Serial Ports: Difference between revisions

The Wikipedia page on [[wikipedia:Serial_port|Serial ports]] has a lot of information, and it is summarised here. The serial interface is very simple. There are actually two kinds of serial port: 25-pin and 9-pin. 25-pin ports are not any better, they just have more pins (most unused) and are bigger. 9-pin is smaller and is used more often though in the past the 25-pin ones were used more often. The 9-pin ones are called DE-9 (or more commonly, DB-9 even though DE-9 is its technical name) and the 25-pin ones are called DB-25. They plug in to your computer using a female plug (unless your computer is odd and has a female port, in which case your cable will need a male plug). [[wikipedia:D-subminiature|This Wikipedia page]] has more information on the plug used.

Both have the same basic types of pins. A DB-25 has most of the pins as ground pins or simply unconnected, whereas a DE-9 has only a fewone ground pinspin. There is a transmitting pin (for sending information away) and a receiving pin (for getting information). SomeMost serial ports canrun havein a duplex mode--that is, they can send and receive simultaneously. There are a few other pins, used for hardware handshaking. In the past, there was no duplex mode, so if a computer wanted to send something it had to tell the other device or computer that it was about to transmit, using one of the hardware handshaking pins. The other thingdevice would then use another handshaking pin to tell it to send whatever it wanted to send. Today there is duplex mode, but the handshaking pins are still used.

# The cable needs to have it'sits transmit-receive wires and it's handshaking wires switched. This can be done in the cable itself, or as an extension called a [[Null Modem]]