A DB-25 parallel printer port, as on IBM-PC style, and a few other types of computers. The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate

Micro ribbon 36 pin female, such as on printers and on some (particularly industrial and early- and pre-1980s personal) computers.

A parallel port is a type of interface found on computers (personal and otherwise) for connecting various peripherals. A computer is a Machine that manipulates data according to a list of instructions. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated It is also known as a printer port or Centronics port . Centronics Data Computer Corporation was a pioneering American manufacturer of computer printers now remembered primarily for the parallel interface that bears its name The IEEE 1284 standard defines the bi-directional version of the port. IEEE 1284 is a standard that defines bi-directional parallel communications between computers and other devices

History

The Centronics Model 101 printer was introduced in 1970 and included the first parallel interface for printers. Centronics Data Computer Corporation was a pioneering American manufacturer of computer printers now remembered primarily for the parallel interface that bears its name ^[1] The interface was developed by Dr. An Wang, Robert Howard and Prentice Robinson at Wang Laboratories. Dr An Wang ( February 7, 1920 &ndash March 24, 1990) was a Chinese American computer engineer and inventor and co-founder of computer Wang Laboratories was a computer company founded in 1951 by Dr The now-familiar connector was selected because Wang had a surplus stock of 20,000 Amphenol 36-pin micro ribbon connectors that were originally used for one of their early calculators. The micro ribbon connector is a common type of Electrical connector used particularly in Computer and Telecommunications applications The Centronics parallel interface quickly became a de facto industry standard; manufacturers of the time tended to use various connectors on the system side, so a variety of cables were required. For example, early VAX systems used a DC-37 connector, NCR used the 36-pin micro ribbon connector, Texas Instruments used a 25-pin card edge connector and Data General used a 50-pin micro ribbon connector. Name "VAX" was originally an Acronym for V irtual A ddress e' X' tension, both because the VAX was seen as a 32-bit The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate NCR Corporation ( is a technology company specializing in products for the retail and financial sectors Texas Instruments ( better known in the electronics industry (and popularly as TI, is an American company based in Dallas, Texas, USA Data General was one of the first Minicomputer firms from the late 1960s

Dataproducts introduced a very different implementation of the parallel interface for their printers. It used a DC-37 connector on the host side and a 50 pin connector on the printer side—either a DD-50 (sometimes incorrectly referred to as a "DB50") or the block shaped M-50 connector; the M-50 was also referred to as Winchester. The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate ^[2][3] Dataproducts parallel was available in a short-line for connections up to 50 feet (15 m) and a long-line version for connections from 50 feet (15 m) to 500 feet (150 m). The Dataproducts interface was found on many mainframe systems up through the 1990s, and many printer manufacturers offered the Dataproducts interface as an option.

IBM released the IBM Personal Computer in 1981 and included a variant of the Centronics interface— only IBM logo printers (rebranded from Epson) could be used with the IBM PC. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology An original equipment manufacturer, or OEM is typically a company that uses a component made by a second company in its own product or sells the product of the second company or Epson, is a Japanese company and one of the world's largest manufacturers of inkjet, dot matrix and Laser printers scanners ^[4] IBM standardized the parallel cable with a DB25F connector on the PC side and the Centronics connector on the printer side. The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate Vendors soon released printers compatible with both standard Centronics and the IBM implementation.

IBM implemented an early form of bidirectional interface in in 1987. HP introduced their version of bidirectional, known as Bitronics, on the LaserJet 4 in 1992. The HP LaserJet 4 (abbreviated sometimes to LJ4 or HP4 is a group of monochrome Laser printers produced in the early to mid-1990s as part of the LaserJet series by The Bitronics and Centronics interfaces were superseded by the IEEE 1284 standard in 1994. IEEE 1284 is a standard that defines bi-directional parallel communications between computers and other devices

Uses

Before the advent of USB, the parallel interface was adapted to access a number of peripheral devices other than printers. Probably one of the earliest devices to use parallel were dongles used as a hardware key form of software copy protection. A dongle is a small piece of hardware that connects to a Computer. Zip drives and scanners were early implementations followed by external modems, sound cards, webcams, gamepads, joysticks and external hard disk drives and CD-ROM drives. The Zip drive is a medium-capacity removable Disk storage system introduced by Iomega in late 1994 Historical precedent Scanners can be considered the successors of early telephotography input devices consisting of a rotating drum with a single Photodetector at Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information A sound card (also known as an audio card is a Computer Expansion card that facilitates the input and output of audio signals to/from a computer under Webcams ( web cameras) are small cameras (usually though not always Video cameras, whose images can be accessed using the World Wide Web, instant A gamepad, also called joypad or control pad, is a type of Game controller held in the hand where the digits (especially thumbs are used to provide input A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable Adapters were available to run SCSI devices via parallel. Other devices such as EPROM programmers and hardware controllers could be connected parallel. An EPROM, or E rasable P rogrammable '''''R'''ead-'''O'''nly '''M'''emory'', is a type of memory chip that retains its

Current use

At the consumer level, the USB interface—and in some cases Ethernet—has effectively replaced the parallel printer port. Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs Many manufacturers of personal computers and laptops consider parallel to be a legacy port and no longer include the parallel interface. A legacy port is a port or connector on a PC that is considered fully or partially Obsolete. USB to parallel adapters are available to use parallel-only printers with USB-only systems.

Implementation on IBM personal computers

Port addresses

Traditionally IBM PC systems have allocated their first three parallel ports according to the configuration in the table below.

If there is an unused LPTx slot, the port addresses of the others are moved up. In Computing, an interrupt is an asynchronous signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change Memory-mapped I/O ( MMIO) and port I/O (also called port-mapped I/O or PMIO) are two complementary methods of performing Input/output Memory-mapped I/O ( MMIO) and port I/O (also called port-mapped I/O or PMIO) are two complementary methods of performing Input/output (For example, if a port at 0x3bc does not exist, the port at 0x378 will then become LPT1. ) The IRQ lines, however, remain fixed (therefore, 0x378 at LPT1 would use IRQ 7). Unfortunately the default IRQ used by the first two addresses is the same, and it's difficult to get correct interrupt behaviour if both of these addresses are in use. The port addresses assigned to each LPTx slot can be determined by reading the BIOS Data Area (BDA) at 0000:0408.

Bit to Pin Mapping for the Standard Parallel Port (SPP):

~ indicates a hardware inversion of the bit. In Computing, the most significant bit ( msb) is the Bit position in a binary number having the greatest value In Computing, the least significant bit ( lsb) is the Bit position in a binary Integer giving the units value that is determining

Program interface

In versions of Windows that did not use the Windows NT kernel (as well as MS-DOS and some other operating systems), programs could access the parallel port with simple outportb() and inportb() subroutine commands. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. Windows NT is a family of Operating systems produced by Microsoft, the first version of which was released in July 1993 MS-DOS (short for M icro' s' oft D isk O perating S ystem is an Operating system commercialized by Microsoft. In operating systems such as Windows NT and Unix (NetBSD, FreeBSD, Solaris, 386BSD, etc), the microprocessor is operated in a different security ring, and access to the parallel port is inhibited, unless using the required driver. Windows NT is a family of Operating systems produced by Microsoft, the first version of which was released in July 1993 Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer NetBSD is a freely redistributable Open source version of the Unix -derivative Berkeley Software Distribution (BSD Computer Operating FreeBSD is a Unix-like free Operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD branch through Solaris is a Unix -based Operating system introduced by Sun Microsystems in 1992 as the successor to SunOS. 386BSD, sometimes called " JOLIX " is a free BSD Unix Operating system for PC compatible computer systems based This improves security and arbitration of device contention. On Linux, inb() and outb() can be used when a process is run as root and an ioperm() command is used to allow access to its base address. In Computing, a base address is an Address serving as a reference point ("base" for other addresses

Pinouts

Pinouts for a DB25 connector are:

Unidirectional parallel ports

In early parallel ports the data lines were unidirectional (data out only) so it was not easily possible to feed data in to the computer. Pinout is a term used in Electronics to describe how an Electrical connector is wired However, a workaround was possible by using 4 of the 5 status lines. A circuit could be constructed to split each 8-bit byte into two 4-bit nibbles which were fed in sequentially through the status lines. A nibble (often nybble) is the Computing term for a four- Bit aggregation or half an octet (an octet being an 8-bit Byte Each pair of nibbles was then re-combined into an 8-bit byte.

See also

• Parallel communications
• Parallel transmission
• IEEE 1284

References

• Axelson, Jan (2000). Janet Louise Axelson (b 1949 is an author of technical books in English Parallel Port Complete. Lakeview Research. ISBN 0-9650819-1-5.
• The (Linux) Parallel Port Subsystem by Tim Waugh

External links

• Interfacing to the Standard Parallel Port