ATtiny44 datasheet(19/236 Pages) ATMEL

19 / 236 page

8006H–AVR–10/09

ATtiny24/44/84

The next code examples show assembly and C functions for reading the EEPROM. The exam-

ples assume that interrupts are controlled so that no interrupts will occur during execution of

these functions.

Note:

See “Code Examples” on page 6.

5.3.7

Preventing EEPROM Corruption

During periods of low V

CC, 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. Sec-

ondly, 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 V

CC reset protection circuit can

Assembly Code Example

EEPROM_read:

; Wait for completion of previous write

sbic

EECR, EEPE

rjmp

EEPROM_read

; Set up address (r18:r17) in address registers

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 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;

}

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