Rainbow Electronics ATtiny861_V - Manual (Page 81)

81
2588B–AVR–11/06
ATtiny261/461/861
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 OCR0A/B registers.
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 TCNT0H/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 TCNT 0 to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNT 0H,r17
out TCNT 0L,r16
; Read TCNT 0 into r17:r16
in r16,TCNT 0L
in r17,TCNT 0H
...
C Code Example
unsigned int i;
...
/* Set TCNT0 to 0x01FF */
TCNT0H = 0x01;
TCNT0L = 0xff;
/* Read TCNT0 into i */
i = TCNT0L;
i |= ((unsigned int)TCNT0H << 8);
...