The FX3U PLC can be fitted with a mini USB connection option that is typically used for PLC programming access. It is not so well known that this connection can also be used for general communications with MX Sheet.
If the FX3U-USB-BD option has been fitted to an FX3U PLC, no further settings are required for it to function correctly. At the PC end, if MX Sheet has been installed or other up-to-date Mitsubishi PLC programming software, the FX USB driver will have been installed.
Windows Device Manager can be used to find which serial port has been assigned to the FX USB driver (comm 6 for example).
To set up communications with MX Sheet, simply select a serial CPU port connection using the comm. port found with Windows Device Manager.
For further information, please refer to help within MX Sheet and appropriate FX manuals such as the communications manual and the BD board manual.