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2635A
Users Manual
C-4
byte6: temperature units and rate (0x10 bit means degrees Fahrenheit, else
Centigrade; 0x01 bit means fast rate, else slow rate)
byte7: Alarm outputs
byte8: Digital I/O
• Totalizer value as 32-bit single-precision IEEE floating point number stored using
the byte ordering shown below. The format of this number is explained under
"Floating Point Conversion".
byte 9: MMSB of float
byte 10: MLSB of float
byte 11: LMSB of float
byte 12: LLSB of float
• Measurement data; only defined channels are included (exactly like LOG?query);
same floating point format, but with a wider range of values. NaN (Not a Number)
is used to indicate open thermocouple, and plus or minus Inf (infinity) to indicate
overload. The bit values for NaN and Inf are explained in the next section.
byte 13: MMSB of float
byte 14: MLSB of float
byte 15: LMSB of float
byte 16: LLSB of float
bytes 17-20: Second measurement result, if any
bytes 21-24: Third measurement result, if any
...
Since the ASCII decoding (explained above) creates data multiples of three in length, it
is possible that there will be one or two unused bytes at the end of the decoded byte
stream.
Floating Point Conversion
ANSI/IEEE Std 754-1985, "IEEE Standard for Binary Floating-Point Arithmetic,"
describes the single-precision floating point format used to return measurement data.
This standard defines the format for single-precision floating point as:
X = (-1)
s
2
(e-127)
(1.m )
where
s = sign
e = exponent
m = mantissa
The floating point format used is 32-bit with a 1-bit sign, 8-bit exponent, and 24-bit
mantissa with the most significant bit hidden under the LSB of the exponent. The
number is formatted as shown in Table C-1.
For all other measurement queries, Hydra Series II returns the string "+9E+9" for open
thermocouple (OTC) measurement values. However, for the LOG_BIN?query, NaN (not
a number) is returned instead. The IEEE floating point standard defines NaN as a
positive, maximum exponent number with non-zero mantissa bits. Hydra Series II sets