Hi, folks!!!

Well, today I have relative success making a "do-it-yourself" ICD.
I have followed the schematics from Patrick Touzet, and it seems to
work (only te final and most important test lacks: programming a target,
I will do soon).

Some things that I have encountered:

1) Communications: The ICD is formed like a DCE equipment, and needs a
RS232 cable for computer-to-modem (NOT null-modem). I need some try-and-error
befre making a workable cable (this ended vey simple,  a DB9female to DB9
male straight cable).
I change the capacitors attached to the MAX232 to 10 microfarads,
and works OK (100 nanofarads is too small for some kinds of MAX232).
With no computer attached,the LED blinks
at 1Hz. The LED is fixed "on" when proper communications are established.

2)Voltages: I have canged the supply 100 microfarads capacitor for a 1000
microfarads
(the power has drops with 100 micros).
 The LED must be a green LED. It needs to have a votage drop of 2V, because
is used as voltage reference. One time the communication with ICD was
established,
one needs to adjust a bit R1 and R22 for the correct reading
of the VDD and VPP voltages.
 VDD can be measured with a multimeter, then adjust
R1. VPP can be measured using an oscilloscope; when one touch the button
"Self Test" in MPLAB, the ICD generates high voltage. The point of measure is
the union of R21 with R28.

3) Crystal: The crystal of 3,6864 MHz is very hard to find. Yes, I know, it
allows exact
baud rate generation, but:  why Microchip do not have used
a much more common  3,58MHz (or 4MHz) crystal? Finnally, I have build a
separate
oscilator using a 7,3728MHz surplus crystal and a 74HC04 plus 74LS74 as a
divider.
(ugh!! ugly but works! I was lucking obtaining this rare crystal)

The Touzet's site is:
http://www.multimania.com/silicium31/
more exactly:
http://www.multimania.com/silicium31/Electronique/PIC/free_icd.htm

I am interested in to read experiences of other peoples that have build
ICDs.

Cheers!!!
                Alejandro    alejol@adinet.com.uy

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