ATmega48/88/168
17. 8-bit Timer/Counter2 with PWM and Asynchronous Operation
17.1 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 32 kHz Watch Crystal Independent of the I/O Clock
17.2 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 17-1. For the actual placement of
I/O pins, refer to “Pinout ATmega48/88/1682545M” 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 154.
The PRTIM2 bit in “Minimizing Power Consumption” on page 42 must be written to zero to
enable Timer/Counter2 module.
Figure 17-1. 8-bit Timer/Counter Block Diagram
Count
TOVn
(Int.Req.)
Clear
Control Logic
Clock Select
Direction
clkTn
Edge
Detector
Tn
TOP
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
=
=
0
OCnA
(Int.Req.)
Waveform
Generation
OCnA
OCnB
=
OCRnA
Fixed
TOP
Value
OCnB
(Int.Req.)
Waveform
Generation
=
OCRnB
TCCRnA
TCCRnB
141
2545M–AVR–09/07