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Data ModelModbus Term

1-Based Addressing

The human-readable naming convention used in datasheets: 40001 = first holding register.

Definition

1-based addressing is a naming convention common in datasheets and SCADA displays — not the on-wire protocol. Holding register 40001 corresponds to protocol address 0, 40002 to address 1, and so on. The leading digit identifies the table (4x = holding, 3x = input, 1x = discrete, 0x = coil). When configuring requests you must always subtract 1 from the datasheet address.

Quick Facts

Holding prefix4 (40001–49999)
Input prefix3 (30001–39999)
Discrete prefix1 (10001–19999)
Coil prefix0 (00001–09999)

Related Terms

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ModPackQT Modbus Glossary · Updated 2026