Check Probe Calconstant Checksum (Cksm Probe); Walking Ones Test (Walk Ones) - Tektronix 11A52 Service Manual

Diagnostics
Test Failure
The Expected field for this test is zero, indicating that the test should return zero if the checksum was correct.
Failure of this routine should flag the user that the calconstants currently residing in the amplifier's NVRAM
are corrupted, and that the amplifier should be recalibrated before expecting normal operation.
Check Probe Calconstant Checksum (CKSM PROBE)
Amplifier calconstants are protected by a checksum generated after a calibration cycle, or after the amplifier
calconstants are modified using the CAL CONST_SET command. This calconstant checksum helps the
amplifier detect corruption of calconstants caused by external problems, such as alpha-particle hits, bad
NVRAM battery, or other unknown phenomena.
The probe calconstant checksum test runs a checksum algorithm on calconstants related to probes currently
installed, and compares the calculated checksum with the checksum stored (with calconstants) in NVRAM. If
the calculated checksum does not match the stored checksum, it indicates that the calconstants (or the
checksum) have changed due to some outside influence.
Note that setting the calconstants to factory defaults will not cause a new calconstant checksum to be generated
for the factory default calconstants. The probe calconstant checksum test will continue to fail until the
amplifier is either run through a calibration cycle, or the CAL CONST_SET command is used to force a new
calconstant checksum to
be
generated, or one or more changes in probe attachment status have occurred. The
Address field is not used
in
this test, and is zero. The Actual field will be zero if the checksum was correct, and
nonzero (with no significance to the value) if the checksum was incorrect.
Test Failure
The Expected field for this test is zero, indicating that the test should return zero if the checksum was correct.
Failure of this routine should warn the user that the calconstants currently residing in the amplifier's NVRAM
are corrupted, and that the probe(s) should be recalibrated, before expecting normal operation.
Walking Ones Test (WALK ONES)
This test sequences a "walking-one" through all the external latches used to interface the processor to the rest
of the amplifier hardware. The test always passes because the processor cannot determine if the outputs are
actually working. The test is intended to be run with the user manually observing the latch outputs with an
oscilloscope or logic analyzer. The test works by setting all output latches to zero, then individually setting
each output bit in tun:t to a one, while leaving all other outputs zero.
Test Failure
If the user finds inactive output latch bits (stuck high/low), the fault is either in the latch chips, on the
circuitry connected to the latch output pin, or in the circuitry interfacing the latch to the processor.
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11A52 Extended Service Manual
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