Modbus Addresses

 

For Modbus protocol, the RTU port and the node number of the targeted equipment determine the net and node fields:

 

 

Register Address

Description

Size / Limitation

Catalyst SNA

0xxxx

Coil number xxxx

1-bit

1*node*0xxxx

1xxxx

Input number xxxx

1-bit

1*node*1xxxx

3xxxx

Input register number xxxx

16-bit

1*node*3xxxx

4xxxx

Output register number xxxx

16-bit

1*node*4xxxx

5xxxx

Floating Point register

32-bit

1*node*5xxxx

Note: The 5x and 4x references share the same data space. That is, an address of the form 5nnnn takes the 32 bits beginning at location 4nnnn and extending through 4nnnn+1. These 32 bits are then interpreted as an IEEE floating point number.

 

The following list identifies special issues with regard to this addressing scheme: