M68HC08 datasheet(131/288 Pages) FREESCALE

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Timer Interface Module (TIM)

MC68HC908BD48 — Rev. 2.1

Data Sheet

Freescale Semiconductor

Timer Interface Module (TIM)

131

10.5.3.2 Buffered Output Compare

Channels 0 and 1 can be linked to form a buffered output compare

channel whose output appears on the TCH0 pin. The TIM channel

registers of the linked pair alternately control the output.

Setting the MS0B bit in TIM channel 0 status and control register (TSC0)

links channel 0 and channel 1. The output compare value in the TIM

channel 0 registers initially controls the output on the TCH0 pin. Writing

to the TIM channel 1 registers enables the TIM channel 1 registers to

synchronously control the output after the TIM overflows. At each

subsequent overflow, the TIM 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 TIM channel 1 status and control

TCH1, 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.

10.5.4 Pulse Width Modulation (PWM)

By using the toggle-on-overflow feature with an output compare channel,

the TIM can generate a PWM signal. The value in the TIM counter

modulo registers determines the period of the PWM signal. The channel

pin toggles when the counter reaches the value in the TIM counter

modulo registers. The time between overflows is the period of the PWM

signal.

As Figure 10-2 shows, the output compare value in the TIM channel

registers determines the pulse width of the PWM signal. The time

between overflow and output compare is the pulse width. Program the

TIM to clear the channel pin on output compare if the state of the PWM

pulse is logic one. Program the TIM to set the pin if the state of the PWM

pulse is logic zero.

M68HC08 Datasheet(PDF) 131 Page - Freescale Semiconductor, Inc