PLC REAL and IEEE 754 conversion checks
Decode a 32-bit single-precision floating-point value only after proving the source bytes, word order, special values, and expected engineering range.
- Product
- PLC REAL and IEEE 754 data
- Level
- Advanced
- Read time
- 11 min
- Reviewed
- 2026-07-15
- Author
- Toolbox editorial team
- Reviewer
- Technical review
What to establish before troubleshooting
A 32-bit IEEE 754 single-precision value contains sign, exponent, and fraction fields. PLCs commonly call this a REAL, but protocols may transport the four bytes as two registers in different word orders.
Prove byte and word order first. A mathematically correct IEEE decoder cannot repair bytes assembled in the wrong sequence.
Abbreviated worked example
Recognize REAL 12.5
The intended 32-bit IEEE 754 value is 12.5.
- 112.5 is represented by hexadecimal 16#41480000 in standard byte order.
- 2Across two high-word-first registers that is 16#4148 followed by 16#0000.
Result: A decoder should return 12.5 after the four bytes are assembled correctly.
Caution: If the registers arrive low-word-first, swap the words before decoding; do not reverse all four bytes without evidence.
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