Communications Interface - Data General DASHER D100 User Reference

Chapter 3
INTERFACING AND CABLING
DASHER D100/D200 display terminals contain a serial
asynchronous interface that supports full-duplex
communication with a computer or communications
system. The interface accommodates both 20mA current
loop and EIA RS232-C connections and provides a subset
of standard EIA modem control functions.
DASHER D100/D200 terminals equipped with the split
baud and printer option contain a_ second serial
asynchronous interface and support logic. The optional
(printer) interface performs the following functions:
e It transmits serial data to an ASCII-based printer.
¢ It defines the transmission rate of data transmitted by
the terminal, when selected.
Thus, the split baud portion of the option allows the
terminal to support a communications line with two
bandwidths, one high-speed and one low-speed.
COMMUNICATIONS INTERFACE
The terminal's communications interface transmits and
receives serial data bursts that consist of 1 start bit, 7 data
bits, an optional parity bit and 1 or 2 stop bits.
transmission rate. When operating at 110 baud and below,
split baud option is enabled, 1 stop bit is selected for all
baud rates.
Start Data Parity Stop
bit bits bit bit *
* 2 stop bits used at or below 110 baud unless split
baud option is enabled.
Figure 3.1 Communications Data Format
Cabling
In general, the choice of communications line, 20mA
current loop or EIA, depends upon the cable length
required, the presence of a modem, and the configuration
of the host system. When a long cable is required to connect
the terminal directly to a system, the 20mA current loop
connection can be used. It supports a 1500 foot (457.2 meters)
cable at transmission rates up to 9600 baud and a 500 foot
(152.4 meters) cable at 19,200 baud. When a short cable (50
feet/15.2 meters, maximum) is required or the terminal is
interfaced to a Bell 103, 113 or 212 compatible modem, the
EIA connection can be used.
Figure 3.2 shows the 25-pin Cannon connector (located at
the back of the terminal) that joins the terminal's EIA
interface to a computer or modem via an EIA cable. Figure
3.3 lists the EIA cables that are available from Data General
and identifies the pin connections. When using a cable not
shown in Figure 3.3, wire the terminal end as shown in
Figure 3.4.
139. —j
25 pin Cannon connector
Figure 3.2 Communications Connector