ATmega169P datasheet(138/393 Pages) ATMEL

138 / 393 page

138

8018N–AVR–08/09

ATmega169P

17. 8-bit Timer/Counter2 with PWM and Asynchronous Operation

Timer/Counter2 is a general purpose, single compare unit, 8-bit Timer/Counter module. The

main features are:

• Single Compare Unit Counter

• Clear Timer on Compare Match (Auto Reload)

• Glitch-free, Phase Correct Pulse Width Modulator (PWM)

• Frequency Generator

• 10-bit Clock Prescaler

• Overflow and Compare Match Interrupt Sources (TOV2 and OCF2A)

• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock

17.1

Overview

A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 17-1. For the actual

placement of I/O pins, refer to ”64A (TQFP)and 64M1 (QFN/MLF) Pinout ATmega169P” on page

2. 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 locations are listed in the ”8-bit Timer/Counter Register Description”

on page 153.

Figure 17-1. 8-bit Timer/Counter Block Diagram

17.1.1

Registers

The Timer/Counter (TCNT2) and Output Compare Register (OCR2A) are 8-bit registers. Inter-

rupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register

Timer/Counter

TCNTn

Waveform

Generation

OCnx

= 0

Control Logic

= 0xFF

TOP

BOTTOM

count

clear

direction

TOVn

(Int.Req.)

OCnx

(Int.Req.)

Synchronization Unit

OCRnx

TCCRnx

ASSRn

Status flags

clk

I/O

clk

ASY

Synchronized Status flags

asynchronous mode

select (ASn)

TOSC1

T/C

Oscillator

TOSC2

Prescaler

clk

I/O

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