Mitsubishi MELSEC-Q Series QJ71C24N Serial Communication Module

Description

• MC Protocol (Binary / ASCII): Allows a PC or HMI to read/write Q CPU device memories (D, M, X, Y, etc.) via standard Mitsubishi serial commands — widely used for SCADA, OPC (via serial), and touchpanel links.
• Non-Protocol (User-defined Frame): Send/receive arbitrary ASCII/binary strings via sequential instructions (from ladder — SEND/ RCV/ RSwith special D registers for C24N control) — ideal for 3rd-party barcode readers, weigh scales, or printers.
• Modbus RTU Slave/Master​ (on some FW versions — typically supported in QJ71C24N after certain FW rev; check label — earlier may need GX Works2 protocol setting activation): Enables acting as Modbus RTU slave to a Modbus master (e.g., 3rd-party HMI/SCADA) or polling Modbus slave devices (weigh scale with Modbus RTU).
• Data Link (Optional — C24N can do simplified peer-to-peer serial linking between Q PLCs with C24N modules — less common than MELSECNET/H but possible for small data exchange)

Key Features

• Channels: 2 independent serial ports (Ch.1 & Ch.2) — each can be set RS-232C or RS-422A/485 independently (physical interface depends on port type: Ch.1 = 9-pin D-Sub (RS-232C natively; RS-422 needs QC24N-R4 or cable adapter); Ch.2 = Terminal Block (RS-422A/485 native; RS-232 possible with adapter — check manual)
• Max. Baud Rate: Up to 115.2 kbps (some FW 230.4 kbps — verify)
• Protocols: MC (Binary/ASCII), Non-Protocol (user frame), Modbus RTU (Slave/Master — FW dependent), Simple Link (C24↔C24)
• Isolation: Photocoupler isolation on RS-422/485 side; RS-232 typically not isolated port-to-port but isolated from bus
• Diagnostics: Module has RUN/ERR LEDs; communication status monitorable via special relays (SM) and buffers (BFM) in ladder
• Country of Origin: Japan (Mitsubishi Electric)

Model & Variant Reference (Q Series Serial Communication Modules)

⚠️ Important Installation & Wiring Notes:

1. Port Physical Layer:
   • Ch.1 (9-pin D-Sub on module face): Native RS-232C pinout (DCD/DSR/DTR/RTS/CTS cross-over per Mitsubishi standard — null-modem cable often needed for PC connection). To use Ch.1 as RS-422/485 you need an external converter (QC24N-R4 or cable with built-in Xcvr)​ — the on-board D-Sub does NOT auto-switch.
   • Ch.2 (Removable terminal block, 8-screw typical): Native RS-422A/485 (TxD+/-, RxD+/-, GND, SG). For RS-232 on Ch.2 you’d need adapter — uncommon; most wire Ch.2 as RS-485 to multi-drop devices (HMI network, Modbus RTU daisy-chain).
2. Termination (RS-485): On Ch.2 in RS-485 multi-drop — terminate both ends with 120Ω resistor (some devices have internal — check; C24N does NOT have built-in termination resistor — add externally across TxA+/TxB- at furthest node).
3. MC Protocol Default Settings: After enabling MC Protocol in GX Works2 parameter for a channel, default is often 9600 bps, 7/Even/2 (or 8/None/1 — check regional default — Japan often 7E2; Intl often 8N1) — CHANGE to match your HMI/PC!​ Many connection failures are due to baud/parity mismatch.
4. GX Works2 Parameter: You MUST configure each channel in “Serial Communication Setting” tab — check “Use Channel 1 / Channel 2”, select Protocol Type (MC / Non-Proto / Modbus), set Baud, Data Bits, Parity, Stop Bits, Sum Check (for MC ASCII), then download PLC parameters + restart PLC (or write from peripheral & re-boot)​ — settings are NOT active until PLC re-reads params.
5. Cable for PC (RS-232): Use Mitsubishi standard programming cable (USB-SC09 or QC30R2 + null modem) for Ch.1 — pinout differs from straight-through — use correct Mitsubishi null-modem pinout (or USB-SC09 which handles it internally).

Technical Specifications (QJ71C24N — 2-Ch Serial Interface, RS-232C + RS-422/485)

Warranty & After-Sales

• Factory new units: 12 months warranty
• Refurbished units: 3-6 months warranty (loopback test — connect Ch1↔Ch2 with null-modem or wrap plug → send/receive via GX Works2 monitor)
• Technical support for:
  • GX Works2 parameter setup (enable Ch1/Ch2, select MC/Non-Proto/Modbus, set baud/parity/stop, checksum)
  • RS-232 null-modem cable pinout (Mitsubishi D-Sub 9-pin vs PC standard — often needs crossed TXD/RXD & DSR/DTR/CD loopback)
  • RS-485 daisy-chain wiring (Ch2 terminal block: RDA+/RDA- (receive same as Tx+/- on 422), SDA+/SDA- (send), GND, SG(shield) — termination resistor advice)
  • Non-Protocol ladder programming (SEND/ RCV/ RSinstructions with C24N special D register usage — BFM read/write)
  • Modbus RTU configuration (slave address, register mapping — if FW supports)
  • Cross-ref to QJ71C24N-R2 (dual RS-232) if both ports need RS-232
• Optional RS-422 converter (QC24N-R4), programming cables (USB-SC09), and termination resistors available

Delivery Time

• Standard delivery: 3-5 working days (stock items)
• Express shipping available upon request

Why Choose Our Store

• Genuine Mitsubishi MELSEC-Q communication modules — not clones with incorrect UART timing
• Global supply network with competitive pricing
• Expertise in Q-series serial comms (MC Protocol, Non-Proto ladder, Modbus RTU, cable pinouts)
• Comprehensive technical documentation (D-Sub 9-pin pinout diagram, GX Works2 param screenshot, RS-485 daisy-chain example)
• Responsive customer service and support

Applications

• HMI / Touchpanel Link: Connect Pro-face / Weintek / Mitsubishi GOT via RS-232 (Ch1) or RS-485 (Ch2) — use MC Protocol.
• Barcode / RFID Reader: Non-Protocol mode — send trigger cmd, receive scanned data into D-registers via RCV.
• Weigh Scale / Print Scale: Modbus RTU Slave (scale as slave → Q reads weight) or Non-Proto ASCII parse.
• PC Data Logging (Legacy): PC with serial port (or USB-RS232 adapter) reads/writes Q CPU D/M registers via MC Protocol — no Ethernet needed.
• Retrofit / Spare: Replace failed QJ71C24N — same article number drops into rack; download parameters (already in PG project) → restart.