Datasheet

88
2545F–AVR–06/05
ATmega48/88/168
13. 8-bit Timer/Counter0 with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output
Compare Units, and with PWM support. It allows accurate program execution timing (event man-
agement) and wave generation. The main features are:
•
Two Independent Output Compare Units
• Double Buffered Output Compare Registers
• Clear Timer on Compare Match (Auto Reload)
• Glitch Free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
13.1 Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 13-1. 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 99.
The PRTIM0 bit in ”Power Reduction Register - PRR” on page 40 must be written to zero to
enable Timer/Counter0 module.
Figure 13-1. 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