ATMEGA8_08 Datasheet, PDF (72/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

8-bit
Timer/Counter
Register
Description
Timer/Counter Control
Register – TCCR0
Bit
7
6
5
4
3
2
1
0
–
–
–
–
–
CS02
CS01
CS00
TCCR0
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
• Bit 2:0 – CS02:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter.
Table 34. Clock Select Bit Description
CS02 CS01 CS00 Description
0
0
0
No clock source (Timer/Counter stopped).
0
0
1
clk_I/O/(No prescaling)
0
1
0
clk_I/O/8 (From prescaler)
0
1
1
clk_I/O/64 (From prescaler)
1
0
0
clk_I/O/256 (From prescaler)
1
0
1
clk_I/O/1024 (From prescaler)
1
1
0
External clock source on T0 pin. Clock on falling edge.
1
1
1
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
Read/Write
Initial Value
7
6
5
4
3
2
1
0
TCNT0[7:0]
TCNT0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
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
Read/Write
Initial Value
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
–
R/W
0
0
TOIE0
R/W
0
TIMSK
• 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, i.e., when the TOV0 bit is set in the Timer/Counter Interrupt
Flag Register – TIFR.
72 ATmega8(L)
2486T–AVR–05/08