Datasheet

78
ATmega8A [DATASHEET]
8159E–AVR–02/2013
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. See “About Code Examples” on page 6.
The assembly code example requires that the r17:r16 Register pair contains the value to be written to TCNT1.
17.3.1 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, 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.
17.4 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 (CS12:0) bits located in the Timer/Counter Control Regis-
ter B (TCCR1B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers”
on page 71.
17.5 Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 17-2 shows
a block diagram of the counter and its surroundings.
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;
}