Rainbow Electronics ATmega103L - Manual (Page 37)

ATmega603/103
37
Figure 31. Timer/Counter2 Block Diagram
Note: Figure 31 shows the block diagram for Timer/Counter2.
The 8-bit Timer/Counter0 can select clock source from PCK0 or prescaled PCK0. The 8-bit Timer/Counter2 can select
clock source from CK, prescaled CK, or an external pin. Both Timer/Counters can be stopped as described in the specifica-
tion for the Timer/Counter Control Registers - TCCR0 and TCCR2.
The different status flags (overflow, compare match and capture event) are found in the Timer/Counter Interrupt Flag Reg-
ister - TIFR. Control signals are found in the Timer/Counter Control Registers - TCCR0 and TCCR2. The interrupt
enable/disable settings are found in the Timer/Counter Interrupt Mask Register - TIMSK.
When Timer/Counter2 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To
assure proper sampling of the external clock, the minimum time between two external clock transitions must be at least one
internal CPU clock period. The external clock signal is sampled on the rising edge of the internal CPU clock.
The 8-bit Timer/Counters feature a high resolution and a high accuracy usage with the lower prescaling opportunities. Sim-
ilarly, the high prescaling opportunities make these units useful for lower speed functions or exact timing functions with
infrequent actions.
Both Timer/Counters support two Output Compare functions using the Output Compare Registers - OCR0 and OCR2 as
the data source to be compared to the Timer/Counter contents. The Output Compare functions include optional clearing of
the counter on compare match, and action on the Output Compare Pins - PB4(OC0/PWM0) and PB7(OC2/PWM2) - on
compare match.
Timer/Counter0 and 2 can also be used as 8-bit Pulse Width Modulators. In this mode the Timer/Counter and the output
compare register serve as a glitch-free, stand-alone PWM with centered pulses. Refer to page 40 for a detailed description
on this function.
8-BIT D
A
T
A
B
U
S
T/C2 CONTROL
REGISTER (TCCR2)
TIMER INT. FLAG
REGISTER (TIFR)
TIMER/COUNTER2
(TCNT2)
8-BIT COMPARATOR
OUTPUT COMPARE
REGISTER2 (OCR2)
TIMER INT. MASK
REGISTER (TIMSK)
0
0
0
7
7
7
T/C CLK SOURCE
UP/DOWN
T/C CLEAR
CONTROL
LOGIC
CS22
COM21 PWM2
OCF0 TO
V
0
TO
V
1
OCF2A OCF2B
ICF1 TO
V
2
OCF2
OCF2 TO
V
2
OCIE0 T
OIE0
T
OIE1
OCIE1A OCIE1B TICIE1 T
OIE2
OCIE2
CS21
COM20
CS20 CTC2
CK
T/C2 OVER-
FLOW IRQ
T/C2 COMPARE
MATCH IRQ
6