ATmega8(L)
Table 34. Clock Select Bit Description
CS02
CS01
CS00
Description
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
No clock source (Timer/Counter stopped)
clkI/O/(No prescaling)
clkI/O/8 (From prescaler)
clkI/O/64 (From prescaler)
clkI/O/256 (From prescaler)
clkI/O/1024 (From prescaler)
External clock source on T0 pin. Clock on falling edge
External clock source on T0 pin. Clock on rising edge
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
Timer/Counter
Register – TCNT0
Bit
7
6
5
4
3
2
1
0
TCNT0[7:0]
TCNT0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter.
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
–
0
TOIE0
R/W
0
TIMSK
Read/Write
Initial Value
R/W
0
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set (one), the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter0 occurs, that is, when the TOV0 bit is set in the Timer/Counter Inter-
rupt 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
–
0
TOV0
R/W
0
ICF1
R/W
0
TIFR
Read/Write
Initial Value
R/W
0
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set (one) when an overflow occurs in Timer/Counter0. TOV0 is cleared by hard-
ware when executing the corresponding interrupt Handling Vector. Alternatively, TOV0 is
cleared by writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow
Interrupt Enable), and TOV0 are set (one), the Timer/Counter0 Overflow interrupt is executed.
72
2486AA–AVR–02/2013
ATMEL [ ATMEL ]
