Patent ID: 7398336

Claim:
A switching device automatically selecting a main communication port from either of Recommended Protocol 232 (RS-232) or Universal Serial Bus (USB) via switching, comprising: a microprocessor having a Universal Synchronous Asynchronous Receiver Transmitter (USART); a first diode having an anode and a cathode; an RS-232/USART converter element connecting to the microprocessor through the first diode wherein the anode of the first diode electrically connects to the RS-232/USART converter element, and the cathode of the first diode electrically connects to the microprocessor; an RS-232 serial port connecting to the RS-232/USART converter element; a second diode having an anode and a cathode; a USB/USART converter element connecting to the microprocessor through the second diode, wherein the anode of the second diode electrically connects to the USB/USART converter element, and the cathode of the second diode electrically connects to the microprocessor as well as the cathode of the first diode; a USB serial port connecting to the USB/USART converter element; at least one photo-coupler device including a first terminal and a second terminal, the first terminal of the photo-coupler device being a control input, and the second terminal of the photo-coupler device including a controllable switch to disable the USB/USART converter element or RS-232/USART converter element from transmitting data to the microprocessor; and a current-limiting resistor including a first end and a second end, the first end of the current-limiting resistor connecting to the first terminal of the photo-coupler device with the second end of the current-limiting resistor selectively connecting to a control signal, whereby one of the RS-232 serial port and the USB serial port has a high priority for communication with the microprocessor, and wherein said disabled one of said RS-232/USART converter element or USB/USART converter element can still receive data from the microprocessor even though it is disabled from transmitting data to the microprocessor.