Mitsubishi QJ71MT91 MELSEC‑Q MODBUS/TCP Interface Module 100BASE‑TX

Mitsubishi Electric QJ71MT91 is a dedicated MODBUS/TCP communication module for the MELSEC‑Q series programmable logic controller system. Equipped with an RJ45 10BASE‑T/100BASE‑TX Ethernet port and supporting full MODBUS/TCP protocol stack, the module can operate simultaneously as both a Modbus master and a Modbus slave. As a master, it reads and writes holding registers, input registers, coils, and discrete inputs from up to 32 Modbus TCP slave devices (energy meters, drives, sensors, remote I/O). As a slave, it exposes MELSEC‑Q device data (D registers, M relays, X inputs, Y outputs) to up to 16 Modbus TCP master clients (SCADA systems, HMI panels, third‑party PLCs). Communication parameters are configured in GX Works2/GX Developer — no PLC ladder programming is required for Modbus TCP data exchange, substantially reducing engineering effort compared to socket programming with the general‑purpose QJ71E71‑100 Ethernet module.

Applications:

• Connecting MELSEC‑Q PLCs to Modbus TCP slave devices (drives, meters, sensors, remote I/O)

• Exposing MELSEC‑Q device data to SCADA systems and HMI panels via Modbus TCP

• Third‑party device integration without Mitsubishi MC protocol driver requirements

• Factory automation networks requiring Modbus TCP as standard communication protocol

Core Specifications:

Advanced Specifications:

• Data exchange methods: Automatic communication (periodic polling via parameters), dedicated instructions (MBRW, MBREQ), or auto‑refresh to PLC device memory via GX Configurator‑MB

• Automatic refresh: Configurable data exchange between module buffer memory and MELSEC‑Q device addresses without FROM/TO buffer memory instructions in the PLC program

• Slave function: automatic response to request messages — no sequence program required

• KeepAlive function: checks for communication status and cuts off unnecessary TCP connections

• Router relay function: communication with MODBUS/TCP devices via router supported

• GX Developer connection via Ethernet: enables PLC maintenance over the network

• MODBUS® is a registered trademark of Schneider Electric SA

System Integration:

• This module belongs to the Mitsubishi Electric MELSEC‑Q series.

• Installs into any MELSEC‑Q series main base unit (Q3□B, Q5□B, Q6□B series) or extension base unit slot.

• Compatible with Q series CPU modules (Q00J, Q00, Q01, Qn, QnH, QnPH, QnPRH, QnU series).

• Parameter settings and slave configuration performed using GX Works2 or GX Developer together with GX Configurator‑MB utility package.

• Connection to the network via standard RJ‑45 Ethernet cable.

Related Products:

• QJ71MB91 – MODBUS interface module (RS‑232 / RS‑422/485)

• QJ71E71‑100 – General‑purpose Ethernet module (requires socket programming for Modbus TCP)

• Q03UDECPU – MELSEC‑Q CPU module with built‑in Ethernet

• GX Configurator‑MB – Utility package for configuration and monitoring