PicDude wrote:
> So I took a break from that and switched to another chip -- the
> 16F88.  With the ICD2 & MPLAB, I was able to successfully program
> this device, with MCLRE on (serving as a reset pin).  When I changed
> MCLRE to off, programming failed.  Since that, the programmer fails
> to recognize the 16F88's device ID anymore and fails programming.
> Google found me some info that indicated newer PICs can get locked up
> in this way and un-reprogrammable when both internal-oscillator and
> MCLR-as-IO was selected, but I had been using the external RC
> oscillator config setting throughout all of this.

Google is only partially right.  If you programmer doesn't pay attention to
Vdd and Vpp order and sometimes Vpp rise time, then this can happen.  I just
checked the 16F88 and 16F818/819 programming specs, and both of them require
Vdd before Vpp and a fast rise time on Vpp.

It is always possible to completely erase and reprogram any properly
functioning flash PIC regardless of the state it was previously programmed
in.  There are usually two problems when this isn't working: The programmer
doesn't perform the correct sequence or the external circuit is interfering
in the case of in-circuit programming.

> Are the 16F819 and 16F88 really Vdd-before-Vpp
> devices?

Yes.


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