Ieee 488 Gpib Vamsi

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IEEE 488/ GPIB



The communications standard now known as the GPIB (General(GeneralPurpose Interface Bus),Purpose Interface Bus), was originally developed by ewlett Pin !"#$% to connect and control their programmable test instrume

'ue to its speed% (e)ibility% and use*ulness in connecting

programmable instruments to computers% it gained widespreadacceptance% and was adopted by di+erent manu*acturers *or theiprogrammable instrumentation&

In !"8,% the IEEE -tandard 488&. was introduced to dene data*ormats% status reporting% controller *unctionality% error handling% common commands& IEEE 488&. concentrates on so*tware protocissues and maintains *ull compatibility with devices that comply w

the hardware0oriented IEEE 488&! standard&In !""1% a group o* instrument manu*acturers announced a *urthe)tension o* the standard% known as -2PI 3standard commands *oprogrammable instruments% which uses IEEE 488&. as a basis andenes a common command set that can be used *or programminstruments with any hardware link



5part *rom the three standards associated with the term IEEE3IEEE 488&!% IEEE 488&.% and the -2PI the term GPIB is o*ten interchangeably&

The GPIB is an inter*ace design that allows the simultaneousconnection o* up to !$ devices or instruments on a common

parallel data communications bus



Figure 1: National Instruments PCI-GPIB Board with GPIB cable



GPIBGPIBCONNECTOCONNECTOR (IEEER (IEEE488) AND488) ANDPINPIN

ASSIGNENASSIGNENTSTS



The .4 lines% in each cable% consist o* 8 data lines and 8 3!# o* control and bus management lines&

The data lines are used e)clusively to carry data% in a paconguration% one byte at a time% along the bus&

The control and bus management lines are used *or variomanagement tasks that synchroni6e the (ow o* data&

7hen data or commands are sent down the bus% the busmanagement lines distinguish between the two&

The GPIB uses the logic convention called low0true9 or

negative logic% where the lower voltage state is true9 andhigher voltage state is *alse9& -tandard TT: voltage levelused&

;or e)ample% when a line is true% or asserted% the TT: vollevel is low 3<1&8 =% and when the line is *alse9% or unasthe TT: level is high 3>.&1=&



HOW DOES IT WORK? GPIB is a digital% 80bit parallel communications inter*ace with trans*er rates o* !?byte/s and higher% using a three0wire

handshake& The bus supports one -ystem 2ontroller% usually a computer%up to !4 additional instruments& These instruments can eithearranged in a -tar conguration or in a linear conguration&

The GPIB is a .40conductor parallel bus that consists o* eight lines% ve bus management lines 35T@% EAI% I;2% E@% and -three handshake lines% and eight ground lines&

GPIB uses a byte0serial% asynchronous data trans*er scheme& means that whole bytes are seDuentially handshaked across bus at a speed that the slowest participant in the trans*erdetermines&

Because the unit o* data on the GPIB is a byte 3eight bits% themessages trans*erred are *reDuently encoded as 5-2II characstrings&



5ll GPIB devices and inter*aces must have a uniDue GPIBaddress between 1 and 1& 5ddress 1 is normally assignthe GPIB inter*ace& The instruments on the GPIB can useaddresses ! through 1& GPIB devices can be talkers%listeners% or controllers& 5 talker sends out data message

:isteners receive data messages& The controller% usuallycomputer% manages the (ow o* in*ormation on the bus& denes the communication links and sends GPIB commato devices& The GPIB =Is automatically handle the addreand most other bus management *unctions&



The .4 bus lines are divided to *our categoriesF

data and commands lines 3'IA!0'IA8

handshake lines 3'5=% @'52% @;'

bus management lines 35T@% I;2% E@% -C% EAI

ground lines used *or shielding and signal returns



DATA !INESDATA !INES

The eight data lines '!1! to '!18 carry both data and command mecommands and most data use the ,0bit 5-2II code% in which case the'!18% is either unused or used *or parity& The state o* the attention 35determines whether the in*ormation is data or commands& 2ommand

sent with the 5T@ line asserted% while data messages are sent with thunasserted&

INTER"ACE ANAGENT !INESINTER"ACE ANAGENT !INES

;ive signal lines manage the (ow o* in*ormation across the GPIB& Thedescribed below&

5T@ 3attention H The controller asserts the 5T@ line true9 when it u

lines to send commands& 5ll devices become listeners and participatcommunication& 7hen 5T@ is unasserted% in*ormation on the bus is idata&

I;2 3inter*ace clear H This line can only be controlled by the systemwhich drives the I;2 line to initiali6e the bus and become controller i

The I;2 line is the master reset o* the GPIB and when asserted all deknown Duiescent state&



E@ 3remote enable H The system controller drives the E@devices into a remote state& 7hen the E@ line is asserted anaddressed to listen% the device is placed into a remote progra

-C 3service reDuest H 5ny device can drive the -C line tasynchronously noti*y the 2I2 that it needs service& Itis the rethe 2I2 to monitor the -C line% poll the device% and determinservice the device needs& -C will remain asserted until the 2device reDuesting service&

EAI 3end or identi*y H The EAI line has two purposes& Its rsa talker asserts the EAI line to indicate the last byte o* data instring& 5 listener stops reading data when EAI is asserted tru

use *or the EAI line is to tell devices to identi*y their responsepoll&



#AND S#A$E !INES#AND S#A$E !INES

Three handshake lines asynchronously control the trans*er message bytes between devices& The GPIB uses a three0wiinterlocking handshake scheme that guarantees that messbytes on the data lines are sent and received without error

• @;' 3not ready *or data H The @;' handshake line indicateswhether a device is ready to receive a message byte or not& 7hreceiving commands% the line is driven by both talkers and listenand only by listeners when receiving data messages&

• @'52 3no data accepted H This line indicates whether a devicehas not accepted a message byte& @'52 is driven by all devices

talkers and listeners when receiving commands% and only by liswhen receiving data messages&

•'5= 3data valid H The '5= handshake line indicates whether sigon the data lines are stable and there*ore valid and can be accepby devices& The controller controls '5= when sending commandthe talker controls '5= when sending data&



The 'evices An The GPIB 2an

2onnected In A Star A StarConfgurationConfguration, Ar In A Chain A Chain(Linear) Confguration(Linear) Confguration

5 star conguration is one whereeach instrument is connected% bymeans o* a separate GPIB cable%directly to the controller&

The connectors are all connectedto the same port at the controller&

5 drawback to this simpleconguration is that all o* thedevices on the bus must berelatively close to the controllerbecause o* the length limitation&



In the chain conguration% each device% including the controllerconnected to the ne)t in a chain&

It is a controller only in the sense that it co0ordinates the eventbus& Physically and electrically% it is similar to any other deviceto the GPIB& This conguration is usually the most convenient wconnect eDuipment&

5 disadvantage o* the chain conguration is that the so*tware mreconguration i* a device and its cable are removed&



5lthough the star and chain congurations are suggested *or GPIB%connections can be made in any other way% provided that the *ollowrules are observedF

5ll devices are connected to the bus

@o more than !$ devices% including the controller% may be on the with no

less than two thirds powered on

2able length between any two devices may not e)ceed 4 meters

average separation o* . meters over the entire bus

Total cable length may not e)ceed .1 meters



;rom a data communications standpoint% there are *our di+erent go* devices that communicate on a GPIB inter*aceF

Tal%ersTal%ers

5 talker is a one0way communicating device that can only send dalistening device& It does not receive data& The talker waits *or a sig

*rom the controller and then places its data on the bus& Anly one dcan talk at a time& 2ommon e)amples are simple '=?s 3digitalvoltmeters and some 5/' converters&

!&steners!&steners

5 listener is a one0way communicating device that can only receive*rom another device& It does not send data& It receives data when tcontroller signals it to read the bus& 2ommon e)amples are printer

plotters% and recorders&Tal%ers'!&stenersTal%ers'!&steners

5 talker/listener has the combined characteristics o* both talkers alisteners& owever% it is never a talker and a listener at the same tcommon e)ample is a programmable '=?% which isa listener whilerange is being set by the controller and a talker while it sends the rback to the controller&



ControllersControllers

5 controller manages and controls everything that happens oGPIB& It is usually an intelligent or programmable device% suchP2 or a microprocessor0controlled device& It determines whichdevices will send data 3talkers and which will receivedata3listeners% and when& To avoid con*usion in any GPIBapplication% there can only be one active controller% called thecontroller in charge 32I2&

Ieee 488 Gpib Vamsi

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