Rainbow-electronics ATmega128L Uživatelský manuál stáhnout pdf (Strana 153)

153

ATmega128(L)

2467B–09/01

If external pin modes are used for the Timer/Counter2, transitions on the T2 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 –

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.

Timer/Counter Interrupt Mask

• Bit 7- OCIE2: Timer/Counter2 Output Compare Match Interrupt Enable

When the OCIE2 bit is written to one, and the I-bit in the Status Register is set (one), the

Timer/Counter2 Compare Match interrupt is enabled. The corresponding interrupt is

executed if a compare match in Timer/Counter2 occurs, i.e. when the OCF2 bit is set in

the Timer/Counter Interrupt Flag Register – TIFR.

Table 68. Clock Select Bit Description

CS22 CS21 CS20 Description

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

001

clk

I/O

/(No prescaling)

010

clk

I/O

/8 (From prescaler)

011clk

I/O

/32 (From prescaler)

100

clk

I/O

/256 (From prescaler)

101

clk

I/O

/1024 (From prescaler)

1 1 0 External clock source on T2 pin. Clock on falling edge

1 1 1 External clock source on T2 pin. Clock on rising edge

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 value00000000

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 value00000000

Bit 76543210

OCIE2 TOIE2 TICIE1 OCIE1A OCIE1B TOIE1 OCIE0 TOIE0 TIMSK

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

1 2 ... 148 149 150 151 152 153 154 155 156 157 158 ... 330 331

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