[Linux-parport] PC-to-PC parallel port cable

Robert Heller heller at deepsoft.com
Sun Feb 22 13:52:51 GMT 2004

  Dave Strauss <dstrauss at alum.mit.edu>,
  In a message on Sun, 22 Feb 2004 09:36:52 -0500 (EST), wrote :

DS> Most of these issues have been covered in this list before; see
DS> for example http://www.cyberelk.net/tim/parport/archive/current/5769.html
DS> and http://www.cyberelk.net/tim/parport/archive/current/5772.html.
DS> The rest of this thread may also be of interest to you.
DS> If you want to understand more about how the parallel port on PCs
DS> works, I suggest this site:
DS>   http://www.beyondlogic.org/
DS> and in particular these pages:
DS>   http://www.beyondlogic.org/spp/parallel.htm
DS>   http://www.beyondlogic.org/parlcd/parlcd.htm
DS>   http://www.beyondlogic.org/epp/epp.htm
DS>   http://www.beyondlogic.org/ecp/ecp.htm
DS> The documents are DOS-centric but they give a pretty good overview of
DS> the standard parallel port hardware found in PCs.  Finally, if you
DS> want to understand the standards behind ECP and EPP mode you can get
DS> the IEEE1284 standard from ieee.org.
DS> Whenever this issue comes up, I always have to ask why someone is
DS> trying to connect two PCs together via the parallel port.  Why not
DS> just connect them with an ethernet cable?  Unlike the parallel port,
DS> ethernet was designed for bidirectional communications and the
DS> software to do it is already there.

Most 'out of the box' PCs don't have an EtherNet interface.  They do
have parallel ports, which are really designed for printers in a master
(PC) to slave (printer) situation.  PCs *DO* have serial ports, which,
like EtherNet, is designed for bidirectional communications between
'equals' -- you just need a 'null modem' cable (available at your local
Radio Shack).  And yes, Linux does come with software for
communications over a serial port (minicom or mingetty with x/y/zmodem)
OR pppd with Tcp/Ip).

DS> -- Dave Strauss
DS> On Sat, 21 Feb 2004 19:27:53 -0800 (PST), Ravi Shah <shahravi20 at yahoo.com> wrote:
DS> >  
DS> >  Thanks for your response.
DS> >  
DS> >  I am sorry, but I am getting confused. Can you please explain, what
DS> >  difference is it making? Now since you can connect two PCs using
DS> >  SPP or nibble mode and share data, why not in ECP/EPP?
DS> >  
DS> >  There is a document ECP Specifications from Microsoft, where this
DS> >  type of thing is getting done using a special cable (which
DS> >  unfortunately is not available in market)?
DS> >  
DS> >  Thanks a lot for your help,
DS> >  Ravi
DS> >  
DS> >  --- Dave Strauss <dstrauss at alum.mit.edu> wrote:
DS> >  > On Sat, 21 Feb 2004 13:12:30 -0800 (PST), Ravi Shah <shahravi20 at yahoo.com> wrote:
DS> >  > >  
DS> >  > >  Hi,
DS> >  > >  
DS> >  > >  Does anybody know of a parallel port cable that can be used to
DS> >  > >  connect two PCs through ECP/EPP protocol??
DS> >  > >  
DS> >  > >  Thanks in advance for help,
DS> >  > >  Ravi
DS> >  > >  
DS> >  > 
DS> >  > You basically can't do that, because ECP and EPP are both master/slave
DS> >  > protocols -- from both the hardware and the software point of view --
DS> >  > and a PC only contains the hardware to do the master end.  You can
DS> >  > use a LapLink parallel port cable to connect two PCs, but you can't
DS> >  > do ECP or EPP over the cable.
DS> >  > 
DS> >  > -- Dave Strauss
DS> >  
DS> >  
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Robert Heller                        ||InterNet:   heller at cs.umass.edu
http://vis-www.cs.umass.edu/~heller  ||            heller at deepsoft.com
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