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MC68331TS/D

6 General-Purpose Timer Module

The 11-channel general-purpose timer (GPT) is used in systems where a moderate level of CPU control

is required. The GPT consists of a capture/compare unit, a pulse accumulator, and two pulse-width

modulators. A bus interface unit connects the GPT to the intermodule bus.

Figure 15 GPT Block Diagram

6.1 Overview

The capture/compare unit features three input capture channels, four output compare channels, and

one channel that can be selected as an input capture or output compare channel. These channels share

a 16-bit free-running counter (TCNT) which derives its clock from a nine-stage prescaler or from the ex-

ternal clock input signal, PCLK.

Pulse accumulator channel logic includes an 8-bit counter; the pulse accumulator can operate in either

event counting mode or gated time accumulation mode.

Pulse-width modulator outputs are periodic waveforms whose duty cycles can be independently select-

ed and modified by user software. The PWM circuits share a 16-bit free-running counter that can be

clocked by the same nine-stage prescaler used by the capture/compare unit or by the PCLK input.

All GPT pins can also be used for general-purpose input/output. The input capture and output compare

pins form a bidirectional 8-bit parallel port (PORTGP). PWM pins are outputs only. PAI and PCLK pins

are inputs only.

GPT input capture/output compare pins are bidirectional and can be used to form an 8-bit parallel port.

The pulse-width modulator outputs can be used as general-purpose outputs. The PAI and PCLK inputs

can be used as general-purpose inputs.

The GPT control register address map is shown below. The “Access” column in the GPT address map

indicates which registers are accessible only at the supervisor privilege level and which can be assigned

to either the supervisor or user privilege level, according to the value of the SUPV bit in the GPTMCR.

GPT BLOCK

PULSE ACCUMULATOR

PWM UNIT

BUS INTERFACE

IMB

CAPTURE/COMPARE UNIT

PRESCALER

IC1/PGP0

IC2/PGP1

IC3/PGP2

PCLK

PWMB

PWMA

PAI

IC4/OC5/OC1/PGP7

OC4/OC1/PGP6

OC3/OC1/PGP5

OC2/OC1/PGP4

OC1/PGP3

Freescale Semiconductor, Inc.

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