Description:

The Mitsubishi QJ71MB91 is a Modbus serial communication module designed for the MELSEC-Q series PLC platform, enabling communication between the PLC and external Modbus-compatible devices. It supports both master and slave functionality, allowing integration with third-party equipment such as drives, HMIs, sensors, and remote I/O. Commonly installed in control systems and industrial networks, it is used by maintenance teams and system integrators for system communication, networking, and protocol conversion.

Applications:

The Mitsubishi QJ71MB91 communication module is used in industrial automation systems requiring reliable serial communication and integration with Modbus devices. Typical applications include PLC-to-HMI communication, inverter and drive control, multi-device networking, and integration of third-party field devices where stable Modbus communication and data exchange are critical to system performance.

Technical Specifications:

• Manufacturer Part Number (MPN): QJ71MB91
• Product Type: Modbus Communication Module
• Series: MELSEC-Q
• Communication Protocol: Modbus RTU / Modbus ASCII
• Communication Modes: Master and Slave
• Interfaces:
• RS-232: 1 channel
• RS-422/485: 1 channel
• Communication Speed: 300 bps to 115200 bps
• Max Transmission Distance:
• RS-232: up to 15 m
• RS-422/485: up to 1200 m
• Max Number of Slaves: 32 devices per channel
• Data Handling Capacity: Up to 4K words (input/output)
• Modbus Device Points: Up to 64K points per type
• I/O Occupation: 32 points (intelligent module)
• Power Supply: 5 VDC (from PLC backplane)
• Current Consumption: Approx. 0.31 A
• Dimensions: 98 × 27.4 × 90 mm
• Weight: Approx. 0.2 kg
• Mounting Type: Rack-mounted (Q-series base unit)
• Status: Active / standard module

Common Replacements:

• Mitsubishi QJ71MT91 (Modbus TCP version)
• Mitsubishi QJ71E71-100 (Ethernet module alternative)
• Mitsubishi FX5-485-BD (for iQ-F platform, not direct swap)