MC68HC11KA4TS Datasheet, PDF (62/68 Pages) Motorola, Inc – 8-Bit Microcontroller

12 Pulse-Width Modulation Timer
The MC68HC11KA4/KA2 MCU contains a PWM timer that is composed of a four-channel 8-bit modu-
lator. Each of the modulators can create independent continuous waveforms with software-selectable
duty rates from 0% to 100%.
The PWM provides up to four pulse-width modulated waveforms on specific port H pins. Each channel
has its own counter. Pairs of counters can be concatenated to create 16-bit PWM outputs based on 16-
bit counts. Three clock sources (A, B, and S) give the PWM a wide range of frequencies.
Four control registers configure the PWM outputs — PWCLK, PWPOL, PWSCAL, and PWEN. The PW-
CLK register selects the prescale value for PWM clock sources and enables the 16-bit counters. The
PWPOL register determines each channel's polarity and selects the clock source for each channel. The
PWSCAL register derives a user-scaled clock, based on the A clock source, and the PWEN register
enables the PWM channels.
Each channel has a separate 8-bit counter, period register, and duty cycle register. The period and duty
cycle registers are double buffered so that if they are changed while the channel is enabled, the change
does not take effect until the counter rolls over or the channel is disabled.
With channels configured for 8-bit mode and E = 4 MHz, PWM signals of 40 kHz (1% duty cycle reso-
lution) to less than 10 Hz (approximately 0.4% duty cycle resolution) can be produced. By configuring
the channels for 16-bit mode with E = 4 MHz, PWM periods greater than one minute are possible.
In 16-bit mode, duty cycle resolution of almost 15 parts per million can be achieved (at a PWM frequen-
cy of about 60 Hz). In the same system, a PWM frequency of 1 kHz corresponds to a duty cycle reso-
lution of 0.025%.
MOTOROLA
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MC68HC11KA4
MC68HC11KA4TS/D