Bit timer/counters t/c0 and t/c2 – Rainbow Electronics ATmega103L User Manual
Page 36
ATmega603/103
36
The clock source for Timer/Counter0 prescaler is named PCK0. PCK0 is by default connected 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/Counter 0 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.
8-bit Timer/Counters T/C0 and T/C2
Figure 30 shows the block diagram for Timer/Counter0.
Figure 30. Timer/Counter0 Block Diagram
8-BIT DATA BUS
8-BIT ASYNCH T/C0 DATA BUS
ASYNCH. STATUS
REGISTER (ASSR)
TIMER INT. FLAG
REGISTER (TIFR)
TIMER/COUNTER0
(TCNT0)
SYNCH UNIT
8-BIT COMPARATOR
OUTPUT COMPARE
REGISTER0 (OCR0)
TIMER INT. MASK
REGISTER (TIMSK)
0
0
0
7
7
7
T/C CLK SOURCE
UP/DOWN
T/C CLEAR
CONTROL
LOGIC
OCF0
TO
V
0
TO
V
1
OCF2A
OCF2B
ICF1
TO
V
2
OCF2
OCF0
TO
V
0
OCIE0
T
OIE0
T
OIE1
OCIE1A
OCIE1B
TICIE1
T
OIE2
OCIE2
OCR0UB
TC0UB
ICR0UB
PCK0
CK
TCK0
T/C0 OVER-
FLOW IRQ
T/C0 COMPARE
MATCH IRQ
T/C0 CONTROL
REGISTER (TCCR0)
CS02
COM01
PWM0
AS0
CS01
COM00
CS00
CTC0