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The pulse width modulator (PWM) module contains six identical channels, PWM5 –
PWM0.
15.1 Overview
Each PWM channel consists of a simple free-running counter with two compare reg-
isters. Each compare register performs a particular task when it matches the count
value. The period comparator causes the output pin to be set and the free-running
counter to reset when its value matches the period value. The width comparator
causes the output pin to reset when the counter value matches. With a suitable low-
pass filter, the PWM channel can be used as a digital-to-analog converter.
Figure 15-1 is a block diagram of a single PWM channel.
System Clock
Clockgen
(Prescaler)
By feeding a stream of sample values to the PWM into the width register and provid-
ing a low-pass filter on the output, the output pin can provide a digitally-generated
sound source. The reconstruction rate is determined by the selected period. Typically,
for voice quality, the rate is between 6 kHz and 8 kHz. Figure 15-2 relates the pulse
stream to the filtered audio output.
Pulse Stream
Filtered Audio
MMC2001
REFERENCE MANUAL
Freescale Semiconductor, Inc.
SECTION 15
PULSE WIDTH MODULATOR
Width Compare
Counter
Period Compare
Figure 15-1 PWM Block Diagram
Figure 15-2 PWM Generating Audio
PULSE WIDTH MODULATOR
For More Information On This Product,
Go to: www.freescale.com
Output
Pulse Output
Control
MOTOROLA
15-1
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