117
2467S–AVR–07/09
ATmega128
The following code examples show how to do an atomic write of the TCNTn Register contents.
Writing any of the OCRnA/B/C or ICRn Registers can be done by using the same principle.
Note:
1. See “About Code Examples” on page 9.
The assembly code example requires that the r17:r16 register pair contains the value to be
written to TCNTn.
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.
Assembly Code Example
TIM16_WriteTCNTn:
; Save global interrupt flag
in
r18,SREG
; Disable interrupts
cli
; Set TCNTn to r17:r16
out
TCNTnH,r17
out
TCNTnL,r16
; Restore global interrupt flag
out
SREG,r18
ret
C Code Example
void
TIM16_WriteTCNTn(
unsigned
int i
)
{
unsigned
char
sreg;
unsigned
int
i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
__disable_interrupt();
/* Set TCNTn to i */
TCNTn = i;
/* Restore global interrupt flag */
SREG = sreg;
}
