Modbus function reference
Modbus Function Code 05 — Write Single Coil
Write one boolean output state
05
Write one boolean output state
Data model
Coils (0xxxx reference family)
Access
Write one boolean output state
Protocol quantity
Exactly 1 coil
Worked example
Write ON to the coil at protocol address 172. ON is encoded FF00 and OFF is encoded 0000.
Typical use: Sending a single boolean command when the device map explicitly permits a coil write.
Request PDU
05 00 AC FF 00Normal response PDU
05 00 AC FF 00PDU examples omit the Modbus TCP MBAP header and the Modbus RTU unit-address/CRC envelope. Multi-byte values are shown in network byte order.
Run the reference
Compose the request publicly, then use Pro for advanced graded exceptions, saved fixtures, complete history and project sharing.
Industrial communications path
Choose the physical layer, frame the request, inspect the mapped data and diagnose exception evidence in one connected sequence.