ADVICE SOUGHT INTERFACING ISSUE

I'm a little rusty when it comes to some interfacing
issues so I humbly cast my inquiry regarding a "current"
(no pun intended) issue facing me in my Taig mill
conversion onto the great bubbling pool of experience
and wisdom which constitutes the CAD_CAM_EDM_DRO group.

I am converting my Taig to Step&Dir using 4 PacSci
NEMA 34 bipolars and 4 matching 6410 bipolar drives.
The choice was primarily economical ... the above were
free ... long story ... interesting ... possibly involving
South American drug cartels and missing persons ...
but long ... custom equipment, ordered, paid for, but
unclaimed after nearly 4 years ... off the books ...

Them: "Ken can you get rid of this stuff I'm tired
of moving it around"

Me : "Well of course ... if you insist ... (trying
to keep from grinning insanely) ..."

I'm using the original three motors and phase drive
which came with the Taig CNC mill (which I bought 2nd hand)
on my Taig lathe CNC conversion project (ain't I havin'
fun!!!!)

anyway ...

I'm going to use SuperCAM through PC parallel port to
handle the S&D to the 6410's. I don't know a lot
about the electrical properties of the parallel
ports on a PC and there seem to be a few flavors
as well. The 6410's inputs are opto-isolated
(this is good) and PacSci shows a little schematic
of the interface (see group files section under

http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
files/KWJ-files/6410interface.jpg

The schematic shows single input NAND logic gates
feeding the inputs (which, if you think about it
is a tad odd in and of itself) and these gates are
sourced with +5VDC. Now the parallel port doesn't
have a +5VDC pin. I know there are some on the
game port (pin 1 for example) but I don't want
the the extra cable just to get +5VDC from the
PC (unless I have too). I have built myself a
breakout box to separate out the 25 signals from
the parallel port from an old disk drive. As an
aside, these old disk drives are great project
boxes. Tear out the 30MB drive and can it, and you
have a nice metal box, +12, +5, a fan, some connectors,
an LED power on light, D-power cord connection and
AC switch. Funny that they are worth more for those
components than for the drive itself.

So ... finally to my question 2 parts ...

1. Can I build up a little logic circuit on a board
inside my HD case to drive the opto's in the 6410
and power it using the old HD power supply in my
case even though the logic inputs to the gates
are coming from the PC (as long as I tie the COMMON
from my box to the ground pins from the PC) or does
this create some type of potential ground loop problem
and a possible source for noise? If anyone wants to
wax eloquent regarding ground loops and noise issues
further, you would certainly have my undivided attention.
I can bring out the +5 off the PC game port but it's not
as clean as just having the one cable from the LPT port
by itself also there may be additional logic, limit
switches that need +5 and perhaps some Solid State relays
I might add to my box later and I don't know what is
left over from the PC's +5VDC supply after taking care
of it's own business. Also I kind of like the idea of
having some logic ahead of the opto's in the 6410 because
I know what they can drive whereas I'm unsure what the
current sourcing/sinking of the parallel port signals
are.

2. If you look at the interface schematic referenced above
two lines are shown terminating in thin air which make up
the ENABLE function input for the 6410. I can show those here:

| inside 6410
?___________ENABLED (collector) _____J1________ | -o 5Vdc
| |----/
| | / ---photo diode
?___________ENABLED (emitter) _______J1________ | -0 DRIVER ENABLED (NOT)
|
How do I provide the correct circuit and signal to these lines
in order to produce the ENABLE signal? The signal out from the
PC (and SuperCam) is ENABLE (logical high sourcing) and I want
to feed this signal to all 4 motor drives simultaneously.

ok ... 3 parts.

3. When I do the logic circuits, what are the best devices to
use? TTL, Low power TTL, Schottkey TTL? I always remember TTL
being very susceptible to noise especially when there are brush
motors near by ... or am I just paranoid?

Sorry it's so long ... I figure if you're going to ask a question
then you're obligated to provide as much info as possible.

Since this is fairly specific to what I'm doing you may want to
spare the group and respond to me directly.

Thanks in advance for any help, pointers, info,


Ken Jenkins
kjenkins@...