External Interfaces

Example: Reading Binary Data

This example illustrates how you can download the TDS 210 oscilloscope screen display to MATLAB. The screen display data is transferred and saved to disk using the Windows bitmap format. This data provides a permanent record of your work, and is an easy way to document important signal and scope parameters.

Because the amount of data transferred is expected to be fairly large, it is asynchronously returned to the input buffer as soon as it is available from the instrument. This allows you to perform other tasks as the transfer progresses. Additionally, the scope is configured to its highest baud rate of 19,200.

1. Create a serial port object - Create the serial port object s associated with serial port COM1.

• s = serial('COM1');
  

2. Configure property values - Configure the input buffer to accept a reasonably large number of bytes, and configure the baud rate to the highest value supported by the scope.

• s.InputBufferSize = 50000;
  s.BaudRate = 19200;
  

3. Connect to the device - Connect s to the oscilloscope. Because the default value for the ReadAsyncMode property is continuous, data is asynchronously returned to the input buffer as soon as it is available from the instrument.

• fopen(s)
  

4. Write and read data - Configure the scope to transfer the screen display as a bitmap.

• fprintf(s,'HARDCOPY:PORT RS232')
  fprintf(s,'HARDCOPY:FORMAT BMP')
  fprintf(s,'HARDCOPY START')
  

1. Wait until all the data is sent to the input buffer, and then transfer the data to the MATLAB workspace as unsigned 8-bit integers.

   • out = fread(s,s.BytesAvailable,'uint8');
     

5. Disconnect and clean up - When you no longer need s, you should disconnect it from the instrument, and remove it from memory and from the MATLAB workspace.

• fclose(s)
  delete(s)
  clear s
  

Viewing the Bitmap Data

To view the bitmap data, you should follow these steps:

1. Open a disk file.
2. Write the data to the disk file.
3. Close the disk file.
4. Read the data into MATLAB using the imread function.
5. Scale and display the data using the imagesc function.

Note that the file I/O versions of the fopen, fwrite, and fclose functions are used.

• fid = fopen('test1.bmp','w');
  fwrite(fid,out,'uint8');
  fclose(fid)
  a = imread('test1.bmp','bmp');
  imagesc(a)
  

Because the scope returns the screen display data using only two colors, an appropriate colormap is selected.

• mymap = [0 0 0; 1 1 1];
  colormap(mymap)
  

The resulting bitmap image is shown below.

Example: Parsing Input Data Using strread

Events and Callbacks

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