[volt-nuts] 3458A - calibration constants coding
frank.stellmach at freenet.de
Sat Nov 5 10:27:40 UTC 2011
I have analysed the content of the calibration NVRAM (U132, DS1220Y).
I assume that the 253 cal constants are stored as 8 Bytes of Double
Real, because that perfectly fits into the 2k size, and because the
instruments already defines DReal as an output format.
The content of the first two constants by MEMREAD:
might represent the actual Ohm and Volt calibration values, together
with their corresponding DReal translations according to IEEE-754:
One can easily see from the first 5 bytes of each DReal number, that the
first bit of each Byte of the DReal number read by MEMREAD is inverted.
The last three bytes deviate by rounding to 9 decimal places.
So I assume, that HP'encrypted' the constants, either directly in the
RAM, or during readout by MEMREAD.
This is my question: Is the content of the NVRAM, if read out on a
programmer, also encrypted as described above, or does this occur only
by the MEMREAD function?
This would make a difference for a future replacement and reprogramming
of the cal. NVRAM.
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