AT90PWM2 datasheet(85/361 Pages) ATMEL

85 / 361 page

4317J–AVR–08/10

AT90PWM2/3/2B/3B

14. 8-bit Timer/Counter0 with PWM

Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output

Compare Units, and with PWM support. It allows accurate program execution timing (event man-

agement) and wave generation. The main features are:

• Two Independent Output Compare Units

• Double Buffered Output Compare Registers

• Clear Timer on Compare Match (Auto Reload)

• Glitch Free, Phase Correct Pulse Width Modulator (PWM)

• Variable PWM Period

• Frequency Generator

• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)

14.1

Overview

A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 14-1. For the actual

placement of I/O pins, refer to “Pin Descriptions” on page 8. CPU accessible I/O Registers,

including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit loca-

tions are listed in the “8-bit Timer/Counter Register Description” on page 95.

The PRTIM0 bit in “Power Reduction Register” on page 42 must be written to zero to enable

Timer/Counter0 module.

Figure 14-1. 8-bit Timer/Counter Block Diagram

14.1.1

Definitions

Many register and bit references in this section are written in general form. A lower case “n”

replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Com-

pare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or

bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing

Timer/Counter0 counter value and so on.

Timer/Counter

TCNTn

Waveform

Generation

OCnA

Control Logic

count

clear

direction

TOVn

(Int.Req.)

OCRnx

TCCRnA

Clock Select

Edge

Detector

( From Prescaler )

clkTn

OCnA

(Int.Req.)

OCRnx

Waveform

Generation

OCnB

(Int.Req.)

TCCRnB

Fixed

TOP

Values

= 0

TOP

BOTTOM

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