Using a Serial Board

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Using a Serial Board

The communications portPC port used for sending and receiving serial data (also called serial or COM ports). on the computer is not designed for high-speed communications and reduces system performance. Instead, install a high-speed serial board (such as a DigiboardA high-speed serial board manufactured by the Digiboard Corporation.). High-speed serial boards have several ports (usually 4, 8, or 16) to let you connect several I/O devices to your Citect SCADA system.

You can use identical I/O devices or I/O devices supplied by different manufacturers; Citect SCADA supports many popular I/O devices. You can connect any number of I/O devices; the only limitation is the size of your computer. High-speed serial boards are available for RS-232An industry standard for serial communication. The standard specifies the lines and signal characteristics that are used to control the serial transfer of data between devices., RS-422An industry standard for serial communication. The standard specifies the lines and signal characteristics that are used to control the serial transfer of data between devices. RS-422 uses balanced voltage interface circuits., or RS-485An industry standard for serial communication. The standard specifies the lines and signal characteristics that are used to control the serial transfer of data between devices. RS-485 uses balanced voltage interface circuits in multi-point systems. communication.

If you have several I/O devices from the same manufacturer and these I/O devices support multi-drop communication, you can connect them to an RS-422 or RS-485 high-speed serial board installed in your computer. (The RS-232 standard does not support multi-drop communication.)

Not every high-speed serial board supports RS-422. You can use an RS-232/RS-422 or RS-232/RS-485 converter to achieve the same arrangement.

Note: Using a converter can introduce handshaking/timing considerations.

To set up Citect SCADA to use a serial board:

Install the board in your computer and set it up under Windows as per the accompanying instructions. Use the latest driver from the board manufacturer.
Check that the boards configuration has COMx as the Type, and the Address set to 0. The I/O Port, Interrupt, and Special Opt can be left blank.
Enter the Port Number in the Ports configuration. The COM port number is usually greater than 2 and set in the Ports section of the Control Panel. Use the Special Options field to modify the behavior of the COMx driver. (See COMx Driver Special Options Reference for more information).

Notes

If using your computer's COM port, you don't need to install additional software.
You only need to define the COMx board once. You can then add several ports that use the same Citect SCADA board. For example, a COM port and two serial boards could be defined as one COMx board in Citect SCADA, with multiple ports.