PLC Simulator
Modbus function reference

Modbus Function Code 06 — Write Single Register

Write one 16-bit register

06
Load in Modbus sandbox

Data model

Holding registers (4xxxx reference family)

Access

Write one 16-bit register

Protocol quantity

Exactly 1 register

Worked example

Read the PDU field by field.

Write value 1 to protocol address 10. A normal response echoes the address and value.

Typical use: Sending a setpoint, mode or command value to one documented holding register.

Example protocol data units

Request PDU

06 00 0A 00 01

Normal response PDU

06 00 0A 00 01

PDU examples omit the Modbus TCP MBAP header and the Modbus RTU unit-address/CRC envelope. Multi-byte values are shown in network byte order.

Common implementation mistakes

  • Writing an engineering value without applying the documented scale
  • Using signed values without two’s-complement handling
  • Assuming an echoed write means the command was accepted by application logic

Run the reference

Turn a protocol table into evidence.

Compose the request publicly, then use Pro for advanced graded exceptions, saved fixtures, complete history and project sharing.

Open sandbox
01 Read coils03 Read holding02 Illegal address