ATmega325P datasheet(112/364 Pages) ATMEL

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112

8023F–AVR–07/09

ATmega325P/3250P

The following code examples show how to do an atomic write of the TCNT1 Register contents.

Writing any of the OCR1A/B or ICR1 Registers can be done by using the same principle.

Note:

1. See Section “5.” on page 10.

The assembly code example requires that the r17:r16 register pair contains the value to be writ-

ten to TCNT1.

15.3.1

Reusing the Temporary High Byte Register

If writing to more than one 16-bit register where the high byte is the same for all registers written,

then the high byte only needs to be written once. However, note that the same rule of atomic

operation described previously also applies in this case.

15.4

Timer/Counter Clock Sources

The Timer/Counter can be clocked by an internal or an external clock source. The clock source

is selected by the Clock Select logic which is controlled by the Clock Select (CS12:0) bits

located in the ”TCCR1B – Timer/Counter1 Control Register B” on page 130. For details on clock

sources and prescaler, see ”Timer/Counter0 and Timer/Counter1 Prescalers” on page 100.

Assembly Code Example(1)

TIM16_WriteTCNT

; Save global interrupt flag

r18,SREG

; Disable interrupts

cli

; Set TCNT

1 to r17:r16

out

TCNT

1H,r17

out

TCNT

1L,r16

; Restore global interrupt flag

out

SREG,r18

ret

C Code Example

(1)

void

TIM16_WriteTCNT

1( unsigned int i )

{

unsigned char

sreg;

unsigned int

/* Save global interrupt flag */

sreg = SREG;

/* Disable interrupts */

__disable_interrupt();

/* Set TCNT

1 to i */

TCNT

1 = i;

/* Restore global interrupt flag */

SREG = sreg;

}

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