Table J - 15: Modbus Data Types
Basically, the Modbus register mapping can be summarized as this:
• “Binary In” are mapped to “Modbus coils status” and to “Modbus input status”.
• “Binary Out” are mapped to “Modbus coils”.
• “Analog In” and “Analog Out” are mapped to “Modbus Holding Registers” and
“Modbus Input Registers”.
Refer to J.5 for mapping details.
J.4.1 Data Access – read from H201Ti via Modbus
J.4.1.1 Holding Registers (Analog Inputs)
For improved flexibility and better compatibility with different SCADA, the Hydran
201Ti provides three different mappings for most Analog Input data objects: 16-bit
signed integer, 32-bit signed integer, and 32-bit floating point. All three mappings are
equivalent (subject to their respective range and precision).
• 16-bit signed integer mapping provides access to Analog Input values that fit
in 16 bits, in order to minimize the amount of the data to exchange on the
communication link. It provides compatibility with widest range of Modbus
Masters.
• 32-bit signed integer mapping provides access to Analog Inputs with sufficient
precision and allows for interoperation with Modbus Masters that don’t
support floating-point data.
• 32-bit floating-point mapping provides access to Analog Inputs with full
precision available to the Hydran 201Ti.
To represent Analog Inputs with necessary precision, values accessed via integer
mappings are pre-multiplied with a scale factor specific to each Analog Input. These
scale factors can be found in the Section J-5.b.
16-Bit Integer Analog Input Read
In the 16-bit mapping, an object value exceeding 32767 or below -32768 is clamped.
A Hydran 201Ti Analog Input object corresponds to a Modbus 16-bit data object.
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