Instrument Control Toolbox

Events and Callbacks

You can enhance the power and flexibility of your instrument control application by using events. An event occurs after a condition is met, and might result in one or more callbacks.

While the instrument object is connected to the instrument, you can use events to display a message, display data, analyze data, and so on. Callbacks are controlled through callback properties and callback functions. All event types have an associated callback property. Callback functions are M-file functions that you construct to suit your specific application needs.

You execute a callback when a particular event occurs by specifying the name of the M-file callback function as the value for the associated callback property.

Example: Introduction to Events and Callbacks

This example uses the M-file callback function instrcallback to display a message to the command line when a bytes-available event occurs. The event is generated when the EOSCharCode property value is read.

• g = gpib('ni',0,1);
  g.BytesAvailableFcnMode = 'eosCharCode';
  g.BytesAvailableFcn = @instrcallback;
  fopen(g)
  fprintf(g,'*IDN?')
  readasync(g)
  

The resulting display from instrcallback is shown below.

• BytesAvailable event occurred at 17:30:11 for the object: 
  GPIB0-1.
  

End the GPIB session.

• fclose(g)
  delete(g)
  clear g
  

You can use the type command to display instrcallback at the command line.

Example: Understanding EOI and EOS

Event Types and Callback Properties