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'[PIC] MCLR Isolation '
2005\04\02@153637 by Vic Fraenckel

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I am reading MicroChip's ICSP Design Guide. It states that the /MCLR /Vpp
pin should be decoupled from a capacitive load with a Schottky diode. Would
someone suggest a suitable device for this?

Any enlightenment will be appreciated.

TIA

Vic Fraenckel
________________________________________________________

Victor Fraenckel - The Windman
victorf ATSIGN windreader DOTcom
KC2GUI


2005\04\02@155719 by John J. McDonough

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----- Original Message -----
From: "Vic Fraenckel" <spam_OUTvictorfTakeThisOuTspamwindreader.com>
Subject: [PIC] MCLR Isolation


> I am reading MicroChip's ICSP Design Guide. It states that the /MCLR /Vpp
> pin should be decoupled from a capacitive load with a Schottky diode.
Would
> someone suggest a suitable device for this?
>
> Any enlightenment will be appreciated.

Vic

Any old thing will work here.  You need a diode simply to prevent the +13 or
so from the programmer from getting into your circuit's Vdd supply.  The
Schottky simply makes it a little faster.  The Schottky is nice, but pretty
much any old thing you have laying around will work.

--McD


2005\04\02@173136 by Harold Hallikainen

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Is such a diode really necessary? I don't have my design schematics here
at home, but I typically just do a 10k pull-up to +5V and an RC to ground
on -MCLR. If Vpp goes up to +13V, that's only 800uA through the 10k.
Shouldn't really cause any problem unless you have a VERY lightly loaded
power supply (where injecting 800uA into the +5V supply would cause the
+5V supply to go too high).

Harold
"The ideal design has zero parts"

{Quote hidden}

--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\04\02@203106 by Bob Axtell

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Vic Fraenckel wrote:

>I am reading MicroChip's ICSP Design Guide. It states that the /MCLR /Vpp
>pin should be decoupled from a capacitive load with a Schottky diode. Would
>someone suggest a suitable device for this?
>
>Any enlightenment will be appreciated.
>
>TIA
>
>Vic Fraenckel
>________________________________________________________
>
>Victor Fraenckel - The Windman
>victorf ATSIGN windreader DOTcom
>KC2GUI
>
>
>  
>
What they are saying is.. if there HAS to be a cap on the MCLR line,
isolate it from programming
signals. Does NOT say you have to do it.

I never use caps on MCLR\ at all; the internal powerup logic is flawless.

--Bob

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