ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 92

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Timer/Counter Register –
TCNT0
92
ATmega325/3250/645/6450
Table 50. Compare Output Mode, Phase Correct PWM Mode
Note:
• Bit 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 51. Clock Select Bit Description
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.
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.
Bit
Read/Write
Initial Value
CS02
COM0A1
0
0
0
0
1
1
1
1
0
0
1
1
1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case,
CS01
the compare match is ignored, but the set or clear is done at TOP. See “Phase Cor-
rect PWM Mode” on page 87 for more details.
0
0
1
1
0
0
1
1
R/W
COM0A0
7
0
CS00
0
1
0
1
0
1
0
1
0
1
0
1
R/W
6
0
Description
No clock source (Timer/Counter stopped)
clk
clk
clk
clk
clk
External clock source on T0 pin. Clock on falling edge.
External clock source on T0 pin. Clock on rising edge.
Description
Normal port operation, OC0A disconnected.
Reserved
Clear OC0A on compare match when up-counting. Set OC0A on
compare match when counting down.
Set OC0A on compare match when up-counting. Clear OC0A on
compare match when counting down.
I/O
I/O
I/O
I/O
I/O
/(No prescaling)
/8 (From prescaler)
/64 (From prescaler)
/256 (From prescaler)
/1024 (From prescaler)
R/W
5
0
R/W
4
0
TCNT0[7:0]
R/W
3
0
R/W
2
0
(1)
R/W
1
0
R/W
0
0
2570A–AVR–09/04
TCNT0