About Safety, PDOs, and Variables

This topic discusses PDOs, safety objects, and variable mapping. Within the PDO PDO is a type of protocol frame used in some fieldbuses. A PDO contains one or more object dictionary entries, which define the application data transferred between devices. Selection / Mapping tab any safety-related objects are clearly identifiable by being in a yellow table. Mapping a variable to an object is easily done by any of the following methods.

Double-clicking on the object and then selecting or creating a variable
Right-clicking on the object and selecting Map and then selecting or creating a variable
Dragging an existing variable from the Dictionary to the object

Variables assigned to a safety object must be Read Only. Variables that are Read/Write will not show up in dialogs, nor will drag-and-drop work.

Once a variable is assigned, there is no further validation until the project is compiled. That means a variable could be changed to Read/Write and still be assigned. When you compile the project an error will be generated.