MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 115
Chapter 12 Pulse-Width Modulator for Motor Control (PWMMC)

12.1 Introduction

This section describes the pulse-width modulator for motor control (PWMMC, version A). The PWM
module can generate three complementary PWM pairs or six independent PWM signals. These
PWM signals can be center-aligned or edge-aligned. A block diagram of the PWM module is shown in
Figure 12-2.
A12-bit timer PWM counter is common to all six channels. PWM resolution is one clock period for
edge-aligned operation and two clock periods for center-aligned operation. The clock period is dependent
on the internal operating frequency (fOP) and a programmable prescaler. The highest resolution for
edge-aligned operation is 125 ns (fOP = 8 MHz). The highest resolution for center-aligned operation is
250 ns (fOP=8MHz).
When generating complementary PWM signals, the module features automatic dead-time insertion to the
PWM output pairs and transparent toggling of PWM data based upon sensed motor phase current
polarity.
A summary of the PWM registers is shown in Figure 12-3.

12.2 Features

Features of the PWMMC include:
Three complementary PWM pairs or six independent PWM signals
Edge-aligned PWM signals or center-aligned PWM signals
PWM signal polarity control
20-mA current sink capability on PWM pins
Manual PWM output control through software
Programmable fault protection
Complementary mode featuring:
Dead-time insertion
Separate top/bottom pulse width correction via current sensing or programmable software bits