Vmetro VBAT-PB, User Manual, Page: 128 / 186

9 VBAT-PB VME bus anomaly trigger
the overall system performance. Using this feature to reduce "noise", it allows
you to look for the VMEbus violations that really cause the problems.
Complements the VBT-325
One of the most difficult parts of debugging solely with a bus analyzer like the
VBT-325 is determining on what to trigger. Often the symptom of failure gives
no clue as to its cause. The 104 parallel triggers of the VBAT continuously
comb the bus for illegal activity, and can often establish an immediate trigger
on extremely obscure bugs. This combination of the VBAT-PB and VBT-325
is a very powerful troubleshooting aid, eliminating the trial and error approach
often required to devise a suitable triggering strategy. This makes the VBAT-
PB ideal for field service/customer support purposes. The VBAT-PB is even
fast enough to trigger some oscilloscopes on repetitive violations.
The capabilities of the VBAT significantly enhance the utility of the VBT-325.
While the VBT-325 is monitoring the bus for defined states, the 104
concurrently active trigger elements of the VBAT screen for violations of the
bus specifications which may not be detected by other means. It is through such
sheer "brute force" fault coverage that the automatic triggering of the VBAT
becomes practical for debugging. Also, its asynchronous triggers find faults of
much shorter duration than that can be detected by the triggering circuitry of
the VBT-325. Finally, the edge-sequence-rule-based triggering nature of the
VBAT recognizes events that cannot be directly detected using the VBT-325
alone. For example, the VBAT-PB automatically recognizes "instability", (i.e.
changes on a line) on all address and data lines at once, without the need to be
told the correct state of these lines beforehand. This is essential for concurrently
screening for all address and data stability violations in all VMEbus cycles.
This capability further enables the VBAT-PB to detect extraneous transitions
on strobe lines due to metastability and bus ringing and noise.
Related documents
For more details on the VMEbus behaviour for the possible VMEbus violations
that can be found by the VBAT-PB (including timing waveforms), please also
refer to the following documents:
"Ultraview, VBAT User's Manual, June 1988"
'The VMEbus Specifications, IEEE STD1014-1987".
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