24
2467S–AVR–07/09
ATmega128
The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (e.g., by disabling interrupts
globally) so that no interrupts will occur during execution of these functions. The examples also
assume that no flash boot loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic
EECR,EEWE
rjmp
EEPROM_write
; Set up address (r18:r17) in address register
out
EEARH, r18
out
EEARL, r17
; Write data (r16) to data register
out
EEDR,r16
; Write logical one to EEMWE
sbi
EECR,EEMWE
; Start eeprom write by setting EEWE
sbi
EECR,EEWE
ret
C Code Example
void
EEPROM_write(
unsigned int
uiAddress,
unsigned char
ucData)
{
/*
Wait for completion of previous write
*/
while(EECR & (1<<EEWE))
;
/* Set up address and data registers */
EEAR = uiAddress;
EEDR = ucData;
/*
Write logical one to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by setting EEWE */
EECR |= (1<<EEWE);
}
