Modbus Addressing


The address of any Tag that belongs to a Modbus data source should follow the following syntax format:


<Function Code>;<Index>


Following are different examples:


  • Holding Registers (Words): Starts with 4

Examples:

4;1

4;120


  • Bit Of Word:

Examples:

4;1.0

4;1.15


  • Reading Floats or Long Integers (Double Words):


To read/write float variables (two words) or integers larger than (32,767), specify the address of the first word and choose the Data Type: Real


In the case of long integer, define the variable as Real (or Float) in your device.


Examples:


4;1 and Data Type Real means to read both the holding registers 1 and 2


4;9 and Data Type Real means to read both the holding registers 9 and 10



  • Coils: Start with 0

Examples:

0;1

0.324


Note: Coils are only supported in Modbus TCP client driver (Master) and not supported in Modbus Server.


  • Input Registers: Starts with 3

Example: 3;1


  • Input Floats: Starts with 3

Example: 3;1 and data type is Real


  • Input Status: Starts with 1

Example: 1;1


Example screen shot

Function: Holding Register

Index: 2