Rainbow-electronics ATmega64L Manuel d'utilisateur télécharger pdf (Page 79)

ATmega16(L)

2466B–09/01

Note: 1. A special case occurs when OCR0 equals TOP and COM01 is set. In this case, the

compare match is ignored, but the set or clear is done at TOP. See “Phase Correct

PWM Mode” on page 74 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.

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.

Table 41. Compare Output Mode, Phase Correct PWM Mode

(1)

COM01 COM00 Description

0 0 Normal port operation, OC0 disconnected.

01Reserved

1 0 Clear

OC0 on compare match when up-counting. Set OC0 on compare

match when downcounting.

11Set

OC0 on compare match when up-counting. Clear OC0 on compare

match when downcounting.

Table 42. Clock Select Bit Description

CS02 CS01 CS00 Description

0 0 0 No clock source (Timer/counter stopped)

001

clk

I/O

/(No prescaling)

010clk

I/O

/8 (From prescaler)

011

clk

I/O

/32 (From prescaler)

100

clk

I/O

/256 (From prescaler)

101clk

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 Value 0 0 0 0 0 0 0 0

1 2 ... 74 75 76 77 78 79 80 81 82 83 84 ... 297 298

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Rainbow-electronics ATmega64L Manuel d'utilisateur Page 79

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