Eastron SDM120C, User Manual, Page: 7 / 10

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5. Setting Up
To enter set-up mode, pressing the button for 3 seconds, until the lcd display the -SET-
5.1 Set-up Entry Methods
After successfully enter the SET model,then the set-up can be realized via RS485 communication
with the correct Modbus Protocol.
The electrical interface is 2-wire RS485,via 2 screw terminal.Connection should be made using
twisted pair screened cable(Typically 22 gauge Belden 8761 or equivalent).A total maximum
length of 3900 feet(1200 meters) is allowed for the RS485 network.A maximum of 32 electrical
nodes can be connected,including the controller.The address of SDM120C smart meter can be set
to any value between 1 and 247.Broadcast mode(address 0)is not supported.
All data values in the SDM120C smart meter are transferred as 32 bit IEEE754 floating print
numbers,therefore each SDM120C smart meter value is transferred using two Modbus Protocol
registers.All register read requests and data write requests must specify and even number of
registers.Attempts to read/write and odd number of registers prompt the SDM120C smart meter
to return a Modbus Protocol exception message.
The Modbus Protocol establishes the format for the master's query by placing into it the device
address,a function code defining the requested action,any data to be sent,and an error checking
field.The slave's response message is also constructed using Modbus Protocol.
Modbus Protocol function code 04/03 is used to read data.
For example:
to request 01 04 00 00 00 02 CRC to read the voltage
to request 01 04 00 12 00 02 CRC to read apparent power
For example:
to request 01 10 00 14 00 02 04 40 00 00 00 CRC to set meter address as 02
(Hex 40 00 00 00 equals float 2)
to request 01 10 00 1C 00 02 04 40 00 00 00 CRC to set baud rate as 9600
(Hex 40 00 00 00 equals float 2)
5.2 The detailed register map information of SDM120C are as follows:
Part 1
*Parameters to be read by function code
04 :
Address
(Register) Input Register Parameter Modbus Protocol Start
Address Hex
Parameter Units Format Hi byte Lo byte
30001 Voltage Volts Float 00 00