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'[PIC]: 12CE674-JW odd behavior?'
2001\06\01@133227 by Dan Michaels

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Dale Botkin wrote:

>Last night I spent several hours wondering why a new project wouldn't work
>most of the time.  I was using a 12CE674-JW part, and could NOT get it to
>run reliably -- maybe one in 20 tries it would start.

>I am assuming it's not usually this bad to get something going using
>internal RC and no MCLR int eh 8-pin package.  I did think of the exposed
>chip and tried it several times with the window covered (by my thumb),
>which seemd to make no differene at all.  I looked in teh data sheet to
>see if I could spot any -JW specific quirks and didn't see any...  anyone
>have any bright ideas, something I missed? This is the first time I've
>tried using internal RC and no MCLR, needless to say the results were not
>encouraging.  I have to assume it was something I did wrong...
>


Dale, I have used the 12C672, but not CE parts, in that mode
many times, and had no problem. Maybe try programming with the
window "covered".

Also, I have found other Mchp JW parts a little quirkly regarding
how long to erase them, etc. Sometimes the programmer says they are
erased, but still they do not run properly after programming, even
though they would verify properly - so try at least once with a much
longer erasure period than you are using.

I have some errata notes regarding some of my previous experiences
with other JW parts - FYI:

http://www.oricomtech.com/piclinks.htm#Alert2

best regards,
- dan michaels
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2001\06\02@050550 by Roman Black

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> >Last night I spent several hours wondering why a new project wouldn't work
> >most of the time.  I was using a 12CE674-JW part, and could NOT get it to
> >run reliably -- maybe one in 20 tries it would start.
>
> >I am assuming it's not usually this bad to get something going using
> >internal RC and no MCLR int eh 8-pin package.  I did think of the exposed
> >chip and tried it several times with the window covered (by my thumb),
> >which seemd to make no differene at all.  I looked in teh data sheet to
> >see if I could spot any -JW specific quirks and didn't see any...  anyone
> >have any bright ideas, something I missed? This is the first time I've
> >tried using internal RC and no MCLR, needless to say the results were not
> >encouraging.  I have to assume it was something I did wrong...


It sounds like a latchup problem. One specific difference
between the internal RC osc and XT mode is the RC modes
have no startup delay. The XT and HS modes have an automatic
1024 inst delay to allow crystal to stabilise before the
program starts executing. Remember your 5v rail can take
up to 500ms to get to proper value also.

If the input pins are floating during this critical start
up time they can latch up. My preference is to immediately
set the pins to outputs, allow about a 250ms delay in
software (maybe longer if you have more than 47uF after
the regulator) then switch them to ins/outs as needed
and start program operation. Never start a PIC up with
pins as inputs.
:o)
-Roman

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2001\06\02@132039 by Alexandre Domingos F. Souza

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>the regulator) then switch them to ins/outs as needed
>and start program operation. Never start a PIC up with
>pins as inputs.

       Hmmm, great tip, goes to the "black book" :o)

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