ATmega16U4 datasheet(162/408 Pages) ATMEL

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7766D–AVR–01/09

ATmega16U4/ATmega32U4

The following code examples show how to do an atomic write of the TCNTn register contents.

Writing any of the OCRnA/B/C/D registers can be done by using the same principle.

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 requires that the r17:r16 register pair contains the value to be writ-

ten to TCNTn.

15.11.1

Reusing the temporary high byte register

If writing to more than one 10-bit register where the high byte is the same for all registers written,

then the high byte only needs to be written once. However, note that the same rule of atomic

operation described previously also applies in this case.

Assembly Code Example

TIM1_WriteTCNT

; Save global interrupt flag

r18,SREG

; Disable interrupts

cli

; Set TCNT

n to r17:r16

out

nH,r17

out

TCNT

n,r16

; Restore global interrupt flag

out

SREG,r18

ret

C Code Example

void

TIM1_WriteTCNTn( unsigned int i )

{

unsigned char

sreg;

unsigned int

/* Save global interrupt flag */

sreg = SREG;

/* Disable interrupts */

_CLI();

/* Set TCNTn to i */

TCnH = (i >> 8);

TCNTn = (unsigned char)i;

/* Restore global interrupt flag */

SREG = sreg;

}

ATmega16U4 Datasheet(PDF) 162 Page - ATMEL Corporation

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