Interfacing to External EEPROM
From Mech
Using an external EEPROM can be useful for several different reasons. External EEPROMs also allow much more data to be stored than is available on the 18F4520. In addition, EEPROM saves state when power is cycled.
Circuit
We used a Microchip 24FC515 external EEPROM. (http://ww1.microchip.com/downloads/en/devicedoc/21673E.pdf)