MOTOROLA
Pulse-Width Modulator (PWM)
22-1
Chapter 22
Pulse-Width Modulator (PWM)
The pulse-width modulator (PWM) of the MC9328MX1 is optimized to use 16-bit resolution and a 4
×
16
data FIFO to generate high quality sound from stored audio files and to generate tones. Figure 22-1
illustrates the block diagram of the pulse-width modulator.
Figure 22-1. Pulse-Width Modulator Block Diagram
22.1 Introduction
The PWM can be programmed to select one of two clock signals as its source frequency. The selected
clock signal is passed through a divider and a prescaler before being input to the counter. The output is
available at the pulse-width modulator output (PWMO) external pin.
22.2 PWM Signals
22.2.1 Clock Signals
As shown in Figure 22-1, the clock source (CLKSRC) bit in the PWM control (PWMC) register selects the
source clock—PERCLK1 (the default) or CLK32—to be used by the PWM. The selected clock signal is
then sent through a divider and a prescaler to produce the PCLK signal.
The clock selection (CLKSEL) field in the PWMC selects the frequency of the output of the divider chain.
The incoming clock source is divided by a binary value between 2 and 16.
For 16 kHz audio applications, CLKSEL = 01, divide by 4. For DC-level applications, CLKSEL = 11,
divide by 16. See Table 22-7 on page 22-8 for a complete list of settings for the PWMC register.
PCLK
Sample Compare
PWMO
Output
Control
Prescaler
Counter
PERCLK1
4-Word FIFO
MPU Interface
Divider
CLK32
Period
CLKSRC
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