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'[PIC]: my 16f87x and RS232 is quite fuzzy'
2002\07\25@183206 by Fredrik Axtelius

picon face
Standard 16f874 with a MAX232CPE to pins RX and TX.
Im using Shane Tolmies Bootloader (which is great by the way) to download my code and it works, kinda.

If im not grounded and move my hand nearby the circuit communication fails.
If the code is running I can move my hand as much as i like so the pic part of my circuit seems to be OK.

This is quite annoying since I cant press the resetswitch to download new code without touching my computer chassie with my another hand :)

I have tried moving things around, shortend the wires, added a few caps.

Any ideas anyone?

tia
/frax

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2002\07\25@185048 by Barry Gershenfeld

face picon face
>If im not grounded and move my hand nearby the circuit communication fails.
>If the code is running I can move my hand as much as i like so the pic part
of my circuit seems to be OK.
>
>I have tried moving things around, shortend the wires, added a few caps.
>
>Any ideas anyone?

 (1) Floating input pin.
 (2) MPLAB ICD debug code inadvertently left in.
 (3) The fish is not dead yet.

Barry

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2002\07\25@190412 by Fredrik Axtelius

picon face
> >If im not grounded and move my hand nearby the circuit communication fails.
> >If the code is running I can move my hand as much as i like so the pic part
> of my circuit seems to be OK.
> >
> >I have tried moving things around, shortend the wires, added a few caps.
> >
> >Any ideas anyone?
>
>   (1) Floating input pin.

All pins set as output, still same thing or did you mean the MAX232?
Im only using half the MAX232, should I do anything with the in/out pins I dont use?

>   (2) MPLAB ICD debug code inadvertently left in.

Nops

>   (3) The fish is not dead yet.

Nops

/frax

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2002\07\25@191734 by Tony Nixon

flavicon
picon face
Fredrik Axtelius wrote:
>
> > >If im not grounded and move my hand nearby the circuit communication fails.
> > >If the code is running I can move my hand as much as i like so the pic part
> > of my circuit seems to be OK.
> > >
> > >I have tried moving things around, shortend the wires, added a few caps.
> > >
> > >Any ideas anyone?
> >
> >   (1) Floating input pin.
>
> All pins set as output, still same thing or did you mean the MAX232?
> Im only using half the MAX232, should I do anything with the in/out pins I dont use?

The 232 chip has internal pullups and pulldowns.

Is the GND connection between the PIC and terminal equipment ok?

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Tony

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2002\07\25@192319 by Fredrik Axtelius

picon face
> Is the GND connection between the PIC and terminal equipment ok?

Yes, but the powersupply I use for the pic and the max232 is not grounded, could that be a problem?

/frax

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2002\07\25@193614 by Barry Gershenfeld

face picon face
>/frax
>>   (1) Floating input pin.
>
>All pins set as output, still same thing or did you mean the MAX232?
>Im only using half the MAX232, should I do anything with the in/out pins I
dont use?

I meant the PIC, although after I ran out of ideas I would certainly
tie up the unused MAX232 inputs if it were easily done.  And what's
on the other end?  A PC? well, I guess that's okay.

Now, *you* set all the pins to output, but what did *Shane* do?  You
said the bootload fails but not your own application.

>>   (2) MPLAB ICD debug code inadvertently left in.
>
>Nops

Too bad, I've had this happen, right down to the hand waving.

>>   (3) The fish is not dead yet.
>
>Nops

Shucks, that was my best line.

Barry

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2002\07\25@194431 by Fredrik Axtelius

picon face
> >>   (1) Floating input pin.
> >
> >All pins set as output, still same thing or did you mean the MAX232?
> >Im only using half the MAX232, should I do anything with the in/out pins I
> dont use?
>
> I meant the PIC, although after I ran out of ideas I would certainly
> tie up the unused MAX232 inputs if it were easily done.  And what's
> on the other end?  A PC? well, I guess that's okay.
>
> Now, *you* set all the pins to output, but what did *Shane* do?  You
> said the bootload fails but not your own application.

Doh, 1.30 am, brain is kinda not working. Your absolutely correct but theres nothing helpful in his docs. I cant be expected to tie every unused pin can I?

/frax

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2002\07\25@201421 by Barry Gershenfeld

face picon face
>> Now, *you* set all the pins to output, but what did *Shane* do?  You
>> said the bootload fails but not your own application.
>
>Doh, 1.30 am, brain is kinda not working. Your absolutely correct but
theres nothing helpful in his docs. I cant be expected to tie every unused
pin can I?

Probably not.  We could expect the documentation to tell you what's
set to what, but if we don't have that then we just have to find
out which pin is causing this.  Something like holding one end of
a resistor and touching each pin with the other.  While you
touch ground, or, while you touch +5.  Whatever it takes.  Dead
fish don't lie.

BTW I've never used this bootloader but I know it's been around
awhile.  A lot of people have used it.   While I doubt it has
bugs like this maybe your chip's got more inputs than originally
designed for.  I found the site for it but nothing in the FAQ
about intermittent operation.
Enough PIClist'ers are fooling with this, someone ought to be
able to help.

Oh, and don't just look at the data pins.  Something like MCLR
would really do a number no matter what the code said.

Barry

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