MC68HC708AS48 FREESCALE [Freescale Semiconductor, Inc], MC68HC708AS48 Datasheet - Page 218

• Manufacturer Part Number: MC68HC708AS48
• Description: Advance Information
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Timer Interface (TIM)
16.4.3 Output Compare
16.4.3.1 Unbuffered Output Compare
Advance Information
218
With the output compare function, the TIM 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 TIM can set, clear, or toggle the channel pin. Output compares can
generate TIM 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 TIM channel registers.
An unsynchronized write to the TIM 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 TIM overflow interrupt routine to write a new, smaller output
compare value may cause the compare to be missed. The TIM 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 channel
x TIM overflow interrupts and write the new value in the TIM
overflow interrupt routine. The TIM 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 (TIM)
16.4.3 Output
Compare. The pulses are
MC68HC708AS48
MOTOROLA
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Rev. 4.0