Ref: 03190001
Title: Using HP Plotters with 3Com 3+ Networks
Date: 12/6/89

Copyright 3Com Corporation, 1991.  All rights reserved.

As 3+ systems are increasingly used in the fields of presentation
graphics and CAD, shared plotter support becomes even more
important.  3+ does support shared plotter devices.

This note describes the proper integration of a Hewlett-Packard
7550A plotter with a 3Com 3+ network.  Other Hewlett-Packard
plotter devices work in a similar fashion, so these notes should
apply.  However, each device differs from the others in sometimes
subtle ways, so proper pre-sale testing is always recommended.
In particular, different models may require the serial interface
to be configured by means of switch settings; the 7550A settings
can all be configured from the front panel.  Proper interfacing
requires the right serial cable, configuration of the plotter's
serial interface and configuration of the server's serial
interface.  Finally, application software configuration may be
required.

Test Environment

Our test environment for this application note was an Ethernet
network with a 3Server3 running 3Com's 3+ operating system,
version 1.1.  The workstation was a Compaq 386.  Application
Software tested included Software Publishing's Harvard
Presentation Graphics, and AutoDesk's AutoCAD.

Physical Connection

The plotter is connected to the server by means of a serial cable
available from Hewlett-Packard as part number 17255F.  The cable
is female at both ends, and is connected between a shared serial
port on the server and the "computer/modem" port on the 7550A.  A
similar cable, the 17255D, is male at one end and female at the
other for connection to models 7470A, 7475A, 7580B, 7585B and
7586B.  This latter cable is frequently available and referred to
as an "IBM PC/XT to HP Laserjet" cable.  Not all of the above
mentioned plotter models have been tested on 3+ networks.

If the above cable is not available, the following schematic
describes the appropriate connections:


                 1---------------------------------1
                 2---------------------------------3
                 3---------------------------------2
                 7---------------------------------7
                 5----------|----------------------20
                 6----------|      |---------------5
                20-----------------|---------------6

                     Pins not shown are not used.

Server Configuration

Using the 3+ Installation and Configuration menus, select
Configure Services, Change Share, Configure Printers, and
configure a COM: port on the server as follows:

 ---------------------------------------------------------------
| 3+Share Network Printer Config Ver 1.1.1 Memory Used:xxxx     |
|                                                               |
|                                                               |
| Configure COM1: as network printer?    Y                      |
| Description                            Hewlett-Packard 7550A  |
| Eject a page between jobs?             N                      |
| Translate IBM to Laserjet (Form Type)  0                      |
|                                                               |
| Form Type      1               Print Banners?     N           |
| Baud rate      N               Parity             3           |
| Protocol Type  1               Retry Count        10          |
| Buffer size    4096            Interrupt level    0           |
|                                                               |
| Change reset sequence?  N    Reset sequence name  HP-GL       |
| Reset retries    10                                           |
|                                                               |
 ----------------------------------------------------------------

Define a custom reset sequence by answering Y in the Change Reset
Sequence? field.  Name the sequence HP-GL.  Define the sequence
as follows:   41,46,3B

The HP-GL command is AF;.  The purpose of this reset sequence is
to ensure the automatic loading of a clean sheet of paper (or
transparency) at the beginning of a new job if the previous
application did not already perform this function.  Proper
operation of this feature requires that the plotter must be in
automatic feed mode (an * must appear in the plotter's display
window below the auto feed key, which toggles this option.)

Note that the reset sequence does not actually perform a reset
(HP-GL: ESC.R) on the plotter.  This is because the execution of
this command puts the plotter in a state where it accepts
characters from the host and loses them until the reset is
complete.  Although there is a programmatic mechanism a directly
connected host can use to determine when it is safe to send more
output, the 3+Print despooler does not support this convention.
The result of using the reset sequence will be the loss of the
first part of a new plot file.  It is important to understand
then, that if an application places the plotter in a non-standard
state and fails to reset it explicitly, results may be
unpredictable for subsequent jobs, particularly if they are
generated by different applications.

Plotter Configuration

The HP 7550A has a front panel allowing the user to control many
aspects of the plotter's operation.  Please refer to the HP 7550
Operation and Interconnection Manual for further information.

Proper network operation requires that the plotter is set up with
standard defaults, with the following essential parameters:

               Interface:            Standard Serial
               Data Flow:            Remote, Standalone
               Bypass:               Off
               Handshake:            XON/XOFF, Direct
               Duplex:               Half
               Parity:               8 bits, Off
               Baud:                 9600

To review or change any of these parameters, refer to the HP
manual.  Generally, you touch the Enter Key immediately followed
by the Next Display key to enter the configuration section.
There are several submenus that the unlabled keys lead to.  Once
on a menu where a parameter can actually be changed, an asterisk
will flash in the upper right hand corner of the display, near
the Enter key.  Use the appropriate blank keys to toggle through
the available options, press Enter to accept the current choice.
To exit that menu without changing anything, press Next Display.
To leave the set-up menus and return to the normal plotter
operation menus, press Enter, then Next Display.

Application Configuration

Applications must be configured to send HP-GL formatted output to
a device that can be redirected across the network to the shared
port.  Generally, this device appears to the application as
LPT1:, which is linked to the shared device with the 3P LINK
command.

For Harvard Presentation Graphics, select the HP 7550A as
the plotter device, and LPT1: as the output port.

Some applications, like AutoCAD, may assume that the only
connection to the plotter is serial.  This presents a problem,
since you cannot redirect output to COM1: across the network.
AutoCAD provides a useful workaround, however.  When the plotter
is configured, answer YES to the question "Plot to file?".  When
prompted for a file name, supply PRN: as the name.  This
name can be supplied as the default name as well.

Finally, some applications expect interactive communication with
the plotter.  HP-GL supports queries such as "is the pen up or
down?" or "what color pen is loaded?".  Spooled
devices cannot support such interactivity; results from such
applications may be unpredictable.  In any case where "plot to
file" is an option, that option must assume there can be no
interactivity, so it is safe to assume that the application
does not require it, at least when in the "plot-to-file" mode.

