2 Printer Parallel With Only One Connection

2 Printer Parallel With Only One Connection

Calculator interface

Parallel port

2 Printer Parallel With Only One Connection

connector often used for a parallel printer port on
IBM PC compatible
computers, with the printer icon.

Blazon Point-to-betoken
Production history
Designer Centronics,
Designed 1970–1981
Manufacturer Centronics, Dataproducts, Intel, IBM, Compaq, Nortel, etc
Superseded by USB
General specifications
Length 2.3 cm (0.91 in)
Hot pluggable Usually not
External Yeah
Cablevision Usually upward to 25 wires including ground; optionally shielded
Pins eight information, 4 output control, 5 input control, 8 ground
Connector DB-25,
“Centronics” 36-pin Amphenol,
DC-37, others
Signal 0 to +5.0 volt
World Dedicated pins
Max. voltage 5 volts DC
Information point Parallel
Width Variable
Bitrate PP:

two.five MB/south
Max. devices 2
Protocol Application dependent

25 Pin D-sub pinout.svg
IBM PC-uniform parallel port pinout

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

Mini-Centronics 36-pin male connector (top) with Micro ribbon 36-pin male Centronics connector (lesser)

The Apple tree 2 Parallel Printer Port connected to the printer via a folded ribbon cable; one end connected to the connector at the top of the card, and the other stop had a 36-pin Centronics connector.

computing, a
parallel port
is a blazon of
found on early
and otherwise) for connecting
peripherals. The name refers to the manner the data is sent; parallel ports send multiple
of data at once (parallel communication), as opposed to
serial advice, in which bits are sent 1 at a time. To do this, parallel ports require multiple data lines in their cables and
connectors and tend to be larger than contemporary
serial ports, which only crave one information line.

At that place are many types of parallel ports, but the term has go about closely associated with the
printer port
Centronics port
found on most personal computers from the 1970s through the 2000s. It was an manufacture

de facto

for many years, and was finally standardized as
IEEE 1284
in the tardily 1990s, which defined the
Enhanced Parallel Port
(EPP) and
Extended Capability Port
(ECP) bi-directional versions. Today, the parallel port interface is virtually non-existent in new computers because of the rise of
Universal Serial Bus
(USB) devices, along with
network printing
connected printers.

The parallel port interface was originally known every bit the
Parallel Printer Adapter
on IBM
computers. It was primarily designed to operate
that used IBM’south eight-bit
extended ASCII
graphic symbol set
to print text, merely could also exist used to adapt other peripherals. Graphical printers, forth with a host of other devices, have been designed to communicate with the system.





An Wang, Robert Howard and Prentice Robinson began development of a low-cost printer at
Centronics, a subsidiary of
Wang Laboratories
that produced specialty
computer terminals. The printer used the
dot matrix printing
principle, with a print head consisting of a vertical row of vii metal pins connected to
solenoids. When ability was applied to the solenoids, the pivot was pushed forward to strike the paper and leave a dot. To brand a complete grapheme
glyph, the print head would receive power to specified pins to create a single vertical pattern, then the print head would move to the right by a pocket-size amount, and the process repeated. On their original pattern, a typical glyph was printed as a matrix vii high and 5 wide, while the “A” models used a print caput with 9 pins and formed glyphs that were 9 by 7.

This left the problem of sending the
data to the printer. While a
serial port
does so with the minimum of pins and wires, it requires the device to buffer up the data as it arrives flake by bit and turn information technology dorsum into multi-bit values. A parallel port makes this simpler; the unabridged ASCII value is presented on the pins in complete form. In addition to the eight information pins, the system too needed various command pins too every bit electrical grounds. Wang happened to have a surplus stock of 20,000
36-pin micro ribbon connectors that were originally used for i of their early on calculators. The interface only required 21 of these pins, the rest were grounded or not connected. The connector has become so closely associated with Centronics that information technology is now popularly known every bit the “Centronics connector”.

Centronics Model 101
printer, featuring this connector, was released in 1970.

The host sent ASCII characters to the printer using seven of viii data pins, pulling them high to +5V to correspond a 1. When the data was ready, the host pulled the
pivot depression, to 0 V. The printer responded by pulling the
line high, press the character, so returning BUSY to low again. The host could and so send another grapheme. Control characters in the data caused other actions, similar the
EOF. The host could also have the printer automatically beginning a new line by pulling the
line loftier, and keeping information technology there. The host had to carefully lookout man the Decorated line to ensure information technology did not feed information to the printer also rapidly, especially given variable-time operations like a newspaper feed.


The printer side of the interface quickly became an manufacture

de facto
, but manufacturers used diverse connectors on the arrangement side, so a variety of cables were required. For example,
used the 36-pin
micro ribbon
connector on both ends of the connection, early
systems used a
Texas Instruments
used a 25-pivot carte du jour
edge connector
Data Full general
used a l-pin micro ribbon connector. When
implemented the parallel interface on the
IBM PC, they used the
connector at the PC-stop of the interface, creating the now familiar parallel cable with a DB25M at one end and a 36-pivot micro ribbon connector at the other.

In theory, the Centronics port could transfer information as quickly as 75,000 characters per second. This was far faster than the printer, which averaged well-nigh 160 characters per second, meaning the port spent much of its time idle. The performance was divers by how rapidly the host could respond to the printer’southward BUSY point asking for more information. To improve performance, printers began incorporating
so the host could transport them information more rapidly, in bursts. This not only reduced (or eliminated) delays due to latency waiting for the next character to get in from the host, but also freed the host to perform other operations without causing a loss of operation. Performance was farther improved by using the buffer to store several lines and then printing in both directions, eliminating the delay while the print head returned to the left side of the page. Such changes more doubled the functioning of an otherwise unchanged printer, as was the example on Centronics models like the 102 and 308.

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released the
IBM Personal Calculator
in 1981 and included a variant of the Centronics interface— just IBM logo printers (rebranded
Epson) could be used with the IBM PC.

IBM standardized the parallel cable with a
connector on the PC side and the 36-pin Centronics connector on the printer side. Vendors presently released printers compatible with both standard Centronics and the IBM implementation.

The original IBM parallel printer adapter for the IBM PC of 1981 was designed to support limited bidirectionality, with 8 lines of data output and 4 lines of data input.[

citation needed


This immune the port to exist used for other purposes, not merely output to a printer. This was achieved by allowing the data lines to be written to by devices on either end of the cable, which required the ports on the host to be bidirectional. This feature saw lilliputian utilize, and was removed in later revisions of the hardware. Years later, in 1987, IBM reintroduced the bidirectional interface with its
series, where it could exist enabled or disabled for compatibility with applications hardwired not to expect a printer port to be bidirectional.



As the printer market expanded, new types of printing mechanisms appeared. These often supported new features and fault weather that could not exist represented on the existing port’s relatively few status pins. While the IBM solution could back up this, it was not petty to implement and was not at that fourth dimension being supported. This led to the Bi-Tronics system, introduced by
on their
LaserJet 4Si
in April 1993.

This used four existing condition pins, ERROR, SELECT, PE and Busy to represent a
nibble, using two transfers to send an 8-bit value. Bi-Tronics way, now known every bit nibble fashion, was indicated by the host pulling the SELECT line high, and information was transferred when the host toggles the AUTOFEED low. Other changes in the handshaking protocols improved functioning, reaching 400,000 cps to the printer, and most 50,000 cps back to the host.

A major advantage of the Bi-Tronics system is that it can be driven entirely in software in the host, and uses otherwise unmodified hardware – all the pins used for data transfer back to the host were already printer-to-host lines.



The introduction of new devices like
multi-function printers
demanded much more performance than either the Bi-Tronics or IBM style backchannels could handle. Two other standards have go more pop for these purposes. The Enhanced Parallel Port (EPP), originally defined by
Zenith Electronics, is similar to IBM’s byte fashion in concept, but changes details of the handshaking to allow upwards to two MB/due south.

The Extended Capability Port (ECP) is essentially an entirely new port in the same physical housing that also adds
direct retention admission
based on
run-length encoding
to compress the data, which is especially useful when transferring simple images similar
or black-and-white scanned images. ECP offers performance upward to ii.v MB/due south in both directions.

All of these enhancements are collected as role of the
IEEE 1284
standard. The first release in 1994 included original Centronics mode (“compatibility mode”), crumb and byte modes, likewise as a change to the handshaking that was already widely used; the original Centronics implementation called for the Decorated pb to toggle with each alter on any line of data (busy-by-line), whereas IEEE 1284 calls for Busy to toggle with each received character (decorated-by-character). This reduces the number of BUSY toggles and the resulting interruptions on both sides. A 1997 update standardized the printer condition codes. In 2000, the EPP and ECP modes were moved into the standard, as well equally several connector and cable styles, and a method for
daisy chaining
up to eight devices from a single port.

Some host systems or print servers may utilise a strobe bespeak with a relatively low voltage output or a fast toggle. Any of these issues might cause no or intermittent printing, missing or repeated characters or garbage press. Some printer models may take a switch or setting to fix busy by character; others may crave a handshake adapter.[

citation needed




introduced a very different implementation of the parallel interface for their printers. It used a
connector on the host side and a 50 pin connector on the printer side—either a
(sometimes incorrectly referred to as a “DB50”) or the block shaped K-50 connector; the Chiliad-fifty was also referred to as Winchester.


Dataproducts parallel was available in a brusk-line for connections upwards to 50 anxiety (15 m) and a long-line version using
differential signaling
for connections to 500 feet (150 1000). The Dataproducts interface was plant on many mainframe systems up through the 1990s, and many printer manufacturers offered the Dataproducts interface as an option.

A wide variety of devices were eventually designed to operate on a parallel port. Nigh devices were uni-directional (i-fashion) devices, only meant to respond to information sent from the PC. However, some devices such equally
Zip drives
were able to operate in bi-directional style. Printers also eventually took up the bi-directional system, allowing various condition study data to exist sent.

Historical uses


C4381A CD-Writer Plus 7200 Series
, showing parallel ports to connect between a printer and the calculator.

Earlier the appearance of
USB, the parallel interface was adapted to access a number of peripheral devices other than printers. One early use of the parallel port was for
used as hardware keys which were supplied with application software equally a form of software copy protection. Other uses included
optical disc drives
such as
readers and writers,
Goose egg drives,
scanners, external
gamepads, and
joysticks. Some of the primeval portable
MP3 players
required a parallel port connection for transferring songs to the device.

Adapters were bachelor to run
devices via parallel. Other devices such equally
programmers and hardware controllers could be connected via the parallel port.

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Most PC-compatible systems in the 1980s and 1990s had one to three ports, with communication interfaces divers like this:

  • Logical parallel port one:
    I/O port
    7 (usually in monochrome graphics adapters)
  • Logical parallel port 2: I/O port 0x378, IRQ 7 (dedicated IO cards or using a controller built into the mainboard)
  • Logical parallel port 3: I/O port 0x278, IRQ 5 (defended IO cards or using a controller built into the mainboard)

If no printer port is present at 0x3BC, the second port in the row (0x378) becomes logical parallel port i and 0x278 becomes logical parallel port 2 for the BIOS. Sometimes, printer ports are jumpered to share an interrupt despite having their own IO addresses (i.e. only one can be used interrupt-driven at a time). In some cases, the BIOS supports a quaternary printer port as well, simply the base of operations address for information technology differs significantly between vendors. Since the reserved entry for a fourth logical printer port in the
BIOS Information Area
(BDA) is shared with other uses on PS/2 machines and with S3 compatible graphics cards, information technology typically requires special drivers in virtually environments. Nether DR-DOS 7.02 the BIOS port assignments can be changed and overridden using the
(and optionally



DOS-based systems make the logical parallel ports detected by the BIOS bachelor under device names such as
(corresponding with logical parallel port 1, 2, and 3, respectively). These names derive from terms like Line Print Last, Local Print Concluding, or Line Printer. A similar naming convention was used on
systems, besides as in

DOS, the parallel printers could be accessed directly on the
command line. For example, the command “Blazon C:\AUTOEXEC.BAT > LPT1:” would redirect the contents of the
file to the printer port. A
device was too bachelor as an alias for LPT1. Some operating systems (similar
Multiuser DOS) permit to change this stock-still assignment by unlike ways. Some DOS versions use resident driver extensions provided by MODE, or users can change the mapping internally via a
PRN=north directive (equally under DR-DOS 7.02 and college). DR-DOS seven.02 also provides optional built-in back up for
if the underlying BIOS supports it.

PRN, along with CON, AUX and a few others are invalid file and directory names in DOS and Windows, fifty-fifty in Windows XP. There is even an MS-DOS device in path name vulnerability in Windows 95 and 98, which causes the computer to crash if the user types “C:\CON\CON”, “C:\PRN\PRN” or “C:\AUX\AUX” in the Windows Explorer address bar.[

citation needed


has released a patch to prepare this issues, only newly installed Windows 95 and 98 operating systems will still have the bug.

A special “Print” control likewise existed to accomplish the aforementioned effect.
Microsoft Windows
still refers to the ports in this manner in many cases, though this is oft fairly hidden.

Linux, the beginning parallel port is available via the filesystem every bit
/dev/lp0. Linux IDE devices tin utilize a
(parallel port IDE) driver.

Notable consumer products


Etherpocket-SP parallel port
adaptor (circa 1990,
drivers). Supports both coax and ten Base of operations-T. Supplementary ability is drawn from a
PS/2 port
passthrough cable.

Current use


For consumers,
computer networks
accept replaced the parallel printer port, for connections both to printers and to other devices.

Many manufacturers of personal computers and laptops consider parallel to be a
legacy port
and no longer include the parallel interface. Smaller machines take less room for large parallel port connectors. USB-to-parallel adapters are available that tin make parallel-but printers work with USB-just systems. At that place are PCI (and PCI-limited) cards that provide parallel ports. There are besides some
print servers
that provide an interface to parallel ports through a network. USB-to-EPP fries tin can also permit other non-printer devices to go on to work on modern computers without a parallel port.

For electronics hobbyists the parallel port is still often the easiest manner to connect to an external circuit lath. It is faster than the other common legacy port (serial port), requires no serial-to-parallel converter, and requires far less interface logic and software than a USB target interface. However, Microsoft operating systems later than Windows 95/98 prevent user programs from directly writing to or reading from the LPT without additional software (kernel extensions).

CNC Milling Machines
besides oftentimes make use of the parallel port to directly control the machine’southward motors and attachments.

IBM PC implementation


Port addresses


Traditionally IBM PC systems have allocated their showtime three parallel ports according to the configuration in the table below (if all three printer ports exist).





If there is an unused slot, the port addresses of the others are moved up. (For instance, if a port at 0x3BC does non be, the port at 0x378 will and then go the outset logical parallel port.)

The base address 0x3BC is typically supported by printer ports on MDA and Hercules brandish adapters, whereas printer ports provided by the mainboard chipset or addition cards rarely permit to exist configured to this base address. Therefore, in absence of a monochrome display adapter, a common assignment for the showtime logical parallel port (and therefore also for the respective LPT1 DOS device driver) today is 0x378, even though the default is still 0x3BC (and would be selected by the BIOS if it detects a printer port at this address). The IRQ lines are typically configurable in the hardware as well. Assigning the same interrupt to more than one printer port should be avoided and will typically cause one of the corresponding ports to work in polled mode only. The port addresses assigned to slot can be adamant by reading the
BIOS Data Area
(BDA) at 0000h:0408h.

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Bit-to-pivot mapping for the Standard Parallel Port (SPP):


Bit: vii 6 five 4 3 2 1 0
Base of operations (Data port) Pin: 9 8 seven half-dozen 5 4 3 ii
Base+1 (Status port) Pin: ~11 10 12 13 15
Base+ii (Control port) Pin: ~17 xvi ~14 ~1

~ indicates a hardware inversion of the bit.

Program interface


In versions of
that did not use the
Windows NT
kernel (as well as
and some other operating systems), programs could admission the parallel port with elementary outportb() and inportb() subroutine commands. In operating systems such equally
Windows NT
386BSD, etc.), the microprocessor is operated in a different security ring, and access to the parallel port is prohibited, unless using the required driver. This improves security and arbitration of device contention. On Linux, inb() and outb() can exist used when a procedure is run every bit root and an ioperm() command is used to permit access to its
base address; alternatively, ppdev allows shared admission and can be used from userspace if the advisable permissions are prepare.

The cross-platform library for parallel port access, libieee1284, also is available on many Linux distributions and provides an abstruse interface to the parallel ports of the system. Access is handled in an open up-claim-release-close sequence, which allows for concurrent admission in userspace.



The older parallel printer ports had an viii-bit data bus and four pins for control output (Strobe, Linefeed, Initialize, and Select In), and five more for command input (ACK, Busy, Select, Error, and Paper Out). Its information transfer speed is at 150 kB/southward.

The newer EPPs (Enhanced Parallel Ports) have an 8-bit information jitney, and the aforementioned control pins as the normal parallel printer port. Newer ports attain speeds of up to 2 MB/s.


better source needed


for parallel port connectors are:

for parallel port connectors.

Pin No (DB25) Pin No (36 pin) Signal name Direction Annals – chip Inverted
1 ane Strobe In/Out Control-0 Aye
two ii Data0 Out Data-0 No
three iii Data1 Out Data-1 No
4 four Data2 Out Information-ii No
5 v Data3 Out Data-3 No
6 6 Data4 Out Data-4 No
7 vii Data5 Out Data-v No
8 eight Data6 Out Information-vi No
9 9 Data7 Out Data-7 No
10 10 Ack In Status-6 No
xi 11 Decorated In Status-7 Yes
12 12 Paper-Out In Status-5 No
xiii 13 Select In Status-iv No
14 14 Linefeed In/Out Control-ane Yeah
xv 32 Error In Status-3 No
16 31 Reset In/Out Control-two No
17 36 Select-Printer In/Out Control-3 Yes
18-25 19-30,33,17,sixteen Ground

Inverted lines are truthful on logic low. If they are not inverted, then logic high is truthful.

Pivot 25 on the DB25 connector might not exist connected to footing on mod computers.[



See also


Hardware IC chips:

  • For host reckoner, see
    Super I/O
  • For peripheral side, parallel port interface chips: PPC34C60 (SMSC) and W91284PIC (Warp Nine)
  • For USB-printer purpose, example USB fries: PL-2305 (Prolific) and CH341 (QinHeng)



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External links


2 Printer Parallel With Only One Connection

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