Datasheet

161
7766E–AVR–04/10
ATmega16U4/ATmega32U4
The following code examples show how to do an atomic write of the TCNTn register contents.
Writing any of the OCRnA/B/C/D 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 writ-
ten to TCNTn.
15.11.1 Reusing the temporary high byte register
If writing to more than one 10-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.
Assembly Code Example
TIM1_WriteTCNTn:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Set TCNTn to r17:r16
out TCnH,r17
out TCNTn,r16
; Restore global interrupt flag
out SREG,r18
ret
C Code Example
void TIM1_WriteTCNTn( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNTn to i */
TCnH = (i >> 8);
TCNTn = (unsigned char)i;
/* Restore global interrupt flag */
SREG = sreg;
}