Timer/counter interrupt flag register – tifr, Timer/counter prescaler, Atmega32(l) – Rainbow Electronics ATmega32L User Manual
Page 128
128
ATmega32(L)
2503C–AVR–10/02
Timer/Counter Interrupt Flag
Register – TIFR
• Bit 7 – OCF2: Output Compare Flag 2
The OCF2 bit is set (one) when a compare match occurs between the Timer/Counter2
and the data in OCR2 – Output Compare Register2. OCF2 is cleared by hardware when
executing the corresponding interrupt handling vector. Alternatively, OCF2 is cleared by
writing a logic one to the flag. When the I-bit in SREG, OCIE2 (Timer/Counter2 Com-
pare match Interrupt Enable), and OCF2 are set (one), the Timer/Counter2 Compare
match Interrupt is executed.
• Bit 6 – TOV2: Timer/Counter2 Overflow Flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared
by hardware when executing the corresponding interrupt handling vector. Alternatively,
TOV2 is cleared by writing a logic one to the flag. When the SREG I-bit, TOIE2
(Time r/Cou nter2 Ove rf lo w In terrupt Enab le), and TOV2 a re set (one ), th e
Timer/Counter2 Overflow interrupt is executed. In PWM mode, this bit is set when
Timer/Counter2 changes counting direction at $00.
Timer/Counter Prescaler
Figure 64. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clk
T2S
. clk
T2S
is by default connected to
the main system I/O clock clk
IO
. By setting the AS2 bit in ASSR, Timer/Counter2 is asyn-
chronously clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real
Time Counter (RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from
Port C. A crystal can then be connected between the TOSC1 and TOSC2 pins to serve
as an independent clock source for Timer/Counter2. The Oscillator is optimized for use
with a 32.768 kHz crystal. Applying an external clock source to TOSC1 is not
recommended.
Bit
7
6
5
4
3
2
1
0
OCF2
TOV2
ICF1
OCF1A
OCF1B
TOV1
OCF0
TOV0
TIFR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
clk
I/O
clk
T2S
TOSC1
AS2
CS20
CS21
CS22
clk
T2S
/8
clk
T2S
/64
clk
T2S
/128
clk
T2S
/1024
clk
T2S
/256
clk
T2S
/32
0
PSR2
Clear
clk
T2