Modbus Addressing Explained (4-Digit, 5-Digit, 6-Digit)

Modbus addressing is one of the most confusing aspects of industrial communication because different formats are used across documentation, tools, and SCADA systems.

This guide explains the differences and how to convert them correctly.

4-Digit, 5-Digit, and 6-Digit Modbus Addresses

4-Digit Reference

Example: 0001, 0002

This is a raw register number without function code information.

5-Digit Address

Example: 40001

• • • 4xxxx → Holding Registers

    • 3xxxx → Input Registers

    • 1xxxx → Discrete Inputs

    • 0xxxx → Coils

6-Digit Address

Example: 400001

Used in modern SCADA systems to support larger address ranges.

0-Based vs 1-Based Addressing

Modbus documentation uses 1-based addressing, but the protocol uses 0-based.

Example:

• 40001 → 0

• 40002 → 1

This difference is the most common cause of Modbus errors.

Why Modbus Addressing Matters

• Wrong register readings

• Off-by-one errors

• Misinterpreted data

• Debugging delays

Use the Modbus Address Calculator

Convert all formats instantly:

👉 Open Modbus Address Calculator