Datasheet

43
ATmega323(L)
1457E11/01
Figure 31. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named PCK2. PCK2 is by default connected to
the main system clock CK. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchro-
nously clocked from the PC6(TOSC1) pin. This enables use of Timer/Counter2 as a
Real Time Counter (RTC). When AS2 is set, pins PC6(TOSC1) and PC7(TOSC2) are
disconnected from Port C. A crystal can then be connected between the PC6(TOSC1)
and PC7(TOSC2) pins to serve as an independent clock source for Timer/Counter2.
The oscillator is optimized for use with a 32.768 kHz crystal. Applying an external clock
source to TOSC1 is not recommended. Setting the PSR2 bit in SFIOR resets the pres-
caler. This allows the user to operate with a predictable prescaler.
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
CK
PCK2
XTAL1
AS2
CS20
CS21
CS22
PCK2/8
PCK2/64
PCK2/128
PCK2/1024
PCK2/256
PCK2/32
0
PSR2
Clear
TCK2