Vaisala Optimus OPT100, User Manual

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Appendix A. Modbus Reference
A.1 Default Communication Settings
Table 21 Default Modbus Serial Communication Settings
Description Default Value
Serial bit rate 19200
Number of data bits 8
Parity E
Number of stop bits 1
Modbus slave ID 240
A.2 Function Codes
Table 22 Supported Function Codes
Function Code (Decimal) Function Code (Hexadecimal) Name
03 03
hex
Read Holding Registers
A.3 Modbus Registers
Registers are numbered in decimal, starting from one. Register
addresses in actual Modbus messages (Modbus Protocol Data Unit (PDU) are in
hexadecimal and start from zero. Subtract 1 from the register number presented
in this manual to get the address used in the Modbus message. For example, the
register number 23 (present value of acetylene) corresponds to address 16
hex
in
the Modbus message.
CAUTION!
Accessing unavailable (temporarily missing) measurement data does not generate an
exception. “Unavailable” value (a quiet NaN for floating point data) is returned instead. An
exception is generated only for any access outside the applicable register ranges.
OPT100 User Guide M211858EN-E
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