The Mitsubishi FX3U-232ADP-MB is a dedicated RS-232C communication adapter for the FX3U series PLCs, supporting Modbus RTU/ASCII as master or slave, plus no-protocol and computer link modes. It draws 30 mA at 5 VDC from the PLC backplane, so no external power supply is needed — the bus provides it. The D-SUB 9-pin male connector mates directly to a standard serial port; transmission distance is limited to 15 m at RS-232C levels, which is typical for this physical layer. Protocol selection and baud rate are set in the PLC program, not DIP switches.
PLC firmware compatibility
This adapter works across the FX3S, FX3G, FX3U, FX3GC, and FX3UC families, but the firmware version determines which communication functions are available. For FX3U, MODBUS communication requires V2.40 or later; earlier versions support only no-protocol and computer link modes. On FX3G and FX3UC, MODBUS requires V1.30 and V2.40 respectively. FX3S and FX3GC support all functions from V1.00 onward. If you are swapping this into an existing panel, check the PLC firmware version before committing the BOM line.
MODBUS baud rate timing
The MODBUS communication speed ranges from 300 to 115200 bps. Units manufactured before July 2012 (serial number below 127xxxx) are limited to 38400 bps maximum on MODBUS. The higher rates — 57600 and 115200 bps — are supported only on units with serial number 127xxxx or later. For no-protocol and computer link modes, the top speed is 38400 bps on FX3U and FX3UC from V2.41 onward. If your application requires 115200 bps MODBUS, verify the serial number on the nameplate.
Environmental and isolation ratings
Operating temperature range is 0 to 55 °C, storage from -25 to 75 °C, with 5 to 95% RH non-condensing. The adapter uses photocoupler insulation between the D-SUB connector and the PLC ground terminal, rated for AC 500 V for one minute, with insulation resistance above 5 MΩ at DC 500 V. Vibration resistance when DIN-rail mounted is 10 to 57 Hz at 0.035 mm half-amplitude; direct mounting allows 0.075 mm. Impact rating is 147 m/s² for 11 ms half-sine pulse in X, Y, Z directions. The unit is not rated for use above 2000 m altitude or in pressurized environments.