Datasheet

176
ATmega640/1280/1281/2560/2561
2549K–AVR–01/07
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
Overview A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 59.. For the
actual placement of I/O pins, see “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 locations are listed in the “Register Description” on page 191.
The Power Reduction Timer/Counter2 bit, PRTIM2, in “PRR0 – Power Reduction Regis-
ter 0” on page 55 must be written to zero to enable Timer/Counter2 module.
Figure 66. 8-bit Timer/Counter Block Diagram
Timer/Counter
DATA BUS
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
clk
Tn
ASSRn
Synchronization Unit
Prescaler
T/C
Oscillator
clk
I/O
clk
ASY
asynchronous mode
select (ASn)
Synchronized Status flags
TOSC1
TOSC2
Status flags
clk
I/O