MC68HC08XL36 Datasheet, PDF (171/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Pulse Width
Modulation
9-tim4_b
MOTOROLA
Freescale Semiconductor, Inc.
Timer Interface Module (TIM)
Functional Description
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 3 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 1. Program the TIM to set the pin if the state of the PWM
pulse is logic 0.
OVERFLOW
OVERFLOW
PERIOD
OVERFLOW
TCHx
PULSE
WIDTH
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 3. PWM Period and Pulse Width
OUTPUT
COMPARE
The value in the TIM counter modulo registers and the selected
prescaler output determines the frequency of the PWM output. The
frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIM counter modulo registers produces a PWM
period of 256 times the internal bus clock period if the prescaler select
value is $000. See TIM Status and Control Register on page 178.
The value in the TIM channel registers determines the pulse width of the
PWM output. The pulse width of an 8-bit PWM signal is variable in 256
Timer Interface Module (TIM)
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MC68HC08XL36
171