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Usually you connect to the serial port of the computer using a female DB9 or female DB25 connector. Also referred to as a female 9 pin, or female 25 pin, D-shell connector. The serial port is RS232C (or RS-232C). RS232 stands for Recommended Standard number 232, and the C stands for revision C. Each RS232 device at our site connects to an RS232C serial port through a cable you provide (unless otherwise noted). 3 wires are generally used: Signal Ground, Trasmitted Data (TD), and Received Data (RD), otherwise referred to as Ground, Transmit and Receive. At both ends of the cable, pin 1 is Ground. At the computer, Receive is pin 2, while at the peripheral (e.g., temperature controller) it is pin 3. At the computer, Transmit is pin 3, while at the peripheral it is pin 2. The connection is made via "twisted pair" - which means the Transmit and Receive lines are twisted around each other along their length, from one end to the other. For the cable, solid copper wire is preferred over stranded wire simply because there are no strands at the end that can break off, or bend out, and short the connection. With appropriate converters you could connect by other means, such as infra-red light (e.g., IrDA).