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PICList Thread
'about ICSP'
1999\04\23@141002 by engelec

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Hi to all engineers.

I like to know when I program PIC in circuit besides
5 pins do I need to connect crystal too ?

Andre

1999\04\27@031955 by Caisson

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> Van: Andre Abelian <spam_OUTengelecTakeThisOuTspamearthlink.net>
> Aan: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Onderwerp: about ICSP
> Datum: vrijdag 23 april 1999 20:08
>
> Hi to all engineers.

Hello Andre,

> I like to know when I program PIC in circuit besides
> 5 pins do I need to connect crystal too ?

No !  One of the things stated in the documentation regarding programming a
PIC is that the rise-time of the Reset/Program-power pin should be fast
enough.  Why ?  Because if it isn't the crystal could generate a
Clock-pulse, forcing the Program-counter from address Zero to One (or even
beyond that).  That would mean that your program is not placed (programmed)
from address Zero, but from address One (or beyond).

It's one of the more common problems with ISP, because the cappacitance of
the Reset/Programming-line on combination with the drivers
output-resistance could form a R.C combination, causing this low rise-time.

Personally I think it's a good idea to connect the controllers/crystals
incoming pin to the Ground, disallowing any clock-puls generation (only do
this with crystals that can withstand the pic's supply-voltage !)

Greetz,
 Rudy Wieser

1999\04\27@122733 by w. v. ooijen / f. hanneman

picon face
> > I like to know when I program PIC in circuit besides
> > 5 pins do I need to connect crystal too ?
>
> No !  One of the things stated in the documentation regarding programming
a
> PIC is that the rise-time of the Reset/Program-power pin should be fast
> enough.  Why ?  Because if it isn't the crystal could generate a
> Clock-pulse, forcing the Program-counter from address Zero to One (or
even
> beyond that).  That would mean that your program is not placed
(programmed)
> from address Zero, but from address One (or beyond).

On the other hand, if you want to program in-circuit make sure that
your programmer works even when the highest frequency xtal is
connected!

Wouter.

1999\04\29@174427 by paulb

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Caisson wrote:

> Personally I think it's a good idea to connect the controllers/
> crystals incoming pin to the Ground, disallowing any clock-pulse
> generation (only do this with crystals that can withstand the pic's
> supply-voltage !)

 I'd be terribly surprised to find a crystal, even a "fork" one, which
would object to the supply voltage applied permanently (as against
being overdriven at the resonant frequency), but just in case, put a
jumper next to the crystal to *short it out* during ICP.

 I rather like the concept, for *production* units, of circle pads on
the PCB pattern and a "bed of nails" jig to program them.  Unit cost:
virtually nil, and no compromises in PCB layout including the crystal
region.

 The "bed of nails" itself could be a PCB with spring pins fitted (and
on which the programmer hardware is constructed) or even solid pins
mounted on "tongue" slot-outs on the PCB!
--
 Cheers,
       Paul B.

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