Timer/counter register – tcnt0, Output compare register – ocr0, Timer/counter interrupt mask register – timsk – Rainbow Electronics ATmega162V User Manual
Page 101: Atmega162/v
101
ATmega162/V
2513E–AVR–09/03
• Bit 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
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
The Timer/Counter Register gives direct access, both for read and write operations, to
the Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes)
the Compare Match on the following timer clock. Modifying the counter (TCNT0) while
the counter is running, introduces a risk of missing a Compare Match between TCNT0
and the OCR0 Register.
Output Compare Register –
OCR0
The Output Compare Register contains an 8-bit value that is continuously compared
with the counter value (TCNT0). A match can be used to generate an output compare
interrupt, or to generate a waveform output on the OC0 pin.
Timer/Counter Interrupt Mask
Register – TIMSK
• Bit 1 – 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 Tim er/Counter0 occurs, i.e., w hen the TOV0 bit is set in the
Timer/Counter Interrupt Flag Register – TIFR.
Table 51. 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.
Bit
7
6
5
4
3
2
1
0
TCNT0[7:0]
TCNT0
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
Bit
7
6
5
4
3
2
1
0
OCR0[7:0]
OCR0
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
Bit
7
6
5
4
3
2
1
0
TOIE1
OCIE1A
OCIE1B
OCIE2
TICIE1
TOIE2
TOIE0
OCIE0
TIMSK
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