Re: Parallel port

[Jon Elson <jmelson-at-artsci.wustl.edu>]

JohnDRoc-at-aol.com wrote:

> Jon,
>
> Is there a difference between the ground opposite the input on the STG board
> and a physical ground, such as the ground shield on the cable?

The ground shield on WHAT cable?  The STG card has a 50-pin
ribbon cable connector on it.  You can hook up any sort of cable
you want, but there is no ground terminal provided for a cable
shield, specifically.  Ribbon cables with a shield usually have a
'drain' wire that is connected to one pin on the connector.

But, if you were to use the computer case as the signal reference, you
might have a lot of zero offset.  It would be fine to use the computer case
as a ground terminal for grounding a cable shield, however.  It is considered
the best practice to ground shields at one end, only, to eliminate induced
signals from current flowing through the shield.  This assumes a good
ground conductor is provided to carry any ground currents.

And, yes, I believe the grounds associated with the STG card's analog
outputs is different from the other digital grounds.  It may be isolated by
a small inductor on the board, or just a one-point connection.

Jon