Controlling Data Acquisition
During an acquisition, the logic analyzer examines the input voltage
at each input probe at a sampling rate defined by the time base setting
(Time/Div knob). At each sample, it compares the input voltage to the
logic threshold. If the voltage is above the threshold, the analyzer
stores a “1” in sample memory; otherwise, it stores a “0.” When sample
memory is full, the display logic reconstructs the input waveform from
the pattern of bits stored in sample memory. To control the
HP 54620A/C acquisition process, you can
• perform continuous acquisitions by pressing the Run/Stop key, and
stop them by pressing it again,
• make one acquisition, then stop, by pressing the Single key,
• store the results of several acquisitions by pressing Autostore, or
• erase the results of all acquisitions by pressing Erase.
Chapter 1, “Getting Started,” explains how to use the Run and Stop
functions. The others are explained in this section.
Auto Glitch Detect
The HP 54620A/C automatically enables Auto Glitch Detect upon
powerup. When the Auto Glitch Detect feature is enabled, it puts the
instrument in glitch detect mode at all sweep speeds of 1
µ
s/div and
slower where the sampling speed must be reduced, thereby
preventing aliases from being displayed.
When Auto Glitch Detect is disabled, the HP 54620A/C acquisition
system has a record length of 8K samples at all sweep speeds. In
addition, you can extend the sweep speed to 2 s/div and 5 s/div in the
Main display mode. See “Glitch Detection” in chapter 4.
When Auto Glitch Detect is enabled, a waveform display that contains
glitches, separated by the sampling intervals, is an indication that the
waveform is being undersampled. A faster Time/Div setting is needed
to obtain a correct display of the waveform. This easy indication of
undersampling is not available when Auto Glitch Detect is disabled.
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