To add Modbus server proxy points

Once a slave Modbus device is added and its register ranges defined, you can add server proxy points. Use the following procedure:

To create server Modbus proxy points in a device:

1. In the Device Manager, in the Exts column, double-click the Points icon   in the row representing the device you wish to create proxy points.

   This brings up the Modbus Server Point Manager.

2. (Optional) Click the New Folder button to create a new points folder to help organize points, and give it a short name, such as “Hldg1_to_64”, or whatever name works for your application. You can repeat this to make multiple points folders, or simply skip this step to make all proxy points in the root of Points.

   Note that all points folders have their own Modbus Server Point Manager view, just like Points. If making points folders, double-click one to move to its location (and see the point manager).

3. At the location needed (Points root, or a points folder), click the New button.

   The New points dialog appears, in which you select a point “Type,” “Number to Add,” “Starting Address,” and “Data Type” (latter applies only if selecting type: Numeric Point or Numeric Writable).

   Generally, it is unwise to expose any coil or holding register as a writable point if the Modbus master may also write to this same item—otherwise “write contention” issues may result. In other words, writable point types are better suited to items exposed as Modbus (status) “inputs” and “input register s”.

   For more details, see Modbus server proxy points and Types of Modbus server proxy points.

4. Click OK.

   This brings up another New dialog to name the point(s), enter data addresses as well as enter other information, such as point facets and conversion. Default point names use a convention similar to: “<PointType><Address>”, for example: “Numeric Point40012” or “Boolean Writable6”.

   Details on related entries in this step are in Modbus server point ProxyExt properties, and background information is given in the section Modbus Meets NiagaraAX.

5. Click OK to add the proxy point(s) to the Points extension (or to the current points folder), where each shows as a row in the point manager.

   If addressed correctly, each point should have a status of “{ok}” with a value displayed.

   If a point shows a “{fault}” status, check its ProxyExt “Fault Cause” property value, which typically includes a Modbus “exception code” string, such as “Read fault: illegal data address”.

   In such a case, re-check the address in the point against the defined register ranges in the parent slave device. For related details, see Exception codes, and sections Data address format in NiagaraAX, and Modbus Register Range Tables.

6. Continue to add proxy points as needed under the Points extension of each server Modbus device.

   As needed, double-click one or more existing points for the Edit dialog, similar to the New dialog used to create the points. This is commonly done for re-editing items like data addresses, names, or facets.