The QJ71E71-100 is Mitsubishi Electric’s 100BASE-TX Ethernet communication module for the MELSEC-Q series programmable controller platform — providing a dedicated 10/100 Mbps Ethernet network interface for MELSEC-Q CPU units to enable TCP/IP and UDP/IP socket communication, MC protocol (MELSEC Communication protocol) data exchange with SCADA systems and HMI panels, and iQ Works / GX Works2 remote programming and monitoring access via standard Ethernet infrastructure. Atlantech Drives holds stock of the QJ71E71-100. Contact us for fast worldwide delivery and competitive pricing.
What Is the QJ71E71-100?
The QJ71E71-100 is a MELSEC-Q series special function module providing a 100BASE-TX Ethernet port (RJ45 connector, auto MDI/MDI-X, auto-negotiation 10/100 Mbps) for MELSEC-Q CPU units installed in Q-series base units. The module enables the MELSEC-Q PLC to communicate with Ethernet-networked devices using standard TCP/IP and UDP/IP protocols — SCADA systems reading PLC data via MC protocol, GOT HMI panels connecting via Ethernet for display and control, GX Works2 engineering software connecting for remote programming and online monitoring, and PC-based data collection applications using socket communication to exchange custom data frames with the PLC program. The QJ71E71-100’s MC protocol implementation (formerly called MELSEC Communication protocol or MELSEC-NET/Ethernet protocol) provides standardised register read/write access to MELSEC-Q device data (D registers, M relays, X inputs, Y outputs, T timers, C counters) from any Ethernet-connected device with an MC protocol driver — enabling integration with virtually any SCADA, DCS, or MES platform that supports the widely implemented MC protocol or equivalent Mitsubishi Ethernet communication standard. The module supports multiple simultaneous connections — up to 16 connection definitions configurable in GX Works2’s Ethernet parameter settings — allowing multiple clients (multiple SCADA nodes, multiple HMI panels, GX Works2 sessions) to communicate with the MELSEC-Q CPU simultaneously through the QJ71E71-100.
Key Technical Specifications
- Model: QJ71E71-100
- Network Standard: 100BASE-TX (IEEE 802.3u), auto-negotiation 10/100 Mbps
- Connector: RJ45 (auto MDI/MDI-X)
- Protocols: TCP/IP, UDP/IP, MC Protocol (Binary/ASCII mode), socket communication
- Maximum Simultaneous Connections: 16 (configurable in GX Works2 Ethernet parameters)
- IP Address: Static IP (configured via GX Works2 Ethernet parameters)
- Compatible CPUs: Q02UCPU, Q03UDECPU, Q04UDEHCPU, Q06UDEHCPU, Q13UDEHCPU, Q26UDEHCPU and compatible Q-series CPUs
- Installation: Q-series base unit intelligent function module slot
- Power Consumption: 5 VDC internal bus, approx. 0.55 A
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 27.4 mm × 98 mm × 90 mm
- Weight: Approx. 0.1 kg
Compatibility & System Integration
The QJ71E71-100 is compatible with the MELSEC-Q series CPU units — Q02UCPU, Q03UDECPU, Q04UDEHCPU, Q06UDEHCPU, Q13UDEHCPU, Q26UDEHCPU, and other compatible Universal model Q-series CPUs — installed in any Q-series main base unit (Q3□B, Q5□B, Q6□B, Q3DB series) in any intelligent function module slot. The module communicates with the CPU via the Q-series internal bus using the MELSEC-Q FROM/TO buffer memory protocol — the CPU reads received data from and writes transmit data to the QJ71E71-100’s buffer memory using FROM/TO instructions in the PLC ladder program, or uses the GX Works2 auto-refresh parameter to automatically transfer buffer memory data to/from specified CPU device addresses each scan cycle without explicit FROM/TO instructions. For SCADA integration, the QJ71E71-100 supports Mitsubishi’s MC protocol in both ASCII and binary format over TCP/IP — the binary format provides approximately 40% higher data throughput than ASCII for equivalent data quantities, recommended for high-frequency data polling applications. GOT2000 HMI panels connect to the QJ71E71-100 via Ethernet using Mitsubishi’s GOT Ethernet connection setting — configure the GOT’s host controller as «MELSEC-Q (Ethernet)» with the QJ71E71-100’s IP address and port 5006 (MC protocol default) for seamless HMI-to-PLC data exchange. For GX Works2 remote programming access, add the QJ71E71-100’s IP address as an Ethernet connection in GX Works2’s connection settings — enabling remote ladder monitoring, online program modification, and device monitoring from any networked engineering workstation without requiring physical USB or RS-232C connection to the PLC.
Troubleshooting Guide
For QJ71E71-100 modules where the ERR LED is lit after power-up, the most common cause is an IP address conflict on the network — another device has already claimed the IP address configured in the QJ71E71-100’s Ethernet parameter settings. Connect GX Works2 via a direct USB connection to the MELSEC-Q CPU and check the QJ71E71-100’s buffer memory special register BFM#0 (error status) and BFM#1 (error code) using the device monitor — error code 0xC110 indicates IP address conflict. Resolve by assigning a unique IP address in the QJ71E71-100’s Ethernet parameters and writing the corrected parameters to the CPU. For SCADA systems that intermittently lose communication with the QJ71E71-100 after initially connecting successfully, check the TCP connection keep-alive settings — some SCADA Ethernet drivers do not send TCP keep-alive packets, causing the QJ71E71-100 to close the TCP connection after the configured keep-alive timeout period (default 90 seconds of inactivity). Configure the SCADA driver to send periodic keep-alive packets or reduce the polling interval below the keep-alive timeout to maintain continuous TCP connection. For GX Works2 remote programming connections that drop during large program uploads, verify the network switch between the engineering workstation and the QJ71E71-100 does not have aggressive flow control or connection timeout settings that interrupt long data transfers — use managed switch SPAN port monitoring to confirm whether the TCP session is being terminated by the switch or by the QJ71E71-100.
Frequently Asked Questions
Q: Can the QJ71E71-100 communicate with third-party devices that do not support Mitsubishi MC protocol, such as Modbus TCP devices?
A: The QJ71E71-100 does not natively support Modbus TCP or other non-Mitsubishi protocols as a built-in function. For Modbus TCP device integration, the QJ71E71-100’s socket communication function can be used to implement a custom Modbus TCP client in the MELSEC-Q ladder program — the PLC program constructs and sends Modbus TCP request frames via the socket communication instructions and parses the Modbus response frames received from the slave device. Alternatively, a third-party Modbus TCP-to-MC protocol gateway can bridge between the Modbus TCP device and the QJ71E71-100’s MC protocol interface without PLC programming.
Q: What is the difference between the QJ71E71-100 and the newer QJ71E71N-100 module?
A: The QJ71E71N-100 is an enhanced version of the QJ71E71-100 providing additional network functions including e-mail notification, FTP file transfer, and extended socket communication capability. For applications requiring only standard MC protocol SCADA integration and GX Works2 remote programming, the QJ71E71-100 provides all necessary functions. The QJ71E71N-100 is appropriate when e-mail alarm notification or FTP-based data file transfer is required from the MELSEC-Q system.
Q: How many QJ71E71-100 modules can be installed in a single MELSEC-Q base unit?
A: Multiple QJ71E71-100 modules can be installed in the same MELSEC-Q base unit — up to the base unit’s total intelligent function module slot count. Each QJ71E71-100 provides an independent 100BASE-TX Ethernet port with its own IP address and connection configuration, enabling the MELSEC-Q system to connect to multiple separate Ethernet networks simultaneously (for example, a SCADA network and a separate engineering network) by installing one QJ71E71-100 per network in the base unit.
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