Where are the Symbol Files Stored?
When building a project, the symbol file <Projectname>.sdb is saved to the project directory. If the generation of symbol files has been configured in EPAS-4, this file contains the respective entries. (Also refer to When is a symbol file created?)
When downloading (loading) a project to the controller, the symbol file <Projectname>.sdb is copied to the gateway server to the directory Gateway server (default C:\\WINNT\GATEWAY FILES).
Prerequisite: A connection is configured via EPAS-4 > Online > Communication parameters....
When transferring the project to the controller, the symbol file can also be transferred.
As of V12, two symbol files are available on the controller. This is necessary since the controller as of V12 supports online change and program change. The controller verifies that the symbol file provided matches the loaded program. Out-dated symbol files are automatically deleted.
The symbol file download.sdb contains the files of the loaded program code. The symbol file boot.sdb contains the information that corresponds to the program file default.prg.
If the option Update symbol file in EPAS-4 > Project > Options, category Login is enabled, the symbol file is copied from the project directory to the controller during project download where it is saved as boot.sdb.
When restarting the controller, the symbol file boot.sdb is automatically copied to the download.sdb file. This helps to ensure that the download.sdb file matches the boot project.
The download.sdb file is read if a client calls the symbol information from the controller.
If a client loads a project from the controller, the symbol file download.sdb is retrieved from the controller and copied to the upload directory of the gateway where it is saved as file named <Projectname>.sdb. (If the project name could not be determined, the file is saved with the name download.sdb.)
Thus, in the case of further uploads the client can retrieve the symbol information from this gateway directory, which takes less time than reading from the controller.
When the OPC server (which is the gateway server) establishes a connection, it attempts to load the symbol file download.sdb from the controller. At first, it is verified if the symbol file in the upload directory is identical to that on the controller.
If it is not identical, the file is uploaded from the controller to the upload directory.
If no symbol file is found on the controller, the symbol file is searched in the Gateway files directory (of the gateway that is used for the communication).
If no symbol file is found there either, no data exchange is possible between client and controller.
