We've been selling a product based on a 16C57 for a couple of years.
Suddenly the same code fails to run properly. But it's more weird than
that. The old code, when burned into an eraseable device works fine, but
not in the OTP parts.
Did I hear than Microchip had changed the die on these parts a few months ago?
We're using the PIC to output address data to a 27C010 Eprom. The addresses
get clocked out okay on ports RB and RC, but all output bits on RA seem to
get set to zero at the very end of the sequence in OTP parts, but NOT in
eraseable parts. In debugging, I've explicity set RA.2 to 1, but it goes to
zero anyway as if the code were shutting down before it finished the loop.
> The old code, when burned into an eraseable device works fine, but
> not in the OTP parts.
Bryan:
Take one of your working windowed 16C57s and cover its window with
something OPAQUE (black electrical tape or one of those silver
floppy-disk write-protect tabs), then try it again and let us know
whether it still works.
> We've been selling a product based on a 16C57 for a couple of years.
> Suddenly the same code fails to run properly. But it's more weird than
> that. The old code, when burned into an eraseable device works fine, but
> not in the OTP parts.
Have you tried NEW JW parts with the same date date code as the OTP
parts that won't work ?
> Did I hear than Microchip had changed the die on these parts a few months ago?
Dunno.
> We're using the PIC to output address data to a 27C010 Eprom. The addresses
> get clocked out okay on ports RB and RC, but all output bits on RA seem to
> get set to zero at the very end of the sequence in OTP parts, but NOT in
> eraseable parts. In debugging, I've explicity set RA.2 to 1, but it goes to
> zero anyway as if the code were shutting down before it finished the loop.
Is the watchdog kicking in early, try and disable it completely in the
programmer for a sample chip and see if this copuld be the problem. The
process variations for the WDT are very loosely characterised and you may
be working at a optimistic point especially since you indicate the fault
occurs at the end of a long function.
Also the chip might have supplemental Brownout stuff that is more
sensitive to power dips.
Bryan Mumford wrote:
>
> We've been selling a product based on a 16C57 for a couple of years.
> Suddenly the same code fails to run properly. But it's more weird than
> that. The old code, when burned into an eraseable device works fine, but
> not in the OTP parts.
>
> Did I hear than Microchip had changed the die on these parts a few months ago?
>
> We're using the PIC to output address data to a 27C010 Eprom. The addresses
> get clocked out okay on ports RB and RC, but all output bits on RA seem to
> get set to zero at the very end of the sequence in OTP parts, but NOT in
> eraseable parts. In debugging, I've explicity set RA.2 to 1, but it goes to
> zero anyway as if the code were shutting down before it finished the loop.
>
> Any ideas?????
>
> Bryan Mumford
> Santa Barbara, California
Read Answer #1 on 'Fast Forward Engineering - The Answers Page' at:
www.geocities.com/SiliconValley/2499/answers.html
This may solve the riddle.
The most Frequently Asked Questions about PICs are on this one page.
Do what I did. Print it out, staple it together, then check it on a
regular basis when you get stuck for an answer.
SLI, the serial LCD that auto detects baud rates from 30 to 125K bps.
SimmStick(tm) A PIC proto PCB the size of a 30 pin Simm Memory Module.
EASY PIC'n Beginners Guide to using PIC 16/17 MicroChip products.
Kalle Pihlajasaari gets the prize. The watchdog timer was kicking in.
Evidently our previous parts were on the threshold of a WDT timeout but
never slipped over. The last batch of PICs we bought must have a slightly
shorter period. I was fooled (for several reasons) but largely because the
timeout happened coincidentally at THE EXACT end of a routine. The old and
new eraseable parts and the old OTPs make it through the loop and go to
sleep before the watchdog wakes up.
Makes me wonder if products in the field might develop a hiccup in aging. I
think low battery voltage won't be a problem because it seems to lengthen
the watchdog time.
I was at my wit's end, but sometimes it seems like a short trip....
MITVMA.MIT.EDU> wrote:
