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EncodingModbus Term

Byte Order (Endianness)

The arrangement of bytes across registers when storing multi-byte values.

Definition

Byte order (also called endianness) describes which byte of a multi-byte value is stored in the lower register address and which byte is in the high position of each register. Modbus transmits registers MSB first (big-endian) within a single 16-bit register, but there is no standard for how two registers combine into a 32-bit value. Always check your device datasheet for the byte order used.

Quick Facts

Within a registerAlways big-endian (MSB first)
Across registersVendor-specific
Most commonAB-CD and CD-AB (word-swap)
Standard?No Modbus standard for 32-bit order

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ModPackQT Modbus Glossary · Updated 2026