Table 1. RS-422/485 Port
| Terminal | | RS-422/485 |
| Block | | Signal |
| Signal | Description | Direction of |
| | | Port |
| FR GND | Frame Ground | <------> |
| TD(A)(-) | Transmit Data (A)(-) | Output |
| TD(B)(+) | Transmit Data (B)(+) | Output |
| RD(A)(-) | Receive Data (A)(-) | Input |
| RD(B)(+) | Receive Data (B)(+) | Input |
| GND | Signal Ground | <------> |
| +12VDC | Power Supply | Input |
RS-232 Port | | |
The RS-232 DTE port is an asynchronous port that supports TD and RD signals. In order to make the proper connections to the RS- 232 port. It is necessary to have a basic understanding of the terms DCE and DTE. The original design for connecting RS-232 devices together uses DB25 connectors, and connects a DTE (Data Terminal Equipment) device to a DCE (Data Communication Equipment) device. Each device will have inputs on pins that correspond to outputs on the same pins of the other device. For example, a DTE device transmits data out on pin 2 and a DCE device receives data in on pin 2. IBM PC's are DTE devices and modems are DCE devices. Only TD and RD of the RS-232 port pass through to the RS-485 port when the 485DSS is ON. The 485DSS raises and lowers the RTS output signal on the RS-232 port to reflect the connect state of the port. This signal can notify the RS- 232 device to start communicating to the Host or it can be an alarm output. The Host can monitor the CTS input line to determine if the RS-232 device is requesting access to the network. This input line could also be an alarm input. NOTE: If using RTS or CTS lines as alarms the user may have to design additional circuitry to properly interface to the alarm circuits. Refer to cable charts in Appendix C for making your own cables.
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