ATmega165 datasheet(21/336 Pages) ATMEL

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ATmega165/V

2573G–AVR–07/09

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.

EEPROM Write During Power-

down Sleep Mode

When entering Power-down sleep mode while an EEPROM write operation is active, the

EEPROM write operation will continue, and will complete before the Write Access time

has passed. However, when the write operation is completed, the clock continues run-

ning, and as a consequence, the device does not enter Power-down entirely. It is

therefore recommended to verify that the EEPROM write operation is completed before

entering Power-down.

Preventing EEPROM

Corruption

During periods of low V

CC, the EEPROM data can be corrupted because the supply volt-

age 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:

Assembly Code Example

EEPROM_read:

; Wait for completion of previous write

sbic

EECR,EEWE

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

r16,EEDR

ret

C Code Example

unsigned char

EEPROM_read(unsigned int uiAddress)

{

/* Wait for completion of previous write */

while(EECR & (1<<EEWE))

;

/* 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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