XC912BC32CFU8 Motorola Semiconductor Products, XC912BC32CFU8 Datasheet - Page 133

• Manufacturer Part Number: XC912BC32CFU8
• Description: M68HC12B Family Data Sheet
• Manufacturer: Motorola Semiconductor Products

11.1 Introduction
M68HC12B Family — Rev. 8.0
MOTOROLA
Data Sheet — M68HC12B Family
The pulse-width modulator (PWM) subsystem provides four independent 8-bit
PWM waveforms or two 16-bit PWM waveforms or a combination of one 16-bit and
two 8-bit PWM waveforms. Each waveform channel has a programmable period
and a programmable duty cycle as well as a dedicated counter. A flexible clock
select scheme allows four different clock sources to be used with the counters.
Each of the modulators can create independent, continuous waveforms with
software-selectable duty rates from 0 percent to 100 percent. The PWM outputs
can be programmed as left-aligned outputs or center-aligned outputs. See
Figure
The period and duty registers are double buffered so that if they change while the
channel is enabled, the change does not take effect until the counter rolls over or
the channel is disabled. If the channel is not enabled, then writes to the period
and/or duty register go directly to the latches as well as the buffer, thus ensuring
that the PWM output is always either the old waveform or the new waveform, not
some variation in between.
A change in duty or period can be forced into immediate effect by writing the new
value to the duty and/or period registers and then writing to the counter. This
causes the counter to reset and the new duty and/or period values to be latched.
In addition, since the counter is readable it is possible to know where the count is
with respect to the duty value and software can be used to make adjustments by
turning the enable bit off and on.
The four PWM channel outputs share general-purpose port P pins. Enabling PWM
pins takes precedence over the general-purpose port. When PWM outputs are not
in use, the port pins may be used for discrete input/output.
11-1,
Figure
Pulse-Width Modulator (PWM)
11-2, and
Section 11. Pulse-Width Modulator (PWM)
Figure
11-3.
Data Sheet
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