Master data points are a key feature which makes WinCC OA a powerful object oriented modeling tool. The ability to create a template and reuse it to ensure consistency is very important for large complex projects.
From time to time, I have seen situations where the _mp_ master data point forgets configs. I don't know why or when this happens, but it happens. Sometimes, we want to add or adjust a master data point without having the system make any changes to all of your instances. For these situations, we need a way to make changes to the master dp outside of using the _mp_ features of PARA.
PARA has some very special functionality when it comes to the _mp_ instance. When you create a master data point, it makes an instance of an internal data point.
For example, we have created a data point type: MyDataType If you create the master data point for this, now you have an instance _mp_MyDataType under the MyDataType Para also creates an instance under _DynamicDatapoints and it is called _dt_MyDataType
Every instance found under the _DynamicDatapoints has only two elements, both are dyn_strings:
- Leaf - contains the element name and the config type (special type name that is a translation keyword)
- DynamicAttribute - contains the list of config type choices (fixed vs. other choices)
The number of items in the dyn arrays are identical, the order is critical as the Leaf uses the DynamicAttribute together to know what configs are being used.
For my example MyDataType, I have two data point elements: PV and Setpoint
| Leaf items | DynamicAttribute items |
|---|---|
| _mp_MyDataType.PV:_archive | _da_archive |
| _mp_MyDataType.PV:_alert_hdl | _da_alert_hdl_3 |
| _mp_MyDataType.PV:_address | _da_address_S7_in_simple |
| _mp_MyDataType.PV:_pv_range | _da_pv_range |
| _mp_MyDataType.PV:_smooth | _da_smooth |
| _mp_MyDataType.PV:_common | _da_common_5 |
| _mp_MyDataType.Setpoint:_archive | _da_archive |
| _mp_MyDataType.Setpoint:_address | _da_address_S7_in_simple |
| _mp_MyDataType.Setpoint:_pv_range | _da_pv_range |
| _mp_MyDataType.Setpoint:_common | _da_common_5 |
If you want to learn what these keywords like _da_common_5 mean, they are found in a message catalog found in the base version called da.cat
- _da_common_5 = Var: Alias, Unit, Format and description
- _da_alert_hdl_3 = Alert handling with 3 ranges
As you can see, those translation phrases are the choices from the type of config you used.
As with anything internal with WinCC OA, be very careful. I have been successful in rebuilding broken _mp_ and got them working again without altering the instances which were already working.