Datasheet

87
8024A–AVR–04/08
ATmega8HVA/16HVA
The following code examples show how to access the 16-bit timer registers assuming that no
interrupts updates the temporary register. The same principle can be used directly for accessing
the OCRnB/A registers.
Note: 1. See “About Code Examples” on page 7.
The assembly code example returns the TCNTnH/L 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 registers,
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.
Assembly Code Example
...
; Set TCNTn to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNTnH,r17
out TCNTnL,r16
; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH
...
C Code Example
unsigned int i;
...
/* Set TCNTn to 0x01FF */
TCNTn = 0x1FF;
/* Read TCNTn into i */
i = TCNTn;
...