At 09:05 17/06/99 -0700, you wrote:

Hi Eric,

The picstart plus is not designed for in system programming but it can
handle it if the conditions are favorable.

I suggest that you add a 1K resistor between MCLR/VPP and ground. This may
make all the difference as the PIC needs to enter the programming mode from
a POR condition. There is no MCLR pull down device, either active or passive,
on the picstart plus.

You will also need to consider the current your target board draws. I do not
know what exactly the picstart plus can source but I would count on much
over 40mA tops. Power is switched  through DG411 quad switches so and not
bipolar transistors that can handle heavier loads. If you have a large
current
requirement on your target you can always power the board via its own PSU and
not bother connecting the VDD signal from the PSP.

If your programming signal lines are isolated via 10k loads then this should
not interfere with ISP however capacitance is another matter. It is not
easy to
buffer the ISP signals as one of them is bidirectional and there is no
direction control available.

I would be trying to first read a programmed chip in circuit then proceed onto
programming.

As far as alternatives go, there are a lot of different programmers available
but relatively few are actually designed for genuine in-system-programming.
One problem with alternative programmers is that the VDD may be sourced only
though an I/O pin of a pic firmware chip. (Eg, Parallax/techtools, DIY-HK
(A.K.A. kits 'r' us) PICALL) This is not always very helpful but you can self
power the target board of course.

Other designs rely on passive pull-up resistors to drive the data signals
and this
again is not helpful to your cause.
(EPIC, P16PRO and other DIY-HK programmers, DT001, PROPIC I&II, and other
TAIT style
derivatives)

For possible workable programmers have a look at.

http://www.propic2.com (Though it is not the propic II you are interested in,
there is a purpose designed ISP programmer on offer linked somewhere to this
page.)

Also see my web site for possible alternatives but really the best option is
a Ver 2 warp-3 but unfortunately these are no longer available. The warp-13
is still a possibility if you lift the ISP signals from the programming
socket. You can drive the warp-13 with MPLAB too so no need to change
software.

BTW. Look carefully on both web sites and see if you can _piece_ together a
_very_ (Very!) low cost production programmer. I have and that is what I
use to
program all my non '5x and 17Cxxx pics. Works absolutely fantastic!


Jim



>Hi Folks,
>
>I am new to the list, and relatively new to PICS.  I poked thru the
>archives looking for this answer, but didn't find it. (It may be there,
>though: that's a big archive)
>
>I tried what someone else had tried: i wired the picstart into my
>circuit to program the pic 12c672.  For me, in circuit means the chip is
>in the final application, with no dips, etc to isolate it. I generally
>have 10k loads on the pins.
>
>Is there a modification you can make to the picstart (a buffer, etc)
>that will allow it to program in circuit?  Is there another relatively
>inexpensive programmer that will do this?  The microchip pro-mate costs
>$1000, which i will spend if we go into production with this circuit,
>but for prototyping, it's a little high.
>
>Thanks for any help,
>eric
>
>Eric Hufstedler
>Kilovac Division of CIIT
>Research & Development
>805-684-4575 x152
>erich@kilovac.com
>
________________________________________
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MPLAB compatible PIC programmers and firmware
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