Atmel ATmega8535L - Re-using the Temporary High Byte Register

94
ATmega8535(L)
2502K–AVR–10/06
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 “About Code Examples” on page 7.
The assembly code example requires that the r17:r16 register pair contains the value to
be written to TCNT1.
Re-using 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.
Assembly Code Example
(1)
TIM16_WriteTCNT1:
; Save Global Interrupt Flag
in r18,SREG
; Disable interrupts
cli
; Set TCNT1 to r17:r16
out TCNT1H,r17
out TCNT1L,r16
; Restore Global Interrupt Flag
out SREG,r18
ret
C Code Example
(1)
void TIM16_WriteTCNT1( unsigned int i )
{
unsigned char sreg;
/* Save Global Interrupt Flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore Global Interrupt Flag */
SREG = sreg;
}