The oscilloscope captures multiple repetitions of the test packet on Channels 1 and 2 (D+ and D− respectively). A math trace (Channel 1 − Channel 2) represents the differential voltage waveform. This differential trace is exported as a csv file and loaded into the USB-IF Electrical Analysis Tool, which applies the normative eye mask template and reports pass/fail results.

Two test fixture modes defined by USB-IF:

• HSNE (High Speed Near End): No captive 1-meter cable between DUT and fixture. The inner eye mask for HSNE is more stringent than HSFE. Use HSNE when connecting the DUT directly to the fixture without a captive cable.
• HSFE (High Speed Far End): A 1-meter captive cable is included between DUT and fixture. The inner eye mask for HSFE is relaxed compared to HSNE. Use HSFE only when a captive cable is present in the test path.