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Data ModelModbus Term

0-Based Addressing

The actual protocol addressing: addresses start from 0 in PDU requests.

Definition

In Modbus protocol frames, register addresses are 0-based — the first holding register is address 0x0000 in the request PDU. This is the 'raw' address you put in the request bytes. Datasheets and SCADA software often display 1-based numbers (40001, 40002…) which require subtracting 1 to get the protocol address.

Quick Facts

First holding regAddress 0x0000 in PDU
Datasheet equivalent40001
Confusion sourceDatasheets often use 1-based

Related Terms

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ModPackQT Modbus Glossary · Updated 2026