120
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
Note:
1.
See ”About Code Examples” on page 8.
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 TCNT1.
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,
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.
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
(CS12:0) bits
located in the
Timer/Counter control Register B
(TCCR1B). For details on clock sources and
prescaler, see
”Timer/Counter0 and Timer/Counter1 Prescalers” on page 143
Assembly Code Example
TIM16_WriteTCNT
1
:
;
Save global interrupt flag
in
r18,SREG
;
Disable interrupts
cli
;
Set TCNT
1
to
r17:r16
out
TCNT
1
H,r17
out
TCNT
1
L,r16
;
Restore global interrupt flag
out
SREG,r18
ret
C Code Example
void
TIM16_WriteTCNT
1
(
unsigned int i
)
{
unsigned char
sreg;
unsigned int
i;
/*
Save global interrupt flag
*/
sreg = SREG;
/*
Disable interrupts
*/
_CLI();
/*
Set TCNT
1
to i
*/
TCNT
1
= i;
/*
Restore global interrupt flag
*/
SREG = sreg;
}