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PICList Thread
'Self reseting with RA4 pin'
1998\07\12@005137 by Dmitry Kiryashov

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Hello Piclisters. Some theoretical question...

Did anyone have experienced with PIC selfreseting via RA4 pin? I think
it should be practically possible in case if PORTA internal hardware
switched to input mode after all internal hardware is reseted. I ask
anyone to responce who practically was tested and applied this idea.
Also I ready to hear any negative thinking about this.

WBR Dmitry.

PS. MCLR is pulled through resistor to +Ucc and connected to RA4.

1998\07\12@062315 by Frank Tamminga

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Dmitry Kiryashov wrote:

> Did anyone have experienced with PIC selfreseting via RA4 pin? I think
> it should be practically possible in case if PORTA internal hardware
> switched to input mode after all internal hardware is reseted. I ask
> anyone to responce who practically was tested and applied this idea.
> Also I ready to hear any negative thinking about this.

Why don't you use the WD to reset the PIC? Just create a simple loop
like 'goto $-1' and the watchdog will kick in...

Frank (spam_OUTp.f.tammingaTakeThisOuTspamhgt.nl)

1998\07\12@073701 by Dmitry Kiryashov

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Frank Tamminga wrote:

> > Did anyone have experienced with PIC selfreseting via RA4 pin? I think
> > it should be practically possible in case if PORTA internal hardware
> > switched to input mode after all internal hardware is reseted. I ask
> > anyone to responce who practically was tested and applied this idea.
> > Also I ready to hear any negative thinking about this.
>
> Why don't you use the WD to reset the PIC? Just create a simple loop
> like 'goto $-1' and the watchdog will kick in...

Thank you Frank.
I really know tricks to playing with WDT you hint me about.
It is necessary to reset PIC and some hardware around it phisically i.e.
through RESET signal but I'm prefer to not apply additional external
reset
chip for instance such as MC34064 due to device should be as low cost as
possible. Well, for my point of view it will be one pull up resistor and
one capasitor to ground with RA4 connected to MCLR. I think this idea
should work.

WBR Dmitry.

1998\07\13@032625 by Frank Tamminga

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Frank Tamminga wrote in answer to Dmity Kiryashov:

> > > Did anyone have experienced with PIC selfreseting via RA4 pin? I
think
{Quote hidden}

You may be right, but; If you intend to discharge the capacitor over the
RA4 output you will damage the output (maybe not instantly, ...) There will
be a current flow for u-sec's, exceeding the current specs for that pin.
I still woult opt for the WD solution with one addition. Use another pin
like RA3 for the job with a pull-down resistor. When the PIC resets due to
the WD or Power Up, all pins will go to a high state (input). The pull-down
will pull the pin down, resetting the rest of your application. In the
init. part of your programm, you can tell the PIC to wait as long as you
like before setting the RA3 pin to output/high.
I think this is safer, and you got rid of the capacitor as well.

Frank

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