From: cummings@natinst.com (Rodney Cummings)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Interfacing HPIB plotter to centronics
Date: 17 Nov 1992 14:14:57 -0600
Organization: National Instruments, Austin, TX
NNTP-Posting-Host: falcon.natinst.com

In article <1992Nov16.181921.24183@fwi.uva.nl> stolk@fwi.uva.nl (Bram) writes:
>I have a HP plotter, model 9872C which I would like to connect to
>an IBM PC compatible.
>
>The problem is the interfacing.
>The HP has a connector for a HPIB aka GPIB aka IEEE-448 aka IEC-625 bus.
>This is a bus system, whereas my PC has a simple IO port, being
>the Centronics parallel port.
>
>I was wondering if there is any chance that I can interface my
>computer and plotter.
>I was thinking along this kinda line:
>Suppose I make a conversion cable between the centronics and the
>HPIB pin layout.
>Then I write a simple piece of code that sends data to the parallel port
>which will setup my system such that the computer is the only talker,
>and the plotter is the only listener (listen-only).
>Then, I hope, I should be able to use regular plotter drivers from
>standard PC software to drive my plotter.
>
>There are several things that may screw up my plan, as outlined above.
>First of all, some pins on GPIB may have no centronics counterpart,
>or visa versa.

The GPIB bus has 8 control lines : 1 that is always asserted by the
device, 3 that are always asserted by the host, and 4 that can be
asserted by either side.  Most Centronics parallel ports have 9 control
lines : 5 that are always asserted by the device, and 4 that are always
asserted by the host.  This makes it impossible to get a fully functional
GPIB port by using a conversion cable alone.

>Second, it may be that every now and then GPIB bus commands must be
>xmitted, so that a pre configuring the system before using DOS applications
>won't do.

Here's where your problem comes in.  The GPIB bus normally requires
"addressing" before a transfer can begin.  This addressing involves
raising the ATN line and sending the "talk address" of the host and the
"listen address" of the plotter.  Doing this by way of a conversion cable
would be pretty tricky.

If your plotter has a dip switch that allows you to configure it to be
"listen-only", then you may be able to get away with not doing the
addressing.  In this case, a simple conversion cable that ties the
GPIB data lines to the Centronics data lines, and ties the appropriate
handshake lines together may be all you need.  If this is the case,
I *think* that HP sells such a conversion cable... you might try
comp.sys.hp to find out.

>Third, it may be the case that the HP9872C does not use the common
>plotter language HP-GL, as I was hoping.
>This will mean that regular DOS drivers won't be able to cope with
>the plotter.

I dunno about this one... 

>
>If you know how to connect GPIB devices to a centronics port,
>or, maybe, you know for a fact that the thing I want is unviable,
>please drop me line,

As long as your DOS drivers are compatible with the plotter, it is
definitely possible.  If you find out that the plotter requires
GPIB addressing (and thus a conversion cable won't work), we
(National Instruments) sell a Centronics to GPIB conversion box.
It has an internal processor that handles all the needed conversions
between the two ports, including GPIB addressing and data buffering.
Mail me if you're interested...

>
>		Thanx in advance,
>
>			Bram Stolk
-- 
     Rodney Cummings            cummings@natinst.com
     National Instruments       Austin, Texas
Newsgroups: comp.sys.ibm.pc.hardware