You need to assign a variable tag to each I/O DeviceAn item of equipment that communicates with plant-floor control or monitoring equipment (sensors, controllers, and so on). The most common I/O devices are PLCs (programmable logic controllers); however, supports a wide range of I/O devices, including loop controllers, bar code readers, scientific analyzers, remote terminal units (RTUs), and distributed control systems (DCS). can communicate with any I/O device that has a standard communications channel or data highway. variable that CitectSCADA uses in your runtime system. To define your variable tags, you declare them in the variable tag database. The variable tag becomes a label, used to reference the data value of the I/O Device register at the specified address. Using labels has several benefits:
You need to define your variables as a specific data type. The most common variables supported by I/O Devices are digital and integer. CitectSCADA also supports real, string, byte, bcd, long, and longbcd data types.
After you have defined your variable tags, you can use them to:
The most common variables supported by I/O Devices are digital and integer variables, although some I/O Devices support other numeric variables and strings.