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RS-232 Connector
Connecting to a
Modem
Computer Interfaces 4-16
To RS-232 Connector
RS-232 Cable
Figure 4-3, Using the RS-232 Interface
If you wish to connect the 1256 directly to a modem instead of a
computer or data terminal, the connection will be DCE-to-DCE. A
DCE-to-DCE connection requires a special serial cable, known as
a null-modem. In a null-modem cable, the Received Data (RxD)
and Transmitted Data (TxD) signals are reversed at one connector,
and the Clear-to-Send (CTS) and Request-to-Send (RTS) signals
are also reversed at one connector. This can be accomplished by
constructing a special nine-pin serial cable with the signals wired
as shown in Figure 4-4b, Using the 1256 with a Modem. Note
that the RS-232 connector at the 1256 is a 9-pin female D-
Subminiature (DB-9) type.
1256E User Manual
Racal Instruments © 2002
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