Datasheet

80
ATmega32A [DATASHEET]
Atmel-8155D-AVR-ATmega32A-Datasheet_02/2014
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.
15.9.2 TCNT0 – Timer/Counter Register
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. Modify-
ing the counter (TCNT0) while the counter is running, introduces a risk of missing a compare match between
TCNT0 and the OCR0 Register.
15.9.3 OCR0 – Output Compare Register
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.
15.9.4 TIMSK – Timer/Counter Interrupt Mask Register
• Bit 1 – OCIE0: Timer/Counter0 Output Compare Match Interrupt Enable
When the OCIE0 bit is written to one, and the I-bit in the Status Register is set (one), the Timer/Counter0 Compare
Match interrupt is enabled. The corresponding interrupt is executed if a compare match in Timer/Counter0 occurs,
that is, when the OCF0 bit is set in the Timer/Counter Interrupt Flag Register – TIFR.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
Table 15-6. Clock Select Bit Description
CS02 CS01 CS00 Description
0 0 0 No clock source (Timer/Counter stopped).
001clk
I/O
/(No prescaling)
010
clk
I/O
/8 (From prescaler)
011
clk
I/O
/64 (From prescaler)
100
clk
I/O
/256 (From prescaler)
101
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 76543210
TCNT0[7:0] TCNT0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR0[7:0] OCR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 7 6 5 4 3 2 1 0
OCIE2 TOIE2 TICIE1 OCIE1A OCIE1B TOIE1 OCIE0 TOIE0 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