Parallel ports

From: Hans B Pufal <>
Date: Sat Jan 31 22:33:45 1998

Barry Peterson wrote:
> On Fri, 30 Jan 1998 21:20:22 -0600 (CST), you said:
> >At 02:39 AM 1/30/98 -0500, you wrote:
> >>> Have you ever seen a Zenith "MiniSport"? Uses 2" floppies? I found
> >[...]
> >>do its upload and you've got at least one disk, you can probably
> >>(don't count on it, but probably) attach a parallel Zip drive).
> >
> >Question: when did parallel ports become bi-directional (i.e., useable for
> >zip drives and such)?
> I thought they always were bi-directional on IBM-compats. I've run
> Laplink on almost every PC I've ever owned.

Not quite. There are two ways of getting bidirectional data transfers
out of a parallel port. The first which will work on any compatible is
to use the normal data lines for output and the status lines for input.
This limits the speeed since only 4 bits at a time can be read. Later
implementations of the parallel port allowed full 8 bit bidirectional
transfers on the data lines, providing a higher possible data rate.

It is my understanding that most (older) software can work in either of
the two modes.

 Hans B. Pufal : <>
 Comprehensive Computer Catalogue : <>
Received on Sat Jan 31 1998 - 22:33:45 GMT

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