Appendix
MultiExact Gas Analyser
A3.7 Floating point numbers
Floating point numbers (e.g. 12.34, –1012.32, etc.), are digitally represented using the
IEEE–754 format. Single precision floating point numbers are used throughout and
they require 32 bits of data. Since a Modbus register holds 16 bits it takes 2 registers
to represent a floating point number. We default to having the most significant word of
the float, bits 16 – 31, in the first register, and the least significant word, bits 0 – 15, in
the next register. This order can be reversed by setting a coil in the system control
mapping (Appendix A3.14).
A3.8 System data mapping
Read-only access to system data will be provided in a block of 100 registers. These
can be accessed as input registers using function code 04.
Register
Name
Comments
1 – 7
Serial number
ASCII text, 14 characters max,
terminated by a zero.
8 – 15
Software version
ASCII text, 16 characters max,
terminated by a zero.
A3.9 Transducer data mapping
Each transducer will provide read-only access to its measurements and associated
data in blocks of input registers that can be read with function code 04.
The first block of registers provides just the measurement data from all transducers
allowing all measurements to be obtained with a single request. Each register
provides 2 bytes of data so it takes 2 registers each to store a 4 byte floating point
measurement value.
Register
Name
Comments
5001 – 5002
Transducer 1
Floating point number
5003 – 5004
Transducer 2
A block of 100 registers is allocated for each transducer to provide the means of
supplying the measurement and other transducer related data as follows:
Register
Name
Comments
101 – 200
Transducer 1
Measurements and data for each transducer
201 – 300
Transducer 2
106
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