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.
See How To Set Up a Variable to Monitor Safety Data for step-by-step instructions.
