I'm guessing that since you've mentioned negative voltages, your either not
familiar with the way the JDM design works, or you've connected it to the
wrong pins on your serial port.

Since most modern serial ports can't put out voltages as high as 14 volts
the JDM "fakes" a ground reference to the lowest negative voltage the port
can produce. Usually that puts the programmer "ground" at about 10 volts
below the PC "ground" (this is often a problem when trying to do in-circuit
programming)

If you use pic pin #31 (Vss) as the "ground", none of the programming
connections should ever be below 0v (if they are, you're killing the pic)

Take a look over at http://www.olimex.com/dev/pic-pg2c.html It's a
commercial JDM programmer a lot like you've designed. Schematics and
documentation is available at the above link. When I found out I could buy
one for ~$12 us (including shipping) I couldn't justify building my own.
But take a look at the schematics and see if you can find the problem.


And I'm assuming that since you can manipulate the voltage levels, you've
overcome the limitations of XP?.

Good Luck
-Denny



Sent: Saturday, March 13, 2004 1:07 PM
Subject: [PIC:] Weird JDM Measurements


Hi, this is my first post, so be gentle ;).

I just made myself a JDM programmer, but when I measure everything like
they say
on this page (http://www.ucapps.de/mbhp_jdm.html) I get some very funky
readings:

MCLR: 8.6V (Off: -5.8V/-0.5V) (Should be: 14V)
Vcc: 4.0V (Off: 0.42V) (Should be: 5V)
Clock: 11.8V -> -7.7V (keeps lowering) (Off: -0.3V) (Should be: 5V +- 1V)
Data Out: 3.6V/0.1V/... (Off: -2.9V) (Should be: 5V +- 0.5V)

Off means when I have the box unchecked in IC-Prog Hardware Test.
As you can see everything is way off, sometimes I even get different
results
when I turn a signal on/off a few times. This makes absolutely no sense to
me.

My PCB layout can be found here:
http://members.lycos.nl/anthonyvh/index.php?page=jdm
I just checked everything and I can't find any errors.
My Eagle files can be found here:
http://members.lycos.nl/anthonyvh/etc/jdm.zip

My motherboard is an Abit IT7, so it doesn't have COM ports. I'm using a
parallel + dual serial PCI card from VSCom
(http://vscom.de/produkte/vscom_210h_pci.html).

I configured IC-Prog as shown on the UCapps site (first link). I'm using
WinXP (no service packs).

Does anybody know why I get these readings?

Thanks, Anthony Van Herrewege

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