Connecting rs-422 serial devices, Dte versus dce, Db9 serial cables and loopback plugs – Comtrol RocketPort Plus 422 Universal PCI User Manual
Page 9: Refer to
RocketPort uPCI Plus 422 User Guide: 2000370 Rev. B
Connecting RS-422 Serial Devices - 9
Connecting RS-422 Serial Devices
This section provides information about the RocketPort uPCI Plus 422 connectors,
in the event that you need to build cables or loopback plugs.
A loopback plug is a serial port plug with pins wired together that you can use
with application (for example, the diagnostic, Test Terminal, or minicom) to test
serial ports. See
Before Calling Technical Support
on Page 13 for information
about using the test application shipped with the RocketPort uPCI Plus 422.
DTE Versus DCE
The DIP switch for the RocketPort uPCI Plus 422 ports are set to DTE at the
factory.
Most serial devices, except modems, are Data Terminal Equipment (DTE) devices.
Modems are Data Communication Equipment (DCE) devices.
How you build a cable depends on which device your are connecting to (DTE or
DCE). For example, you need a null-modem cable to connect the COM ports
(COM1 or COM2) on the computer or the RocketPort uPCI Plus 422 ports to
printers, terminals, bar code readers or DNC equipment. If you are connecting a
DTE device to a DCE device you need a straight-through modem cable.
•
Straight-through cable (DTE to DCE) - connects TxD to TxD and RxD to RxD.
•
Null-modem cable (DTE to DTE) - connects TxD to RxD and RxD to TxD.
Note: DTE and DCE modes are controlled with the DIP switch on the RocketPort
uPCI Plus 422 (see
Card and Interface Installation
on Page 7 for
information).
DB9 Serial Cables and Loopback Plugs
The following figures and table illustrate the signals present on DB9 connectors if
you need to build your own null-modem or straight-through DB9 serial cables.
Quadcables and octacables use DB9 male connectors.
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