How to address tags in a Modbus device

The memory of Modicon systems is divided into four basic areas – discrete inputs, discrete outputs, input registers, holding registers. In Modicon systems, these areas are addressed absolutely (see the "Modicon addressing" column in the table below). In a Reliance project, tags are addressed relatively always starting at 0 (see the "Reliance addressing" column in the table below).

Addressing tags in a Modbus device

Memory area

Modicon addressing

Reliance addressing

Register type


1. Discrete outputs (Coils)

from 00001

Outputs (Coils)

from 0

2. Discrete inputs

from 10001


from 0

3. Input registers

from 30001

Input registers

from 0

4. Holding registers

from 40001

Holding registers

from 0


In a Reliance project, a tag at 40011 is configured this way:
Register type: Holding registers; Address: 10

For more information, go to the page with a description of Modbus Communication Driver.

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