Variable Definition

A Variable is a container that holds information on equipment such as a PLC or a data server (i.e., OPC data server) for process control and supervision purposes. There are many different types of variables depending on the PLC or the server used. Access a variable by using a name or a physical address in the equipment memory. Variables can be read or written in any equipment, according to need.

For example, a variable can be the ongoing temperature of an industrial oven. This value is stored in the oven's PLC and can be controlled by another PLC or accessed and supervised by a SCADA system. The same value can be read by another PLC which controls the heating system.

Variable Use

Reading and writing variables inside a network is strictly controlled. Pay close attention if an unplanned change occurs, especially if it is a new, written variable. Such behavior could be an attacker attempting to take control of the process. Cisco Cyber Vision reports the variables' messages detected on the equipment of the industrial network.

Find details on Variable accesses in a component's technical sheet. Use Sort arrows to see a table containing the following:

• The name of the variable

• Its type (READ or WRITE) but not the value itself

• Which component accessed the variable

• The first and last time the component accessed the variable

  

The entry "2 different accesses" (1) indicates that two components have read the variable.

Variable Location

View the number of variable accesses per component on the component list view. Sort the var column by ascending or descending number.

For component details, click a component. The right panel opens.

For a detailed list of variable accesses, see the component's technical sheet (see the first figure above) and use the Automation tab or see the PLC reports.