Datasheet

138
2545F–AVR–06/05
ATmega48/88/168
16. 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, OCF2A and OCF2B)
• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
16.1 Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 16-1. For the actual
placement of I/O pins, refer to ”Pinout ATmega48/88/168” on page 2. CPU accessible I/O Regis-
ters, 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 149.
The PRTIM2 bit in ”Power Reduction Register - PRR” on page 40 must be written to zero to
enable Timer/Counter2 module.
Figure 16-1. 8-bit Timer/Counter Block Diagram
Clock Select
Timer/Counter
DATA BU 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