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8 Introduction
Communications
This terminal is equipped with three ports. The two serial ports are intended for
connecting to either a host/modem or a serial printer. The remaining port is a
Centronics-compatible printer port. The port you use as the printer port depends on
whether you have a serial or a parallel interface to the printer. Another factor affecting
your port selection is your choice of connecting the terminal to one or two host
computers.
The first host/printer serial port (SES1-EIA) can communicate with your computer or
printer at a baud rate of 110 to 134,400 baud (bits per second). The second
host/printer serial port (SES2-AUX) can communicate at speeds from 110 baud to
38,400 baud. Either port can be used to connect to a host computer/modem or serial
printer.
You have the choice of using either the second serial port or the parallel printer port as
your printer interface. Refer to the following sections for further information on these
ports.
In single host mode, you have the choice to use the second serial port or to use the
parallel printer port, as your printer interface. In dual host mode, the natural choice is
to use the parallel port, although other options are available (See the Installation
chapter). Refer to the following sections for further information on these ports.
Receive Flow Control
Because devices can receive data faster than they can process it, data flow control
(selectable in the PORTS menu of Setup) should be used to prevent data loss. Software
flow control relies on the Xon and Xoff characters (“g” and “e” characters in Scan
Code key mode) to indicate when the terminal is able or unable to store further data.
The Xon signal transmits the DC1 character (11h) and the Xoff signal transmits DC3
(13h).
When “EIA (or Aux) Rcv” in the Setup menu for PORTS is “Xon-Xoff,” the
terminal issues an Xoff character, indicating to the host that it should stop transmitting
data. The terminal will then continue to process data until its receive buffer is empty.
It will then issue an Xon character to the host, indicating that it can resume sending
data to the terminal.