Hi,
Exactly as You stated, one of address line blown by ESD.
The strange thing is all the time the same lines blown, probably the
most sensitive and weaker as ESD goes.
I have 4 device with absolutely the same problem and same addresses not
deletable. So it can not be the circuit because it quaranteed I have
different one.

Peter

jimford wrote:

> Peter Schultz wrote:
> >
> > Hi,
> > It happened to me also and it caused by ESD.
> > Peter
> >
> > Caisson wrote:
> >
> > > Hello Pic-Listers,
> > >
> > >   Just now something strange happened to me, or rather to both 16C74A
 Pic's
> > > I've got here.  Before today they worked fine.  Programmed & erased them
> > > some
> > > times (about 2-3 times a day for 3 months, nothing special I think).  But
> > > suddenly
> > > my programmer (PicStart+) told me that my Pic's where not empty.  O.k I
> > > tought,
> > > lets erase them some more (50 minutes totally).  Nothing changed, they
> > > still
> > > where not totally erased.  O.k. , lets read and check them.  To my
 surprise
> > > the
> > > first 0400 hex bytes where fine, the rest (from 0400 up) were Zero's.
> > >
> > > eehhmmm...  That could be the Code-protect !  Let's check it ... No, its
> > > still Off,
> > > even after read-out of the Pic's memory.   Now I'm baffeled,  No
> > > Code-protect,
> > > Nothing strange in my program, but _BOTH_ my pic's showing this strange
> > > behavour.
> > >
> > > Anyone there who knows what happened here ?
> > >
> > > Greetz,
> > >    Rudy Wieser
> > >
> > > P.s.
> > > My question allready found his way to MicroChip (Holland) and they asked
 me
> > > toe send them the Pic's, cause the didn't know what could be wrong either
> > > ..
>
> Sounds like one/more of the address lines on your devices has got blown.
> Could be something wrong with the target u are plugging them into, hence
> 2 failed in same way.    The fact that the EPROM data is bad from a
> round address (like 0400h) suggests an address problem to me.
>
> jim ford