AT&T 7400B Plus User Manual page 176

APPENDIX D: LOOPBACK DATA TESTS
Page D-4
Figure D RS-232 Connector Wired as a Loopback Plug
Using the Loopback Data
Test Arrangement
A looparound plug must now be connected to the RS-232 interface
of the 7400B Plus. A looparound plug connects pin number 2 to
pin number 3 on the 7400B Plus Data Module's RS-232 interface
using a modified RS-232 connector. The modified RS-232
connector is shown in Figure D.
The user calls the Loopback Data Test Arrangement from a
terminal/PC. Once connected the user checks to see if characters
entered from the keyboard are successfully echoed back. If the
terminal/PC is set for full duplex and the user types in
The cat
then
The cat
is echoed back in a successful test.
If the terminal/PC is set for half duplex then characters will be
duplicated. For example if set for half duplex (local echo) and the
user slowly types in
The cat
then
TThhee ccaatt
is echoed back in a successful test.
DEFINITY Communications System
7400B Plus Data Module
User´s Guide