The debugger displays output and receives user input through a serial communication port of the computer on which it runs. To use the debugger, you must connect a cable from this serial port to either a serial terminal or the serial port of another computer. A three-wire null modem cable is the minimum cable requirement for this connection. In a three-wire null modem cable, the TxD (transmit data) and RxD (receive data) lines are in opposite positions at the two ends of the cable, but the signal ground is connected straight through. DTR (data-terminal-ready) and CTS (clear-to-send) handshaking is not used.
Typically, users connect the cable to a second computer and use their favorite communications software to open the serial port and interact with the debugger.