I've had this on the 16F819 with both the internal Osc and internal Mclr 
selected.  I've been using an ICD2 lately programming directly from MPLAB and 
it actually warns of this.


On Tuesday 12 June 2007 08:57, Peter Todd wrote:
> Anyone else had bugs where writing a specific firmware to a PIC would
> prevent it from being programmed again? And I don't mean code protect
> stuff, I am doing a full voltage erase, and code protection was never
> enabled in the first place.
>
> Basically I've found that on 16lf819's (tried with SO package only)
> after burning certain firmware versions to them any further attempt to
> erase the device fails and does absolutely nothing. Yet, if I burn a new
> firmware version to it, while the erase fails, the firmware appears and
> then the chip works just fine. Even weirder is I haven't been able to
> track down a "known-bad" firmware, after burning a "good" firmware in
> successfully suddenly everything is working again, even what I thought
> were bad firmwares. At the same time, sometimes what I thought was a
> "good" firmware version is "bad" It's more that if I try burning a
> *different* firmware to the chip, I'm pretty much guaranteed for it to
> start working again.
>
> Also if I wait a day, burning works fine again, for about twenty or so
> burns.
>
> I've ruled out stacks of issues, this problem appears on two different
> programmers, different computers, after reboots, on bare chips or in
> circuit, PGM low, high, floating whatever, temperature, body oder etc.
>
> I checked the errata sheets. I think my PICs, which according to pk2 are
> "Rev 5" aren't even covered by the errata's, which are for "Rev A4" and
> "Rev B0"
>
>
> Ideas?
>
> --
> http://petertodd.org
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