MEGA128CAN Datasheet, PDF (112/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

Code Examples
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 OCRnx and ICRn Registers. Note that when using “C”, the
compiler handles the 16-bit access.
Assembly Code Examples⁽¹⁾
...
; Set TCNTn to 0x01FF
ldi r17,0x01
ldi r16,0xFF
sts TCNTnH,r17
sts TCNTnL,r16
; Read TCNTn into r17:r16
lds r16,TCNTnL
lds r17,TCNTnH
...
C Code Examples⁽¹⁾
unsigned int i;
...
/* Set TCNTn to 0x01FF */
TCNTn = 0x1FF;
/* Read TCNTn into i */
i = TCNTn;
...
Note: 1. The example code assumes that the part specific header file is included.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an inter-
rupt 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 regis-
ter, the main code must disable the interrupts during the 16-bit access.
112 AT90CAN128
4250E–CAN–12/04