Rainbow-electronics Atmega169L Manuel d'utilisateur télécharger pdf (Page 98)

ATmega169V/L

2514A–AVR–08/02

Therefore, when both the main code and the interrupt code update the temporary regis-

ter, the main code must disable the interrupts during the 16-bit access.

The following code examples show how to do an atomic read of the TCNT1 Register

contents. Reading any of the OCR1A/B or ICR1 Registers can be done by using the

same principle.

Note: 1. The example code assumes that the part specific header file is included.

For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”,

and “SBI” instructions must be replaced with instructions that allow access to

extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and

“CBR”.

The assembly code example returns the TCNT1 value in the r17:r16 register pair.

Assembly Code Example

(1)

TIM16_ReadTCNT1:

;

Save global interrupt flag

in r18,SREG

;

Disable interrupts

cli

; Read TCNT

1 into r17:r16

in r16,TCNT

in r17,TCNT

;

Restore global interrupt flag

out SREG,r18

ret

C Code Example

(1)

unsigned int TIM16_ReadTCNT1( void )

{

unsigned char sreg;

unsigned int i;

Save global interrupt flag

sreg = SREG;

Disable interrupts

_CLI();

Read TCNT

into i

i = TCNT

Restore global interrupt flag

SREG = sreg;

return i;

}

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Rainbow-electronics Atmega169L Manuel d'utilisateur Page 98

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