Table 2. RS-232 DTE DB25P Connector Chart
| | | Signal |
| | | Direction of |
| | | RS-232 DTE |
Pin # | Signal | Description | Port |
1 | FR GND | Frame Ground | <------> |
2 | TD | Transmit Data | Output |
3 | RD | Receive Data | Input |
4 | RTS | Request to Send | Output |
5 | CTS | Clear to Send | Input |
7 | SG | Signal Ground | <------> |
RS-422/485 Wiring
RS-485 receivers also have an enable/disable control line. The 2W/4W jumper selects when to enable and disable RS-485 receiver. Setting the jumper to the 4W position constantly enables the receiver which is the same as operating in an RS-422/485 4-wire mode. In this position and connected to a 2-wire network, all data being transmitted by the RS-485 driver echos back through the RS-
485receiver. Setting the jumper to 2W (RS-485, 2-wire mode)
automatically enables the receiver when the RS-485 driver disables and visa versa.
To configure the 485DSS for a typical 2-wire party line network, set the jumper in the 2W position. Refer to Figure 2 for the jumper location.
The EIA RS-485 Specification labels data lines with an "A" and "B" designator. Some RS-485 equipment uses a "+" and "-" designator. In almost all cases, the "A" line is the equivalent of the "- " line and the "B" line is the equivalent of the "+" line. See Figure 3 for a wiring example.
2-Wire Mode
RS-485 allows half-duplex communications of multiple drivers having a control line for enabling and disabling (tri-stating) their outputs. When the 485DSS transmits a status reply message to the Host, the microcontroller will automatically enable the driver before transmitting the first character of the reply and disable the driver after the last character of the reply. When the 485DSS is ON (selected) and the RS-232 device is transmitting data to the Host the Send Data (SD) control circuit enables and disables the driver. The 485DSS disables the driver when it is not transmitting data to the Host and listens to (receives) all communications on the network.
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PH (815) 433-5100 -- FAX (815) 434-7094