ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 20

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

6.3.6
20
Atmel ATtiny24/44/84 [Preliminary]
Preventing EEPROM Corruption
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 execu-
tion of these functions.
Note:
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. A regular write sequence to the
EEPROM requires a minimum voltage to operate correctly, and the CPU itself can execute
instructions incorrectly if the supply voltage is too low. These issues are the same as for board
level systems using EEPROM, and the same design solutions should be applied.
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
circuit can be used. If a reset occurs while a write operation is in progress, the write operation
will be completed provided the power supply voltage is sufficient.
Assembly Code Example
C Code Example
EEPROM_read:
unsigned char EEPROM_read(unsigned char ucAddress)
{
}
; 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
ret
/* Wait for completion of previous write */
while(EECR & (1<<EEPE))
/* Set up address register */
EEARL = ucAddress;
/* Start eeprom read by writing EERE */
EECR |= (1<<EERE);
/* Return data from data register */
return EEDR;
The code examples are only valid for
addressing mode.
;
r16,EEDR
Atmel
®
ATtiny24 and
Atmel
ATtiny44, using 8-bit
CC
reset protection
7701E–AVR–02/11