ATmega16 datasheet(71/357 Pages) ATMEL

71 / 357 page

2466S–AVR–05/09

ATmega16(L)

8-bit

Timer/Counter0

with PWM

Timer/Counter0 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

• External Event Counter

• 10-bit Clock Prescaler

• Overflow and Compare Match Interrupt Sources (TOV0 and OCF0)

Overview

A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 27. For the actual place-

ment of I/O pins, refer to “Pinout ATmega16” 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 83.

Figure 27. 8-bit Timer/Counter Block Diagram

Registers

The Timer/Counter (TCNT0) and Output Compare Register (OCR0) are 8-bit registers. Interrupt

request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag

(TIMSK). TIFR and TIMSK are not shown in the figure since these registers are shared by other

timer units.

The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on

the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter

uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source

is selected. The output from the Clock Select logic is referred to as the timer clock (clk

T0).

The double buffered Output Compare Register (OCR0) is compared with the Timer/Counter

value at all times. The result of the compare can be used by the waveform generator to generate

a PWM or variable frequency output on the Output Compare Pin (OC0). See “Output Compare

Timer/Counter

TCNTn

Waveform

Generation

OCn

= 0

Control Logic

= 0xFF

BOTTOM

count

clear

direction

TOVn

(Int.Req.)

OCRn

TCCRn

Clock Select

Edge

Detector

( From Prescaler )

clkTn

TOP

OCn

(Int.Req.)

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