I think I have experienced this with a PIC 16C74/JW but I never checked Vcc.

I erased and reprogrammed it about 100 times or so.

The eraser was excellent and I had erase times down to 10 mins.

Occassionally the PIC  would reprogramme but  wouldn't run reliably, (may be my
programming).

I found that every now and then a 45 -60 min erase was neccessary and good
practise.

On one occasion my ISP lead 5v VCC wire broke while i was downloading  and upon
blank check it showed the code protection had been enabled on the upper 3/4.
Panic, Panic, but a 60 min erase sorted it out.


ASH -UK-






on 24 Jun 98, pic microcontroller discussion list wrote...

>At 08:07 23/06/98 +0200, you wrote:
>>Hi guys,
>>
>>could you tell me what the 16C559 is? (EEPROM/RAM size, word size, pins,
>>etc.)
>>It is not in may catalogue...
>>
>>Imre
>
>Mistyped 16C558 I'd say.  I think that is what is been taken for granted.
>
>Jim
>
>>
>>On Mon, 22 Jun 1998, Caisson wrote:
>>
>>> > 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
>>>
>>>
>>
>
>