Motorola MVME197LE - Manual (Page 69)

MVME197LE/D2A-1
A
EIA-232-D
INTERCONNECTIONS
The EIA-232-D Standard is the most widely used interface between terminals
and computers or modems, and yet it is not fully understood. This is because
all the lines are not clearly defined, and many users do not see the need to
conform for their applications. A system should easily connect to any other.
Many times designers think only of their own equipment, but the state-of-the-
art is computer-to-computer or computer-to-modem operation.
The DIA-232-D Standard was originally developed by the Bell System to
connect terminals via modems. Therefore, several handshaking lines were
included. In many applications these are not needed, but since they permit
diagnosis of problems, they are included in many applications.
Table A-1 lists the standard DIA-232-D interconnections. To interpret this
information correctly it is necessary to know that EIA-232-D is intended to
connect a terminal to a modem. When computers are connected to computers
without modems, one of them must be configured as a terminal and the other
as a modem. Because computers are normally configured to work with
terminals, they are said to be configured as a modem. Also, the signal levels
must be between +3 and +15 volts for a high level, and between -3 and -15 volts
for a low level. Any attempt to connect units in parallel may result in out of
range voltages and is not allowed by the EIA-232-D specifications.