PLC word order and byte order troubleshooting
Separate byte swaps from 16-bit word swaps when PLCs, HMIs, gateways, historians, and Modbus devices exchange 32-bit integers or floating-point values.
- Product
- PLC and gateway data exchange
- Level
- Intermediate
- Read time
- 10 min
- Reviewed
- 2026-07-15
- Author
- Toolbox editorial team
- Reviewer
- Technical review
What to establish before troubleshooting
Byte order describes the order of bytes inside a word; word order describes the order of 16-bit registers inside a 32-bit value. These are separate choices and vendor terms are often inconsistent.
Start with a recognizable hexadecimal pattern. It exposes each byte and word position more clearly than a decimal process value.
Abbreviated worked example
Track 16#12345678 across two registers
The intended 32-bit value is 16#12345678.
- 1Expected high-word-first registers are 16#1234 and 16#5678.
- 2A word-swapped device returns 16#5678 then 16#1234; a byte swap produces 16#3412 and 16#7856.
Result: Identify the observed pattern before selecting a swap operation.
Caution: Labels such as little-endian may describe byte order only and still leave 16-bit register order undefined.
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