PCIF0 datasheet(233/294 Pages) ATMEL

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233

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

21.2.5

Preventing Flash Corruption

During periods of low V

CC, the Flash program can be corrupted because the supply voltage is

too low for the CPU and the Flash to operate properly. These issues are the same as for board

level systems using the Flash, and the same design solutions should be applied.

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):

Keep the Atmel

® 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 voltage is

sufficient.

Keep the Atmel AVR core in Power-down sleep mode during periods of low V

CC. This

will prevent the CPU from attempting to decode and execute instructions, effectively

protecting the SPMCSR Register and thus the Flash from unintentional writes.

21.2.6

Programming Time for Flash when Using SPM

The calibrated RC Oscillator is used to time Flash accesses. Table 21-2 shows the typical pro-

gramming time for Flash accesses from the CPU.

Table 21-2.

SPM Programming Time

Symbol

Min Programming Time

Max Programming Time

Flash write (Page Erase, Page Write,

and write Lock bits by SPM)

3.7ms

4.5ms

PCIF0 Folha de dados(PDF) 233 Page - ATMEL Corporation