Datasheet

145
7593L–AVR–09/12
AT90USB64/128
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 32kHz 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, see “Pin configurations” on page 3. CPU accessible I/O Registers, includ-
ing 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 156.
The Power Reduction Timer/Counter2 bit, PRTIM2, in “PRR0 – Power Reduction Register 0” on
page 54 must be written to zero to enable Timer/Counter2 module.
Figure 16-1. 8-bit Timer/Counter, block diagram.
Timer/counter
DATA B US
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