# Modbus Port - RS-232 or RS-485/RS-422 Physical Network Interface

This section only applies to Catalyst’s shipped with a Rev. D and higher I/O Board and with version 1.70 or higher firmware. To determine if your Catalyst has a Rev. D or higher I/O board refer to the Catalyst Operator’s Manual Section 2.5 for the location of the I/O board revision designator. To determine your Catalyst’s firmware version use Alarmware and go online with the RTU. Open the Diagnostic Menu and select Factory Settings. In the diagnostic window (below the RTU online window) the factory settings will be displayed in the Catalyst Summary Report.

The Modbus Port on Catalysts with the above listed enhancements is capable of optionally interfacing via RS-485/RS-422 in addition to the usual RS-232C interface. This section will cover how to setup the Catalyst’s hardware for the RS-485/RS-422 Modbus interface. Also, included in this section is a very brief discussion of the some issues concerning interfacing via RS-485 and RS-422. A thorough discussion of RS-485 and RS-422 is beyond the scope of this manual. For more information on RS-485 and RS-422 please refer to documentation from the manufacturers of devices being interfaced (i.e. PLCs) and from manufacturers of RS-485/RS-422 conversion products.

Modbus Port Interface Topics

Selecting RS232C or RS-485/RS-422

Why Use RS-485 or RS-422?

Difference between RS-485 and RS-422

Modbus On Multi-drop Networks

Using RS-485/RS-422 to Interface to a Single Modbus Device