107
4317I–AVR–01/08
AT90PWM2/3/2B/3B
The following code examples show how to do an atomic read of the TCNTn Register contents.
Reading any of the OCRnx or ICRn 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 returns the TCNTn value in the r17:r16 register pair.
Assembly Code Example
TIM16_ReadTCNT
n
:
;
Save global interrupt flag
in
r18,SREG
;
Disable interrupts
cli
; Read TCNT
n
into r17:r16
in
r16,TCNT
n
L
in
r17,TCNT
n
H
;
Restore global interrupt flag
out
SREG,r18
ret
C Code Example
unsigned int
TIM16_ReadTCNT
n
(
void
)
{
unsigned char
sreg;
unsigned int
i;
/*
Save global interrupt flag
*/
sreg = SREG;
/*
Disable interrupts
*/
_CLI();
/*
Read TCNT
n
into i
*/
i = TCNT
n
;
/*
Restore global interrupt flag
*/
SREG = sreg;
return
i;
}
