# Waveform Top

Waveform Top is the most prevalent value of the upper 40% of a pulse or eye diagram. This measurement may be compatible with PAM signals, depending on the PAM waveform. The measurement can be restricted to a region. An annotation label is placed at the measurement result.

Depending on the waveform type, one of the following algorithms is employed:

- Histogram Peak Algorithm. Used for square waveforms and low duty-cycle waveforms.
- Maximum Algorithm. Used for waveforms that result in even histogram distributions, such as triangular waveforms. Using the histogram peak algorithm for waveforms that have even histogram distributions would result in an unstable identification of the Waveform Top.

PAM Compatibility. Because this measurement is based on waveform top and base levels and the passing of the waveform's edge through lower, middle, and upper thresholds, the measurement is not designed for PAM signals. However, the measurement may be able to be made on PAM signals if the waveform top and base definitions are manually set. This can be attempted using the Thresholds tab of the Configure Measurements dialog box.

This measurement may be compatible with PAM signals, depending on the PAM waveform.

The display, waveform, or region is used to calculate the result. Therefore, position a single cycle or an integer number of positive pulses in the display or region.

## To measure

1. Click the toolbar's Amplitude tab.
2. Click the toolbar's More buttons to locate the Waveform Top button.
3. Click the button.
4. Select the Region in which to make the measurement:
   - Displayed Waveform — is what you see in the waveform window (which can be a zoomed-in view of the complete waveform).
   - Entire Waveform — specifies the complete waveform.
   - Region N — If regions are enabled for the selected signal, you can select one of those regions.

## SCPI Command

`:MEASure:VERTical:VTOP`