atmega103 ATMEL Corporation, atmega103 Datasheet - Page 38

• Manufacturer Part Number: atmega103
• Description: Atmega103 8-bit With 128k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Timer/Counters
Timer/Counter
Prescalers
38
ATmega103(L)
The ATmega103(L) provides three general purpose Timer/Counters – two 8-bit T/Cs
and one 16-bit T/C. Timer/Counter0 optionally can be asynchronously clocked from an
external Oscillator. This Oscillator is optimized for use with a 32.768 kHz crystal,
enabling use of Timer/Counter0 as a Real Time Clock (RTC). Timer/Counter0 has its
own prescaler. Timer/Counters 1 and 2 have individual prescaling selection from the
same 10-bit prescaling timer. These Timer/Counters can either be used as a Timer with
an internal clock time base or as a counter with an external pin connection that triggers
the counting.
Figure 28. Prescaler for Timer/Counter1 and Timer/Counter2
For Timer/Counters 1 and 2, the four different prescaled selections are: CK/8, CK/64,
CK/256 and CK/1024, where CK is the CPU clock. Observe that CPU clock frequency
can be lower than the XTAL frequency if the XTAL divider is enabled. For
Timer/Counters 1 and 2, added selections as CK, external source and stop can be
selected as clock sources.
Figure 29. The Timer/Counter0 Prescaler
T1
T2
CS20
CS21
CS22
CK
TOSC1
CS00
CS01
CS02
AS0
CK
TIMER/COUNTER2 CLOCK SOURCE
0
PCK0
TCK2
TIMER/COUNTER0 CLOCK SOURCE
10-BIT T/C PRESCALER
10-BIT T/C PRESCALER
PCK0
CS10
CS12
CS11
TIMER/COUNTER1 CLOCK SOURCE
0
TCK1
0945I–AVR–02/07