
116
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
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. 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.
16.3.1
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,
operation described previously also applies in this case.
16.4
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 (CSn2:0) bits
located in the Timer/Counter control Register B (TCCRnB). For details on clock sources and
Assembly Code Example
TIM16_WriteTCNT
n:
; Save global interrupt flag
in
r18,SREG
; Disable interrupts
cli
; Set TCNT
n to r17:r16
out
TCNT
nH,r17
out
TCNT
nL,r16
; Restore global interrupt flag
out
SREG,r18
ret
C Code Example
void
TIM16_WriteTCNT
n( unsigned int i )
{
unsigned char
sreg;
unsigned int
i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT
n to i */
TCNT
n = i;
/* Restore global interrupt flag */
SREG = sreg;
}