This information also included in the minutes of the 12/14 PHY WG call:


To make a mode measurement, create a histogram over the portion of the waveform in question, then use the peak value from the histogram, which represents the most commonly occurring value.
 
If a vertical histogram is created on a scope (assuming you want to determine the amplitude mode), a graphical representation of the distribution of values that occur within the histogram will be displayed. The peak value is the mode.
 
A timing mode measurement may be creating with a horizontal histogram.
 
The next key element of mode measurements is the placement of the histogram on the waveform. The choice is often specified in the associated specification. The results obtained vary depending on if looking at a histogram that covers the entire 100000 UI of a waveform, or only a portion of that waveform.

With regards to the de-emphasis measurement, the mode amplitude value would be the average value of the flat area since the portion without de-emphasis would be a separate node on the histogram of all measured values of the waveform.

Alvin Cox
Seagate Technology, LLC
Tel 405-350-7424
Cell 405-206-4809
E-Mail  alvin.cox@seagate.com