Datasheet

22.10 Timer/Counter Prescaler
Figure 22-12. Prescaler for Timer/Counter2
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
clk
I/O
clk
T2S
TOSC1
AS2
CS20
CS21
CS22
clk
T2S
/8
clk
T2S
/64
clk
T2S
/128
clk
T2S
/1024
clk
T2S
/256
clk
T2S
/32
0
PSR2
Clear
clk
T2
The clock source for Timer/Counter2 is named clk
T2S
. clk
T2S
is by default connected to the main system
clock clk
I/O
. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously clocked from the TOSC1
pin. This enables use of Timer/Counter2 as a Real Time Counter (RTC). When AS2 is set, pins TOSC1
and TOSC2 are disconnected from Port B. A crystal can then be connected between the TOSC1 and
TOSC2 pins to serve as an independent clock source for Timer/Counter2. The Oscillator is optimized for
use with a 32.768kHz crystal. Applying an external clock source to TOSC1 is not recommended.
For Timer/Counter2, the possible prescaled selections are: clk
T2S
/8, clk
T2S
/32, clk
T2S
/64, clk
T2S
/128,
clk
T2S
/256, and clk
T2S
/1024. Additionally, clk
T2S
as well as 0 (stop) may be selected. Setting the PSR2 bit
in SFIOR resets the prescaler. This allows the user to operate with a predictable prescaler.
22.11 Register Description
AVR 8-Bit Microcontroller
8-bit Timer/Counter2 with PWM and Asynchronous Ope...
© 2017 Microchip Technology Inc.
Datasheet Complete
40001974A-page 163