serial port : Computer Hardware Buyers’ Glossary
- serial port
A connector to which you can connect a serial mouse, an external modem or a serial
printer (not recommended!). Modern computers aften have no serial ports, now that
USB (Universal Serial Bus) has become so popular. On the computer the serial port
is a 9 or 25-pin D shaped male connector. There can be up
to four COM (Component Object Model) ports. They must be assigned the
following way for all software to work. If they are improperly done,
likely some software will work. If there is an internal modem taking
up com2: then there must not be an external
com2: port. Never assign com1: and
com3: without a com2:, or any other
skip. Unfortunately, there is only about a 1 in 3 chance your retailer will properly
configure your COM ports.
It is possible to make serial ports work even if you don’t follow the
standard pattern of IRQs (Interrupt Requests)
and port addresses, but life gets extremely complicated. There are then three
different numbering schemes, the hardware one, based on standard port assignments,
which allows you to skip com3: and then have com4:, the BIOS (Basic Input Output System) scheme that
renumbers com4: to com3: if you
skip com3: and the Windows scheme on top of the
which allows com5: and above and logical remapping of
COM numbers to
arbitrary physical port addresses. Your software may use any one of the three
numbering schemes. You must keep all three schemes in sync, never skipping a port,
always using the standard port addresses and IRQs
or you will create massive confusion.
||IRQ (Interrupt Request)|
The serial port is going the way of the dodo bird, replaced by the
USB port which has
smaller simpler cables and the ability to double your ports using a splitter.
Computers used to have serial ports built in to the motherbord. They do not anymore. If you want a serial port, you must add a serial
card. Such cards used to cost about $10. Now, as a specialty item, they start at $40
and go up into the hundreds of dollars. Make sure you get one designed to
fit one of your free slots. For maxium compatibility, you want want with an actual 16950 UART (Universal Asynchronous Receiver/Transmitter) chip on it. You will not likely find one locally.
You will have to buy one on the Internet.
NCIX carries serial port cards, including some inexpensive ones.