Datasheet

97
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
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 OCR1A/B and ICR1 registers. Note that when
using “C”, the compiler handles the 16-bit access.
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 TCNT1 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 Examples
(1)
...
; Set TCNT1 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT1H,r17
out TCNT1L,r16
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
...
C Code Examples
(1)
unsigned int i;
...
/* Set TCNT1 to 0x01FF */
TCNT1 = 0x1FF;
/* Read TCNT1 into i */
i = TCNT1;
...