ATA6617C_14 Datasheet, PDF (42/274 Pages) ATMEL Corporation – 8K/16K Flash Microcontroller with LIN Transceiver, 5V Regulator and Watchdog

The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts
are controlled so that no interrupts will occur during execution of these functions.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by writing EERE
sbi EECR,EERE
; Read data from data register
in
r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned char ucAddress)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
;
/* Set up address register */
EEAR = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
}
4.4.3.6 Preventing EEPROM Corruption
During periods of low Vcc, the EEPROM data can be corrupted because the supply voltage is too low for the CPU and the
EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design
solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to
the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly,
if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation: Keep the AVR^® RESET active
(low) during periods of insufficient power supply voltage. This can be done by enabling the internal brown-out detector
(BOD). If the detection level of the internal BOD does not match the needed detection level, an external low Vcc reset
protection circuit can be used. If a reset occurs while a write operation is in progress, the write operation will be completed
provided that the power supply voltage is sufficient.
42 ATA6616C/ATA6617C [DATASHEET]
9132I–AUTO–06/14