Tektronix 11A52 Service Manual page 69

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Diagnostics
There are only three kernel tests executed at power-up. They are executed in the order given:
1.
ROM Checksum Test
2. Non-volatile RAM Test
3. U600 (M382) function Test
The ROM Checksum test computes a checksum of the content of the firmware ROM, using the standard
Tektronix checksum algorithm (spiral add). This calculated checksum is then compared with a checksum
stored in the last two bytes of the ROM. If the checksums do not match, the test fails, and fault code 1 is
reported. After the fault code is reported by flashing the front panel LEDs, the amplifier will attempt to begin
normal operation, but it is unlikely that the oscilloscope will function properly with a bad ROM checksum.
The Non-Volatile RAM (NVRAM) test verifies that the NVRAM is functioning properly. Because the
NVRAM contains important calibration information which must not be damaged, the test must not alter
critical data. One page (256 bytes) of RAM is set aside as a scratch area, which contains no information
essential for normal amplifier operation. To test the entire RAM, the scratch area is first tested using standard
memory test algorithms. Then, a page of system RAM is copied into the scratch area, the system RAM page is
tested, and after the tests complete, the copy of the original RAM stored in the scratch pages is returned to its
original location. This continues until all pages of the RAM have been tested. If the testing algorithm detects
a failure, the amplifier reports a fault code of 2, and repeatedly loops the RAM test, while generating
signature analysis signals on the appropriate test points. (Each repetition of the test is framed by pulses on the
SA Start and SA Stop test points.) The signal on SA Start(L) goes from high to low at the start of each
repetition, and stays low throughout the test. The signal on SA Stop goes from high to low at the end of the
test.) The oscilloscope will continue looping the RAM test until the power is removed. Until the condition
causing the RAM test to fail is corrected, the amplifier will not be recognized by any oscilloscope in which
it
is
install~d.
The NVRAM test could corrupt calconstant data stored in NVRAM. This can happen if the power is
cycled/removed during a narrow time-window during the NVRAM test. In this case, the Calconstant
Checksum will
be
corrupted, and, at the next power up, the amplifier will reset the Calconstants to default
· ROM settings and report a Amplifier Calconstant Checksum Error during Oscilloscope-invoked power up
diagnostics. After the Oscilloscope/ Amplifier system is run through an Enhanced Accuracy cycle, the amplifier
will once again be properly calibrated. We expect that this scenario will rarely occur.
The M382 Test verifies the functionality of the M382 IC. The M382 (U600) performs many housekeeping chores
of the Amplifier, including channel sequencing, refreshing the Analog Control Voltage System (U630), latching
M377 (output amplifier, U310) step gain settings, and SDI communications with the oscilloscope. This test
exercises the M382 by applying controlled stimulus to the chip, and records the chip's reactions using an
algorithm similar to that used for signature analysis.
If
the resulting signature of the M382 IC does not match a
known good signature, the test is considered to have failed, and a fault code of 3 is reported.
If
the test fails, it
is executed repeatedly, while generating signature analysis signals on the appropriate test points. The signal
on SA ST ART(L) goes from High to Low at the start of each repetition, and remains Low throughout the test.
The signal on SA STOP(L) goes from High to Low at the end of the test. The oscilloscope will continue looping
the M382 test until power is removed. Until the condition causing the M382 test to fail is corrected, the
amplifier will not be recognized by any oscilloscope in which it is installed.
After all power-pn kernel tests have completed and successfully passed, the amplifier commences initializing
its settings and starts dialog with the oscilloscope.
11A52 Extended Service Manual 4-3