Example: Global Variable Lists

TwinCAT PLC Control

After importing an exported file using Export Variables Info... in the TwinCAT System Manager, you will see a variable list named TwinCAT_Import under Resources in the Global_Variables folder.

The variables are composed of the Names configured in the System Manager and the type of terminal, along with the channel number and the definition of the terminal variable. The address in the local BC process image (IEC61131-3 notation) and the data type of the variables are given.

The variables in lines 2 to 8 are Exchange Variables (PLC Variables) to be transferred via the fieldbus.They serve to exchange data between the BC PLC program and the superordinate control system. They can, for instance, be processed further with TwinCAT PLC, TwinCAT OPC or via ADS on the application level. For example, the declared output variables for the outputs process image (lines 2, 3 and 4) are inputs in the superordinate control system. The variables of lines 5 - 8 are correspondingly outputs of the superordinate control system.

The exchange variables in the local BC process image start from offset 128 (as shown in the example). Nevertheless, this offset can also be set in a System Manager dialogue if necessary.

Details on the different Beckhoff Bus Terminal types (e.g. definition of descriptors Ctr1 and State and Data_x) are described under Terminals - Technical Reference.