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PICList Thread
'[PIC]: MCLR vs. ICSP: Clash of Titans'
2002\04\26@122608 by Lawrence Lile

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I am using a circuit (beaten to death last week on the PIClist) with a
capacitor on MCLR, which improves noise immunity.  I discovered when trying
to in-circuit-serial-program, that ICSP does not seem to work when this
capacitor is in place.  Remove the capacitor, and ICSP works OK.  What
exactly does ICSP do to MCLR besides raising it to 13 volts or so?

Now, I am using an adapter hacked into a PICstart plus, admittedly not the
best ICSP adapter.  My target board supplies it's own 5V, so I am not
straining the wimpy 5V supply on  the picstart.

On the bench, this isn't a big problem, just program it and then install the
capacitor.  But in production, we've got a gorilla of a different cage
altogether.  They will want to have the capacitors and PIC all installed,
then squirt the program into the PIC, test the board then assemble the unit.
Nobody wants to have to build the board, then program it, then add some more
components by hand, then assemble it into a unit.

OK, so how are we going to get around this one?

-- Lawrence Lile
Sr. Project Engineer
Salton inc. Toastmaster Div.
573-446-5661 Voice
573-446-5676 Fax

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2002\04\26@124055 by Kevin Blain

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Microchip suggests a R / C / diode arrangement on the PIC for ICSP.

The diode blocks the effect of the capacitor during programming. MCLR
has to rise pretty quickly, IIRC.

Regards, Kevin

> {Original Message removed}

2002\04\26@134135 by Lawrence Lile

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Yep, that is the arrtangement I am using, 10K to 5v, 1 uF to ground, 1n4148
from the junction to MCLR.  I get a verify error every time I program,
although the program seems to operate OK.

--Lawrence
----- Original Message -----
From: "Kevin Blain" <.....kevinbKILLspamspam@spam@WOODANDDOUGLAS.CO.UK>
To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Friday, April 26, 2002 11:33 AM
Subject: Re: [PIC]: MCLR vs. ICSP: Clash of Titans


> Microchip suggests a R / C / diode arrangement on the PIC for ICSP.
>
> The diode blocks the effect of the capacitor during programming. MCLR
> has to rise pretty quickly, IIRC.
>
> Regards, Kevin
>
> > {Original Message removed}

2002\04\26@140034 by Dwayne Reid

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At 11:24 AM 4/26/02 -0500, Lawrence Lile wrote:
>I am using a circuit (beaten to death last week on the PIClist) with a
>capacitor on MCLR, which improves noise immunity.  I discovered when trying
>to in-circuit-serial-program, that ICSP does not seem to work when this
>capacitor is in place.  Remove the capacitor, and ICSP works OK.  What
>exactly does ICSP do to MCLR besides raising it to 13 volts or so?
>
>Now, I am using an adapter hacked into a PICstart plus, admittedly not the
>best ICSP adapter.  My target board supplies it's own 5V, so I am not
>straining the wimpy 5V supply on  the picstart.

Do you have a current booster on the MCLR line from the
programmer?  Microchip has published at least 1 ICSP guide showing this -
essentially, its a unity gain buffer with lots of current gain (1 section
of op-amp, 1 emitter follower transistor, unity gain).  They show 2 of
similar sections: 1 for VDD, 1 for MCLR.

I suspect you are not getting MCLR high enough fast enough.  The current
boost circuit added to your programming adapter may be all you need to fix
the problem.

dwayne


Dwayne Reid   <.....dwaynerKILLspamspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2002\04\26@141129 by Paul Hutchinson

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How about programming the PIC's in a gang programmer before assembly.

Cuts down the man hours per unit as well.

Paul

> {Original Message removed}

2002\04\26@144351 by uter van ooijen & floortje hanneman

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> exactly does ICSP do to MCLR besides raising it to 13 volts or so?

rising it *quickly*

Could you split the R and connect the cap to the split-point?

Wouter van Ooijen
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2002\04\26@154435 by Olin Lathrop

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> Yep, that is the arrtangement I am using, 10K to 5v, 1 uF to ground,
1n4148
> from the junction to MCLR.  I get a verify error every time I program,
> although the program seems to operate OK.

1uF sounds awfully high.  Have you tried 100nF?


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2002\04\29@104525 by Lawrence Lile

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Mebbe that is the problem.  I'll try a smaller cap today.

--Lawrence
----- Original Message -----
From: "Olin Lathrop" <KILLspamolin_piclistKILLspamspamEMBEDINC.COM>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Friday, April 26, 2002 2:43 PM
Subject: Re: [PIC]: MCLR vs. ICSP: Clash of Titans


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