ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 115

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

Reusing the Temporary High
Byte Register
Timer/Counter Clock
Sources
2490G–AVR–03/04
The following code examples show how to do an atomic write of the TCNTn Register
contents. Writing any of the OCRnA/B/C or ICRn Registers can be done by using the
same principle.
Note:
The assembly code example requires that the r17:r16 register pair contains the value to
be written to TCNTn.
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.
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
(CSn2:0) bits located in the Timer/Counter Control Register B (TCCRnB). For details on
clock sources and prescaler, see “Timer/Counter3, Timer/Counter2 and Timer/Counter1
Prescalers” on page 142.
Assembly Code Example
C Code Example
TIM16_WriteTCNTn:
void TIM16_WriteTCNTn( unsigned int i )
{
}
; Save global interrupt flag
in
; Disable interrupts
cli
; Set TCNTn to r17:r16
out TCNTnH,r17
out TCNTnL,r16
; Restore global interrupt flag
out SREG,r18
ret
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Set TCNTn to i */
TCNTn = i;
/* Restore global interrupt flag */
SREG = sreg;
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”.
r18,SREG
(1)
(1)
ATmega64(L)
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