atmega103 ATMEL Corporation, atmega103 Datasheet - Page 39

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

8-bit Timer/Counters
T/C0 and T/C2
0945I–AVR–02/07
The clock source for Timer/Counter0 prescaler is named PCK0. PCK0 is by default con-
nected to the main system clock CK. Observe that CPU clock frequency can be lower
than the XTAL frequency if the XTAL divider is enabled. By setting the AS0 bit in ASSR,
Timer/Counter0 prescaler is asynchronously clocked from the TOSC1 pin. This enables
use of Timer/Counter0 as a Real Time Clock (RTC). A crystal can be connected
between the TOSC1 and TOSC2 pins to serve as an independent clock source for
Timer/Counter0. This Oscillator is optimized for use with a 32.768 kHz crystal.
Figure 30 shows the block diagram for Timer/Counter0. Figure 31 shows the block dia-
gram for Timer/Counter2.
Figure 30. Timer/Counter0 Block Diagram
8-BIT DATA BUS
8-BIT ASYNCH T/C0 DATA BUS
7
7
7
8-BIT COMPARATOR
TIMER/COUNTER0
OUTPUT COMPARE
REGISTER0 (OCR0)
REGISTER (TIMSK)
TIMER INT. MASK
(TCNT0)
TCK0
0
0
0
CK
T/C0 OVER-
FLOW IRQ
T/C CLEAR
T/C CLK SOURCE
UP/DOWN
REGISTER (TIFR)
TIMER INT. FLAG
SYNCH UNIT
T/C0 COMPARE
MATCH IRQ
ATmega103(L)
CONTROL
LOGIC
REGISTER (TCCR0)
REGISTER (ASSR)
ASYNCH. STATUS
T/C0 CONTROL
PCK0
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