MC68HC908LD64 Datasheet, PDF (171/362 Pages) Freescale Semiconductor, Inc – Microcontrollers

Data Sheet — MC68HC908LD64
Section 12. Pulse Width Modulator (PWM)
12.1 Contents
12.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
12.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171
12.4 PWM Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
12.4.1 PWM Data Registers 0 to 7 (0PWM–7PWM). . . . . . . . . . . 173
12.4.2 PWM Control Register (PWMCR) . . . . . . . . . . . . . . . . . . . 174
12.2 Introduction
Eight 8-bit PWM channels are available on the MC68HC908LD64.
Channels 0 to 7 are shared with port-B I/O pins under the control of the
PWM control register.
12.3 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 eight PWM data registers, controlling each PWM
channel. 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 bus 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.
Example of the waveforms are shown in Figure 12-4.
MC68HC908LD64 — Rev. 3.0
Freescale Semiconductor
Pulse Width Modulator (PWM)
Data Sheet
171