MC68HC908AZ32ACFU MOTOROLA [Motorola, Inc], MC68HC908AZ32ACFU Datasheet - Page 285

• Manufacturer Part Number: MC68HC908AZ32ACFU
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

18.4.3 Output Compare
18.4.3.1 Unbuffered Output Compare
68HC908AZ32A — Rev 0.0
MOTOROLA
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.
Any output compare channel can generate unbuffered output compare
pulses as described in
unbuffered because changing the output compare value requires writing
the new value over the old value currently in the TIMA channel registers.
An unsynchronized write to the TIMA channel registers to change an
output compare value could cause incorrect operation for up to two
counter overflow periods. For example, writing a new value before the
counter reaches the old value but after the counter reaches the new
value prevents any compare during that counter overflow period. Also,
using a TIMA overflow interrupt routine to write a new, smaller output
compare value may cause the compare to be missed. The TIMA may
pass the new value before it is written.
Use the following methods to synchronize unbuffered changes in the
output compare value on channel x:
Freescale Semiconductor, Inc.
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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.
Timer Interface Module A (TIMA)
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Output Compare
on page 285. The pulses are
Timer Interface Module A (TIMA)
Functional Description
Advance Information
285