Some Tektronix oscilloscopes, including the TDS 360 for which I wrote this function, can save a waveform to a file in an "internal" format. These files have the extension: ISF. They consist of a text (ASCII) header, followed by binary waveform data.
ISFREAD parses the header into a MATLAB structure, reads the binary data, and calculates the horizontal (x) and vertical (y) points that make up the waveform.
The TDS 360 and similar models can save data in multiple formats, however the internal (ISF) format is the most useful for several reasons. As the data is binary, it is saved very quickly. The files also include important information in the header, such as the oscilloscope settings.