A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash 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.
Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1. If there is no need for a Boot Loader update in the system, program the Boot Loader Lock
Bits to prevent any Boot Loader software updates.
2. 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 operating volt-
age matches the detection level. If not, an external low VCC 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.
3. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will pre-
vent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCR Register and thus the Flash from unintentional writes.
Programming Time for The calibrated RC Oscillator is used to time Flash accesses. Table 81 shows the typical pro-
Flash when using SPM gramming time for Flash accesses from the CPU.
Table 81. SPM Programming Time (1)
Symbol
Min Programming Time Max Programming Time
3.7 ms 4.5 ms
Flash write (page erase, page write,
and write Lock Bits by SPM)
1.Minimum and maximum programming time is per individual operation.
218
ATmega8(L)
2486T–AVR–05/08
ATMEL [ ATMEL ]
