> Van: John P. Leonard <leonard@TARDIS.SVSU.EDU>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: Do 16C559/JW's get tired?
> Datum: vrijdag 19 juni 1998 21:06
>
> I've been using a couple of 16C559/JW's (windowed EPROM's) for
prototyping
> and it appears that after several write/erase cycles, the PIC's will no
> longer start-up if Vcc is < 4.8V.  At the beginning of the day, they will
> fire-up with Vcc=3.6 (they're rated to operate down to 2.5V); but a
couple
> hours and several write/erase cycles later and they won't start-up unless
> I set Vcc to nearly 5V.
>
> I observed this several days ago, also.  The configuration bits aren't
> being changed.  Are Mulder & Scully still subscribed to the list?
> Anybody else been down this weird path?
>
> John

Hello John,

I think your PIC suffers from the Memory-effect on the individual
EPROM-cells.
This means that "unknown logic level" voltage widens (A Zero-state is not
from 0.0 thru 0.7 volts, but only to 0.5 volts for example. The High-state
suffers the same problem).  Heat (dissipation of the PIC itself or
otherwise) will worsen those
problems, because resistance will get higher.

Solution : allways over-erase the pic.

If you have a professional programmer try to verify your PIC at a low
voltage.  It will probably fail ...

Greetz,
  Rudy Wieser