Network Working Group A. Berggreen
Request for Comments: 600
COMPUTER SYSTEMS LABORATORY--UCSB
INTERFACING AN ILLINOIS PLASMA TERMINAL TO THE ARPANET
The PLATO IV System based at the University of Illinois at Urbana is
a highly sophisticated and very powerful approach to Computer Aided
Instruction. The PLATO IV system makes use of a plasma display
terminal that is a unique device with capabilities not presently
found on computer terminals. A number of ARPA supported projects
intend to use the plasma terminal on local connection to computer
resources or by long-distance connection to the PLATO IV System.
One problem in using the PLATO System from any appreciable distance,
is the communication costs involved (i.e. long-distance telephone
rates for many consecutive hours). Also, use of the plasma terminal
in other applications is hampered since the communications scheme
employed in the PLATO System in non-standard.
One approach to reducing the communications cost is to use the
ARPANET for the long-distance connection, since the Network is
potentially one of the most reliable and cost effective means of
transmitting computer data. This approach is reasonable the is a
Network node near the PLATO System, (the PDP-11/ANTS system at the
Center for Advanced Computation at the University of Illinois at
Urbana) and with the increasing number of TIPS and IMPS on the
ARPANET access is becomming easier ad more widespread.
The plasma terminals are designed to be connected directly to
telephone lines using Frequency Shift Keying (FSK) modulation. Using
dedicated telephone lines, the plasma terminal may be run at a data
rate of 1200 bits/sec in full-duplex operation. Using dial-up lines,
the terminal may be run with display information being received at
1200 bits/sec and data to the computer being transmitted at 120
bits/sec using a reverse chanel scheme.
The data and command words used by the plasma terminal differ for
input and output. Input received from the computer arrives in 20-bit
words plus one start bit. Data transmitted to the computer is sent
in 11-bit words plus one start bit.
In order to make the plasma terminal more generally applicable for
standard communication, and specifically adapted to the ARPANET
connection by way of a TIP, the terminal must be interfaced in such a