Electronic – PIC EEPROM after re-programming

eeprompic

I was trying to get my EEPROM read/write working on my PIC.

I first programmed a write cycle, and then reprogrammed it to read it out. (To avoid writing every time I start the program/pic)

But I luckily found out that re-programming your PIC causes EEPROM to get… changed?
I found a way to fix this, by using the setting "Preserve EEPROM".

My questions on this are:

  • Does "Preserve EEPROM" write the EEPROM everytime you program your chip? (So re-programming a million times will break EEPROM theoretically)
  • What value is EEPROM after it's programmed… (val != 0xFF) returns true Can I say it's corrupted after programming, or does it get a default value I could check on?

Using: (though it's more theoretical)

  • MPLAB X IDE
  • PICKIT3
  • PIC18F66K22

Best Answer

'Preserve EEPROM' suggests EEPROM content is not changed when chip is reprogrammed. I am not sure if it means the memory is not touched at all during the process. I might involve Pickit reading the data EEPROM, erasing the whole chip, programming the chip, then writing the data EEPROM with the old values.

If you are using Programmer-to-Go mode of Pickit, preserving EEPROM may not work like this.

If you have the CPD (Data EEPROM code-protected) fuse set, then Pickit can't read the EEPROM. You can work around this with 'Erase Configuration Bits' command.

Also a discussion at Microchip suggested that 'Erase all before programming' option overrides the 'Preserve EEPROM' setting.

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