Configuring a client device for polling

A device-level polling of points permits a single Modbus query message to retrieve a number of consecutive data values. Device-level polling may help overall polling efficiency by reducing the number of polls necessary at the point-level. The table of device poll configuration entries under the frozen slots ModbusAsyncDevice and ModbusTcpGatewayDevice specify the polling properties.

Prerequisites: All needed proxy points exist under a device.

NOTE: In a few cases, a device-level poll did not improve polling efficiency. The target Modbus device took more time to assemble a long data response than it did to handle a number of separate responses (no device poll, point-level polling only) for the equivalent data. While not typical, you should be aware that Modbus devices vary in performance.

Perform the following steps:

In the Nav side bar, expand the Modbus device so you see its Device Poll Config slot (or, open the property sheet of the Modbus device to see this same slot listed with other properties and slots).
To clear any existing polling entries, click Actions > Clear.
To configure polling in a single step right-click Device Poll Config, and select Actions > Learn Optimum Device Poll Config.

Figure 6. Action Learn Optimum Device Poll Config dynamically adds/configures child components

The learn algorithm looks for any consecutively addressed Modbus proxy points, and creates a DevicePollConfigEntry when it finds two or more consecutively addressed points. If you have small gaps between consecutively addressed Modbus proxy points, you may want to manually adjust the created DevicePollConfigEntries to poll over the small gaps. You can always create, configure, and remove DevicePollConfigEntries until you find the most efficient device-polling scheme. This action-learn is the most common method for setting up polling properties. It lets you replace existing device poll entries (start over) or append to the existing device polls.
To manually edit polling properties, duplicate or copy them and edit the copies.

Configuring a client device for polling

Figure 6. Action Learn Optimum Device Poll Config dynamically adds/configures child components

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