146
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
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
. For the actual placement of
I/O pins, refer to
”Pinout ATmega48A/PA/88A/PA/168A/PA/328/P” 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 160
.
The PRTIM2 bit in
”Minimizing Power Consumption” on page 43
must be written to zero to
enable Timer/Counter2 module.
Figure 18-1.
8-bit Timer/Counter Block Diagram
Clock Select
Timer/Counter
DA
T
A
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