ATMEGA48PA_1 Datasheet, PDF (110/448 Pages) ATMEL Corporation – 8-bit Microcontroller with 4/8/16/32K Bytes In-System Programmable Flash

ATmega48PA/88PA/168PA/328P
Table 14-9. 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.
14.9.3
TCNT0 – Timer/Counter Register
Bit
0x26 (0x46)
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. 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 OCR0x Registers.
14.9.4
OCR0A – Output Compare Register A
Bit
0x27 (0x47)
Read/Write
Initial Value
7
6
5
4
3
2
1
0
OCR0A[7:0]
OCR0A
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 Output Compare Register A 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 OC0A pin.
14.9.5
OCR0B – Output Compare Register B
Bit
0x28 (0x48)
Read/Write
Initial Value
7
6
5
4
3
2
1
0
OCR0B[7:0]
OCR0B
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 Output Compare Register B 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 OC0B pin.
8161D–AVR–10/09
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