ATmega16 datasheet(124/315 Pages) ATMEL

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124

ATmega16(L)

2466E–AVR–10/02

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.

Asynchronous Operation

of the Timer/Counter

Asynchronous Status

• Bit 3 – AS2: Asynchronous Timer/Counter2

When AS2 is written to zero, Timer/Counter 2 is clocked from the I/O clock, clk

I/O. When

AS2 is written to one, Timer/Counter2 is clocked from a Crystal Oscillator connected to

the Timer Oscillator 1 (TOSC1) pin. When the value of AS2 is changed, the contents of

TCNT2, OCR2, and TCCR2 might be corrupted.

• Bit 2 – TCN2UB: Timer/Counter2 Update Busy

When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes

set. When TCNT2 has been updated from the temporary storage register, this bit is

cleared by hardware. A logical zero in this bit indicates that TCNT2 is ready to be

updated with a new value.

• Bit 1 – OCR2UB: Output Compare Register2 Update Busy

When Timer/Counter2 operates asynchronously and OCR2 is written, this bit becomes

set. When OCR2 has been updated from the temporary storage register, this bit is

cleared by hardware. A logical zero in this bit indicates that OCR2 is ready to be

updated with a new value.

• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy

When Timer/Counter2 operates asynchronously and TCCR2 is written, this bit becomes

set. When TCCR2 has been updated from the temporary storage register, this bit is

cleared by hardware. A logical zero in this bit indicates that TCCR2 is ready to be

updated with a new value.

If a write is performed to any of the three Timer/Counter2 registers while its update busy

flag is set, the updated value might get corrupted and cause an unintentional interrupt to

occur.

The mechanisms for reading TCNT2, OCR2, and TCCR2 are different. When reading

TCNT2, the actual timer value is read. When reading OCR2 or TCCR2, the value in the

temporary storage register is read.

Bit

765

432

OCR2[7:0]

OCR2

Read/Write

R/W

Initial Value

Bit

210

–

AS2

TCN2UB

OCR2UB

TCR2UB

ASSR

Read/Write

R/W

Initial Value

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