Jim,
I have tried to talk to a Texas Instruments PLC using RS232.  I had many
troubles because some of their protocol included Enc & Ack as part of the
Data String.  I could never work around this.  What I did was to use a
RS232 to Digital Converter.  It has 16 Digital lines that can be either
sensed or switched via RS232 from the HP.  It works well for my three
projects, but may not for yours.  I am controlling two conveyor lines and
a small program to unlock two office doors using these converters.  I
have not tried to do this thru the terminal printer port, but use a ports
from a DTC.

So far the TI PLC is the only RS232 object that I have not been able to
get to work.  If the data stream protocol is more user friendly, you
should be able to at least talk thru a DTC.  I have been able to gather
data from bar code readers, printers, a phone switch, digital converters,
but not that darn TI.

Steve Murphy
Information Systems Manager
Salem Division
World Color
[log in to unmask]

 ----------
From:  Therm-O-Link[SMTP:[log in to unmask]]
Sent:  Wednesday, January 22, 1997 12:32 PM
To:  HP3000-L
Subject:  HP700 Terminals to PLC

Knowledgable Listers:

We are beginning a project to install HP 700 terminals (most likely
/92's) at the operator station on our manufacturing lines.  The
terminals will connect to our HP3000 and present the operator with
scheduled production for his/her shift.  Part of the information
presented will be product specifications.  The line itself is
controlled by Allen Bradley PLC's.  We would like to link the PLC
to the terminal (using the "printer" port on the terminal) and send
commands to the PLC to control the manufacturing equipment.  We will
also receive data back from the PLC to record "events" in the
manufacturing process.

Has anyone ever done this?

Assuming that the PLC's can receive/send ASCII data via RS232, what
problems do you forsee in pursuing this project?

Any other comments or questions?

Jim Phillips                            Manager of Information Systems
E-Mail: [log in to unmask]      Therm-O-Link, Inc.
Phone: (330) 527-2124                   P. O. Box 285
  Fax: (330) 527-2123                   Garrettsville, Ohio  44231