Understanding Communications
This terminal is equipped with three ports. The two serial ports are intended for connecting to a host, a 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. Also, if you use
the parallel port for a printer (or don’t connect to a printer), you can use the serial ports to connect to 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. 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.
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 you set “EIA (or Aux) Rcv” in the Setup menu for PORTS to “Xon-Xoff,” the terminal issues an Xoff character, indicating to the host that it should stop
transmitting data. The terminal then continues to process data until its receive buffer is empty. It then issues an Xon character to the host, indicating that it can
resume sending data to the terminal.
Note:
If you set the “EIA (or Aux) Rcv” in Setup to “No Protocol”, the terminal will continue to accept characters into its receive buffer until it is full. Additional
characters will be lost. Xon-Xoff protocol must also be set on the host computer or printer for proper handshaking.
The serial/host printer ports support both software- and hardware-based “receive” flow control (Xon-Xoff). The SES1-EIA port has an outgoing DTR (Data
Terminal Ready) signal. If you set “EIA Rec” to “DTR” in Setup and the terminal’s receive buffer fills to the level mentioned above, the terminal will set the DTR
signal low to inform the host (serial) device to stop sending data. On the SES2-AUX port, if you set “Aux Recv” to “DSR” in Setup, the outgoing DSR (Data Set
Ready) signal signals the host (serial) device that the terminal is not ready to receive more data.
Transmit Flow Control
In a fashion similar to that described under “Receive Flow Control,” the terminal understands the Xon and Xoff requests from the host when it is transmitting
data (provided you set the “EIA (or Aux) Xmt” to in Setup “Xon-Xoff”). This arrangement is referred to as “transmit” flow control.
This terminal stops transmitting data to the host or printer when it receives an Xoff (DC3) code. However, if the terminal needs to send a receive protocol
character, it transmits that character even if it has received an Xoff code. When the terminal stops transmitting, the data resides in the transmit buffer. Once the
buffer is full, additional keyboard data is lost. When an Xon (DC1) character is received, the terminal can again send data to the attached serial device.
The serial host/printer ports supports both software- and hardware-based “transmit” flow control (Xon-Xoff). To control the flow of data to the serial/host ports,
enable DSR on the SES1-EIA port and DTR on the SES2-AUX port monitor serial (provided EIA and AUX Xmit are “DSR” and “DTR”, respectively, in Setup).
For parallel printers, this terminal monitors the BUSY and ERROR signals that are sent by the printer to determine when data transmission should be stopped or
resumed.
Host/Printer Port 1
This port, labeled “SES1-EIA,” is designed for connection to the host (computer or modem) or a serial printer via a 25-pin D-shell (DB25P) female connector.
This port uses an RS-232-C communication interface, is configured as a DTE (Data Terminal Equipment) device, and can operate from 110 to 134,400 baud. The
supported pins are shown below:
Host/Printer Port 1 Pin Assignments
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