OPC Toolbox 2.1.4

Using Custom Callbacks

This example demonstrates how to use a custom callback for the OPC Toolbox™. The example makes use of the display_opcdata function, which plots recently acquired data in a figure window.

Contents

To run this example on your system, you must have the Matrikon™ Simulation Server installed. Alternatively, you can replace the values used in the creation of the objects with values for a server you can access.

Step 1: Create the OPC Toolbox Object Hierarchy

This example creates a hierarchy of OPC Toolbox objects for the Matrikon Simulation Server.

da = opcda('localhost','Matrikon.OPC.Simulation.1');
connect(da);
grp = addgroup(da,'CallbackTest');
itm1 = additem(grp,'Triangle Waves.Real8');
itm2 = additem(grp,'Saw-toothed Waves.UInt2');

Step 2: Configure Property Values

This example sets the UpdateRate value to 0.2 seconds, and the RecordsToAcquire property to 200. The example also specifies as the value of the RecordsAcquiredFcn callback the event callback function display_opcdata. The object will execute the RecordsAcquiredFcn callback every 5 records, as specified by the value of the RecordsAcquiredFcnCount property.

set(grp,'UpdateRate',0.5);
set(grp,'RecordsToAcquire',200);
set(grp,'RecordsAcquiredFcnCount',5);
set(grp,'RecordsAcquiredFcn',@display_opcdata);

Step 3: Acquire Data

Start the group object. Every time 5 records are acquired, the object executes the display_opcdata callback function. This callback function displays the most recently acquired records logged to the memory buffer.

start(grp)
wait(grp)

Step 4: Clean Up

Always remove OPC Toolbox™ objects from memory, and the variables that reference them, when you no longer need them. Deleting the client object deletes the group and item objects also.

delete(da)
clear da grp itm1 itm2