Appendix A. Modbus reference
A.1 Default Modbus communication settings
Table 25 Modbus TCP communication settings
Property Specification
IP address of Modbus server IP address of DGA monitor on interface ETH0
Modbus server port 502
Table 26 Default Modbus RTU communication settings
Property Specification
Baud rate 19200
Parity Even
Data bits 8
Stop bits 1
Modbus RTU slave address 240
A.2 Function codes
Table 27 Supported function codes
Function code (decimal) Function code (hexadecimal) Name
03 03
hex
Read Holding Registers
A.3 32-bit floating point or 32-bit integer format
Registers using 32-bit float data format are encoded using the binary32 encoding defined in
IEEE 754. The format is also known as "single-precision floating point format".
The least significant 16 bits of a floating point number are placed at the Modbus register listed
in the table, while the most significant 16 bits are placed in the register with number/
address + 1, as specified in Open Modbus TCP Specification, Release 1.0. This is also known as
"little-endian" or "Modicon" word order.
Despite the specification, some Modbus masters may expect a "big-endian" word order (most
significant word first). In such case, you must select "word-swapped" floating point format in
your Modbus master for the Modbus registers of the device.
OPT100 User Guide M211858EN-U
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