Return currents from the drivers need some path to flow.
By using ground wires in the cable, you give the signals
the smallest path to return over. This reduces inductance
of the signal path and provides the best signal quality.
One thing to be careful of is trying to write one signal
high while the other is driving low. If two CMOS outputs
are connected together, then the one that is high
provides a short to VCC, while the other that is low
provides a short to GND - zap!!
Now, generally SPP has 4k7 pull-ups as the data
ports are open-drain. However, I am not sure about
general EPP/ECP ports and how they implement their
Personally I'd get a $25 EPP board and plug it in a
PCI slot and test that first. That way you don't fry your
----- Original Message -----
From: "daniel sheltraw" <firstname.lastname@example.org>
Sent: Thursday, November 16, 2000 1:50 PM
Subject: [PARPORT] parallel port grounding
> Hello parport listees
> I have two parallel ports in my laptop machine. One is on the
> motherboard the other is a PCMCIA card. As a code-test I would
> simply like to send data from one port and read on the other.
> Do I simply connect data port lines to data port lines (pins 2-9
> with direction bits set properly in the control register)
> or do I need to connect the ground pins together as well? In
> other words: Is the common internal grounding of the machine
> good enough?
> Thanks for your help,
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This archive was generated by hypermail 2b29 : Thu Nov 16 2000 - 19:01:30 EST