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[[Image:IEEE-488-Stecker2.jpg|thumb|right|IEEE-488 stacking connectors]]

'''IEEE-488''' is a short-range digital communications [[computer bus|bus]] specification. It was created for use with [[automated test equipment]] in the late 1960s, and is still in use for that purpose. IEEE-488 was created as '''HP-IB''' ('''Hewlett-Packard Interface Bus'''), and is commonly called '''GPIB''' ('''General Purpose Interface Bus'''). It has been the subject of several [[#Standards|standards]].

==Origins==
In the late 1960s, [[Hewlett-Packard|Hewlett-Packard (HP)]]<ref>This part of HP was later spun off as [[Agilent Technologies]].</ref> was manufacturing various automated test and measurement instruments, such as digital [[multimeter]]s and [[logic analyzer]]s. They developed the ''HP Interface Bus (HP-IB)'' to enable easier interconnection between instruments and controllers (computers and other instruments).

The bus was relatively easy to implement using the technology at the time, using a simple parallel [[electrical bus]] and several individual control lines. For example, the HP 59501 Power Supply Programmer and HP 59306A Relay Actuator were both relatively simple HP-IB peripherals implemented only in [[Transistor–transistor logic|TTL]] logic, using no microprocessor.

Other manufacturers copied HP-IB, calling their implementation the General Purpose Interface Bus (GPIB), and it became a [[de facto standard]] for automated and industrial instrument control. As GPIB became popular, it was formalized by various [[standards organization]]s.

==Standards==
In 1975, the [[Institute of Electrical and Electronics Engineers|IEEE]] standardized the bus as ''Standard Digital Interface for Programmable Instrumentation'', '''IEEE-488''' (now IEEE-488.1). It formalized the mechanical, electrical, and basic protocol parameters of GPIB, but said nothing about the format of commands or data.

In 1987, IEEE introduced ''Standard Codes, Formats, Protocols, and Common Commands'', '''IEEE-488.2''', re-designating the previous specification as '''IEEE-488.1'''. IEEE-488.2 provided for basic syntax and format conventions, as well as device-independent commands, data structures, error protocols, and the like. IEEE-488.2 built on -488.1 without superseding it; equipment can conform to -488.1 without following -488.2.

While IEEE-488.1 defined the hardware, and IEEE-488.2 defined the protocol, there was still no standard for instrument-specific commands. Commands to control the same class of instrument (e.g., multimeters) would vary between manufacturers and even models.

The US Air Force<ref>Project Mate in 1985</ref> and later Hewlett-Packard recognized this problem. In 1989, HP developed their TML language<ref>{{cite web
|title=GPIB 101, A Tutorial of the GPIB Bus
|publisher=ICS Electronics
|url=http://www.icselect.com/ab_note.html#anchor338658
|page=5, paragraph=SCPI Commands
}}</ref> which was the forerunner to SCPI [[Standard Commands for Programmable Instrumentation]]. SCPI was introduced as an industry standard in 1990.<ref>{{cite web
|title=History of GPIB
|publisher=National Instruments
|url=http://zone.ni.com/devzone/cda/tut/p/id/3419
|quote=In 1990, the IEEE 488.2 specification included the Standard Commands for Programmable Instrumentation (SCPI) document.
|accessdate=2010-02-06
}}</ref> SCPI added standard generic commands, and a series of instrument classes with corresponding class-specific commands. SCPI mandated the IEEE-488.2 syntax, but allowed other (non-IEEE-488.1) physical transports.

The [[International Electrotechnical Commission|IEC]] developed their own standards in parallel with the IEEE, with'''IEC-60625-1''' and '''IEC-60625-2''', later replaced by IEC-60488.

[[National Instruments]] introduced a backward-compatible extension to IEEE-488.1, originally known as '''HS-488'''. It increased the maximum data rate to 8 [[megabyte|Mbyte]]/s, although the rate decreases as more devices are connected to the bus. This was incorporated into the standard in 2003 (IEEE-488.1-2003),<ref>{{Cite web
|title=Upgraded Standard Boosts Speed of IEEE 488 Instrument Buses Eightfold
|date=6 October 2003
|publisher=IEEE
|url=http://standards.ieee.org/announcements/pr_4881upgrade.html
|accessdate=2010-02-06
}}
</ref> over HP's objections.<ref>{{Cite press release
|title=HP and Other Test and Measurement Companies Urge IEEE to Oppose Revisions of Established IEEE-488 Standard
|publisher=Hewlett-Packard Company
|date=December 1997
|url=http://grouper.ieee.org/groups/imstc8/488/1/hppress12-97.html
|accessdate=2010-02-16
}}</ref><ref>{{cite web
|title=P488.1 Project Home
|publisher=IEEE
|url=http://grouper.ieee.org/groups/imstc8/488/1/
|accessdate=2010-02-16
}}</ref>

In 2004, the IEEE and IEC combined their respective standards into a "Dual Logo" IEEE/IEC standard '''IEC-60488-1''', ''Standard for Higher Performance Protocol for the Standard Digital Interface for Programmable Instrumentation - Part 1: General'',<ref>{{cite web
|title=IEC/IEEE Standard for Higher Performance Protocol for the Standard Digital Interface for Programmable Instrumentation - Part 1: General (Adoption of IEEE Std 488.1-2003)
|publisher=IEEE
|url=http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&isnumber=30476&arnumber=1405845&punumber=9646
|accessdate=2010-02-06
}}</ref> replaces IEEE-488.1/IEC-60625-1, and '''IEC-60488-2''',''Part 2: Codes, Formats, Protocols and Common Commands'',<ref>{{cite web
|title=Standard Digital Interface for Programmable Instrumentation- Part 2: Codes, Formats, Protocols and Common Commands (Adoption of (IEEE Std 488.2-1992)
|publisher=IEEE
|url=http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&isnumber=29721&arnumber=1352831&punumber=9359
|accessdate=2010-02-06
}}</ref> replaces IEEE-488.2/IEC-60625-2.<ref>{{cite web
|title=Replaced or Withdrawn Publications
|url=http://www.iec.ch/cgi-bin/procgi.pl/www/iecwww.p?header=IEC&search=replaced&wwwprog=sea22.p
|publisher=IEC
|accessdate=2010-02-06
}}</ref>

== Characteristics ==
IEEE-488 is an [[8-bit]], electrically [[parallel communication|parallel]] bus. The bus employs sixteen signal lines — eight used for bi-directional data transfer, three for handshake, and five for bus management — plus eight ground return lines.

Every device on the bus has a unique 5-bit primary [[Physical address|address]], in the range from 0 to 30 (31 total possible addresses).<ref name="NI-488.2">{{Cite book
|title=NI-488.2 User Manual
|date=February 2005
|publisher=National Instruments Corporation
|id=NI P/N 370428C-01
|page=A-2
|chapter=GPIB Addressing
|quote=The primary address is a number in the range 0 to 30.
|url=http://www.ni.com/pdf/manuals/370428c.pdf
|accessdate=2010-02-16
}}</ref><ref name="Agilent_82350B">{{Cite book
|title=Agilent 82350B PCI GPIB Interface: Installation and Configuration Guide
|date=20 July 2009
|publisher=Agilent Technologies
|id=Agilent P/N 82350-90004
|page=26
|chapter=Table 1-1: 82350 GPIB interface card configuration parameters
|quote=any address in the range 0 - 30, inclusive, may be used
|url=http://cp.literature.agilent.com/litweb/pdf/82350-90004.pdf
|accessdate=2010-02-16
}}</ref>

The standard allows up to 15 devices to share a single physical bus of up to 20 meters total cable length. The physical topology can be linear or star (forked).<ref>{{Cite web
|title=GPIB Instrument Control Tutorial
|publisher=National Instruments
|date=24 August 2009
|quote=connected in either a daisy-chain or star topology
|url=http://zone.ni.com/devzone/cda/tut/p/id/2761
|accessdate=2010-02-16
}}</ref> Active extenders allow longer buses, with up to 31 devices theoretically possible on a logical bus.

Control and data transfer functions are logically separated; a controller can address one device as a “talker” and one or more devices as “listeners” without having to participate in the data transfer. It is possible for multiple controllers to share the same bus; but only one can be the "Controller In Charge" at a time.<ref>{{Cite book
|title=NI-488.2 User Manual
|date=February 2005
|publisher=National Instruments Corporation
|id=NI P/N 370428C-01
|page=A-1
|url=http://www.ni.com/pdf/manuals/370428c.pdf
|accessdate=2010-02-16
}}</ref>

In the original protocol, transfers use an interlocked, three-wire ''ready–valid–accepted'' [[handshaking|handshake]].<ref>{{Cite book
|title=NI-488.2 User Manual
|date=February 2005
|publisher=National Instruments Corporation
|id=NI P/N 370428C-01
|page=A-3
|chapter=Handshake Lines
|url=http://www.ni.com/pdf/manuals/370428c.pdf
|accessdate=2010-02-16
}}</ref> The maximum data rate is about one [[bit per second|Mbyte/s]]. The later HS-488 extension relaxes the handshake requirements, allowing up to 8 Mbyte/s. The slowest participating device determines the speed of the bus.<ref>{{Cite web
|title=Using HS488 to Improve GPIB System Performance
|publisher=National Instruments Corporation
|date=30 March 2009
|url=http://zone.ni.com/devzone/cda/tut/p/id/4552
|accessdate=2010-02-16
}}</ref>

== Connectors ==
=== IEEE-488 ===
{{Infobox connector
|name=IEEE-488
|pinout_image=[[Image:IEEE-448.svg|300px]]
|pinout_caption=Female IEEE-488 connector
|pin1=Data input/output bit.
|pin1_name=DIO1
|pin2=Data input/output bit.
|pin2_name=DIO2
|pin3=Data input/output bit.
|pin3_name=DIO3
|pin4=Data input/output bit.
|pin4_name=DIO4
|pin5=End-or-identify.
|pin5_name=EOI
|pin6=Data valid.
|pin6_name=DAV
|pin7=Not ready for data.
|pin7_name=NRFD
|pin8=Not data accepted.
|pin8_name=NDAC
|pin9=Interface clear.
|pin9_name=IFC
|pin10=Service request.
|pin10_name=SRQ
|pin11=Attention.
|pin11_name=ATN
|pin12=
|pin12_name=SHIELD
|pin13=Data input/output bit.
|pin13_name=DIO5
|pin14=Data input/output bit.
|pin14_name=DIO6
|pin15=Data input/output bit.
|pin15_name=DIO7
|pin16=Data input/output bit.
|pin16_name=DIO8
|pin17=Remote enable.
|pin17_name=REN
|pin18=(wire twisted with DAV)
|pin18_name=GND
|pin19=(wire twisted with NRFD)
|pin19_name=GND
|pin20=(wire twisted with NDAC)
|pin20_name=GND
|pin21=(wire twisted with IFC)
|pin21_name=GND
|pin22=(wire twisted with SRQ)
|pin22_name=GND
|pin23=(wire twisted with ATN)
|pin23_name=GND
|pin24=
|pin24_name=Logic ground
}}

IEEE-488 specifies a 24-pin [[Amphenol]]-designed [[micro ribbon]] connector. Micro ribbon connectors have a D-shaped metal shell, but are larger than [[D-subminiature]] connectors. They are sometimes called "Centronics connectors" after the 36-pin [[micro ribbon]] connector [[Centronics]] used for their printers.

One unusual feature of IEEE-488 connectors is they commonly use a "double-headed" design, with male on one side, and female on the other (at both ends of the cable). This allows stacking connectors for easy [[daisy chain (electrical engineering)|daisy-chaining]]. Mechanical considerations limit the number of stacked connectors to four or fewer, although a possible workaround involving physically supporting the connectors can expand this.

They are held in place by screws, either [[Unified Thread Standard|UTS]] (now largely obsolete) or [[ISO metric screw thread|metric]] M3.5×0.6 [[screw thread|thread]]s. By convention, metric screws are colored black, as the two threads do not mate.

===IEC-60625===

The IEC-60625 standard prescribes the use of 25-pin [[D-subminiature]] connectors (the same as used for the [[parallel port]] on [[IBM PC compatible|IBM-PC]]s). This connector did not gain significant market acceptance against the established 24-pin connector.

==Capabilities==
{| class="wikitable"
|-
! Function !! Abbreviation !! Description / Example
|-
| Source Handshake || SH || SH1 - complete
|-
| Acceptor Handshake|| AH || AH1 - complete
|-
| Basic Talker || T || T5 - responds to serial poll; untalks when listen address received; talk only capability<br>T6 - untalks when listen address received; no talk only<br>T7 - no serial poll; untalks when listen address received; talk only capability
|-
| Extended Talker || TE || TE0 - no extended talker
|-
| Basic Listener || L || L3 - Listen only mode; unlistens if talk address received<br>L4 - Unlistens if talk address received
|-
| Extended Listener || LE || LE0 - no extended listener
|-
| Service Request || SR || SR0 - no service request capability<br>SR1 - complete
|-
| Remote-Local || RL || RL0 - no local lockout<br>RL1 - complete
|-
| Parallel Poll || PP || PP0 - does not respond to Parallel Poll
|-
| Device Clear || DC || DC1 - complete
|-
| Device Trigger || DT || DT0 - no device trigger capability<br>DT1 - complete
|-
| Controller || C || C0 - no controller function
|-
| || E || E1 - open collector drive electronics<br>E2 - three state drivers
|}
More information see Tektronix.<ref>{{Citation |last=Tilden |first=Mark D. |title=4041 GPIB Programming Guide |year=1983 |chapter=Appendix A: Subsets Describe Interface Functions |pages= 113&ndash;115 |publisher=Tektronix, Inc. |url=http://www.xmission.com/~legalize/vintage/docs/tektronix/070-4696-00_4041_GPIB_Programming_Guide_Sep1983.pdf |doi= }}</ref>

==Use as a computer interface==
{{Ref improve section|date=February 2010}}

HP's designers did not specifically plan for IEEE-488 to be a peripheral interface for general-purpose computers; the focus was on instrumentation. But when HP's early [[microcomputer]]s needed an interface for peripherals ([[disk drive]]s, [[tape drive]]s, [[computer printer|printers]], [[plotter]]s, etc.), HP-IB was readily available and easily adapted to the purpose.

HP computer products which used HP-IB included the [[HP series 80]], [[HP 9800 series desktop computers|HP 9800 series]],<ref>{{cite web
|title=HP 98135A HP-IB Interface 9815
|url=http://www.hpmuseum.net/display_item.php?hw=463
|work=HP Computer Museum
|accessdate=2010-02-06
}}</ref> the [[HP 2100]] series,<ref>{{cite web
|title=59310A HP-IB Interface
|quote=HP-IB interface for HP1000 and HP2000 computers
|url=http://www.hpmuseum.net/display_item.php?hw=522
|work=HP Computer Museum
|accessdate=2010-02-06
}}</ref> and the [[HP 3000]] series.<ref>{{cite web
|title=27113A HP-IB Interface
|quote=CIO HP-IB interface for 3000 Series 900
|url=http://www.hpmuseum.net/display_item.php?hw=786
|work=HP Computer Museum
|accessdate=2010-02-06
}}</ref> Some of HP's advanced pocket calculators of the 1980s, such as the [[HP-41]] and [[HP-71B]] series, also had IEEE-488 capabilities, via an optional [[HP-IL]]/HP-IB interface module.

Other manufacturers adopted GPIB for their computers as well, such as with the [[Tektronix 405x]] line.

The [[Commodore PET]] (introduced 1977) range of personal computers connected their peripherals using the IEEE-488 bus, but with a non-standard card edge connector. Commodore's following 8-bit machines, including the [[Commodore VIC-20|VIC-20]], [[Commodore 64|C-64]], and [[Commodore 128|C-128]], utilized an unrelated, proprietary serial interface, using a round [[DIN connector]], for which they retained the IEEE-488 programming interface and terminology, however.

Eventually, faster, more complete standards such as [[SCSI]] superseded IEEE-488 for peripheral access.

{{Gallery
|width=175
|lines=3
|Image:CBM610 back.jpg|Rear of the [[Commodore CBM-II]] showing [[card edge connector]] IEEE-488 port
|Image:SFD1001 back.jpg|Rear of the [[Commodore International|Commodore]] SFD 1001 [[floppy disk drive]] with IEEE-488 port
|Image:Digitaloszilloskop Schnittstellen IMGP1974 WP.jpg|Rear of a [[Tektronix]] TDS 210 digital [[oscilloscope]] with IEEE-488 port
|Image:Data Acquisition Agilent %282%29.jpg|Rear view of an [[Agilent]] 34970A [[data acquisition]] chassis / [[multimeter]]
|Image:Technofor-IEEE488.JPG|C64 interface
|Image:HP7935_rear_HP-IB_port.jpg|[[HP 7935]] disc drive HP-IB Panel
}}

==Advantages and disadvantages==
{{Unreferenced section|date=February 2010}}

===Advantages===

* Simple hardware interface
* Ease of connecting multiple device to a single host
* Allows mixing of slow and fast devices
* Well-established and mature, widely supported
* Rugged connectors, held in place by screws, means cables can't easily be accidentally removed as they can with [[Firewire]] and [[USB]]

===Disadvantages===
* Mechanically bulky connectors and cables
* Limited speed and expansion
* Lack of command protocol standards (before SCPI)
* Implementation options (e.g. end of transmission handling) can complicate interoperability in pre-IEEE-488.2 devices
* No mandatory galvanic isolation between bus and devices
* High cost (compared to RS-232/[[USB]]/Firewire/Ethernet)
* Limited availability (again compared to RS-232/USB/Firewire/Ethernet)

==See also==
{{Commons category|IEEE 488}}
* [[Standard Commands for Programmable Instruments]] (SCPI)
* [[LAN eXtensions for Instrumentation]] (LXI)
* [[Virtual Instrument Software Architecture]] (VISA)
* [[HP series 80]]
* [[Rocky Mountain BASIC]]

==References==
{{Reflist}}

==External links==
* {{Cite book|title=IEC-60488-1: Higher performance protocol for the standard digital interface for programmable instrumentation
|volume=Part 1: General
|publisher=International Electrotechnical Commission
|date=15 July 2004
|url=http://webstore.iec.ch/webstore/webstore.nsf/artnum/032787
}}
* {{Cite book|title=IEC-60488-2: Standard digital interface for programmable instrumentation
|volume=Part 2: Codes, formats, protocols and common commands
|publisher=International Electrotechnical Commission
|date=7 May 2004
|url=http://webstore.iec.ch/webstore/webstore.nsf/ArtNum_PK/32175
}}

{{Computer-bus}}

{{IEEE standards}}

{{DEFAULTSORT:Ieee-488}}
[[Category:Computer buses]]
[[Category:IEEE standards]]
[[Category:Electronic test equipment]]

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