT REQUEST
2
IDLE
PARITY
CHECKING
SCRF
SCRIE
START
SCR1
MSB
LINR
SCP1
NEIE
FE
FEIE
PE
PEIE
OR
ORIE
NF
NEIE
FE
FEIE
PE
PEIE
Figure 13-5. ESCI Receiver Block Diagram
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
139
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.
SAMPLES
LSB
START BIT
RxD
START BIT
QUALIFICATION
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
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
Start Bit Verification
Noise Flag
000
Yes
0
001
Yes
1
010
Yes
1
011
No
0
100
Yes
1
101
No
0
110
No
0
111
No
0
If start bit verification is not successful, the RT clock is reset and a new search for a start bit begins.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
140
Freescale Semiconductor
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
Data Bit Determination
Noise Flag
000
0
0
001
0
1
010
0
1
011
1
1
100
0
1
101
1
1
110
1
1
111
1
0
NOTE
The RT8, RT9, and RT10 samples do not affect start bit verification. If any
or all of the RT8, RT9, and RT10 start bit samples are 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
Framing Error Flag
Noise Flag
000
1
0
001
1
1
010
1
1
011
0
1
100
1
1
101
0
1
110
0
1
111
0
0
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
141
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
142
Freescale Semiconductor
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
143
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
144
Freescale Semiconductor
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.
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).
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
145
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
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
146
Freescale Semiconductor
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
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
147
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.
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
148
Freescale Semiconductor
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
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
149
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
150
Freescale Semiconductor
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:
Read:
$0013
Bit 7
6
5
4
3
2
1
Bit 0
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
receive a valid character that sets the SCRF bit before an idle condition can set the IDLE bit. Also, after
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
151
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
152
Freescale Semiconductor
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:
$0014
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
BKF
RPF
0
0
0
0
0
0
0
Write:
Reset:
0
= Unimplemented
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
153
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
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 $0018 accesses the read-only received data bits, R7:R0. Writing to address $0018
writes the data to be transmitted, T7:T0. Reset has no effect on the 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
LINT
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)
LINT — LIN Break Symbol Transmit Enable
This read/write bit selects the enhanced ESCI features for master nodes in the local interconnect
network (LIN) protocol (version 1.2) as shown in Table 13-6. Reset clears LINT.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
154
Freescale Semiconductor
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 Slave Node Control Bits
LINT
LINR
M
Functionality
0
0
X
Normal ESCI functionality
0
1
0
11-bit break detect enabled for LIN receiver
0
1
1
12-bit break detect enabled for LIN receiver
1
0
0
13-bit generation enabled for LIN transmitter
1
0
1
14-bit generation enabled for LIN transmitter
1
1
0
11-bit break detect/13-bit generation enabled for LIN
1
1
1
12-bit break detect/14-bit generation enabled for LIN
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
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
SCP[1:0]
0
0
1
1
0
1
0
1
Baud Rate Register
Prescaler Divisor (BPD)
1
3
4
13
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
155
13.8.8 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)
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]
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
Prescaler Divisor (PD)
Bypass this prescaler
2
3
4
5
6
7
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
156
Freescale Semiconductor
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
157
Table 13-11 shows the ESCI baud rates that can be generated with a 4.9152-MHz clock frequency.
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
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
Baud Rate
(ESCI Clock = 4.9152 MHz)
76,800
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
158
Freescale Semiconductor
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).
FRACTIONAL DIVIDE
PRESCALER — FD
1 OR 2  8.9687
(BYPASSED OR
2  831/32)
ESCI CLOCK
(BUS OR 4 x BUS)
SCI BAUD RATE
PRESCALER — BPD
BAUD RATE
DIVIDER — BD
1, 3, 4, or 13
1, 2, 4, . . . 128
4
16
fTx
fRx
ESCI Rx
ACLK = 1
ACLK = 0
9-BIT ARBITER COUNTER
4
Figure 13-18. ESCI Arbiter Counter Clock Selection
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 13-19. 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
159
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
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 13-20. 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
160
Freescale Semiconductor
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 ESCI input clock (= bus or CGMXCLK,
see Figure 5-2. Configuration Register 2 (CONFIG2) for a description of the ESCIBDSRC bit). 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 13-21.
2. ACLK = 1 — The counter is clocked with one quarter of the ESCI input clock divided by the ESCI
prescaler. The counter is started when a logic 0 is detected on RxD (see Figure 13-22). A logic 0
on RxD on enabling the bit time measurement with ACLK = 1 leads to immediate start of the
counter (see Figure 13-23). The counter will be stopped on the next rising edge of RxD. This mode
is used to measure the length of a received break.
MEASURED TIME
CPU READS RESULT
OUT OF SCIADAT
COUNTER STOPS,
AFIN = 1
COUNTER STARTS,
ARUN = 1
CPU WRITES SCIACTL
WITH $20
RXD
Figure 13-21. 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 13-22. Bit Time Measurement with ACLK = 1, Scenario A
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
161
MEASURED TIME
CPU READS RESULT
OUT OF SCIADAT
COUNTER STOPS,
AFIN = 1
COUNTER STARTS,
ARUN = 1
CPU WRITES SCIACTL
WITH $30
RXD
Figure 13-23. Bit Time Measurement with ACLK = 1, Scenario B
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,
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
162
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
163
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
BUS CLOCK
GENERATORS
2
SIM
CS
MONITOR MODE
USER MODE
ICG
Figure 14-2. System Clock Signals
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
164
Freescale Semiconductor
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 14.7.2 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 14.8.2 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 of tILR time. Figure 14-3 shows the relative timing.
CGMOUT
RST
IAB
PC
VECT H
VECT L
Figure 14-3. External Reset Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
165
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 PULLED LOW BY MCU
RST
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
166
Freescale Semiconductor
OSC1
PORRST
4096
CYCLES
32
CYCLES
CGMXCLK
CGMOUT
RST
IAB
$FFFE
$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 ($00). When the MCU comes out of reset, it is forced into monitor mode.
See 19.3 Monitor Module (MON).
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
167
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
168
Freescale Semiconductor
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
169
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
170
Freescale Semiconductor
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
171
14.6 Interrupt Status Registers
The flags in the interrupt status registers identify maskable interrupt sources. Table 14-3 summarizes the
interrupt sources and the interrupt status register flags that they set. The interrupt status registers can be
useful for debugging.
Table 14-3. Interrupt Sources
Priority
Interrupt Source
Highest
Lowest
Interrupt Status Register Flag
Reset
—
SWI instruction
—
IRQ pin
I1
CGM clock monitor
I2
TIM1 channel 0
I3
TIM1 channel 1
I4
TIM1 overflow
I5
TIM2 channel 0
I6
TIM2 channel 1
I7
TIM2 overflow
I8
SCI Error
I9
SCI receiver
I10
SCI transmitter
I11
Keyboard
I12
ADC conversion complete
I13
SPI receiver
I14
SPI transmitter
I15
Timebase module
I16
14.6.1 Interrupt Status Register 1
Address:
$FE04
Bit 7
6
5
4
3
2
1
Bit 0
Read:
IF6
IF5
IF4
IF3
IF2
IF1
0
0
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 14-11. Interrupt Status Register 1 (INT1)
IF6–IF1 — Interrupt Flags 6–1
These flags indicate the presence of interrupt requests from the sources shown in Table 14-3.
1 = Interrupt request present
0 = No interrupt request present
Bit 1 and Bit 0 — Always read 0
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
172
Freescale Semiconductor
14.6.2 Interrupt Status Register 2
Address:
$FE05
Bit 7
6
5
4
3
2
1
Bit 0
Read:
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
Write:
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
R
= Reserved
Reset:
Figure 14-12. Interrupt Status Register 2 (INT2)
IF14–IF7 — Interrupt Flags 14–7
These flags indicate the presence of interrupt requests from the sources shown in Table 14-3.
1 = Interrupt request present
0 = No interrupt request present
14.6.3 Interrupt Status Register 3
Address:
$FE06
Bit 7
6
5
4
3
2
1
Bit 0
Read:
0
0
0
0
0
0
IF16
IF15
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 14-13. Interrupt Status Register 3 (INT3)
IF16–IF15 — Interrupt Flags 16–15
This flag indicates the presence of an interrupt request from the source shown in Table 14-3.
1 = Interrupt request present
0 = No interrupt request present
Bits 7–2 — Always read 0
14.6.4 Reset
All reset sources always have higher priority than interrupts and cannot be arbitrated.
14.6.5 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
173
14.6.6 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.
14.7 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.
14.7.1 Wait Mode
In wait mode, the CPU clocks are inactive while one set of peripheral clocks continues to run.
Figure 14-14 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 14-14. Wait Mode Entry Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
174
Freescale Semiconductor
Figure 14-15 and Figure 14-16 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 14-15. Wait Recovery from Interrupt
64
CYCLES
IAB
IDB
$DE0B
$A6
$A6
RST VCT H RST VCT L
$A6
IRST
CGMXCLK
Figure 14-16. Wait Recovery from Internal Reset
14.7.2 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 14-17 shows stop mode entry timing.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
175
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 14-17. Stop Mode Entry Timing
STOP RECOVERY PERIOD
CGMXCLK
INT
IAB
STOP + 2
STOP +1
STOP + 2
SP
SP – 1
SP – 2
SP – 3
Figure 14-18. Stop Mode Recovery from Interrupt
14.8 SIM Registers
The SIM has three memory mapped registers. Table 14-4 shows the mapping of these registers.
Table 14-4. SIM Registers
Address
Register
Access Mode
$FE00
SBSR
User
$FE01
SRSR
User
$FE03
SBFCR
User
14.8.1 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 14-19. SIM Break Status Register (SBSR)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
176
Freescale Semiconductor
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
14.8.2 SIM Reset Status Register
The SRSR register contains flags that show the source of the last reset. The status register will
automatically clear after reading it. A power-on reset sets the POR bit and clears all other bits in the
register. All other reset sources set the individual flag bits but do not clear the register. More than one
reset source can be flagged at any time depending on the conditions at the time of the internal or external
reset. For example, the POR and LVI bits can both be set if the power supply has a slow rise time.
Address:
Read:
$FE01
Bit 7
6
5
4
3
2
1
Bit 0
POR
PIN
COP
ILOP
ILAD
MENRST
LVI
0
0
0
0
0
0
0
0
Write:
POR:
1
= Unimplemented
Figure 14-20. 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
177
14.8.3 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 14-21. 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
178
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
Alternative Pin
MISO
MOSI
SS
SPSCK
PTC0/MISO
PTC1/MOSI
PTA6/SS
PTA5/SPSCK
PTB3
PTB4
PTC2
PTB5
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
179
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
CONFIGURATION REGISTER
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 15-1. Block Diagram Highlighting SPI Block and Pins
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
15.4 Functional Description
Figure 15-2 shows the structure of the 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.
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
SPR0
SPMSTR
TRANSMITTER CPU INTERRUPT REQUEST
CPHA
MODFEN
SS
CPOL
SPWOM
ERRIE
SPI
CONTROL
SPTIE
RECEIVER/ERROR CPU INTERRUPT REQUEST
SPRIE
SPE
SPRF
SPTE
OVRF
MODF
Figure 15-2. SPI Module Block Diagram
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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.
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 15-2).
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.
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
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.)
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.
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Freescale Semiconductor
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).
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
183
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.
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Freescale Semiconductor
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
185
WRITE
TO SPDR
INITIATION DELAY
BUS
CLOCK
MOSI
MSB
BIT 6
BIT 5
SCK
CPHA = 1
SCK
CPHA = 0
SCK CYCLE
NUMBER
1
3
2
INITIATION DELAY FROM WRITE SPDR TO TRANSFER BEGIN








WRITE
TO SPDR
BUS
CLOCK
EARLIEST LATEST
BUS
CLOCK
WRITE
TO SPDR
EARLIEST
BUS
CLOCK
WRITE
TO SPDR
EARLIEST
BUS
CLOCK
WRITE
TO SPDR
EARLIEST
SCK = INTERNAL CLOCK 2;
2 POSSIBLE START POINTS
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
Figure 15-6. Transmission Start Delay (Master)
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
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Freescale Semiconductor
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
2
READ SPSCR
5
3
READ SPDR
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).
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
187
SPI RECEIVE
COMPLETE
BYTE 1
BYTE 2
BYTE 3
BYTE 4
1
5
7
11
SPRF
OVRF
READ SPSCR
READ SPDR
1
BYTE 1 SETS SPRF BIT.
2
3
2
4
3
6
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
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
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Freescale Semiconductor
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.
15.7 Interrupts
Four SPI status flags can be enabled to generate CPU interrupt requests:
Table 15-2. SPI Interrupts
Flag
Request
SPTE (Transmitter Empty)
SPI Transmitter CPU Interrupt Request (SPTIE = 1)
SPRF (Receiver Full)
SPI Receiver CPU Interrupt Request (SPRIE = 1)
OVRF (Overflow)
SPI Receiver/Error Interrupt Request (SPRIE = 1, ERRIE = 1)
MODF (Mode Fault)
SPI Receiver/Error Interrupt Request (SPRIE = 1, ERRIE = 1, MODFEN = 1)
The SPI transmitter interrupt enable bit (SPTIE) enables the SPTE flag to generate transmitter CPU
interrupt requests.
The SPI receiver interrupt enable bit (SPRIE) enables the SPRF bit to generate receiver CPU interrupt,
provided that the SPI is enabled (SPE = 1).
The error interrupt enable bit (ERRIE) enables both the MODF and OVRF flags to generate a
receiver/error CPU interrupt request.
The mode fault enable bit (MODFEN) can prevent the MODF flag from being set so that only the OVRF
flag is enabled to generate receiver/error CPU interrupt requests.
SPTE
SPTIE
SPE
SPI TRANSMITTER
CPU INTERRUPT REQUEST
SPRIE
ERRIE
SPRF
SPI RECEIVER/ERROR
CPU INTERRUPT REQUEST
MODF
OVRF
Figure 15-9. SPI Interrupt Request Generation
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
189
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.
WRITE TO SPDR
SPTE
1
3
8
5
2
10
SPSCK (CPHA:CPOL = 1:0)
MOSI
MSB BIT BIT BIT BIT BIT BIT LSB MSB BIT BIT BIT BIT BIT BIT LSB MSB BIT BIT BIT
6 5 4 3 2 1
6 5 4 3 2 1
6 5 4
BYTE 1
BYTE 2
BYTE 3
4
SPRF
9
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
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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.
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.)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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 SPI I/O Signals
The SPI module has four I/O pins and shares three of them with a parallel I/O port.
• MISO — Data received
• MOSI — Data transmitted
• SPSCK — Serial clock
• SS — Slave select
• VSS — Clock ground
The SPI has limited inter-integrated circuit (I2C) capability (requiring software support) as a master in a
single-master environment. To communicate with I2C peripherals, MOSI becomes an open-drain output
when the SPWOM bit in the SPI control register is set. In I2C communication, the MOSI and MISO pins
are connected to a bidirectional pin from the I2C peripheral and through a pullup resistor to VDD.
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.
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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
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 15-2.)
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.
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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
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,
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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
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:
6
0
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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SPRF — SPI Receiver Full Bit
This clearable, read-only flag is set each time a byte transfers from the shift register to the receive data
register. SPRF generates a CPU interrupt request if the SPRIE bit in the SPI control register is set also.
During an SPRF CPU interrupt, the CPU clears SPRF by reading the SPI status and control register
with SPRF set and then reading the SPI data register. Any read of the SPI data register clears the
SPRF bit.
Reset clears the SPRF bit.
1 = Receive data register full
0 = Receive data register not full
ERRIE — Error Interrupt Enable Bit
This read-only bit enables the MODF and OVRF flags to generate CPU interrupt requests. Reset
clears the ERRIE bit.
1 = MODF and OVRF can generate CPU interrupt requests
0 = MODF and OVRF cannot generate CPU interrupt requests
OVRF — Overflow Bit
This clearable, read-only flag is set if software does not read the byte in the receive data register before
the next byte enters the shift register. In an overflow condition, the byte already in the receive data
register is unaffected, and the byte that shifted in last is lost. Clear the OVRF bit by reading the SPI
status and control register with OVRF set and then reading the SPI data register. Reset clears the
OVRF flag.
1 = Overflow
0 = No overflow
MODF — Mode Fault Bit
This clearable, read-only flag is set in a slave SPI if the SS pin goes high during a transmission. In a
master SPI, the MODF flag is set if the SS pin goes low at any time. Clear the MODF bit by reading
the SPI status and control register with MODF set and then writing to the SPCR. 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
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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).
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 15-3. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Table 15-3. SPI Master Baud Rate Selection
SPR1:SPR0
00
01
10
11
Baud Rate Divisor (BD)
2
8
32
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:
Read:
Write:
Reset:
$000F
Bit 7
R7
T7
6
R6
T6
5
R5
T5
4
3
R4
R3
T4
T3
Indeterminate after Reset
2
R2
T2
1
R1
T1
Bit 0
R0
T0
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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MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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.
16.2 Features
Features of the TBM module include:
• Software configurable periodic interrupts with divide-by-8, 16, 32, 64, 128, 1024, 2048, 4096, 8192,
16384, 32768, 262,144, 1,048,576, and 4,194,304 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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
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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
16.5 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.
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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 s.
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
262,144
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
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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.
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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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 17-1. Block Diagram Highlighting TIMA Block and Pins
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
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
17.3.2 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
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
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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.
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
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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
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%.
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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
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.
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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.
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.
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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.
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.
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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
6
5
TOIE
TSTOP
1
Read:
TOF
Write:
0
Reset:
0
0
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
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
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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, see if any timer flags are set.
If a timer flag is set, it must be cleared by clearing TSTOP, then clearing the
flag, then setting TSTOP again.
TRST — TIMA Reset Bit
Setting this write-only bit resets the TIMA counter and the TIMA prescaler. Setting TRST has no effect
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMA
counter is reset and always reads as 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
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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
Read:
TACNTH — $0021
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
Write:
Reset:
Register Name and Address
Read:
TACNTL — $0022
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
Write:
Reset:
0
= Unimplemented
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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
Read:
CH0F
Write:
0
Reset:
0
TASC0 — $0025
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
6
Read:
CH1F
Write:
0
Reset:
0
R
TASC1 — $0028
CH1IE
0
5
0
R
0
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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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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
215
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.
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
PTDx/TCHx
TOV = 1
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
TOV = 0
Figure 17-8. CHxMAX Latency
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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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
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MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
218
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.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
219
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure 18-1. Block Diagram Highlighting TIMB Block and Pins
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
220
Freescale Semiconductor
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
CH0F
16-BIT LATCH
MS0A
CHANNEL 1
ELS1B
MS0B
ELS1A
TOV1
CH1MAX
16-BIT COMPARATOR
TBCH1H:TBCH1L
CH0IE
CH1F
16-BIT LATCH
MS1A
CH1IE
PTB6
LOGIC
PTB6/AD6/TBCH0
INTERRUPT
LOGIC
PTB7
LOGIC
PTB7/AD7/TBCH1
INTERRUPT
LOGIC
Figure 18-2. TIMB Block Diagram
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
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
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/AD6/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/AD6/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/AD7/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%.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
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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/AD6/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/AD6/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/AD7/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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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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 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/AD6/TBCH0 and PTB7/AD7/TBCH1. See Chapter 12 Input/Output
(I/O) Ports (PORTS).
18.7.1 TIMB Channel I/O Pins (PTB7/AD7/TBCH1–PTB6/AD6/TBCH0)
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.
PTB6/AD6/TBCH0 and PTB7/AD7/TBCH1 can be configured as buffered output compare or buffered
PWM pins.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
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Freescale Semiconductor
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
6
5
TOIE
TSTOP
1
Read:
TOF
Write:
0
Reset:
0
0
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
227
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, see if any timer flags are set.
If a timer flag is set, it must be cleared by clearing TSTOP, then clearing the
flag, then setting TSTOP again.
TRST — TIMB Reset Bit
Setting this write-only bit resets the TIMB counter and the TIMB prescaler. Setting TRST has no effect
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMB
counter is reset and always reads as 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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
228
Freescale Semiconductor
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
Read:
TBCNTH — $002C
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
Write:
Reset:
Register Name and Address
Read:
TBCNTL — $002D
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
Write:
Reset:
= Unimplemented
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
229
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
230
Freescale Semiconductor
MSxB — Mode Select Bit B
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIMB
channel 0.
Setting MS0B disables the channel 1 status and control register and reverts TBCH1 to
general-purpose I/O.
Reset clears the MSxB bit.
1 = Buffered output compare/PWM operation enabled
0 = Buffered output compare/PWM operation disabled
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
Mode
Output preset
Configuration
Pin under port control; initial output level high
Pin under port control; initial output level low
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
1
X
0
1
1
X
1
0
1
X
1
1
Capture on rising edge only
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
231
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.
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
PTBx/TCHx
TOV = 1
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
TOV = 0
Figure 18-8. CHxMAX Latency
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
232
Freescale Semiconductor
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
233
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
234
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
235
INTERNAL BUS
M68HC08 CPU
USER FLASH
15,872 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
512 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
236
Freescale Semiconductor
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 14.8.3 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 and inhibits input captures.
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
237
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)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
238
Freescale Semiconductor
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
1
SBSW
Note(1)
Reset:
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
239
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 $FFFF are blank, thus reducing the hardware
requirements for in-circuit programming.
Features of the monitor module include:
• Normal user-mode pin functionality
• One pin dedicated to serial communication between MCU and host computer
• Standard non-return-to-zero (NRZ) communication with host computer
• Standard communication baud rate (9600 @ 2.4576-MHz internal operating frequency)
• Execution of code in random-access memory (RAM) or FLASH
• FLASH memory security feature(1)
• FLASH memory programming interface
• Use of external 9.8304 MHz oscillator or ICG to generate internal operating frequency of
2.4576 MHz
• Monitor mode entry without high voltage, VTST, if reset vector is blank ($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, Figure 19-10,
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 are erased or programmed:
– 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 2.45 MHz (nominal 9600 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
240
Freescale Semiconductor
POR RESET
NO
CONDITIONS
FROM Table 19-1
PTA0 = 1,
PTA1 = 0, RESET
VECTOR BLANK?
YES
IRQ = VTST?
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
NO
YES
IS RESET
POR?
YES
YES
ARE ALL
SECURITY BYTES
CORRECT?
NO
EXTENDED SECURITY
= $00?
NO
INFINITE LOOP
ENABLE FLASH
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
241
MC68HC908EY16A/8A
N.C.
VDD
VDD
RST
VDDA
MAX232
1
1 F
+
3
4
1 F
+
VCC 16
C1+
C1–
GND 15
C2+
V+ 2
+
3
VDD
1 F
+
10 k
1 F
PTB4
1 k
VDD
+
DB9
7
10
8
9
0.1F
OSC1
V– 6
5 C2–
2
9.8304-MHz CLOCK
VDD
1 F
74HC125
5
6
74HC125
3
2
IRQ
10 k
9.1 V
PTB3
10 k
PTA1
10 k
PTA0
VSSA
VSS
4
1
5
Figure 19-9. Normal Monitor Mode Circuit
MC68HC908EY16A/8A
N.C.
RST
VDD
VDD
VDDA
MAX232
1
1 F
+
3
4
1 F
+
C1+
VCC 16
C1–
GND 15
C2+
V+ 2
5 C2–
3
5
+
8
1 F
+
1 F
VDD
+
7
N.C.
IRQ
PTB4
N.C.
PTB3
N.C.
10 k
1 F
74HC125
5
6
10
9
0.1F
OSC1
V– 6
DB9
2
9.8304-MHz CLOCK
VDD
74HC125
3
2
PTA1
10 k
PTA0
4
1
VSSA
VSS
Figure 19-10. Forced Monitor Mode (VIRQ = VDD)
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
242
Freescale Semiconductor
MC68HC908EY16A/8A
N.C.
RST
VDD
VDD
VDDA
MAX232
1
1 F
+
3
4
1 F
+
C1+
VCC 16
C1–
GND 15
C2+
V+ 2
5 C2–
3
N.C.
+
+
1 F
9
8
N.C.
PTB3
N.C.
74HC125
5
6
74HC125
3
2
10 k
PTA1
10 k
PTA0
4
1
5
PTB4
10 k*
1 F
10
7
IRQ
VDD
+
OSC1
1 F
V– 6
DB9
2
0.1F
VDD
VSSA
VSS
Figure 19-11. Forced Monitor Mode (VIRQ = 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 internal operating 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.
NOTE
While the voltage on IRQ is at VTST, the ICG module is bypassed and the
external square-wave clock becomes the clock source. Dropping IRQ to
below VTST will remove the bypass and the MCU will revert to the clock
source selected by the ICG (a determined by the settings in the ICG
registers).
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
243
Table 19-1. Monitor Mode Signal Requirements and Options
Mode
IRQ
Reset
RST
Vector
VTST
VDD
or
VTST
VDD
VDD
VSS
VDD
User
VDD
or
VSS
VDD
Not
or
$FFFF
VTST
MON08
Function
[Pin No.]
VTST
[6]
RST
[4]
Normal
Monitor
Forced
Monitor
Serial
Communication
Mode
Selection
Communication
Speed
ICG
fOP
Baud
Rate
OFF Disabled
9.8304
MHz
2.4576
MHz
9600
X
OFF Disabled
9.8304
MHz
2.4576
MHz
9600
X
X
ON
Disabled
—
Nominal
2.45 MHz
Nominal
9600
X
X
ON
Enabled
—
Nominal
1.6 MHz
X
—
—
OSC1
[13]
—
—
PTA1
PTB4
PTB3
1
0
1
0
1
0
X
1
0
X
X
COM
[8]
SSEL
[10]
X
COP
External
Clock
PTA0
$FFFF
(blank)
—
MOD0 MOD1
[12]
[14]
1. PTA0 must have a pullup resistor to VDD in monitor mode.
2. Communication speed in the table is an example to obtain a baud rate of 9600 except the forced monitor IRQ = VSS case.
Baud rate using external oscillator is bus frequency / 256.
4. X = don’t care
5. RST column indicates the state of RST after the monitor entry.
6. MON08 pin refers to P&E Microcomputer Systems’ MON08-Cyclone 2 by 8-pin connector.
NC
1
2
GND
NC
3
4
RST
NC
5
6
IRQ
NC
7
8
PTA0
NC
9
10
PTA1
NC
11
12
PTB3
OSC1
13
14
PTB4
VDD
15
16
NC
19.3.1.2 Forced Monitor Mode
If entering monitor mode without high voltage on IRQ, then PTA1, PTB3, and PTB4 pin requirements and
conditions are not in effect. This is to reduce circuit requirements when performing in-circuit programming.
If the reset vector is blank and monitor mode is entered without VTST on IRQ, the MCU will see an
additional reset cycle after the initial power-on reset (POR). The MCU will initially come out of reset in user
mode. Internal circuitry monitors the reset vector fetches and will assert an internal reset if it detects the
reset vector is erased ($FFFF).
Once the MCU enters this mode any reset other than a POR will automatically force the MCU to come
back to the forced monitor mode. Exiting the forced monitor mode requires a POR. Pulling RST low will
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
244
Freescale Semiconductor
not exit monitor mode in this situation. Once the reset vector has been programmed, the traditional
method of applying a voltage, VTST, to IRQ must be used to re-enter monitor mode after the next POR.
When the forced monitor mode is entered the COP is always disabled regardless of the state of IRQ or
RST.
With VDD on IRQ, an external oscillator of 9.8034 MHz is required for a baud rate of 9600, as the internal
internal operating frequency is automatically set to the external frequency divided by four.
With VSS on IRQ at the monitor entry, the ICG is on. In this case, the internal operating frequency is a
nominal 2.45 MHz and the baud rate is a nominal 9600.
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
245
19.3.1.6 Baud Rate
The monitor communication baud rate is controlled by the frequency of the external or internal oscillator
and the state of the appropriate pins as shown in Table 19-1.
Table 19-1 also lists external frequencies required to achieve a standard baud rate of 9600 bps. The
effective baud rate is the internal operating frequency divided by 256. 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 5V
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. 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
3
ADDRESS
HIGH
READ
READ
3
1
ADDRESS
HIGH
1
ADDRESS
LOW
ADDRESS
LOW
DATA
1
3
2
3
ECHO
RETURN
Notes:
1 = Echo delay, approximately 2 bit times
2 = Data return delay, approximately 2 bit times
3 = Wait approximately 1 bit time before sending next byte
Figure 19-14. Read Transaction
FROM
HOST
WRITE
2
ADDRESS
HIGH
WRITE
1
2
ADDRESS
HIGH
1
ADDRESS
LOW
2
ADDRESS
LOW
1
DATA
DATA
2
1
2
ECHO
Notes:
1 = Echo delay, approximately 2 bit times
2 = Wait approximately 1 bit time before sending next byte
Figure 19-15. Write Transaction
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
246
Freescale Semiconductor
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
247
Table 19-6. IWRITE (Indexed Write) Command
Description
Write to last address accessed + 1
Operand
Single data byte
Data Returned
Opcode
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
248
Freescale Semiconductor
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.
VDD
COMMAND
4096 + 32 CGMXCLK CYCLES
BYTE 8
BYTE 2
FROM HOST
BYTE 1
RST
PA0
3
BREAK
2
1
COMMAND ECHO
1
BYTE 8 ECHO
Notes:
1 = Echo delay, approximately 2 bit times
2 = Data return delay, approximately 2 bit times
3 = Wait approximately 1 bit time before sending next byte
4 = Wait until the monitor ROM runs
1
BYTE 2 ECHO
FROM MCU
3
1
BYTE 1 ECHO
4
Figure 19-17. Monitor Mode Entry Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
249
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).
19.3.3 Extended Security
In addition to the above security, a more secure feature called extended security is implemented in the
MCU to further protect FLASH contents. Once this extended security is enabled, the MCU does not allow
any user to enter the monitor mode even when all 8 security bytes are matched correctly. The extended
security feature can be enabled by programming address $FDFF located in the user FLASH memory with
data $00.
To unlock the extended security feature, the MCU must enter the monitor mode by failing the 8 byte
security check. Then the FLASH must be mass-erased. This unlock process will erase the FLASH
contents completely.
NOTE
To avoid enabling the extended security unintentionally, the user must
make sure that the user software does not contain data $00 at address
$FDFF.
19.4 Routines Supported in ROM
In the ROM, five routines are supported. Because the ROM has a jump table, the user does not call the
routines with direct addresses. Therefore, the calling addresses will not change—even when the ROM
code is updated in the future.
This section introduces each routine briefly. Details are discussed in later sections.
• GetByte — This routine is used to receive a byte serially on the general-purpose I/O PTA0. The
receiving baud rate is the same as the baud rate used in monitor mode. In the GetByte routine, the
GetBit routine is called to generate baud rates.
• PutByte — This routine is used to send a byte serially on the general-purpose I/O PTA0. The
sending baud rate is the same as the baud rate specified in monitor mode.
• Verify — This routine is used to perform one of two options. Using the send-out option, this routine
reads FLASH locations and sends the data out serially on the general-purpose I/O PTA0. Using
the compare option, this routine compares the FLASH data against data in a specific RAM location,
which is referred to as a DATA array. The DATA array locations and the variable locations required
for this routine are at fixed memory addresses.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
250
Freescale Semiconductor
•
•
fProgram — This routine is used to program a contiguous range of FLASH locations.
Programming data is first loaded into the DATA array. The DATA array locations and the variable
locations required for this routine are at fixed memory addresses. fProgram can be used when the
internal operating frequency (fop) is between 1.0 MHz and 8.0 MHz.
fErase — This routine is used to erase either a page (64 bytes) or the whole array of FLASH. The
variable locations required for this routine are at fixed memory addresses. This routine can be used
when the internal operating frequency (fop) is between 1.0 MHz and 8.0 MHz.
19.4.1 Variables Used in the Routines
The Verify, fProgram, and fErase routines require certain registers and/or RAM locations to be initialized
before calling the routines in the user software. Table 19-9 shows variables used in the routines and their
locations.
Table 19-9. Variables and Their Locations
•
•
•
•
Location
Variable Name
Size (Bytes)
Description
$0040–$0048
Reserved
9
Reserved for future use
$0049
CPUSPD
1
CPU speed — the nearest integer of fop (in MHz)  4;
for example, if fop = 2.4576 MHz, CPUSPD = 10
$004A:$004B
LADDR
2
Last address of a 16-bit range
$004C
DATA
Varies
First location of DATA array;
DATA array size must match a programming or
verifying range
CPUSPD — To set up proper delays used in the fProgram and fErase routines, a value indicating
the internal operating frequency (fop) must be stored at CPUSPD, which is located at RAM address
$0049. The CPUSPD value is the nearest integer of fop (in MHz) times 4. For example, if fop is 4.2
MHz, the CPUSPD value is 17. If fop is 2.1 MHz, the CPUSPD value is 8. Setting a correct CPUSPD
value is very important to program or erase the FLASH successfully.
LADDR — A range specifies the FLASH locations to be read, verified, or programmed. The 16-bit
value in RAM addresses $004A and $004B holds the last address of a range. The addresses
$004A and $004B are the high and low bytes of the last address, respectively. LADDR is used for
Verify and fProgram routines.
DATA — DATA is the first location of the DATA array and is located at RAM address $004C. The
array is used for loading program or verify data. The DATA array must be in the zero page and its
size must match the size of the range to be programmed or verified.
Registers H:X — In the Verify and fProgram routines, registers H and X are initialized with a 16-bit
value representing the first address of a range. High and low bytes of the address are stored to
registers H and X, respectively. In the fErase routine, registers H and X are initialized with an
address which is within the page to be erased or with the address of the block protect register
(FLBPR) if the entire array to be erased.
19.4.2 How to Use the Routines
This section describes the details of each routine. Table 19-10 provides necessary addresses used in the
on-chip FLASH routines for each MCU type and summarizes the five routines.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
251
Table 19-10. Summary of On-Chip FLASH Support Routines
Jump Table
Address
Routine
Description
Internal
Operating
Frequency
GetByte
PutByte
Verify
fProgram
fErase
$1000
$100C
$1003
$1009
$1006
Get a data byte
serially through
PTA0
Send a data byte
serially through
PTA0
Read and/or
compare a
FLASH range
Program a FLASH
range
Erase a PAGE or
entire array
N/A
N/A
N/A
1.0 MHz to
8.0 MHz
1.0 MHz to
8.0 MHz
Pullup on PTA0
Pullup on PTA0
For send-out option, N/A
pullup on PTA0
PTA0: Input
(DDRA0 = 0)
PTA0: Input and 0
data bit
(DDRA0 = 0,
PTA0 = 0)
A: data to be sent
H:X: First address
of range
LADDR: Last
address of range
A: A = $00 for
send-out option or
A  $00 for
compare option.
For send-out option,
PTA0: Input and 0
data bit
(DDRA0 = 0,
PTA0 = 0)
For compare option,
DATA array: Load
data to be
compared against
FLASH read data
H:X: First address
H:X: Page erase —
of range
an address within
LADDR: Last
the page
address of range
Mass erase =
CPUSPD: the
FLBPR
nearest integer fop CPUSPD: the
nearest integer fop
(in MHz) times 4
Data array:
(in MHz) times 4
Load data to be
programmed
A: Data received
A, X: No change
through PTA0
PTA0: Input and 0
C-bit: Framing error
data bit
indicator
(DDRA0 = 0,
(error: C = 0)
PTA0 = 0)
A: Checksum
H:X: Next FLASH
address
C-bit: Verify result
indicator
(success:
C = 1)
DATA array: Data
replaced with
FLASH read data
(compare option)
H:X: Next FLASH
address
H:X: No change
I bit is preserved
I bit is preserved
I bit is preserved
I bit is set, then
restored to entry
condition on exit
I bit is set, then
restored to entry
condition on exit
Not Serviced
Not Serviced
Serviced
Serviced
Serviced
(fop)
Hardware
Requirement
Entry
Conditions
Exit
Conditions
I Bit
COP
N/A
Continued on next page
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
252
Freescale Semiconductor
Table 19-10. Summary of On-Chip FLASH Support Routines (Continued) (Continued)
GetByte
Subroutines
Called
PutByte
fProgram
(None)
fErase
(None)
(None)
PutByte for
send-out option
N/A
N/A
LADDR (2 bytes),
CPUSPD, LADDR
DATA array (no
(2 bytes), DATA
size limitation as
array (maximum
long as in the zero
32 bytes)
page)
CPUSPD
6 bytes
6 bytes
9 bytes for verify
option
13 bytes for
send-out option
8 bytes
RAM
Variable
Stack Used
(Including the
Routine’s Call)
Verify
10 bytes
(None)
19.4.2.1 GetByte
GetByte is a routine that receives a byte on the general-purpose I/O PTA0, and the received value is
returned to the calling routine in the accumulator (A). This routine is also used in monitor mode so that it
expects the same non-return-to-zero (NRZ) communication protocol and baud rates.
This routine detects a framing error when a STOP bit is not detected. If the carry (C) bit of the condition
control register (CCR) is cleared after returning from this routine, a framing error occurred during the data
receiving process. Therefore, the data in A is not reliable. The user software is responsible for handling
such errors.
Interrupts are not masked (the I bit is not set) and the COP is not serviced in the GetByte routine. User
software should ensure that interrupts are blocked during character reception.
The baud rate is defined by fop divided by a constant value. In the case of the MC68HC908EY16A, the
baud rate is fop divided by 256. When the internal operating frequency is 2.4576 MHz, the baud rate is
2.4576 MHz/256 = 9600.
To use this routine, some hardware setup is required. The general-purpose I/O PTA0 must be pulled up.
For more information, refer to 19.3 Monitor Module (MON).
Entry Condition
PTA0 must be configured as an input and pulled up in hardware.
Exit Condition
A — Contains data received from PTA0.
C bit — Usually the C bit is set, indicating proper reception of the STOP bit. However, if the C bit is clear,
a framing error occurred. Therefore, the received byte in A is not reliable. Example 19-1 shows how to
receive a byte serially on PTA0.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
253
Example 19-1. Receiving a Byte Serially
GetByte:
equ
$1000
;EY16A/8A GetByte jump address
bclr 0,DDRA
;Configure port A bit 0 as an input
jsr
bcc
;Call GetByte routine
;If C bit is clear, framing error
; occurred. Take a proper action
GetByte
FrameError
NOTE
After GetByte is called, the program will remain in this routine until a START
bit (0) is detected and a complete character is received.
19.4.2.2 PutByte
PutByte is a routine that receives a byte on the general-purpose I/O PTA0. The sent value must be loaded
into the accumulator (A) before calling this routine. This routine is also used in the monitor mode.
Therefore, it uses the same non-return-to-zero (NRZ) communication protocol. The communication baud
rates are the same as those described in GetByte.
To use this routine, some hardware setup is required. The general-purpose I/O PTA0 must be pulled up
and configured as an input and the PTA0 data bit must be initialized to 0.
Interrupts are not masked and the COP is not serviced in the PutByte routine. User software should
ensure that interrupts are blocked during character transmission.
Entry Condition
A — Contains data sent from PTA0
PTA0 — This pin must be configured as an input and pulled up in hardware and the PTA0 data bit must
be initialized to 0.
Exit Condition
A and X are restored with entry values.
Example 19-2 shows how to send a byte ($55) serially on PTA0.
Example 19-2. Sending a Byte Serially
PutByte:
equ
$100C
;EY16A/8A PutByte jump address
bclr
bclr
lda
jsr
0,DDRA
0,PTA
#$55
PutByte
;Configure port A bit 0 as an input
;Initialize data bit to zero PTA0=0
;Load sent data $55 to A
;Call PutByte routine
19.4.2.3 Verify
When using the Verify routine, the user must select one of the function options summarized in
Table 19-11. See Verify Routine Options for details.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
254
Freescale Semiconductor
Table 19-11. Verify Routine Options
Option
Description
Send-out option
Used to read a range of FLASH locations and to send the read data to a
host through PTA0 by using the PutByte routine.
Compare option
Used to read a range of FLASH locations and to compare the read data
against the DATA array
Verify Routine Options
•
•
Send-Out Option — If the accumulator (A) is initialized with $00 at the routine entry, the read data
will be sent out serially through PTA0. The communication baud rate is the same as the baud rate
described in the PutByte routine. When this option is selected, the PTA0 must be pulled up and
configured as an input and the PTA0 data bit must be initialized to 0.
Compare Option — If A is initialized with a non-zero value, the read data is compared against the
DATA array for each byte of FLASH and the DATA array is replaced by the data read from FLASH.
If the data does not match the corresponding value, the data read from FLASH can be confirmed
in the DATA array. All data in the DATA array must be in the zero page, but a range can be beyond
a row size or a page size.
Carry (C) Bit and Checksum
The first and last addresses of the range to be read and/or compared are specified as parameters in
registers H:X and LADDR, respectively. In the compare option, the carry (C) bit of the condition code
register (CCR) is set if the data in the specified range is verified successfully against the data in the DATA
array. However when the send-out option is selected, the status of the C bit is meaningless because this
function does not include the compare operation. Both options calculate a checksum on data read in the
range. This checksum, which is the LSB of the sum of all bytes in the entire data collection, is stored in A
upon return from the function.
Interrupts are not masked. The COP is serviced in Verify. The first COP is serviced at 24 bus cycles after
this routine is called in the user software. However, the COP timeout might still occur in the send-out
option if the COP is configured for a short timeout period.
Entry Condition
H:X — Contains the beginning address in a range.
LADDR — Contains the last address in a range.
A — When A contains $00, read data is sent out via PTA0 (send-out option is selected). When A contains
a non-zero value, read data is verified against the DATA array (compare option is selected).
DATA array — Contains data to be verified against FLASH data. For the send-out option, the DATA array
is not used.
PTA0 — When the send-out option is selected, this pin must be configured as an input and pulled up in
hardware and PTA0 must be initialized to 0.
Exit Condition
A — Contains a checksum value.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
255
H:X — Contains the address of the next byte immediately after the range read.
C bit — Indicates the Verify result (only applies to the compare option).
• When the C bit is set, the verify succeeded.
• When the C bit is cleared, the verify failed.
DATA array — Replaced with data read from FLASH when the compare option is selected.
Example 19-3 shows how to use the compare option. Example 19-4 shows how to use the send-out
option.
Example 19-3. Compare Option
Verify:
equ
$1003
;EY16A/8A Verify jump address
LADDR:
DATA:
equ
equ
$004A
$004C
;Define LADDR address (2 bytes)
;Define DATA start address
ldhx #$0000
lda #$AA
;Index offset into DATA array
;Initial data value to store in array
Data_load:
coma
sta DATA,x
aix #1
cphx #$20
bne Data_load
ldhx #$C01F
sthx LADDR
ldhx #$C000
lda
#$55
jsr
bcc
Verify
Error
;Fill DATA array, 32 bytes data,
; to compare against programmed FLASH
; data (In this example comparing data
; is $55, $AA, $55, $AA....)
;Load last address of range to
; LADDR
;Load beginning address of range
; to H:X
;Write non-zero value to A to select
; the compare option
;Call Verify routine
;If bit C is cleared, compare failed
; Take a proper action
; A contains a checksum value
Example 19-4. Send-Out Option
Verify:
equ
$1003
;EY16A/8A Verify jump address
DATA:
equ
$004C
;Define DATA start address
bclr
bclr
ldhx
sthx
ldhx
0,DDRA
0,PTA
#$C025
LADDR
#$C010
;Configure Port A bit 0 as an input
;Initialize data bit to zero PTA0=0
;Load last address of range to
; LADDR
;Load beginning address of range
; to H:X
;A=0 to select send-out option
;Call Verify routine
; A contains a checksum value
clra
jsr Verify
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
256
Freescale Semiconductor
19.4.2.4 fProgram
fProgram is used to program a range of FLASH locations with data loaded into the DATA array. All bytes
that will be programmed must be in the same row. Programming data is passed to fProgram in the DATA
array. All data in the DATA array must be in the zero page. The size of the DATA array must match the
size of a specified programming range. This routine supports an internal operating frequency between 1.0
MHz and 8.0 MHz.
For this split-gate FLASH, the programming algorithm requires a programming time (tprog) between 30 s
and 40 s. Table 19-12 shows how tprog is adjusted by a CPUSPD value in this routine. The CPUSPD
value is the nearest integer of fop (in MHz) multiplied by 4. For example, if fop is 2.4576 MHz, the CPUSPD
value is 10 ($0A). If fop is 8.0 MHz, the CPUSPD value is 32 ($20).
Table 19-12. tprog vs. Internal Operating Frequency
Internal Operating Freq. (fop)
CPUSPD
tprog (Cycles)
tprog
Case 1
1.0 MHz  fop  1.125 MHz
4
38
33.8 s  tprog  38.0 s
Case 2
1.125 MHz  fop  8.0 MHz
5 to 32
8 x CPUSPD + 5
32.6 s  tprog  40.0 s
All programming is done using one programming algorithm. The algorithm allows for programming a
single byte in each pass through it (one-byte programming method). Or, a whole row may be programmed
by looping within the algorithm to write all the values in the row (row programming method).
• When the COPD bit in CONFIG1 is cleared and COP is therefore enabled, care must be taken to
keep any programming operation from interfering with the servicing of the COP. In this case, each
FLASH byte in the range is programmed using the one-byte programming method. Therefore,
there are no limitations on range size and row/page boundary, but the total time to program multiple
bytes is longer than the row programming method.
• When COPD bit is set (COP is disabled) and all programming addresses are in the same row, all
FLASH bytes can be programmed at the same time using the row programming method. In this
way, the FLASH can be programmed quickly.
• When COPD bit is set (COP is disabled) and a program range extends beyond a row or page, each
FLASH byte in the range is programmed with the one-byte programming method until the
beginning of the last row is reached. Then the bytes in the last row are programmed using the row
programming method. However in this case, a programming range can not cross a boundary from
$xxFF to $xx00. If a range crosses this boundary, programming data will not be guaranteed.
In fProgram, the high programming voltage time is enabled for less than 125 s when programming a
single byte at any internal operating frequency between 1.0 MHz and 8.0 MHz. Therefore, even when a
row is programmed by 32 separate single-byte programming operations, the cumulative high voltage
programming time is less than the maximum tHV (4 ms). The tHV is defined as the cumulative high voltage
programming time to the same row before the next erase. For more information, refer to the memory
characteristics in Chapter 20 Electrical Specifications.
This routine does not confirm that all bytes in the specified range are erased prior to programming. Nor
does this routine perform a verification after programming, so there is no return confirmation that
programming was successful. To program data successfully, the user software is responsible for these
verifying operations. The Verify routine can be used to compare a programmed FLASH range against the
DATA array.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
257
Interrupts are masked (I bit is set) during a programming operation. When returning from this routine, I bit
is restored to the entry condition. If the COP is enabled (COPD = 0), the COP is serviced in this routine.
The first COP is serviced at 42 bus cycles after this routine is called in the user software. When the COP
is disabled (COPD = 1), this row programming method is the fastest way to program the FLASH.
Entry Condition
H:X — Contains the beginning address in a range.
LADDR — Contains the last address in a range.
CPUSPD — Contains the nearest integer value of fop (in MHz) times 4.
DATA array — Contains the data values to be programmed into FLASH.
Exit Condition
H:X — Contains the address of the next byte after the range just programmed.
Example 19-5 shows how to program one full 32-byte row:
Example 19-5. Programming a Row
fProgram: equ
$1009
;EY16A/8A fProgram jump address
CPUSPD:
LADDR:
DATA:
$0049
$004A
$004C
;Define CPUSPD addrss
;Define LADDR address (2 bytes)
;Define DATA start address
equ
equ
equ
ldhx #$0000
lda #$AA
;Index offset into DATA array
;Initial data value (inverted)
coma
sta DATA,x
;Alternate between $55 and $AA
;Fill DATA array, 32 bytes data,
; values to program into FLASH
; (ie. 55, AA, 55, AA....)
Data_load:
aix #1
cphx #$20
bne Data_load
mov
ldhx
sthx
ldhx
#$0A,CPUSPD
#$C01F
LADDR
#$C000
jsr
fProgram
;fop = 2.4576MHz in this example
;Load last address of the row
; to LADDR
;Load beginning address of the
; row to H:X
;Call fProgram routine
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
258
Freescale Semiconductor
fProgram can be used to program a range less than 32 bytes. Example 19-6 shows how to program $55
and $AA at location $E004 and $E005, respectively.
Example 19-6. Programming a Range Smaller than a Row
fProgram: equ
$1009
;EY16A/8A fProgram jump address
CPUSPD:
LADDR:
DATA:
$0049
$004A
$004C
;Define CPUSPD addrss
;Define LADDR address (2 bytes)
;Define DATA start address
equ
equ
equ
ldhx #$55AA
sthx DATA
mov
ldhx
sthx
ldhx
jsr
#$18,CPUSPD
#$E005
LADDR
#$E004
fProgram
;fop = 6.0MHz in this example
;Load last address to LADDR
;Load beginning address to H:X
;Call fProgram routine
19.4.2.5 fErase
fErase can be called to erase a page (64 bytes) or a whole array of FLASH. When the address of the
FLASH block protect register is passed to fErase, the entire array is erased (MASS). Any other valid
FLASH address selects the page erase. This routine supports an internal operating frequency between
1.0 MHz and 8.0 MHz.
In this routine, both PAGE erase time (tErase) and MASS erase time (tMErase) are set between 4 ms and
5.5 ms. The CPUSPD value is the nearest integer of fop (in MHz) times 4. For example if fop is 3.1 MHz,
the CPUSPD is 12 ($0C). If fop is 4.9152 MHz, the CPUSPD is 20 ($14).
Interrupts are masked (I bit is set) during an erasing operation. When returning from this routine, I bit is
restored to the entry condition, and the COP is serviced in ERARNGE. The first COP is serviced on
(51+3xCPUSPD) bus cycles after this routine is called in the user software.
Entry Condition
H:X — Contains an address within a desired erase page or FLBPR for mass erase.
CPUSPD — Contains the nearest integer value of fop (in MHz) times 4.
Exit Condition
None
Example 19-7 shows how to erase an entire array.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
259
Example 19-7. Erasing an Entire Array
fErase:
equ
$1006
;EY16A/8A fErase jump address
CPUSPD:
equ
$0049
;Define CPUSPD addrss
mov #$08,CPUSPD
ldhx #FLBPR
jsr fErase
;fop = 2.0MHz in this example
;Load FLBPR address to H:X
;Call fErase routine
Example 19-8 shows how to erase a page from $E100 through $E13F.
Example 19-8. Erasing a Page
fErase:
equ
$1006
;EY16A/8A fErase jump address
CPUSPD:
equ
$0049
;Define CPUSPD addrss
mov #$0E,CPUSPD
ldhx #$E121
jsr
fErase
;fop = 4.9152MHz in this example
;Load any address within the
; page to H:X
;Call fErase routine
If the FLASH locations that you want to erase are protected due to the value in the FLASH block protect
register (FLBPR), the erase operation will not be successful. However when a high voltage (Vtst) is applied
to the IRQ pin, the block protection is bypassed.
When the FLASH security check fails in the normal monitor mode, the FLASH can be re-accessed by
erasing the entire FLASH array. To override the FLASH security mechanism and erase the FLASH array
using this routine, registers H and X must contain the address of the FLASH block protect register
(FLBPR).
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
260
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 5V 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).
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
261
20.3 Functional Operating Range
Characteristic
Symbol
Value
Unit
TA
–40 to 125
C
VDD
5.0 10%
3.0 10%
V
Operating temperature range
Operating voltage range
20.4 Thermal Characteristics
Symbol
Value
Unit
Thermal resistance
QFP (32 pins)
Characteristic
JA
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
PD x (TA + 273C)
+ PD2 x JA
W/C
TA + (PD x JA)
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 5V DC Electrical Characteristics
Characteristic(1)
Symbol
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
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
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)
Unit
V
V
— Continued on next page
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
262
Freescale Semiconductor
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
A
mA
A
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 125C
Stop (LVI on), –40C to 125C
IDD
I/O ports Hi-Z leakage current(8)
IIL
–10
—
+10
A
Input current – RST, OSC1
IIn
–1
—
+1
A
Capacitance
Ports (as input or output)
COut
CIn
—
—
—
—
12
8
pF
POR rearm voltage(9)
VPOR
750
—
—
mV
POR rise time ramp rate
RPOR
0.035
—
—
V/ms
Monitor mode entry voltage
VTST
VDD+ 3.5
9.1
V
Low-voltage inhibit reset, trip falling voltage(10)
VTRIPF
3.90
4.30
4.50
V
(11)
VTRIPR
4.00
4.40
4.60
V
Low-voltage inhibit reset/recover hysteresis(12)
VHYS
—
90
—
mV
Pullup resistor — PTA0–PTA6/SS(13), IRQ, RST
RPU
24
—
48
k
RPD
24
36
48
k
Low-voltage inhibit reset, trip rising voltage
Pulldown resistor — PTA0–PTA4
(14)
1. VDD = 5.5 Vdc to 4.5 Vdc, VSS = 0 Vdc, TA = –40C to +125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. These values assume the LVI is operating in 5-V mode (i.e. LVI5OR3 bit is set to 1).
11. These values assume the LVI is operating in 5-V mode (i.e. LVI5OR3 bit is set to 1).
12. These values assume the LVI is operating in 5-V mode (i.e. LVI5OR3 bit is set to 1).
13. PTA0–PTA4 pullup resistors are for interrupts only and are only enabled when the keyboard is in use.
14. Pulldown resistors available only when KBIx is enabled with KBIPx = 1.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
263
20.6 5V Control Timing
Symbol
Characteristic(1)
Min
Max
Unit
32
1
8
dc(4)
1
8
100
8
32
100
8
32
kHz
MHz
MHz
kHz
MHz
MHz
Frequency of operation (2)
Crystal option (EXTSLOW = 1, RNGSEL = 0)
Crystal option (EXTSLOW = 0, RNGSEL = 1)
Crystal option (EXTSLOW = 0, RNGSEL = 0)
External clock option (EXTSLOW = 1, RNGSEL = 0)(3)
External clock option (EXTSLOW = 0, RNGSEL = 1)
External clock option (EXTSLOW = 0, RNGSEL = 0)
fOSC
Internal operating frequency
fop
—
8
MHz
Internal clock period (1/fOP)
tcyc
125
—
ns
RST input pulse width low(5)
tIRL
50
—
ns
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
IRQ interrupt pulse width low
(edge-triggered)
(6)
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.
tRL
RST
tILIL
tILIH
IRQ
Figure 20-1. RST and IRQ Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
264
Freescale Semiconductor
20.7 3V DC Electrical Characteristics
Characteristic(1)
Symbol
Min
Typ(2)
Max
VDD –0.3
VDD –1.0
VDD –0.8
—
—
—
—
—
—
—
—
—
—
—
—
0.3
1.0
0.8
Unit
Output high voltage
ILoad = –0.6 mA, all I/O pins
ILoad = –4.0 mA, all I/O pins
ILoad = –10.0 mA, PTA0–PTA6/SS, PTC0–PTC1 only
VOH
Output low voltage
ILoad = 0.5 mA, all I/O pins
ILoad = 6.0 mA, all I/O pins
ILoad = 10.0 mA, PTA0–PTA6/SS, 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
IINJ
–2
—
+2
mA
IINJTOT
–25
—
+25
mA
—
—
—
—
—
—
5.7
1.8
0.52
0.15
1.6
0.15
TBD
TBD
TBD
TBD
TBD
TBD
mA
mA
A
mA
A
mA
Total dc current injection (sum of all I/O)
V
V
VDD + VDDA supply current
Run(3),(4)
Wait(4), (5)
Stop (LVI off) @ 25°C(4), (6)
Stop (LVI on) @ 25°C
Stop (LVI off), –40°C to 125°C
Stop (LVI on), –40°C to 125°C
IDD
Ports Hi-Z leakage current
IIL
–1
±0.1
+1
mA
Input current – RST, OSC1
IIn
–1
—
+1
A
Capacitance
Ports (as input or output)
CIN
COUT
—
—
—
—
12
8
pF
POR rearm voltage
VPOR
750
—
—
mV
POR rise time ramp rate
RPOR
0.035
—
—
V/ms
Monitor mode entry voltage
VTST
VDD + 2.5
—
9.1
V
Low-voltage inhibit reset, trip falling voltage(7)
VTRIPF
2.35
2.60
2.70
V
Low-voltage inhibit reset, trip rising voltage(7)
VTRIPR
2.45
2.66
2.80
V
VHYS
—
60
—
mV
Pullup resistor — PTA0–PTA6/SS, IRQ, RST (8)
RPU
16
26
36
k
Pulldown resistor — PTA0–PTA4(9)
RPD
16
26
36
k
Low-voltage inhibit reset/recover hysteresis
(7)
1. VDD = 2.7 to 3.3 Vdc, VSS = 0 Vdc, TA = TL to TH, unless otherwise noted.
2. Typical values reflect average measurements at midpoint of voltage range, 25•C only.
3. Run (operating) IDD measured using internal oscillator at its 16-MHz rate. VDD = 3.0 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.
4. All measurements taken with LVI enabled.
5. Wait IDD measured using internal oscillator at its 16-MHz rate. All inputs 0.2 V from rail; no dc loads; less than 100 pF on
all outputs. All ports configured as inputs.
6. Stop IDD is measured with no port pin sourcing current; all modules are disabled. OSCSTOPEN option is not selected.
7. These values assume the LVI is operating in 3-V mode (i.e. LVI5OR3 bit is set to 0)
8. RPU is measured at VDD = 3.0 V.
9. Pulldown resistors available only when KBIx is enabled with KBIPx = 1.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
265
20.8 3V Control Timing
Characteristic(1)
Symbol
Min
Max
Unit
32
1
8
dc(4)
1
8
100
8
16
100
8
16
kHz
MHz
MHz
kHz
MHz
MHz
Frequency of operation (2)
Crystal option (EXTSLOW = 1, RNGSEL = 0)
Crystal option (EXTSLOW = 0, RNGSEL = 1)
Crystal option (EXTSLOW = 0, RNGSEL = 0)
External clock option (EXTSLOW = 1, RNGSEL = 0)(3)
External clock option (EXTSLOW = 0, RNGSEL = 1)
External clock option (EXTSLOW = 0, RNGSEL = 0)
fOSC
Internal operating frequency
fOP
—
4
MHz
Internal operating period (1/fOP)
tCYC
250
—
ns
RST input pulse width low(5)
tRL
200
—
ns
IRQ interrupt pulse width low(6) (edge-triggered)
tILIH
200
—
ns
tILIL
Note(7)
—
tCYC
IRQ interrupt pulse period
1. VDD = 2.7 to 3.3 Vdc, VSS = 0 Vdc, TA = TL to TH; 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. The minimum period is the number of cycles it takes to execute the interrupt service routine plus 1 tCYC.
tRL
RST
tILIL
tILIH
IRQ
Figure 20-2. RST and IRQ Timing
20.9 Internal Oscillator Characteristics
Characteristic(1)
Internal oscillator base frequency(2), (3)
Internal oscillator tolerance
Internal oscillator multiplier(4)
Symbol
Min
Typ
Max
Unit
fINTOSC
230.4
307.2
384
kHz
fOSC_TOL
–25
—
+25
%
N
1
—
127
—
1. VDD = 4.5 to 5.5 Vdc, VSS = 0 Vdc, TA = –40C to +125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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
266
Freescale Semiconductor
20.10 External Oscillator Characteristics
Characteristic(1)
Symbol
External clock option(2)(3)
With ICG clock disabled
With ICG clock enabled
External clock option (EXTSLOW = 1, RNGSEL = 0)(4)
External clock option (EXTSLOW = 0, RNGSEL = 1)(4)
External clock option (EXTSLOW = 0, RNGSEL = 0)(4)
fEXTOSC
External crystal options(7)(8)
External cyrstal option (EXTSLOW = 1, RNGSEL = 0)(4)
External crystal option (EXTSLOW = 0, RNGSEL = 1)(4)
External crystal option (EXTSLOW = 0, RNGSEL = 0)(4)
fEXTOSC
Min
Typ
Max
Unit
dc(5)
—
32 (6)
MHz
60
307.2
8
—
—
—
307.2
8
32(6)
kHz
MHz
MHz
30
1
8
32.768
—
100
8
32
kHz
MHz
MHz
Crystal load capacitance(9)
CL
—
12.5
—
pF
(9)
Crystal fixed capacitance
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
M
k
RB
—
1
—
M
Rs
Rs
Rs
—
—
—
20
10
0
—
—
—
k
k
k
EXTSLOW = 0
Feedback bias resistor(9)
Series resistor (9)(10)
fOSCXCLK = 1 MHz
fOSCXCLK = 4 MHz
fOSCXCLK = 8 to 25 MHz
1. VDD = 4.5 to 5.5 Vdc, VSS = 0 Vdc, TA = –40C to +125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.
10. Not required for high-frequency crystals
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
267
20.11 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.
20.11.1 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 125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 125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
20.12 ADC10 Characteristics
Characteristic
Conditions
Supply voltage
Absolute
Supply Current
ADLPC = 1
ADLSMP = 1
ADCO = 1
VDD < 3.3 V (3.0 V Typ)
Supply Current
ADLPC = 1
ADLSMP = 0
ADCO = 1
Supply Current
ADLPC = 0
ADLSMP = 1
ADCO = 1
Supply Current
ADLPC = 0
ADLSMP = 0
ADCO = 1
VDD < 5.5 V (5.0 V Typ)
Symbol
Min
Typ(1)
Max
Unit
VDD
2.7
—
5.5
V
—
55
—
—
75
—
—
120
—
—
175
—
—
140
—
—
180
—
—
340
—
—
440
615
IDD
(2)
IDD
(2)
IDD
(2)
IDD
(2)
VDD < 3.3 V (3.0 V Typ)
VDD < 5.5 V (5.0 V Typ)
VDD < 3.3 V (3.0 V Typ)
VDD < 5.5 V (5.0 V Typ)
VDD < 3.3 V (3.0 V Typ)
VDD < 5.5 V (5.0 V Typ)
Comment
A
A
A
A
— Continued on next page
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
268
Freescale Semiconductor
Characteristic
Conditions
Symbol
High speed (ADLPC = 0)
fADCK
ADC internal clock
Low power (ADLPC = 1)
Conversion time (4)
10-bit Mode
Short sample (ADLSMP = 0)
Conversion time (4)
8-bit Mode
Short sample (ADLSMP = 0)
Sample time
Long sample (ADLSMP = 1)
Long sample (ADLSMP = 1)
Short sample (ADLSMP = 0)
Long sample (ADLSMP = 1)
tADC
tADC
tADS
Min
Typ(1)
Max
0.40(3)
—
2.00
0.40(3)
—
1.00
19
19
20
39
39
40
16
16
17
36
36
37
4
4
4
24
24
24
Unit
Comment
MHz
tADCK = 1/fADCK
tADCK cycles
tADCK cycles
tADCK cycles
Input voltage
VADIN
VSS
—
VDD
V
Input capacitance
CADIN
—
7
10
pF
Not tested
Input impedance
RADIN
—
5
15
k
Not tested
RAS
—
—
10
k
External to
MCU
mV
VREFH/2N
LSB
Includes
quantization
Analog source
impedance
Ideal resolution
(1 LSB)
10-bit mode
Total unadjusted
error
10-bit mode
8-bit mode
8-bit mode
10-bit mode
Differential
non-linearity
8-bit mode
RES
ETUE
DNL
1.758
5
5.371
7.031
20
21.48
0
1.5
2.5
0
0.7
1.0
0
0.5
—
0
0.3
—
LSB
Monotonicity and no-missing-codes guaranteed
Integral non-linearity
Zero-scale error
Full-scale error
Quantization error
Input leakage error
10-bit mode
8-bit mode
10-bit mode
8-bit mode
10-bit mode
8-bit mode
10-bit mode
8-bit mode
10-bit mode
8-bit mode
INL
EZS
EFS
EQ
EIL
0
0.5
—
0
0.3
—
0
0.5
—
0
0.3
—
0
0.5
—
0
0.3
—
—
—
0.5
—
—
0.5
0
0.2
5
0
0.1
1.2
LSB
LSB
VADIN = VSS
LSB
VADIN = VDD
LSB
8-bit mode is
not truncated
LSB
Pad leakage(5) *
RAS
1. Typical values assume VDD = 5.0 V, temperature = 25•C, fADCK = 1.0 MHz unless otherwise stated. Typical values are for
reference only and are not tested in production.
2. Incremental IDD added to MCU mode current.
3. Values are based on characterization results, not tested in production.
4. Reference the ADC module specification for more information on calculating conversion times.
5. Based on typical input pad leakage current.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
269
20.13 5V 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 20-3 and Figure 20-4.
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
270
Freescale Semiconductor
20.14 3V 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 –35
1/2 tcyc –35
64 tcyc
—
ns
ns
5
Clock (SPSCK) low time
Master
Slave
tSCKL(M)
tSCKL(S)
tcyc –35
1/2 tcyc –35
64 tcyc
—
ns
ns
6
Data setup time (inputs)
Master
Slave
tSU(M)
tSU(S)
40
40
—
—
ns
ns
7
Data hold time (inputs)
Master
Slave
tH(M)
tH(S)
40
40
—
—
ns
ns
8
Access time, slave(3)
CPHA = 0
CPHA = 1
tA(CP0)
tA(CP1)
0
0
50
50
ns
ns
9
Disable time, slave(4)
tDIS(S)
—
50
ns
10
Data valid time, after enable edge
Master
Slave(5)
tV(M)
tV(S)
—
—
60
60
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 20-3 and Figure 20-4.
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
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
271
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 20-3. SPI Master Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
272
Freescale Semiconductor
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 20-4. SPI Slave Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
273
20.15 Timer Interface Module Characteristics
Characteristic
Timer input capture pulse
Symbol
Min
Max
Unit
tTH, tTL
2
—
tcyc
tTLTL
Note(2)
—
tcyc
tTCL, tTCH
tcyc + 5
—
ns
width(1)
Timer input capture period
Timer input clock pulse width(1)
1. Values are based on characterization results, not tested in production.
2. The minimum period is the number of cycles it takes to execute the interrupt service routine plus 1 tcyc.
tTLTL
tTH
INPUT CAPTURE
RISING EDGE
tTLTL
tTL
INPUT CAPTURE
FALLING EDGE
tTLTL
tTH
tTL
INPUT CAPTURE
BOTH EDGES
tTCH
TCLK
tTCL
Figure 20-5. Timer Input Timing
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
274
Freescale Semiconductor
20.16 Memory Characteristics
Characteristic
Symbol
Min
Typ
Max
Unit
VRDR
1.3
—
—
V
—
1
—
—
MHz
VPGM/ERASE
2.7
—
5.5
V
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
—
—
s
FLASH high-voltage hold time
tNVH
5
—
—
s
FLASH high-voltage hold time (mass erase)
tNVHL
100
—
—
s
FLASH program hold time
tPGS
5
—
—
s
FLASH program time
tPROG
30
—
40
s
FLASH return to read time
tRCV(2)
1
—
—
s
FLASH cumulative program hv period
tHV(3)
—
—
4
ms
—
10 k
100 k
—
Cycles
—
15
100
—
Years
RAM data retention voltage
FLASH program bus clock frequency
FLASH PGM/ERASE supply voltage (VDD)
FLASH read bus clock frequency
FLASH endurance(4)
FLASH data retention time
(5)
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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
275
20.17 EMC Performance
EMC performance is highly dependant on the environment in which the MCU resides. Board design and
layout, circuit topology choices, location and characteristics of external components as well as MCU
software operation all play a significant role in EMC performance. The system designer should consult
Freescale applications notes such as AN2321, AN1050, AN1263, AN2764, and AN1259 for advice and
guidance specifically geared toward EMC performance.
20.17.1 Radiated Emissions
Microcontroller radiated RF emissions are measured from 150 kHz to 1 GHz using the TEM/GTEM Cell
method in accordance with the IEC 61967-2 and SAE J1752/3 standards. The measurement is performed
with the microcontroller installed on a custom EMC evaluation board including I/O pin loading and board
layer usage while running specialized EMC test software all designed in compliance with the standards.
The radiated emissions from the microcontroller are measured in a TEM cell in two package orientations
(North and East). For more detailed information concerning the evaluation conditions and setup, please
refer to the EMC Evaluation Report for this device.
The maximum radiated RF emissions of the tested configuration in all orientations are less than or equal
to the reported emissions levels.
Parameter
Radiated emissions,
electric field
Symbol
Conditions
VDD = 5 V
VRE_TEM
Conditions — TBD
TA = +25oC
32 QFP
Frequency
fosc/fCPU
Level(1)
(Max)
0.15 – 50 MHz
TBD
50 – 150 MHz
TBD
150 – 500 MHz
TBD
Unit
dBV
4/8
500 – 1000 MHz
TBD
IEC Level
TBD
—
SAE Level
TBD
—
1. Data based on qualification test results.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
276
Freescale Semiconductor
20.17.2 Conducted Transient Susceptibility
Microcontroller transient conducted susceptibility is measured in accordance with an internal Freescale
test method. The measurement is performed with the microcontroller installed on a custom EMC
evaluation board and running specialized EMC test software designed in compliance with the test
method. The conducted susceptibility is determined by injecting the transient susceptibility signal on each
pin of the microcontroller. The transient waveform and injection methodology are in accordance with IEC
61000-4-2 (ESD) and IEC 61000-4-4 (EFT/B). The transient voltage required to cause performance
degradation on any pin in the tested configuration is greater than or equal to the reported levels unless
otherwise indicated by footnotes below the table.
Parameter
Symbol
Conducted susceptibility, electrical
fast transient/burst (EFT/B)
Conditions
fOSC/fCPU
VDD = 5 V
VCS_EFT
TA = +25oC
32 QFP
VCS_ESD
TA = +25oC
32 QFP
Amplitude(1)
(Min)
A
TBD
B
TBD
C
TBD
D
TBD
A
TBD
B
TBD
C
TBD
D
TBD
4/8
VDD = 5 V
Conducted susceptibility,
electrostatic discharge (ESD)
Result
Unit
kV
4/8
kV
1. Data based on qualification test results. Not tested in production.
2. These pins demonstrate particularly low levels of performance:
The susceptibility performance classification is described in the following table.
Result
Performance Criteria
A
No failure
The MCU performs as designed during and after exposure.
B
Self-recovering
failure
The MCU does not perform as designed during exposure. The MCU returns
automatically to normal operation after exposure is removed.
C
Soft failure
The MCU does not perform as designed during exposure. The MCU does not return
to normal operation until exposure is removed and the RESET pin is asserted.
D
Hard failure
The MCU does not perform as designed during exposure. The MCU does not return
to normal operation until exposure is removed and the power to the MCU is cycled.
E
Damage
The MCU does not perform as designed during and after exposure. The MCU cannot
be returned to proper operation due to physical damage or other permanent
performance degradation.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
277
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
278
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
LQFP.
21.2 Ordering Information
Table 21-1. Ordering Numbers
Operating
Temperature Range
Part Number(1)
Automotive Part Numbers(2)
S908EY16AMFJE
–40•C to +125•C
S908EY16AVFJE
–40•C to +105•C
S908EY16ACFJE
–40•C to +85•C
Consumer and Industrial Part Numbers
MC908EY16AMFJE
–40•C to +125•C
MC908EY16AVFJE
–40•C to +105•C
MC908EY16ACFJE
–40•C to +85•C
1. FJ = 32-pin low-profile quad flat package
2. “S” part numbers are tested in accordance with the AEC-Q100 (Automotive Electronics
Council) standard.
FAMILY
PACKAGE
DESIGNATOR
MC908 EY 16 A X XX E
MEMORY
Pb FREE
SIZE
TEMPERATURE
RANGE
Figure 21-1. Device Numbering System
21.3 Package Dimensions
Refer to the following pages for detailed package dimensions.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
279
Package drawing 98ASH70029A page 1 of 3
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Freescale Semiconductor
Package drawing 98ASH70029A page 2 of 3
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Package drawing 98ASH70029A page 3 of 3
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Appendix A
MC68HC908EY8A
A.1 Introduction
The MC68HC908EY8A 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 MC68HC908EY8A 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
• 384 bytes of random-access memory (RAM)
• 36 bytes of user-defined vectors
• 350 bytes of monitor routines in read-only memory (ROM)
• 674 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.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
283
INTERNAL BUS
M68HC08 CPU
USER FLASH
7680 BYTES
5-BIT KEYBOARD
INTERRUPT MODULE
PTA3/KBD3/RxD(1)
PTA2/KBD2/TxD(1)
PTA0/KBD0
PTB7/AD7/TBCH1
FLASH PROGRAMMING (BURN-IN) ROM
674 BYTES
USER FLASH VECTOR SPACE
36 BYTES
ENHANCED
SERIAL COMMUNICATION
INTERFACE MODULE
IRQ
SINGLE EXTERNAL IRQ
MODULE
VREFH
VDDA
VREFL
VSSA
8-CHANNEL, 10-BIT
ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
SERIAL PERIPHERAL
INTERFACE MODULE
CONFIGURATION REGISTER
MODULE
PERIODIC WAKEUP
TIMEBASE MODULE
DDRC
PORT C
DDRD
PORT D
COMPUTER OPERATING
PROPERLY MODULE
DDRE
SYSTEM
INTEGRATION MODULE
PRESCALER
MODULE
PTB5/AD5/SPSCK(1)
PTB4/AD4/MOSI(1)
PTB3/AD3/MISO(1)
PTB2/AD2
PTB1/AD1
PTB0/AD0
ARBITER
MODULE
INTERNAL CLOCK
GENERATOR MODULE
PORT B
PTB6/AD6/TBCH0
2-CHANNEL TIMER INTERFACE
MODULE B
PORT E
MONITOR ROM
350 BYTES
VDD
VSS
PTA5/SPSCK(1)
PTA4/KBD4
PTA1/KBD1
2-CHANNEL TIMER INTERFACE
MODULE A
USER RAM
384 BYTES
RST
PORT A
CONTROL AND STATUS REGISTERS
64 BYTES
SINGLE BREAKPOINT
BREAK MODULE
DDRA
ARITHMETIC/LOGIC
UNIT (ALU)
DDRB
CPU
REGISTERS
PTA6/SS
PTA6/SS(1)
PTC4/OSC1
PTC3/OSC2
PTC2/MCLK/SS(1)
PTC1/MOSI(1)
PTC0/MISO(1)
PTD1/TACH1
PTD0/TACH0
PTE1/RxD(1)
PTE0/TxD(1)
POWER-ON RESET
MODULE
SECURITY
MODULE
BEMF MODULE
NOTE:
1. The locations of the ESCI and SPI pins are user selectable using CONFIG3 option bits.
Figure A-1. MC68HC908EY8A Block Diagram
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
284
Freescale Semiconductor
$FE02
Reserved
$FE03
SIM Break Flag Control Register (SBFCR)
$003F
$FE04
Interrupt Status Register 1 (INT1)
$0040
$FE05
Interrupt Status Register 2 (INT2)
$FE06
Interrupt Status Register 3 (INT3)
$FE07
Reserved
$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)
$0000
I/O Registers
64 Bytes

RAM
384 Bytes

$01BF
$01C0
Unimplemented
3648 Bytes

$0FFF
$1000

Jump Table for FLASH Routines
32 Bytes
$101F
$FE0D
$1020
Integrated FLASH Program
and Erase Routines
512 Bytes

$121F
$FE1F
$FE20

$1220
Unimplemented
350 Bytes

$137D
$137E
Integrated FLASH Program
and Erase Routines
130 Bytes

$13FF
$1400
Reserved
19 Bytes

Monitor ROM 350 Bytes
FF7D
$FF7E
FLASH Block Protect Register (FLBPR)
$FF7F
Unimplemented
$FF80
5V ICG Trim Value (Optional) (ICGT5V)
$FF81
3V ICG Trim Value (Optional) (ICGT3V)
$FF82
Unimplemented
52,224 Bytes


$DFFF
$FFDB
$E000
$FFDC
FLASH Memory
7,680 Bytes

$FDFF

Unimplemented
90 Bytes
FLASH Vectors
36 Bytes
$FFFF
$FE00
SIM Break Status Register (SBSR)
$FE01
SIM Reset Status Register (SRSR)
Note:
Locations $FFF6–$FFFD are used for the eight
security bytes.
Figure A-2. MC68HC908EY8A Memory Map
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
285
A.4 Ordering Information
Table A-1. Ordering Numbers
Operating
Temperature Range
Part Number(1)
Automotive Part Numbers(2)
S908EY8AMFJE
–40•C to +125•C
S908EY8AVFJE
–40•C to +105•C
S908EY8ACFJE
–40•C to +85•C
Consumer and Industrial Part Numbers
MC908EY8AMFJE
–40•C to +125•C
MC908EY8AVFJE
–40•C to +105•C
MC908EY8ACFJE
–40•C to +85•C
1. FJ = 32-pin low-profile quad flat package
2. “S” part numbers are tested in accordance with the AEC-Q100 (Automotive Electronics
Council) standard.
FAMILY
MC908 EY
8
PACKAGE
DESIGNATOR
A X XX E
MEMORY
Pb FREE
SIZE
TEMPERATURE
RANGE
Figure A-3. Device Numbering System
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
286
Freescale Semiconductor
Appendix B
Differences Between 908EY16A and 908EY16
B.1 Introduction
The 908EY16A is a new revision of the existing 908EY16. The 908EY16A was designed using the latest
HC08 design technology. Emphasis was placed on maintaining compatibility with the existing 908EY16
during the design stage. While this was largely realized, there are a few differences introduced by
customer requested improvements and by the use of the latest, enhanced modules. The purpose of this
appendix is to point out the differences between the two versions of the part.
B.2 Configuration
A CONFIG3 register has been added to allow for new configuration features of the ESCI, SPI, and ICG.
This replaces a reserved register location at address $0009.
Address:
$0009
Bit 7
6
5
4
3
2
1
Bit 0
908EY16:
R
R
R
R
R
R
R
R
908EY16A:
NA
RNGSEL
ESCISRE
SPISRE
MCLKSRE
PORTSRE
ESCISEL
SPISEL
0
1
0
0
0
0
0
0
R
= Reserved
Reset:
Figure B-1. Configuration Register 3 (CONFIG3)
B.2.1 Enhanced Serial Communications Interface Module (ESCI)
Enhanced transmitter functions are available for the local interconnect network (LIN). The LINT bit has
been added to ESCI Baud Rate register. (The bit location was previously reserved.)
Address:
$0016
Bit 7
6
5
4
3
2
1
Bit 0
908EY16:
R
LINR
SCP1
SCP0
R
SCR2
SCR1
SCR0
908EY16A:
LINT
LINR
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
0
0
R
= Reserved
Reset:
Figure B-2. ESCI Baud Rate Register (SCBR)
The transmit and receive pins can be remapped to the PTA2 and PTA3 pins. This is selected in the
CONFIG3 register. The reset state of these bits maps the ESCI transmit and receive to the same pins as
on the 908EY16.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
287
B.2.2 Serial Peripheral Interface Module (SPI)
The four pins associated with the SPI can be remapped to alternate assignments on PTB and PTC. The
alternated assignment is selected in the CONFIG3 register. The reset state of these bits maps the SPI
functions to the same pins as on the 908EY16.
B.2.3 Internal Clock Generator Module (ICG)
An option to allow the use of high frequency (8 – 32 MHz) crystals for the external oscillator has been
added. There is now a range select bit in the CONFIG3 register to select this high frequency range.
B.2.4 Keyboard Interface Module (KBI)
The ability to select whether a keyboard interrupt is triggered by a rising or falling edge has been added.
A reserved register has been replaced with the Keyboard Polarity register (KBIPR) at address $000C.
While the falling edge trigger was the only mode available on the 908EY16, with the 908EY16A you can
set either rising or falling edge and the reset state of the polarity bits will match the original state.
Address: $000C
Bit 7
6
5
4
3
2
1
Bit 0
908EY16:
R
R
R
R
R
R
R
R
908EY16A:
0/NA
0/NA
0/NA
KBIP4
KBIP3
KBIP2
KBIP1
KBIP0
0
0
0
0
0
0
0
0
R
= Reserved
Reset:
Figure B-3. Keyboard Interrupt Polarity Register (KBIPR)
B.2.5 Analog-to-Digital Converter Module (ADC)
The original ADC module has been replaced with the improved ADC10 module. While the modules are
extremely similar, there are some differences that need to be evaluated for impact on existing software.
• The conversion complete (COCO) bit now functions slightly differently. COCO is now always a
read-only bit and will get set regardless of the state of the AIEN bit.
• The divide-by-6 clock selection has been removed. (ADIV2 bit replaced by ADLPC)
• The two left-justified modes for the ADC data format are no longer available.
• A long sample time option has been added to conserve power at the expense of longer conversion
times. This option is selected using the new ADLSMP bit in the ADCLK register. (The bit location
was previously reserved.)
• The ADC10 will now run in stop mode if the ACLKEN bit is set to enable the asynchronous clock
inside the ADC10 module. Utilizing stop mode for an ADC conversion gives the quietest operating
mode to get extremely accurate ADC readings. (The bit location now used by ACLKEN was
unimplemented — it always read as a 0 and writes to that location had no affect.)
• The ADC10 conversion time is now anywhere from 21 ADC clock cycles to 44 ADC clock cycles
depending on ACLKEN. The original ADC module in the 908EY16 had a conversion time of 16 to
17 ADC clock cycles. The bits that control these clocking operations are in the ADCLK register.
These changes are shown in Figure B-4.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
288
Freescale Semiconductor
Address:
$003F
Bit 7
6
5
4
3
2
908EY16:
ADIV2
ADIV1
ADIV0
ADICLK
MODE1
MODE0
R
0/NA
908EY16A:
ADLPC
ADIV1
ADIV0
ADICLK
MODE1
MODE0
ADLSMP
ACLKEN
0
0
0
0
0
0
0
0
R
= Reserved
Reset:
1
Bit 0
Figure B-4. ADC10 Clock Register (ADCLK)
•
Enabling an ADC channel no longer overrides the digital I/O function of the associated pin. To
prevent the digital I/O from interfering with the ADC read of the pin, the data direction bit associated
with the port pin must be set as input.
B.3 Monitor Mode
B.3.1 Monitor Extended Security
An extended security feature has been added to the 908EY16 monitor operation. When the extended
security location is programmed with zero and all 8 byte security matches, the monitor is terminated in an
infinite loop automatically. To unlock extended security, the part must enter monitor mode with failed
security and then the FLASH must be mass-erased to erase the whole FLASH. The extended security
location in the 908EY16A is located at address $FDFF. The user should check this location in their
software to ensure that it will not cause unexpected operation.
B.3.2 Zeroes in Security Bytes
An additional check has been added to the verification of the security bytes. The number of zero bytes
used for the security bytes is limited to 5. More than 5 bytes of zero out of the 8 security bytes will cause
the security check to fail. The user should check the values programmed into locations $FFF6–$FFFD to
ensure that this requirement is not violated.
B.3.3 Forced Monitor Mode Baud Rate
The baud rate used for the 908EY16 Forced Monitor Mode was set at ~6300 baud. In the 908EY16A, this
has been changed to 9600 baud. In addition, the trim value stored in FLASH is used in this mode to ensure
that the tolerance required for communicating at this rate is met.
B.4 Monitor ROM FLASH Programming Routines
B.4.1 Erase
The existing 908EY16 call for erase uses a RAM variable called CTRLBYT to determine whether the call
is for page or mass erase. The 908EY16A routine uses the address passed to determine the page to be
erased. (If ADDR = FLBPR, then a mass erase is performed.) If the parameters for the current 908EY16
routine are passed to the new 908EY16A routine for a page erase, it would work correctly. Using an
existing 908EY16 call to mass erase the 908EY16A will not work.
A minor difference is that the new 908EY16A routine preserves the original state of the I bit while the
existing 908EY16 erase routine sets the I bit and leaves it set on exit.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
Freescale Semiconductor
289
B.4.2 Program
The existing 908EY16 routine uses the row programming method to program any range of addresses
(starting address in H:X and ending address in RAM at LADDR, data to be programmed is in RAM starting
after LADDR). This routine is interrupted every 6 bytes to service the COP.
The 908EY16A routine uses the same variables, so the call setup would be the same. In the 908EY16A,
the COPD bit is checked. If COP servicing is required, then a byte-by-byte algorithm is used to program
the range. If no COP servicing is required, then a combination of byte-by-byte and row programming is
used for a faster algorithm. (In fact, the fastest programming would occur if the start address is the start
of a row and the end address is the end of the same row. Then only the faster row programming method
would be used.) To this point, the routines are compatible. However, there is a range limitation on this
second algorithm. If a range is passed that crosses an xxFF to xx00 boundary, then it will fail. The
byte-by-byte algorithm does not have this limitation.
Table B-1. Programming Routine Comparison
Routine
908EY16
908EY16A
Page erase
I bit set on exit
I bit restored to value at time of call
Mass erase
Selected with CTRBYT
Selected with ADDR = FLBPR
Program
No restrictions on range
to be programmed
If COPD = 1, range cannot include
xxFF/xx00 boundary
The maximum number of bytes required for the stack for all FLASH programming routines is now 13
bytes. In the 908EY16, the maximum number of stack locations was 12 bytes. The user should check to
verify that enough stack space is set aside to accommodate this one byte increase.
MC68HC908EY16A • MC68HC908EY8A Data Sheet, Rev. 2
290
Freescale Semiconductor
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MC68HC908EY16A
Rev. 2, 09/2010