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2. COMMUNICATION INTERFACE
2.5: Function code
The function code communicates to the slave device what to execute. Function code data is
classified by type below.
Analog setting: each setting information type. Numerical value within 16 bits:
-32768 to 32767
Analog input data: measurement, status and other data. Numerical value within 16 bits.
Code
Function
Unit
MODBUS original function (reference)
03
Read analog settings
16 bit
Read content of maintenance register
04
Read analog input data
16 bit
Read content of input register
06
Write analog settings
16 bit
Write to single maintenance register
2.6: Data
Data configuration varies according to function code.
At the time of request from the master, data is composed of code number, data count, etc. of
target data to be read and written.
Response from the slave consists of data in relation to the request.
Basic MODBUS data is all integers of 16-bit, and the presence or absence of a sign is defined for
each data. Accordingly, by assigning a decimal to another address to convert into an integer or
fixing the decimal position, it is normalized and expressed on scale upper/lower limits.
2.7: Reference number
A reference number is assigned to data and it is necessary for reading and writing the data.
Reference number range is categorized as "analog input data" and "analog setting value"
according to data type.
Data type
Reference number
Relative number
Analog input data
30001-40000
Reference number -30001
Analog setting value
40001-50000
Reference number -40001
Relative number is the address number used during actual communication.
