Rainbow-electronics ATmega64L Manual de usuario descargar pdf (Pagina 123)

123

ATmega16(L)

2466B–09/01

Note: 1. A special case occurs when OCR2 equals TOP and COM21 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 118 for more details.

• Bit 2:0 - CS22:0: Clock Select

The three clock select bits select the clock source to be used by the Timer/Counter, see

Table 54.

Timer/Counter Register –

TCNT2

The Timer/Counter Register gives direct access, both for read and write operations, to

the Timer/Counter unit 8-bit counter. Writing to the TCNT2 register blocks (removes) the

compare match on the following timer clock. Modifying the counter (TCNT2) while the

counter is running, introduces a risk of missing a compare match between TCNT2 and

the OCR2 register.

Output Compare Register -

OCR2

The Output Compare Register contains an 8-bit value that is continuously compared

with the counter value (TCNT2). A match can be used to generate an output compare

interrupt, or to generate a waveform output on the OC2 pin.

Table 53. Compare Output Mode, Phase Correct PWM Mode

(1)

COM21 COM20 Description

0 0 Normal port operation, OC2 disconnected.

01Reserved

1 0 Clear

OC2 on compare match when up-counting. Set OC2 on compare

match when downcounting.

11Set

OC2 on compare match when up-counting. Clear OC2 on compare

match when downcounting.

Table 54. Clock Select Bit Description

CS22 CS21 CS20 Description

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

001

clk

T2S

/(No prescaling)

010clk

T2S

/8 (From prescaler)

011

clk

T2S

/32 (From prescaler)

100

clk

T2S

/64 (From prescaler)

101clk

T2S

/128 (From prescaler)

110clk

/256 (From prescaler)

111clk

/1024 (From prescaler)

Bit 76543210

TCNT2[7:0] TCNT2

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

Bit 76543210

OCR2[7:0] OCR2

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 ... 118 119 120 121 122 123 124 125 126 127 128 ... 297 298

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