Rainbow Electronics ATmega161L - Manual (Page 41)

41
ATmega161(L)
1228C–AVR–08/02
Figure 32. Timer/Counter2 Block Diagram
The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK or an external
pin.The 8-bit Timer/Counter2 can select clock source from CK, prescaled CK or external
TOSC1.
Both Timer/Counters can be stopped as described in sections “Timer/Counter0 Control
Register
– TCCR0” and “Timer/Counter2 Control Register – TCCR2”.
T h e va r io u s Sta tu s F l a g s ( O ve rfl o w an d C om pa r e M a tch ) ar e fo un d i n th e
Timer/Counter Interrupt Flag Register (TIFR). Control signals are found in the
Timer/Counter Control Register (TCCR0 and TCCR2). The interrupt enable/disable set-
tings are found in the Timer/Counter Interrupt Mask Register (TIMSK).
When Timer/Counter0 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 both a high resolution and a high accuracy usage with
the lower prescaling opportunities. Similarly, the high prescaling opportunities make the
Timer/Counter0 useful for lower speed functions or exact timing functions with infre-
quent actions.
Timer/Counters 0 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 44 for a detailed description of
this function.
8-BIT DATA BUS
8-BIT ASYNCH T/C2 DATA BUS
ASYNCH. STATUS
REGISTER (ASSR)
TIMER INT. FLAG
REGISTER (TIFR)
TIMER/COUNTER2
(TCNT2)
SYNCH UNIT
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
OCF2 TOV2 TOIE0 TOIE1 OCIE1A OCIE1B TICIE1 TOIE2 OCIE2
OCR2UB
TC2UB ICR2UB
TOSC1
CK
TCK2
T/C2 OVER-
FLOW IRQ
T/C2 COMPARE
MATCH IRQ
AS2
TOV1
OCF1B OCF1A
ICF1 TOV2 OCF2 OCF0 TOV0
OCIE0
T/C2 CONTROL
REGISTER (TCCR2)
CS22
COM21 PWM2
CS21
COM20
CS20 CTC2 FOC2 PSR2
PSR10
SPECIAL FUNCTIONS
IO REGISTER (SFIOR)
CK