[volt-nuts] 3458A - calibration constants coding
Frank Stellmach
frank.stellmach at freenet.de
Sat Nov 5 10:27:40 UTC 2011
Hello,
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:
C06308E271D02044
C09C528491C5543B
might represent the actual Ohm and Volt calibration values, together
with their corresponding DReal translations according to IEEE-754:
40003.0920 40E38862F1A9FBE7
7.20509364 401CD2041131AB9F
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.
Frank
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