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HomeResourcesModbus GlossaryFC05 — Write Single Coil
Function CodesModbus Term

FC05 — Write Single Coil

Set a single output coil to ON (0xFF00) or OFF (0x0000).

Definition

Function Code 05 forces a single coil to a specified state. The data value must be exactly 0xFF00 (ON) or 0x0000 (OFF) — any other value causes an exception 03 response. The slave echoes back the entire request as confirmation. Only one coil can be written per request; use FC15 to write multiple.

Quick Facts

FC hex0x05
ON value0xFF00
OFF value0x0000
ResponseEcho of request

Related Terms

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ModPackQT Modbus Glossary · Updated 2026