The following code examples show how to do an atomic write of the TCNTn register contents. Writing any of the OCRnx 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
out
TCNTnH,r17
TCNTnL,r16
; Restore global interrupt flag
out
ret
SREG,r18
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 written to TCNTn.
13.2.1 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, 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.
13.3 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 prescaler, see Section 11. “Timer/Counter0 and Timer/Counter1 Prescalers” on page 75.
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ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
