|
The
Parallel Port
By Matt Western.
Quite
possibly the first high speed external connection PC's had was
the parallel port.
Data
is transmitted through the parallel port one bit at a time on
multiple wires, so therefore it is possible to send data to an
externally connected device faster than via a standard serial
port.
Just
about every PC in existence has a parallel port. The parallel
port connector on your PC has a 25-pin interface cable (also called
DB-25).
Here's
a picture of a parallel port connector above
2 serial port connectors.
Normally the parallel port is connected to a printer, however
it can be connected to anything that is designed to interface
to a parallel port, for example, plotters, scanners, CD ROMS,
tape drives etc..
Possibly
the best thing about the parallel port is its' ease of use.
When
you connect devices up to a serial port you need to make sure
that both devices share the same transmission speed (baud rate),
the same number of stop bits, the same type of parity etc.
With
parallel ports you can basically just plug a device into it and
be almost 100% sure everything will work.
Since
the early days, the parallel port has undergone some modifications
to make it more powerful and more useful.
Standards
These
days, the typical parallel port in an average PC is capable of
supporting devices that conform to different standards that have
evolved for the parallel port over the years.
Here's
a quick list of those standards:
-
SPP -- The early Standard Printer Ports (SPP). The SPP standard
implemented eight data lines.
-
BPP -- The Bi-directional Printer Port (BPP). The BPP standard
added the capability to read 8-bit data from the peripheral to
the host.
-
EPP -- The Enhanced Parallel Port (EPP).
-
ECP -- The Extended Capabilities Port (ECP).
Both
EPP and ECP ports may be operated in either SPP or Bi-Directional
(BPP) modes. However, operation in these feature modes requires
both compatible peripherals and appropriate software drivers.
Generally,
EPP is used primarily by non-printer peripherals, CD ROM, tape
drive, hard drive, network adapters, etc., while ECP is aimed
at newer generation of printers and scanners.
The
Centronics Port
The
parallel port is also known as the Centronics port. Centronics
is the name of a compnay that invented a standard for data transfer
to a printer via 36 pin connection.
Plugs
used to connect to Centronics ports are known as Centronics connectors.
Here's
a typical Centronics connector (lower connector) on
a typical parallel printer cable.
The
above picture shows a typical printer cable. One end has a blue
Centronics connector attached and the other has a standard DB
25 style connector.
Parallel
Cables
The
parallel port can be programmed and so therefore it can be interfaced,
or connected to, anything.
Because
of this, a parallel cable cable can have any type of connector
connected to either end.
However
the two most popular types of parallel cables are:
-
The Centronics parallel cable
- The 25 pin D type cable
The
Centronics cable is used mainly to connect to printers. The 25
pin D type cable is used to connect to devices such as plotters,
scanners, CD ROM's etc.
Article
© Matt Western - deTechnify.com
**********************************************************
Matt Western has been working in the electronics and IT areas
since 1983. These days he heads up deTechnify.com a web site aimed
at clearing away the technical haze surrounding computers computing
and the internet.
You can contact Matt via http://www.detechnify.com
---{--} |
