Modbus Interface 4-7
© 2012 HMS Industrial Networks AB
Doc.Id. HMSI-168-25
Modbus Addressing
The I/O data tables are addressed directly using standard Modbus addressing.
Modbus functions that reference outputs (Coils and Holding Registers) will
address the Output table. Modbus functions that reference inputs (Status bits and
Input Registers) will address the Input table.
Only the areas of the I/O tables that are configured with J1939 I/O data points are
addressable. If a Modbus request is made to an address outside of the configured
I/O table space, an exception response will be returned to the Modbus master.
Register Functions
Modbus functions that use Word addressing address the I/O tables using 16-bit
words. The first byte of the table is addressed as 1, word address 2 accesses the
third byte of the table, and so on.
Input
Register
Input
Table Offset
30001
0
30002
2
...
31024
2046
Holding
Register
Output
Table Offset
40001
0
40002
2
...
41024
2046