What are the PROFIBUS Bus Parameters and how does Design Pad calculate them?
PROFIBUS network bus parameters consist of various changeable parameters that allow the user to customize the way a PROFIBUS master device (such as a NIM-7) interacts with other devices on the network (timings, etc.) See the Design Pad Manual here for a description of each PROFIBUS network bus parameter.
The bus parameters are accessed through the Network View tab in the workspace window via right-clicking and selecting properties on the PROFIBUS logical network. Next, select 'Bus Parameters'.
If the Optimize Parameters Automatically option is selected, Design Pad will execute a series of calculations based on the configured network settings to create a set of recommended driver parameters. These calculated values are shown in the dialog box, but are greyed out (unmodifiable). PROFIBUS bus parameters are loaded into the driver during initialization, meaning the program must be downloaded to the PROFIBUS master device (i.e. NIM-7) and reset for them to be effective. These values will not change again unless the program changes, is re-processed by Design Pad, downloaded, and the device reset again.
The parameter values generated follow the guidelines provided in the Profibus specification and have been authenticated through PROFIBUS certification. From our experience, they have worked unchanged in a majority of the PROFIBUS configurations. For this reason, Fairmount recommends using auto-calculated settings. However, there are many variables in a PROFIBUS implementation and these calculations cannot account for every one. Automatic bus parameter calculation can be disabled, so that the user can be manually adjust them when necessary. Unchecking “Optimize Parameters Automatically” leaves the last calculated values in the dialog box, and enables manual edits to the parameters. In our experience, however, the need to alter these parameters is typically caused by issues with the physical layer of the PROFIBUS network (incorrect cables, termination, etc.)