MC68HC705P9 Datasheet, PDF (115/160 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Timer
I/O Registers
9.7.6 Output Compare Registers
When the value of the 16-bit counter matches the value in the read/write
output compare registers (OCRH and OCRL), the planned TCMP pin
action takes place. Writing to OCRH before writing to OCRL inhibits
timer compares until OCRL is written. Reading or writing to OCRL after
reading the timer status register clears the output compare flag (OCF).
$0016 Bit 7
6
5
4
3
2
1
Bit 0
Read:
Bit 15
14
13
12
11
10
Write:
9
Bit 8
Reset:
Unaffected by reset
$0017 Bit 7
6
5
4
3
2
1
Bit 0
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Write:
Reset:
Unaffected by reset
Figure 9-17. Output Compare Registers (OCRH and OCRL)
To prevent OCF from being set between the time it is read and the time
the output compare registers are updated, use the following procedure:
1. Disable interrupts by setting the I bit in the condition code register.
2. Write to OCRH. Compares are now inhibited until OCRL is written.
3. Clear bit OCF by reading the timer status register (TSR).
4. Enable the output compare function by writing to OCRL.
5. Enable interrupts by clearing the I bit in the condition code register.
MC68HC705P9 — Rev. 4.0
MOTOROLA
Timer
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Technical Data
115