ONICON System-10 Dualnet User Manual
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System-10 Dual Network Interface Installation Guide 05/14 - 0972-1
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SECTION 3.0: MODBUS MEMORY MAP
ONICON System-10 DUALNET Btu meters can be configured to provide energy and volume rate
data, and totalized energy and volume data in a variety of engineering units via MODBUS RTU
RS485 or MODBUS RTU TCP/IP. You select the engineering units you wish to use by mapping
to the appropriate registers.
3.1 MODBUS REGISTER FORMAT AND NETWORKING INFORMATION
1. All registers are 16 bit MODBUS Holding Registers.
2. MODBUS Holding Registers are used in 4 different ways.
a. As an Analog Value: In some cases these values are scaled by multiplying the
register contents by a fixed multiplier.
b. As a status indicator where the register value can only be “1” or “2”.
c. As a mode indicator where the value indicates current operating mode such as
“1” = single, “2” = dual, or “3” = bi-directional.
d. As a control register where the host can write a value to reset total(s).
3. Registers 40001 through 40068 are unsigned integer registers (0 to 65,535) except for
40024 and 40025. These are 16 bit signed integer values (-32,768 to +32,767). Registers
41003 through 41081 are 32 bit single precision floating point values. 41001, 41002 and
41065 through 41069 are unsigned integer registers.
4. System-10 MODBUS register addresses are formatted as follows:
Example: address 4
0001
4 = Holding register
0001 = Address that corresponds to memory location 0000
5. MODBUS function codes supported:
CODE
DESCRIPTION
03
Read Holding Registers
06
Preset Single Registers
16
Preset Multiple Registers
17
Report Slave ID
i
IMPORTANT NOTE
ONICON provides data in integer and floating point format. We recommend the use of
floating point registers to transmit data to the network. The use of floating point data
eliminates the need for scaling and additional mathematical operations to totalize energy
and flow.