ATMEGA640 datasheet(25/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

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.

Note:

1. See “About Code Examples” on page 10.

8.3.2

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.

Assembly Code Example(1)

EEPROM_read:

; Wait for completion of previous write

sbic

EECR,EEPE

rjcmp

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

r16,EEDR

ret

C Code Example(1)

unsigned char

EEPROM_read(unsigned int uiAddress)

{

/* Wait for completion of previous write */

while(EECR & (1<<EEPE))

;

/* Set up address register */

EEAR = uiAddress;

/* Start eeprom read by writing EERE */

EECR |= (1<<EERE);

/* Return data from Data Register */

return EEDR;

}

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