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Data ModelModbus Term

Register Offset

The relationship between a 1-based datasheet address (40001) and its 0-based protocol address (0).

Definition

The register offset describes how to translate a 1-based PLC address to the 0-based protocol address used in Modbus frames. For holding registers the offset is 40000 — subtract 40000 from the datasheet address to get the protocol address. For input registers subtract 30000, for discrete inputs subtract 10000, and for coils subtract 0 or 1 depending on convention.

Quick Facts

Holding offset40000 (40001 → 0, 40002 → 1)
Input offset30000 (30001 → 0)
Discrete offset10000 (10001 → 0)
Coil offset0 or 1 depending on tool

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ModPackQT Modbus Glossary · Updated 2026