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'12C50x Watchdog timeout, and strangeness on output'
1997\01\27@063911 by Frank A. Vostenbosch

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I'm using a 12C508 with one of it's output pins tied directly to the RxD
pin on a PC's printer port (i.e. 0..5V levels rather than true RS232 --
but works without problems since minimal cable lengths).
Even though I set this output pin to 1 within 10us after reset, I still
get <Break>s on the PC every time the PIC resets on the WDT (at 9600bps).
Why?

Frank

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Frank A. Vorstenbosch                           Phone:  +44-181-941 7899
Electronics & Software Engineer                 Mobile:  +44-976-430 569
Eidos Technologies Ltd., Hampton, Middx         Fax:    +44-181-941 7895

1997\01\27@070440 by Jan van der Watt

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I have no idea, but...

Quote from Microchip ERRATA sheet for rev A1 12c5XX silicon:

If INTRC mode is selected, and GP5 = output, pin will become INPUT after
exec. of SLEEP instruction.

If XT/LP selected, GP4 will become and INPUT after exec. of SLEEP.

Maybe this is relevant, and just hasn't been picked up by MC in the specific
case you mentioned. (You didn't specify a PIN number)

ALSO, page 28 of the 12c508 book says that the TRIS register is set to --11
1111 after wake-up, reset, WDT etc. This means that your IO pin goes HIGH Z,
and the PC's pull-up/down (your guess what the manufacturer put in there)
can cause your problem.

ALSO, just a thought, check that you write the desired value into the GPIO
register BEFORE you set the TRIS register. Otherwise you may get a (very)
short LOW pulse just before you set it high.

Hope it helped.

At 10:46 AM 1/27/97 +0000, you wrote:
{Quote hidden}

Jan van der Watt
[Consultants never charge too much - they work too litlle !]

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