ATTINY88 Datasheet, PDF (21/246 Pages) ATMEL Corporation – High Endurance Non-volatile Memory Segments

ATtiny88 Automotive
5.3.6
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.
Assembly Code Example
EEPROM_read:
; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read
; Set up address (r17) in address register
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 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;
}
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 keeping the RESET active (low) during peri-
ods 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 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.
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