ATMEGA162_14 Datasheet, PDF (111/324 Pages) ATMEL Corporation – High-performance, Low-power AVR

ATmega162/V
The following code examples show how to do an atomic write of the TCNTn Register contents.
Writing any of the OCRnA/B or ICRn Registers can be done by using the same principle.
Assembly Code Example⁽¹⁾
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⁽¹⁾
void TIM16_WriteTCNTn( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save Global Interrupt Flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNTn to i */
TCNTn = i;
/* Restore Global Interrupt Flag */
SREG = sreg;
}
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 requires that the r17:r16 register pair contains the value to be writ-
ten 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.
2513L–AVR–03/2013
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