Hi Jerry,

you can write many bytes in the page mode (8 bytes on the 24C02, up to 128 bytes on the 24C512).
So you need only less CPU time and a small cap on your EEPROM to power until the internal write cycle was completed.

E.g to transfer 8 bytes at 400kHz (many EEPROM support 400kHz) you need 250µs CPU time and for the following 10ms write cycle only the EEPROM must be powered.

E.g. to power the AT24C512-10PC-2.7 until write was completed you need a cap of:
C = 1.5mA * 10ms / (4.5V-2.7V) = 10µF

and to power the CPU AT89C4051 at 12MHz until data transferred:
C = 10mA * 250µs / (4.5V-3V) = 2µF

4.5V was assumed as power fail detection threshold.

If you bring the CPU in the power down mode after transferring the data to the EEPROM, you can use the same cap for both (e.g. use 22µF).

22µF is not a big material consumption.


Peter