Purchase now the Mitsubishi FX3U-232-BD — the RS-232C serial communication board designed for direct installation into the FX3U programmable logic controller.
What Is the Mitsubishi FX3U-232-BD?
The FX3U-232-BD is a plug-in communication board manufactured by Mitsubishi Electric for the FX3U PLC series. It adds a single RS-232C serial port to the FX3U base unit by installing directly into the dedicated board slot on the left side of the PLC — no external adapter or power supply is required. This board enables the FX3U to communicate with external devices such as HMIs, barcode readers, weighing instruments, printers, and SCADA systems using RS-232C protocol, including Mitsubishi’s own MC Protocol (formerly MELSEC Communication Protocol) and general-purpose serial (non-protocol) communication.
Key Technical Specifications
- Communication standard: RS-232C
- Number of channels: 1
- Connector type: D-Sub 9-pin (DB9) male
- Baud rates supported: 300 to 115,200 bps
- Data bits: 7 or 8
- Parity: None, Even, Odd
- Stop bits: 1 or 2
- Communication protocols: MC Protocol, Inverter communication, Non-protocol (free-format), Modbus RTU
- Cable length: Maximum 15 m (RS-232C standard)
- Power supply: Supplied from FX3U base unit
- Compatible PLCs: FX3U, FX3UC (with FX3UC-CNV-BD adapter)
Supported Communication Modes
The FX3U-232-BD supports the following communication modes, selectable via PLC parameters in GX Works2 or GX Developer:
- MC Protocol: For SCADA, HMI, and PC-based monitoring applications that read/write PLC data registers directly
- Non-protocol (RS instruction): For custom serial communication with instruments and devices using FX3U ladder logic RS instructions
- Inverter communication: For direct parameter read/write to Mitsubishi FR-series inverters via RS-232C
- Modbus RTU: For communication with Modbus-compatible third-party devices
Installation Advice
Before installing the FX3U-232-BD, power down the FX3U base unit completely — inserting or removing the board with power applied risks damage to both the board and the PLC. Open the left-side board cover of the FX3U base unit and seat the FX3U-232-BD firmly into the dedicated slot, ensuring the connector is fully engaged before replacing the cover. Only one communication board can be installed in the FX3U board slot at a time; if a second serial port is required, use an FX3U special adapter (e.g., FX3U-232ADP-MB) connected to the left-side adapter port instead. After installation, configure the communication parameters (baud rate, data bits, parity, stop bits) via GX Works2 PLC parameters under Serial Communication Settings before downloading the project.
Expert Tips
- RS-232C has a practical cable length limit of 15 metres. For longer distances or electrically noisy environments, use the RS-485 equivalent board (FX3U-485-BD) with an RS-232C-to-RS-485 converter at the remote device end, or switch to Ethernet communication (FX3U-ENET-ADP).
- When using non-protocol communication (RS instruction), always implement a timeout mechanism in your ladder program — if the external device does not respond within the expected window, the RS instruction will hold and block further communication until the FX3U CPU is reset.
- For Mitsubishi GOT HMI connections using MC Protocol over RS-232C, set the FX3U communication format to match the GOT’s default settings (typically 19,200 bps, 8-bit, Even parity, 1 stop bit) to avoid time-consuming debugging of communication parameter mismatches.
Frequently Asked Questions
Q: Can the FX3U-232-BD be used with FX3G or FX2N PLCs?
A: No. The FX3U-232-BD is designed exclusively for the FX3U (and FX3UC with adapter) base units. FX3G has its own communication board range (FX3G-232-BD), and the FX2N series uses a different and incompatible expansion connector.
Q: How many communication boards can be installed in an FX3U?
A: Only one board can be installed in the FX3U’s dedicated board slot. For additional serial ports, use the left-side special adapter ports (up to 2 adapters can be connected).
Q: Is Modbus TCP supported by the FX3U-232-BD?
A: No. Modbus TCP requires Ethernet connectivity — use the FX3U-ENET-ADP for Modbus TCP. The FX3U-232-BD supports Modbus RTU only, which operates over the RS-232C serial interface.
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