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ManualsBrandsMICROCHIP TECHNOLOGY ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller PDIP 40 8-Bit 16 MHz I/O number 32
61626364656667686970
67
ATmega323(L)
1457E–11/01
The calibrated oscillator is used to time the EEPROM accesses. Table 25 lists the typi-
cal programming time for EEPROM access from the CPU.
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 the 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 for executing instructions is too low.
EEPROM data corruption can easily be avoided by following these design recommen-
dations (one is sufficient):
1. Keep the AVR RESET active (low) during periods of insufficient power sup-
ply voltage. This can be done by enabling the internal Brown-out Detector
(BOD) if the operating voltage matches the detection level. If not, 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 is voltage is sufficient.
2. Keep the AVR core in Power-down Sleep Mode during periods of low V
CC
.
This will prevent the CPU from attempting to decode and execute instruc-
tions, effectively protecting the EEPROM registers from unintentional writes.
3. Store constants in Flash memory if the ability to change memory contents
from software is not required. Flash memory can not be updated by the CPU
unless the boot loader software supports writing to the Flash and the Boot
Lock bits are configured so that writing to the Flash memory from CPU is
allowed. See “Boot Loader Support” on page 172 for details.
Table 25. EEPROM Programming Time.
Symbol
Number of Calibrated
RC Oscillator Cycles
Min Programming
Time
Max Programming
Time
EEPROM write (from
CPU)
2048 1.9 ms 3.8 ms