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2.5
Modbus Data Format
Data Types - General
2.5.1
The following data types are used for storing variables in the Modbus registers.
•
Measured value
•
Date/time
•
Indication
•
Controllable indication
•
Counter
•
String
NOTE
i
i
The following convention applies when storing variables consisting of more complex data types to the
Modbus holding register (that is variables which are larger than a holding register, for example 32-bit
measured values):
The register with the lowest address contains the most significant byte (MSB), the register with the highest
address contains the least significant byte (LSB).
Data Type - Measured Value (Read)
2.5.2
The
Measured Value data type is transferred into 2 holding registers in 32-bit floating-point format (single
precision) according to IEEE standard 754.
Structure of the Format
The 32-bit floating-point format consists of a sign bit (S), exponent and mantissa:
[dw_MeasuredValue, 1, en_US]
Figure 2-2
Value Range
The 32-bit floating-point format has the value range: ±(10
Value of the Measured Values
The value of a measured value is obtained as follows:
Exponent = 0: Resulting value = 0
Exponent = 255, mantissa = 0: Resulting value = (-1)
Exponent = 255, mantissa not equal to 0: Resulting value = NaN
0 < Exponent < 255: Resulting value = (-1)
SICAM, Multifunctional Recorder, Manual
E50417-C1040-C606-A3, Edition 03.2017
Data Type - Measured Value
<sign>
-38
to 10
+38
).
<sign>
* +Inf
* 2
(<exponent> - 127)
* 1, <mantissa>
Communication Modbus
2.5 Modbus Data Format
21
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