Serial Ports: Difference between revisions

Serial ports are a legacy communications port which has pretty much been succeeded by [[USB]] and other modern communications technology. However, it is much easier to program than USB, and it is still found in a lot of computers (especially older ones such as the ones the brokefinancially limited amateur OS writer/tester might use). Also, a lot of phone modems (which are still used to access the Internet quite often, even though broadband is very accessible and affordable) connect via the serial interface.

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 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 it's 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. MostA DB-25 has most of the pins areas notground used.pins, Mostwhereas ofa theDE-9 pinshas only a arefew ground pins. There is a transmitting pin (for sending information away) and a receiving pin (for getting information). Some serial ports can have 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 thing 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.