Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet

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ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]

Atmel-8271H-AVR- ATmega-Datasheet_08/2014

Note:

1.

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.

The following code examples show how to do an atomic read of the TCNT1 Register contents. Reading any of 
the OCR1A/B or ICR1 Registers can be done by using the same principle.

Assembly Code Examples

...

; Set TCNT

r17,0x01

r16,0xFF

TCNT

1H,r17

TCNT

1L,r16

; Read TCNT

1 into r17:r16

r16,TCNT

1L

r17,TCNT

1H

...

C Code Examples

unsigned int i;

...

/* Set TCNT

1 to 0x01FF */

TCNT

1 = 0x1FF;

/* Read TCNT

1 into i */

i = TCNT

1;

...