internal EEPROM read/write and Code Protection CPD WRTD

[cformer]

I'm trying to use the internal data EEPROM to store a serial number.

I use the write_eeprom() and read_eeprom() commands to read and write bytes and it works fine.

However, when I clear the CPD and WRTD configuration bits (0=write protection enabled), the program cannot write or read as before.

According to the Microchip datasheet ( PIC18F86K22_39960d.pdf ) this should still work though:

"Data EEPROM memory has its own code-protect bits in
the Configuration Words. External read and write
operations are disabled if code protection is enabled.
The microcontroller itself can both read and write to the
internal data EEPROM, regardless of the state of the
code-protect Configuration bit."

Any idea anyone?

[PCM programmer]

Your quote is referring to the CPD config bit. But you are also clearing
(ie, enabling) the WRTD bit. The 18F86K22 data sheet says that WRTD
prevents the PIC from writing to its internal data eeprom:
http://ww1.microchip.com/downloads/en/DeviceDoc/39960d.pdf

[cformer]

Thank you very much PCM programmer!

That fixed it. I hadn't spotted the other paragraph you quoted, and the one I was referring to was not really clear (to me anyway, proven by my misinterpretation).