Sean Breheny wrote:

> I have a small production run of 60 boards using 16LF88s. Most are
> working fine but after several firmware updates, I now have three or
> four which can no longer be programmed, they always read all zeros for
> the program memory. Examining the config word, I find the following:
> 
> Normal (programmable) PIC config word: 3F 35 3FFC
> Abnormal PIC config word (on the few that will not program): 1E 35 3FFC
> 
> That is, there are two bits altered: flash AND data memory code
> protect has been turned on.
> 
> There are two programmable devices on this board which are programmed.
> The procedure is to erase the PIC, leave the board powered up
> (including the PIC), program the other device (it is a Maxstream radio
> module and IS connected to the PIC's pins but uses no high voltages in
> programming), then program the PIC using MCLR (high voltage
> programming - LVP is turned off in the config word).

After erasing the LVP bit is turned on. If you haven't pulled down the PGM 
pin and are wiggling the programming pins, strange things could happen.

> Are there any known bugs which could cause this? Any ideas?

This is not a bug, it is by design :)

Gerhard

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