from Power-save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will
read as the previous value (before entering sleep) until the next rising TOSC1 edge.
The phase of the TOSC clock after waking up from Power-save mode is essentially
unpredictable, as it depends on the wake-up time. The recommended procedure for
reading TCNT2 is thus as follows:
1. Write any value to either of the registers OCR2 or TCCR2.
2. Wait for the corresponding Update Busy Flag to be cleared.
3. Read TCNT2.
•
During asynchronous operation, the synchronization of the Interrupt Flags for the
asynchronous timer takes three processor cycles plus one timer cycle. The timer is
therefore advanced by at least one before the processor can read the timer value
causing the setting of the Interrupt Flag. The output compare pin is changed on the
timer clock and is not synchronized to the processor clock.
Timer/Counter Interrupt Mask
Register – TIMSK
Bit
7
OCIE2
R/W
0
6
TOIE2
R/W
0
5
TICIE1
R/W
0
4
OCIE1A
R/W
0
3
OCIE1B
R/W
0
2
TOIE1
R/W
0
1
OCIE0
R/W
0
0
TOIE0
R/W
0
TIMSK
Read/Write
Initial Value
• Bit 7 – OCIE2: Timer/Counter2 Output Compare Match Interrupt Enable
When the OCIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match interrupt is enabled. The corresponding interrupt is
executed if a compare match in Timer/Counter2 occurs, i.e., when the OCF2 bit is set in
the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 6 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if
an overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the
Timer/Counter Interrupt Flag Register – TIFR.
Timer/Counter Interrupt Flag
Register – TIFR
Bit
7
OCF2
R/W
0
6
TOV2
R/W
0
5
4
OCF1A
R/W
0
3
OCF1B
R/W
0
2
TOV1
R/W
0
1
OCF0
R/W
0
0
TOV0
R/W
0
ICF1
R/W
0
TIFR
Read/Write
Initial Value
• 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
130
ATmega32(L)
2503J–AVR–10/06
ATMEL [ ATMEL ]
