DECSTO__1...,5_9 __ PAGE1.0 TITLE:MASSBUSSpecification TheMassbusInterfaceconceptwassuggestedbyGordonBellIn July,1972.A conmltteewasformedof:TomHastings,Steve Jenkins,VicKu,JohnLevy,andPeteMcLean,whodefined the.Inte"rfacethroughItsfirstseveraldesignIterations. JohnLevyactedassecretaryandpublishedthefollowln, precursorstothisdocument: August2,1972,StandardMassStorageInterface--Prellmlnary SpecificatIon August28,1972,MassStoraseInterfaceStandard October16,1972,MassbusInterfaceStandard March20,1973,MassbusInterfaceSpeclflcatlon--Part1 ThesefourdocumentsaresometimesInformallyreferredtoas"verslon1", ,"version2","version3",and"verslon4"oftheMassbusInterface spec 1fl cat Ion . DATE0#AUTHOR..........."',.vEDREVSECPAGESTITLE MASSBUSSecification DECSTD159 SIZECODENUMBERREV AosEL00159A EN-I047A-16-R27S-(327) ORA'18 DECSTD 159 REVA PAGE2.0 PAGEREVISIONCONTROL

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DECNO.16-(327)-1106-Nl75 ORAB DECSTD 1. 159 REV A CONTENTS INTRODUCTION 1.1 " Motivation 1.2"GoalsofThisSpecification 1.3Glossary 1.4FlowchartnotatIon 2.SUMMARY PAGE5.0 2.1DIvisionofFunctionsBetweenControllerandDrive 2.2Configurations 2.3PhysicalConstraints 2.4GeneralAbstract 3.THECONTROLBUS 3.1Introduction 3.2ControlBusSignals 3.3SequenceandTimIngofControlBusTransfers 3.4CommandInitiation 3.5TheAttentionLine(ATTN) 3.6TheInitializeLine(INIT) 3.7ControlBusParityChecking 3.8OtherControlBusTimingConstraints ~ THEDATABUS 4.1IntroductIon 4.2DataBusSignals 4.3SequenceandTimingofDataBusTransfers 4.4DataBusParItyChecking 4.5ErrorSignalling 4.6DataTransferCommandTennlnatlon 4.7AdditionalDataBusTimingRestrictions 4.8RecommendedPulseDurations 5.DRIVEREGISTERS 5.1Introduction 5.2DescriptionofDriveRegisters-5.3DetailsofMandatoryDriveRegisters 6.COMMANDS 6.1CommandCodes 6.2CommandDescriptions mamlala EN-OI047-1A-16-R17S-(327) ORAU8A DECSTD 159 REV A 7.ERRORCONDITIONS 7.1Introduction 7.2UseofAttentIon(ATTN) 7.3UseofexceptIon(EXC) 7.4ClassAErrorHandlingProtocol 7.5ClassBErrorHand11nlProtocol 7.6ExamplesofClassA Errors 7.7ExamplesofClassBErrors 8.OPTIONS 8.1DualController 9.HARDWAREDESIGNNOTES 9.1Introduction 9.2NotesonMassbusProtocol 9.3NotesonMassbusTlmlnl 9.4NotesontheUseofATA(AttentIonActive) 10.PROGRAMMINGNOTES 10.1Introduction PAGE6.0 10.2GeneralImplIcatIonsoftheMassbusforSoftware 10.3ProgrammingNotesonMassbusTiming 10.4Prograll'lnlngNotesonMassbusConmands 10.5NotesontheAttentionCondition 11.ELECTRICALSPECIFICATION 11.1Introduction 11.2Components 11.3St.andardTransce IverModul es 11.4ApprovedMassbusHardware mamaama EN-OI047-1A-16-R175-(327) ORAU8A DECSTD 1. 1.0 1.0.0 1.1 1.1.0 1.1.1 1.1.2 1.1.3 1.2 1.2.1 1.2.2 1.2.3 159 REV APAGE7.0 I NTKUUU\; II UN GENERAL ThisdocumentspecifiesastandardInterfacebetween andmass-storagedevices.ItIsacompany standardappliedtodisks,drums,tapes,andothermagneticor cyc'llcstoraaemedia. MOTIVATION Thefollowingconsiderationsmotivatedtheceneratlonofa standardInterface. Theexistingnumberofcombinationsofcontrollersanddevices Istoolarge.PastpracticewastodesignandbuIldanew controllerforeachperIpheraldevice.Standardizationallows constructIonofcontrollerswhIchhandlemorethanonedrIve InaserIes(e.g.,RP04,RPOS, )andmorethanonetypeof drive(e.g.,RKandRSdisks).Controllerswithsuch compatibilitynotonlyhavealongermarketlife,butalso givemoreflexibilitytothecustomer. A greatdealof"re-Inventlngthewheel"takesplaceeachtime anewcontrollerIsdesigned.AstandardInterface specificationprovidesabasisfordesIgnofnewcontrollers whentheyarerequIred.AwrIttenspecificationaIds documentationofspecificImplementations,andwhenproperly maintained,providesaforumfordiscussionoffuture evolution. PriorperipheralInterfacedesignswerenotadequateforthe dataratesanticipatedInthenextthreefiveyears.The needtoupgradeourdesignsprovidedanopportunemomentfor standardization. GOALSOFTHISSPECIFICATION ThisInterfacestandardhasbeenappliedImmediatelytothe RS03,RS04,andRP04disksandtheTM02tapesubsystem,andto controllersforthesedrivesInthePDP-10andPDP-11product lines.Futureperipherals,Includingmagnetictape,drums, disks,andpossiblydomainandsemiconductormassmemories shouldalso.conformtothisstandard.Extensiontoother productlinesIsalsoanticipated. EachperipheraldeviceIsexpectedtoImplementasubset thefunctionscalledforInthisInterfacestandard. particular,nodeviceorcontrollertowhichthestandard beenappliedshouldperformInwaysthatconflictwith standardunlesstheexceptionIsdocumentedandapproved. of In has this ItshouldbepossibletodesignInexpensivecontrollersand sohlstlcated"universal"allofwhichconformto 'omBD'D EN-OI047-1A-16-R17S-(327) IIORAU8A DECSTD 1.3 1.3.0 159 REV APAGE8.0 thisstandard. GLOSSARY ThelanguageofthIsspecIficationIsorientedtodIskand drumdevices;whereapplicable,extensionoftheconceptsto magnetictapeandotherdevicesIsIntended.Thefollowing termsareused: 1.DRIVE 2.CONTROLLER 3.MASSBUS 4.THEDATABUS s.THECONTROLBUS 6.MEMORYBUS 7.CRe 8.ECC TheperipheraldevicewhIchattaches totheMassbusandthedevice's associateddigitalelectronIcs. TheunittowhichdataIstransmitted fromthedrive.ThIsunitmayormay notbedistinctfromthecentral processIngunit. Thetransmissionmediumconnect Incthe drivewiththecontroller;the" MASSBUSInterfacestandard.Thename "MASSBUS"IsatrademarkofDIgital EquipmentCorporatIon.Consequently, onlythefollowinggraphIcformsare tobeused: MASSBUS Massbus Thepart transmits synchronous Thepart transml ts InformatIon "handshake". Thewires oftheMassbuswhich hl,h-speeddatausinga clocksIgnal. oftheMassbuswhIch cont ro 1andstatus usinganasynchronous whichconnectacontroller withthecentralprocessorand/orma'n memory. Cyclicredundancycheck,extrawords writtenonthestoragemediumtoaid detectIonoferrorsInwritIngor readingdata. Error-correctingcode,extrawords writtenonthestoragemediumtoaid detectionandcorrectIonoferrors. DECSTD 1.4 1.4.1 1.4.2 159 REV 9.WORD 10.FIELD 11.STORAGEMEDIUM 12.MEDIUM 13.BLOCK 14.SECTOR 15.RECORD 16.HEADER 17.PARITY 18.BITNUMBER FLOWCHARTNOTATION APAGE9,0 / Unlessotherwisespecified,a-wordIs eithersixteenoreighteenbitsof datatransmittedtoorfromthedrive whenreadingorwriting;16bitsof controlorstatusInfonaatlon. A contiguoussequenceofbitswritten onamagneticstoragemedium,without gaps.Also,onmagnetictape,a portionofarecord. Themagneticsurfaceonwhichdata bitsarerecorded. Thestoragemedium. Agroupofcontiguouscharacters recordedonandreadfromamagnetic surfaceasaunit.Ablockmay containoneormorecompleterecords. A portionofadiskstoragemedium, havingauniqueaddress.AsectorIs composedofoneormorefields. A portionofamagnetictapemedium recordedbetweeng.ps. AfieldcontainingIdentifying Informationfor.thesectororblockIn whichItoccurs. Wheneverused,parity15meanttobe oddparity:thenumberof1bitsIs madeoddbygeneratinga0ora1on theparityline. BI tsarenumberedfromtheleast, significantend,startIngwithbito. Insections3and4,aspecialflowchartnotationIs IntroducedtoshowboththesequenceofeventsIncontrollers anddrivesandthetimingrestrictionswhichapplytothese events(see,forexample,3.3.3,theflowchartforaread cycleonthecontrolbus). TheflowchartIsdividedbytwoverticallineswhichrepresent thephysicalandelectricalseparationofthecontrolleranda drive.OntheleftaretheeventsInthecontroller,onthe DECSTD 1.4.3 1.4.3.1 1.4.3.2 1.4.3.3 1 .... 3.4 1.... .. 1.4 .... 1 159REV right,theeventsIn doublelinerepresents transmittedonthebus. A PAGE1Q,Q thedrive.Alinewhichcrossesthe oneormoresignalswhichare TherearefourkindsofenclosuresIntheseflowcharts: boxes,diamonds,ovals,and"butterflies". Boxes(rectangularenclosures)representeventswhichhappen atoneInstantoftime.Forexample,In3.3.3,thesecondbox fromthetoponthecontrollersidecontains"ASSERTDEM", Indicatingtheeventofassertln.thesignalnamedItOEMIon thecontrolbus(atthecontrollerendofthebus). Diamondsaredecisionpoints,asInprogrammingflowcharts. ThepurposeofdiamondsIstodirecttheflowofeventsalong oneoftwopaths.ThedecisionIsalwaysonewhichcanbe madeonthebasisofthestateofthelogicatthattime.No timeIstakentomakethedecision;diamondsneverrepresent actionsoreventsInthelogic,onlyatestmadementallyby thereaderoftheflowchart. Diamondscontaln.astatementwithaquestionmark.Ifthe statement15trueatthattime,theflowlinemarked"y"Is taken;Iffalse,theflowlinemarked"N"Istaken. Somediamondshaveonlyoneflowlineexitingthediamond.If theanswertothestatementInthediamonddoesnotcorrespond totheY orN ontheoneexitingflowlinetheflowstops here. Ovalsareterminals,asInprogrammingflowcharts.Ovalsare eitherstartingpoints,havingoneflowlineexiting,or connectorsorterminationpoints,havingoneflowline entering.Ovalswhichdonotcontain"END"arenormally connectorstoanadditionalflowchart. "ButterflIes"aresmallboxeswithtwocompartmentsandan angledsidewhichattachestoaflowline(ItIsdrawnusinga bisected"offpageconnector"outlinefromaprogral1ll1lng template).Eachcompartmentcontainsanumberora"Uti. Theserepresenttimingrestrictions.Thebottom(or right-hand)numberIsaminimum,thetop(orleft-hand)onea maximum.TimesareInnanoseconds."U"meansthatthetime restrictionIsunspecified.Emptycompartmentsshouldn.ot occur. FLOWLINES Flowlinesdirectthesequenceandtimingofevents.Every flowlinehasaminimumandmaximumtimeassociatedwithIt. momDama EN-OI047-1A-16-R175-(327) .ORAU8A DECSTD 1.4.4.3 1.4.5 1.4.5.1 1.4.5.2 1.4.5.3 159 REV APAGE11.0 FlowlineswhichsplitIntotwolinesareequivalenttotwo linesconnectlnlthesourceboxwiththetwofollowingboxes. Bothbranchesaretobeactivelyfollowedsimultaneously. Whentwoflowlinesmerle,theboxenteredbythemergedline Isactivatedbyflowfromeitherofthesourceflowlines. Conflictsduetomultipleactivationofeventsshouldnot occur. MINIMUMANDMAXIMUMTIMES Aflow11 newh I chhasa"butterfl ylltouch I ngI trepresentsan elapsedtimebetweenthelimitsshownInthetwocompartments. Thistimemaybeunderthecontrolofthedesigner.Thetimes shownarethepermissiblelimitsal.lowedbythis specification. Aflowlinewhichcrossesbetweenthecontrollerandadrive representsane l p ~ e d timeof0nanosecondsminimum,375 nanosecondsmaximum.TheactualtimeIsnotundercontrolof thedesigner,andworst-caseshouldalwaysbeassumed. Allotherflowlinesrepresentanelapsedtimeof0 nanoseconds(0nanosecondsminimum,0nanosecondsmaximum). DECSTD 2. 2.1 2.1.1 2.1.1.1 2.1.1.2 2.1.1.3 2.1.1.4 2.1.1.5 2.1.1.6 2.1.2 2.1.2.1 2.1.2.2 Z.1.2.3 Z.1.2.4 l.1.2.5 l.1.2.6 l.1.2.7 2.1.2.8 1.2 Z.2.1 159 REV A PAGE12.0 SUMMARY DIVISIONOFFUNCTIONSBETWEENCONTROLLERANDDRIVE The.controllerperformsthefo11owlnlfunctions: Interfaceswiththememorybuscablesandsignals. CommunicateswithmainmemoryInordertofetchandstore data. BuffersdataInordertoaccommodatetimingdifferences betweenthedriveandthememory. CommunicateswiththecentralprocessorInordertoreceive commandsandsenderrorandstatusInformation. ImplementscommandswhichmayrequireasequenceoffunctIons Inthedrive(whichmightotherwiserequireaprogrammed sequence). Interfaceswithmultipledrives. Thedriveperformsthefollowingfunctions: Recordsandplaysbackdata. Generatesgapsandsynchronizationmarksontherecording medium(andIngeneralperfonnsallfunctionswhicharehighly medium-dependent). Providesclocksignalstosynchronizedata betweendrIveandcontroller. transmission MaIntainserrorandstatusIndicatorsandgeneratesan attentionsignalwhenexceptionalconditionsoccur. Locatesdatabyaddress(exceptmagnetictape). Providesmechanismsformaintenanceanddiagnostictesting Doeserrordetectiononthedataandprovideserrorcorrection patternsandpositions. DoesverifIcationofheaderInformation. CONFIGURATIONS ThefourconfigurationsshownInfigure2.2.1areallexpected tooccur. momoama EN-OI047-1A-16-R175-(327) ORAU8A DECSTD 159 2.2.1.1SINGLE 2.2.1.2DAISY-CHAIN 2.2.1.3RADIAL 2.2.1.4DUALCONTROLLER REV A PAGE13.0 Onecontrollerandonedrive;this couldbeaspecialcaseofdaisy-chain orradial,below. OnebusIsthreadedamongtheseveral drives. Aseparatebusconnectseachdrive withthecontroller. Twocontrollerswithseparatepathsto thedrivesharetheir. controlofthe drive. DECSTD 159 1.SINGLE K 2.DAISY-CHAIN K 3.RADIAL K 4.DUALCONTROLLERK K mamBD!a EN-OI047-1A-16-R17S-(327) ORAU8A REV o JI 0 I 0 l I A PAGE14.0 FIGURE2.2.2 II1 00 1 00 K-CONTROLLER 0 D-ORIVE 11-1879 DECSTD 159 REVAPAGE15.0 2.3PHYSICALCONSTRAINTS 2.3.1Thefollowinggoalsareexpectedtobeachievedbydesllns conformingtothisspecification. 2.3.1.1Dataratesofupto36MHz(bits). 2.3.1.2Uptoeightdrivesaddressablepercontroller. 2.3.1.3Cable(Massbus)lengthsofupto160feet(allowing10feet perdriveInthedaisy-chainconfiguration). 2.4GENERALABSTRACT 2.4.0ThefollowingarethemainfeaturesoftheMassbus. 2.4.1TheMassbusIscomposedoftwosections,containingatotalof 55signals.Thedatabussection,forhlsh-speeddata transmission,consistsofa19bitparalleldatapathandsix controllines.Thecontrolbussection,forcontroland statusInfonnatlontransfer,containsa17bitpathand14 controllines. 2.4.2Eachdrivecontainsuptothirty-twoaddressableresisters (somedrivesmayImplementonlyasubsetofthese).Someof theseregisters,whenwrittenInto,controlthenormaland maintenanceoperationsofthedrive.Allregistersmaybe readfrom,toobtainstatusInformation. 2.4.3Asectorformat(fordiskanddrum)Isspecifiedcontaining headeranddatarecords.ThelengthoftheheaderrecordIs fixedandspecified(forthosedriveswhichImplementIt). ThelengthofthedatarecordIsnotspecified,and conslderableefforthasbeenmadetoavoidImplicit restrictionsonItslength. ~ l m B D I I I D EN-OI047-1A-16-R17S-(327) ~ ORAU8A DECSTD 3. 3.1 3.1.1 3.2 3.2.1 3.2.1.1 3.2.2 3.2.2.1 3.2.3 3.2.3.1 3.2.3.2 5.2.4 5.2.4.1 5.2.4.2 5.2.5 5.2.5.1 5.2.6 5.2.6.1 5.2.7 159 THECONTROLBUS INTRODUCTION REV A PAGE16.0 ThepurposeofthecontrolbusIstotransmitcontrolcommands andInformationfromcontrollertodrive;totransmitstatus Informationfromdrivetocontroller;tonotifythe controllerwhenanunusual(attention)conditionexistsInone ormoredrives;andtoprovideamasterreset(alldrives) signalfromthecontroller. CONTROLBUSSIGNALS Control(C(0:15;Bidirectional These16bidirectionallinescarrythecontrolandstatus I nformat Ion. ControlParity(CPA);Bidirectional Thisbidirectionallinecarriesaparitybitassociatedwith thecontrollines(oddparity). DriveSelect(OS(0:2;ControllerToDrive Thesethreelinesselectthedrivetobeaccessed. WhentheRegisterSelectlinesRS(0:4)04(base8),theDrive SelectlinesareIgnoredandalldrivesrespond.ThisIsfor transmissionoftheAttentionSummarypsuedoregisterbits. RegisterSelect(RS