ATMEGA329V_14 Datasheet, PDF (105/392 Pages) ATMEL Corporation – High Performance, Low Power Atmel

ATmega329/3290/649/6490
Table 14-5. Compare Output Mode, Phase Correct PWM Mode⁽¹⁾
COM0A1 COM0A0 Description
0
0
Normal port operation, OC0A disconnected.
0
1
Reserved
1
0
Clear OC0A on compare match when up-counting. Set OC0A on
compare match when counting down.
1
1
Set OC0A on compare match when up-counting. Clear OC0A on
compare match when counting down.
Note:
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the com-
pare match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on
page 100 for more details.
• Bit 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 14-6. 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.
14.9.2
TCNT0 – Timer/Counter Register
Bit
7
6
5
4
3
2
1
0
0x26 (0x46)
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
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 OCR0A Register.
14.9.3 OCR0A – Output Compare Register A
Bit
7
6
5
4
3
2
1
0
0x27 (0x47)
OCR0A[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
2552K–AVR–04/11
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