A data diode comprises a USB input port coupled to a first USB to RS422 converter, which is coupled to a first serial port. A second serial port is coupled to a second USB to RS422 converter, which is coupled to a USB output port. The TX-pin of the first serial port is connected to the RX-pin of the second serial port and the TX+ pin of the first serial port is connected to the RX+ pin of the second serial port. The TX ports of the second serial port are not connected to the RX ports of the first serial port, thereby preventing reverse data flow.