M68ICS08GR datasheet(341/408 Pages) FREESCALE

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Timer Interface Module (TIM)

Functional Description

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

Timer Interface Module (TIM)

341

22.5.2 Input Capture

With the input capture function, the TIM can capture the time at which an

external event occurs. When an active edge occurs on the pin of an input

capture channel, the TIM latches the contents of the TIM counter into the

TIM channel registers, TCHxH:TCHxL. The polarity of the active edge is

programmable. Input captures can generate TIM CPU interrupt

requests.

22.5.3 Output Compare

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.

22.5.4 Unbuffered Output Compare

Any output compare channel can generate unbuffered output compare

pulses as described in Output Compare. The pulses are 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 the following methods to synchronize unbuffered changes in the

output compare value on channel x:

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M68ICS08GR Datasheet(PDF) 341 Page - Freescale Semiconductor, Inc