User`s guide

TECHNICAL REFERENCE
87
The Serial Interface
The serial interface is a standard developed by the Electronic Industries Association (EIA). It
defines the signals and voltages used when data is exchanged between a computer and a
modem or serial printer.
The entire standard covers many more functions than are used in most data communications
applications. Data is transmitted between the devices over a shielded serial cable with a 25-pin
male (DB-25) connector to the modem and a 25-pin, 9-pin, 8-pin, or custom-built connector to
the computer.
FCC regulations require the use of a shielded cable when connecting a modem to a computer to
ensure minimal interference with radio and television.
Pin assignments are factory-set in the U.S. Robotics modem to match the standard DB-25
assignments in the following table. DB-9 connectors for IBM/AT-compatible computers should
be wired at the computer end of the cable as shown in the DB-9 column.