M68HC08 datasheet(147/288 Pages) FREESCALE

147 / 288 page

MC68HC908BD48 — Rev. 2.1

Data Sheet

Freescale Semiconductor

Pulse Width Modulator (PWM)

147

Data Sheet — MC68HC908BD48

Section 11. Pulse Width Modulator (PWM)

11.1 Contents

11.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

11.3

Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

11.4

PWM Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

11.4.1

PWM Data Registers 0 to 15 (0PWM–15PWM). . . . . . . . . 150

11.4.2

PWM Control Registers 1 and 2 (PWMCR1:PWMCR2) . . 151

11.2 Introduction

Sixteen 8-bits PWM channels are available on the MC68HC908BD48.

Channels 0 to 7 are shared with port-B I/O pins under the control of the

PWM control register 1. Channels 8 to 15 are shared with port-A I/O pins

under the control of the PWM control register 2.

11.3 Functional Description

Each 8-bit PWM channel is composed of an 8-bit register which contains

a 5-bit PWM in MSB portion and a 3-bit binary rate multiplier (BRM) in

LSB portion. There are 16 PWM data registers as shown in Table 11-1.

The value programmed in the 5-bit PWM portion will determine the pulse

length of the output. The clock to the 5-bit PWM portion is the system

clock, the repetition rate of the output is hence 187.5KHz at 6MHz clock.

The 3-bit BRM will generate a number of narrow pulses which are

equally distributed among an 8-PWM-cycle frame. The number of pulses

generated is equal to the number programmed in the 3-bit BRM portion.

Examples of the waveforms are shown in Figure 11-3.

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