ATMEGA8_08 Datasheet, PDF (104/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

8-bit
Timer/Counter2
with PWM and
Asynchronous
Operation
Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module. The main
features are:
• Single Channel 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 OCF2)
• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 45. For the actual place-
ment of I/O pins, refer to “Pin Configurations” 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 loca-
tions are listed in the “8-bit Timer/Counter Register Description” on page 117.
Figure 45. 8-bit Timer/Counter Block Diagram
TCCRn
count
clear
direction
Control Logic
BOTTOM
TOP
Timer/Counter
TCNTn
= 0 = 0xFF
=
clk_Tn
Prescaler
OCn
(Int. Req.)
Waveform
Generation
TOVn
(Int. Req.)
T/C
Oscillator
TOSC1
TOSC2
clk_I/O
OCn
OCRn
Status Flags
Synchronized Status Flags
Synchronization Unit
ASSRn
asynchronous Mode
Select (ASn)
clk_I/O
clk_ASY
Registers
The Timer/Counter (TCNT2) and Output Compare Register (OCR2) are 8-bit registers. Interrupt
request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register (TIFR).
104 ATmega8(L)
2486T–AVR–05/08