Datasheet

99
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
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. 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 TCNT1.
14.2.1 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.
14.3 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 (CS12:0) bits located in the Timer/Counter control register B (TCCR1B).
For details on clock sources and prescaler, see Section 13. “Timer/Counter0 and Timer/Counter1 Prescalers” on page 92.
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;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNT1 to i */
TCNT1 = i;
/* Restore global interrupt flag */
SREG = sreg;
}