Datasheet

140
2545T–AVR–05/11
ATmega48/88/168
18. 8-bit Timer/Counter2 with PWM and asynchronous operation
18.1 Features
• 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, OCF2A and OCF2B)
• Allows clocking from external 32kHz watch crystal independent of the I/O clock
18.2 Overview
Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module. A simplified
block diagram of the 8-bit Timer/Counter is shown in Figure 18-1. For the actual placement of
I/O pins, refer to “Pinout Atmel ATmega48/88/168.” 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 “Register description” on page 153.
The PRTIM2 bit in “Minimizing power consumption” on page 41 must be written to zero to enable
Timer/Counter2 module.
Figure 18-1. 8-bit timer/counter block diagram.
Clock select
Timer/counter
DATA B U S
OCRnA
OCRnB
=
=
TCNTn
Waveform
generation
Waveform
generation
OCnA
OCnB
=
Fixed
TOP
value
Control logic
= 0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.req.)
OCnA
(Int.req.)
OCnB
(Int.req.)
TCCRnA TCCRnB
Tn
Edge
detector
(From prescaler)
clk
Tn