Datasheet

ATmega48PA/88PA/168PA [DATASHEET]
9223F–AVR–04/14
22
The calibrated oscillator is used to time the EEPROM accesses. Table 8-2 lists the typical programming time for EEPROM
access from the CPU.
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.
Table 8-2. EEPROM Programming Time
Symbol Number of Calibrated RC Oscillator Cycles Typ Programming Time
EEPROM write (from
CPU)
26,368 3.3ms
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEPE
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 EEMPE
sbi EECR,EEMPE
; Start eeprom write by setting EEPE
sbi EECR,EEPE
ret
C Code Example
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address and Data Registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMPE */
EECR |= (1<<EEMPE);
/* Start eeprom write by setting EEPE */
EECR |= (1<<EEPE);
}