The FX3U-USB-DB is a USB communication expansion board for the Mitsubishi FX3U PLC series, model FX3U-USB-BD. It adds a USB Mini-B port to the CPU, supporting baud rates from 9600 up to 115200 bps for programming or data exchange with a PC. Photocoupler isolation between the communication line and the CPU protects the PLC logic from ground loops and transients on the USB cable — a common failure point when connecting a laptop to a live panel. Power draw is 15 mA at 5 VDC when powered from the PLC internal supply, or 30 mA at 5 VDC when bus-powered from the PC's USB connector. The board complies with USB 2.0 full-speed standard.
Dimensions are 4.61 cm x 1.96 cm x 5.35 cm — it mounts directly into the FX3U CPU's expansion slot without additional DIN rail space. The Mini-B connector is recessed; verify cable clearance if the PLC is in a tight enclosure.