Instrument Control Toolbox

Asynchronous Write and Read Operations

Asynchronous write and read operations do not block access to the MATLAB command line. Additionally, while an asynchronous operation is in progress you can

• Execute a read (write) operation while an asynchronous write (read) operation is in progress. This is because serial ports have separate pins for reading and writing.
• Make use of all supported callback properties. Refer to Events and Callbacks for more information about the callback properties supported by serial port objects.

The process of writing data asynchronously is given in Synchronous Versus Asynchronous Write Operations. The process of reading data asynchronously is described in the next section.

Asynchronous Read Operations

For serial port objects, you specify whether read operations are synchronous or asynchronous with the ReadAsyncMode property. You can configure ReadAsyncMode to continuous or manual.

If ReadAsyncMode is continuous (the default value), the serial port object continuously queries the instrument to determine if data is available to be read. If data is available, it is asynchronously stored in the input buffer. To transfer the data from the input buffer to MATLAB, you use one of the synchronous (blocking) read functions such as fgetl, fgets, fscanf, or fread. If data is available in the input buffer, these functions will return quickly.

• s = serial('COM1');
  fopen(s)
  s.ReadAsyncMode = 'continuous';
  fprintf(s,'*IDN?')
  s.BytesAvailable
  ans =
      56
  out = fscanf(s);
  

If ReadAsyncMode is manual, the serial port object does not continuously query the instrument to determine if data is available to be read. To read data asynchronously, you use the readasync function. You then use one of the synchronous read functions to transfer data from the input buffer to MATLAB.

• s.ReadAsyncMode = 'manual';
  fprintf(s,'*IDN?')
  s.BytesAvailable
  ans =
      0
  readasync(s)
  s.BytesAvailable
  ans =
      56
  out = fscanf(s);
  

Writing and Reading Data

Rules for Completing Write and Read Operations