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Q: Connections for RS-485 or RS-422 to the 4WSD9OTB or 4WSD25OTB Converters?
Mode/Switches |
Switch 1 (Tx) |
Switch 2 (Rx) |
Switch 3 (bridge) |
Switch 4 (bridge) |
RS-485 2-Wire Mode (half duplex) |
RS-485 |
Echo Off |
2-Wire |
2-Wire |
RS-485 4-Wire Mode
(full duplex) |
RS-485 |
Echo On |
4-Wire |
4-Wire |
Mode/Switches |
Switch 1 (Tx) |
Switch 2 (Rx) |
Switch 3 (bridge) |
Switch 4 (bridge) |
RS-422 4-Wire Mode
(full duplex) |
RS-422 |
Echo On |
4-Wire |
4-Wire |
Table 1 – Switch Settings for Operating Mode
Mode/Switches |
Switch 1 (Tx) |
Switch 2 (Rx) |
Switch 3 (bridge) |
Switch 4 (bridge) |
RS-485 2-Wire Mode (half duplex) |
RS-485 |
Echo Off |
2-Wire |
2-Wire |
RS-485 4-Wire Mode
(full duplex) |
RS-485 |
Echo On |
4-Wire |
4-Wire |
RS-422 4-Wire Mode
(full duplex) |
RS-422 |
Echo On |
4-Wire |
4-Wire |
Loopback Test Mode* |
As Desired |
Echo On |
2-Wire |
2-Wire |
*Used with HyperTerminal or another terminal program to confirm operation of data through converter.
The ComTest program is available on our website in the Technical Library (Tech Notes) under Software Tools.
Full Duplex 4-wire operation usually works best for RS-232 signals. Half Duplex operation using “2-wire” connections is usually NOT satisfactory because the RS-485 bus takes time to “turn-around” between transmit and receive, some of the first byte sent may be lost. RS-232 devices don’t wait before responding to a data request, but RS-485 devices designed for 2-wire operation wait.
This information should help you make the needed connections.
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