Automatically Shown Traces; Setting Bit Cell Time; Retraining The Filter; Choosing An Analysis Method - LeCroy WaveMaster 8600A Operator's Manual

Compare will have to be used then. The SMART Trigger can be set up as outlined above, except
that the bottom Qualify by: field should be set to time greater than , and the amount of time
from index to just before the data of interest should be entered. This can be used to look at a
particular servo burst, for example.

Automatically Shown Traces

When the source of the head signal is changed from None to an input channel or memory, a trace
showing a zoom of the head signal is automatically created and displayed. If the Filter head signal
checkbox is checked, the data in the trace is filtered. All channel markers selected will appear on
this trace. All channel analysis methods analyze the (possibly filtered) data in the trace waveform
(the entire waveform, not just the part displayed). Byte offset and Worst Error # change the
horizontal position of this trace.
When Store Reference is selected, a trace showing a zoom of the stored reference is
automatically established where possible. This means that whenever Byte offset or Worst Error #
is changed, the reference will be realigned with the Head Signal at the new position. The reference
signal will also be filtered if the Filter head signal checkbox is checked.

Setting Bit Cell Time

The value in the bit cell time menu is used as a starting guess for analyzing VCO Synch. It is also
used by Byte offset and Analog Compare to determine how much time a byte occupies, and to set
the -3 dB frequency of the DDA's equalizing filter (if enabled). It should be set correctly for the zone
being read --- it does not need to be set on each read within the same zone.
Changing the bit cell time changes the filter's -3 dB frequency. The filter's settings should therefore
be updated, or "trained" after the bit cell time has been changed. If the filter is on, the bit cell time
must be fairly close for Find Bit Cell Time to work.

Retraining the Filter

Training the filter adjusts the boost and the -3dB frequency to optimize the mean of the worst 100
SAM values. The training starts by setting the -3dB frequency to 0.5/bit cell time. It then alternates
optimizing the boost with optimizing -3 dB frequency. The 3 dB, boost and group delay values can
also be independently set without having the DDA automatically train.

Choosing an Analysis Method

Which method or methods should be used? Deciding this depends on the type of problem and the
information available.
By definition, a data error occurs in a drive when a bit is interpreted as a "1" when it should be a "0"
or vice-versa. In order to gain insight into the cause of the error, it is generally desirable to examine
the head signal at the location or locations where data errors occur. The DDA provides tools to help
identify the likely location of a data error. In addition, with the instrument's channel emulation
capability you are able to gain further insight into the cause of an error or errors once location is
determined.
Before choosing a method, there are some basic questions that need to be answered:
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