116
8025I–AVR–02/09
ATmega48P/88P/168P/328P
Note:
1.
See ”Code Examples” on page 7.
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 returns the TCNT1 value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register, and the interrupt code
updates the temporary register by accessing the same or any other of the 16-bit Timer Regis-
ters, then the result of the access outside the interrupt will be corrupted. Therefore, when both
the main code and the interrupt code update the temporary register, the main code must disable
the interrupts during the 16-bit access.
The following code examples show how to do an atomic read of the TCNT1 Register contents.
Reading any of the OCR1A/B or ICR1 Registers can be done by using the same principle.
Assembly Code Examples
...
;
Set TCNT
1
to 0x01FF
ldi
r17,0x01
ldi
r16,0xFF
out
TCNT
1
H,r17
out
TCNT
1
L,r16
; Read TCNT
1
into r17:r16
in
r16,TCNT
1
L
in
r17,TCNT
1
H
...
C Code Examples
unsigned int
i;
...
/*
Set TCNT
1
to 0x01FF
*/
TCNT
1
= 0x1FF;
/*
Read TCNT
1
into i
*/
i = TCNT
1
;
...