JUMO mTRON T Manual page 29

Important information on the bit commands
To use bit commands correctly and evaluate the results correctly, it is important to understand
the order in which the data words and the bits they contain are arranged.
The Modbus standard specifies that when reading out word by word the most significant byte
(msb) is specified first. The bit arrangement within the data words, however, starts with the least
significant bit (lsb). This must be observed when reading out bit values.
Example for calculating the bit address from the word address
 Chapter 7 "Modbus address tables", page 77
The word address tables are specified in hexadecimal form in the Modbus address tables in
the left column. The bit addresses must be calculated from this word address to read or write
individual bits. To determine the bit address of bit 8 for the word address 0x0009 in a bit field,
the following calculation must be performed: bit address = (word address
number
Hex
Bit address = (0x0009 × 0x10) + 0x8
Hexadecimal calculation
Result: 98
HEX
3 Modbus protocol description
Bit address = (9 × 16) + 8
× 10
Hex
Decimal calculation
Result: 152
DEC
) + bit
Hex
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