Polling AJAX is a high speed AJAX implementation that updates data on the screen by polling the DataHub Web Server on a periodic basis. The data coming back from the DataHub is interpreted by JavaScript functions in the web page which in turn update various page elements, all without requiring the user to refresh the page.

The example below shows several point values read from the DataPid data domain. To see point values, you must be running the DataPid program.

Key: Trending Up =   ▲       Trending Down =   ▼       Steady State =   ●

The data entry fields displayed below show how you can also send data back to the DataHub from an AJAX web page. When you select a new value from the drop-down list, this causes a JavaScript function to write the new value to the DataHub. Any DataHub script can be called from an AJAX web page using simple JavaScript calls.

Change the Update Frequency of the DataPid: Other 0 1 2 3 4 5 10 15 20 Hz
This change is transmitted to the DataHub and subsequently to DataPid.

Change the polling rate of this AJAX page: 1 2 3 4 5 Hz
This change is local to the browser, and determines the rate at which your browser asks the DataHub for new data.

This page runs a timer to periodically request new data from the DataHub. The page itself is not being updated, just the specific page elements that have been configured to display data from the DataHub.