MC68HC08AB16A Datasheet, PDF (195/380 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Timer Interface Module B (TIMB)
Functional Description
12.5.4 Pulse Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare
channel, the TIMB can generate a PWM signal. The value in the TIMB
counter modulo registers determines the period of the PWM signal.
The channel pin toggles when the counter reaches the value in the
TIMB counter modulo registers. The time between overflows is the
period of the PWM signal.
As Figure 12-3 shows, the output compare value in the TIMB channel
registers determines the pulse width of the PWM signal. The time
between overflow and output compare is the pulse width. Program the
TIMB to clear the channel pin on output compare if the state of the PWM
pulse is logic one. Program the TIMB to set the pin if the state of the
PWM pulse is logic zero.
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
TBCHx
PULSE
WIDTH
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 12-3PWM Period and Pulse Width
OUTPUT
COMPARE
The value in the TIMB 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 TIMB counter modulo registers produces a PWM
period of 256 times the internal bus clock period if the prescaler select
value is $000. See 12.10.1 TIMB Status and Control Register.
The value in the TIMB channel registers determines the pulse width of
the PWM output. The pulse width of an 8-bit PWM signal is variable in
256 increments. Writing $0080 (128) to the TIMB channel registers
produces a duty cycle of 128/256 or 50%.
MC68HC08AB16A — Rev. 2.0
MOTOROLA
Timer Interface Module B (TIMB)
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Technical Data
195