In order to download the source code of your application to the PLC, you must log in to the PLC with application. If there are several applications in the project, then you must switch explicitly to the correct application first.

When you download an application to the PLC, CODESYS performs the following checks:

The list of applications on the PLC is compared with the applications available in the project. If they do not match, then you are prompted to download the application that is not on the PLC yet or delete existing applications.

For "externally implemented" blocks in the application to be downloaded, CODESYS checks whether these are available on the PLC. If they are not available, then the message "unresolved reference(s)" is printed to a dialog prompt and to the message view. Then CODESYS compares the parameters (variables) of the blocks in the application to be downloaded and the parameters of the same-named blocks in the application that exists on the PLC (signature check). If there are any discrepancies, then the message "invalid signature(s)" is printed to a dialog prompt and to the message view.

If the "Download Application Info" check box is selected in the application properties, then additional information about the application contents are downloaded to the PLC.

if multiple applications exist for the same device, then notice that the “I/O Mapping” dialog contains the definition for which of the applications is used for for the I/O mapping of the device.

Transferring an application and starting the program

Requirement: The application contains no errors and the communication settings of the PLC are correct. The application does not exist yet on the PLC: The application and the communication with the controller are not encrypted.