Try this location for a pretty good selection on parallel port info:


http://www.paranoia.com/~filipg/HTML/LINK/PORTS/F_Parallel.html

On the boards you have, the data lines are hardware output only. If your
boards are the "genuine article", then there is a unidirectional line
driver (some boards use an 'LS244) after the 8255 or 8255 like device.
Even if you change the port direction (I can't remember what the
register is called on an 8255), you still have a line driver that makes
the lines output only. There are 5 or 6 handshaking lines which can be
used as inputs, however. Another option is just to buy a couple of cheap
clone I/O boards at about $10 each which have bi-directional/ECP/EPP
ports on them.


Frank Richterkessing
Experimental Methods Engineer
GE Appliances

FRANK.RICHTERKESSING@APPL.GE.COM



> ----------
> From:         Martin McCormick[SMTP:martin@DC.CIS.OKSTATE.EDU]
> Sent:         Thursday, April 10, 1997 11:41AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      More Printer Port Questions (Not Directly PIC Related)
>
>         I just saw a couple of messages about reading a P.C. parallel
> port.
> I am attempting to read 8-bit data from one P.C.'s printer port with
> the
> printer port of another P.C.  The two versions of the parallel port
> that I
> have available as the receiver are the IBM MDA and the Hercules
> Graphics
> Adapter (HGA).  The MDA is the old monochrome board with I think, a
> 6845
> as the video controller.  I understand that there is a hack for
> reading from
> this port.  I will need to read 8 bits at a time and then exercise the
> strobes
> to fool the sending P.C. in to thinking it is talking to a printer.
> This
> will be a somewhat temporary arrangement so I am going for quick and
> dirty,
> right now.  The data will only need to flow one way so only the MDA or
> HGA
> board will need to receive.  I have been warned about the possibility
> of
> burning out one of the ports by doing this and this is the reason for
> asking
> the question.  If the port to be protected is the sender, I can put a
> TTL
> buffer or line driver between it and the hacked receiver.  If it is
> the
> receiver that is in danger, then I need to do something else.  I have
> seen
> this discussion before, but I haven't found the magic search words to
> make
> it resurface, yet.  Many thanks for any ideas.
>
> Martin McCormick
>