MITS 8800b-sm Operator's manual

BiwramiM
asubsidiaryofPertocComputerCorporation
2450AlamoS.E./Albuquerque,NewMexico87106

NOTICE
Informationcontainedwithinthisdocument
maynotbereproduced,distributedordis-
closedinfullorinpartbyanyperson
withoutpriorapprovalofPertecComputer
Corporation,MicrosystemsDivision.
MarketingHeadquarters
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Phone[phone]
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ii

CHANGERECORD
Revision Date Pages
*
A
June, 1978
InitialRelease
m
•
-

TABLEOFCONTENTS
Section£M£
PartI.IntroductionandOperator'sGuide
1.IntroductiontoThisManual. . . . 3
2.IntroductiontotheStandardSystem4
3.UsingThisDocumentationPackage10
PartII.8800bTurnkeyComputer
1.Introduction15
2.TheoryofOperation21
2-1.General23
2-2.CPUBoard.26
2-3.TurnkeyModule.29
3.AdvancedOperations37
3-1.TheFrontPanel39
3-2.TheTurnkeyModule40
3-3.AUTO-START54
3-4.MiscellaneousOptions55
3-5.ThePowerSupply57
4.TroubleshootingHints59
4-1.Introduction61
4-2.PreliminaryConsiderations61
4-3.CPU62
4-4.TurnkeyModule62
PartIII.MinidiskSystem
1.Introduction67
1-1.MITSAltairMinidiskSystemDescription...69
1-2.Specifications69
2.TheoryofOperation73
2-1.General75
2-2.LogicCircuits75
2-3.SchematicReferencing75
2-4.MinidiskBlockDiagram80
2-5.GeneralSystemOperation81
2-6.MinidiskControllerBlockDiagram82
2-7.AddressSelectCircuit87
2-8.Index/SectorCircuit88
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SectionPa9e
2-9.ReadCircuit91
2-10.StatusCircuit94
2-11.DiskEnableCircuit94
2-12.WriteCircuit96
2-13.DiskFunctionControlCircuit.101
2-14.HeadStepping103
2-15.DiskDisableTimer104
2-16.MoveHeadStatus104
2-17.HeadStatus105
2-18.EnableInterrupts105
3.PreliminaryCheckout.107
3-1.DiskEnableTest109
3-2.AltairMinidiskControllerTiming
TestPoints110
3-3.AltairMinidiskTestPrograms123
Appendices
A.Altair8800bBusAssignments125
B.MinidiskProgramming129
Intel8080MicrocomputerSystemUser'sManual143
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248067A 1/(14Blank)

1.Introduction
1-1.IntroductiontothisManual
The8800b-smland-dmareintegratedcomputersystemsthatinclude
theAltair8800bTurnkeymicrocomputeralongwitheitherone (-sm) or
two(dm)AltairMinidiskmassstorageunits.
The8800bTurnkeycomputerincludesthesystempowersupply,the
CentralProcessingUnit(CPU)withthe8080Amicroprocessoranda
TurnkeyModuleboard.TheTurnkeyModuleisa multi-functionboardthat
includesIKbytesofrandomaccessmemory(RAM),provisionsforupto
IKbytesofreadonlymemory(PROM)(includingtheMinidiskBoot
LoaderPROM)anda.serialinput/outputport(SI0)forconnectingthe
computertoa terminal.PartIIofthisdocumentationpackagedocuments
the8800bTurnkeycomputer.Section1 isa descriptionofthecomponents
oftheTurnkeycomputer,andSection2 isa briefsummaryofitstheory
ofoperation.Section3 isanadvancedoperationmanualwhichdetails
proceduresforexpandingandmodifyingthestandardsystem.Section
4isa briefguidetotroubleshootingtheelectronicsofthecomputer.
TheMinidiskmassstoragesubsystemconsistsofoneortwoMinidiskk
drives,a drivecontrollerandaninterfacecardforconnectingthedisk
systemtothecomputer.ThesearealldescribedinPartIIIofthis
documentationpackage.Section1 isa listingofthespecificationsof
theMinidisksubsystem.Section2 isa summaryofthetheoryof
operationandSection3 isa descriptionofproceduresforinitial
checkoutandfaultdiagnosis.
TheAppendicesincludea descriptionoftheAltairbus,instructions
forconvertingthepowersupplyforusewith230voltsAC,a listingof
theMinidiskBootLoaderPROMandaidsforprogrammingtheMinidisk
systeminmachinelanguage.
Finally,theIntel8080AMtcrocomputerSystemUser'sManualdetails
thestructure,timingandinstructionsetofthe8080Amicroprocessor.
ItalsogivestechnicalinformationaboutsomeoftheCPU'sauxiliary
circuits.
13 248067A

1-2.IntroductiontotheStandardSystem
Thestandard8800b-smor-dmsystemconsistsofthe8800b-smor-dm
TM-
computerandeithera TeletypeorCathodeRayTube(CRT)terminal.This
sectionshowshowtoassemblesucha systemfromitscomponentsandhowto
loadandrunBASIContheassembledsystem.
A,Settingupthesystem.Carefullyliftthecomputerunitfrom
itspackingcaseandplaceitona hard,flatsurface.Leaveenough
spaceonallsidessothattheflowofcoolingairisnotimpaired,
Donotconnectthepowercorduntiltheterminalhasbeeninstalled.
RemovetheprotectivetabsfromtheMinidiskdrivesfollowing
thedirectionsprintedonthetabs.
Thecomputerissetatthefactorytomatchtheterminalshipped
withit.Therefore,toinstalltheterminal,itisonlynecessaryto
connectthecomputerandtheterminalwiththecablesuppliedwiththe
terminal.Thediagrambelowshowsthe25pincableconnectorsandthe
matchingconnectorsontheterminalandcomputer.
Figure1-1.25PinCableConnectors
Thepowersupplyisprotectedbya 3 amp,slow-blowfusemounted
onthebackpanelofthecomputer.Itshouldbereplacedasnecessary
onlybythesametypeoffuse.Thepowercordshouldbeconnectedto
asourceof115volts,50-60HzAC.(230VACoperationisavailableas
anoption.SeeAppendixC).
Aftermakingsurethefuseisinstalledandthepowercordsfor
theterminalandcomputerarepluggedin,inserttheBASICdiskette
intodrivezero.
248067A
4

Todothis,opendiskdrivezerobypullingoutonthedoortab
(seeFigure1-2).Inserttheedgeofthedisketteoppositethelabel
intothedrivewiththelabelsidetowardtheopentab.Pushthediskette
allthewayintothedriveandclosethedoortab.
Now,movetheRUN/STOPswitchonthefrontpaneluptotheRUN
positionandturnthepowerswitchon.Thepowerswitchhasthree
positions.At12o1clock,theunitisoffandthekeymayberemoved.
At3 o'clock,thepowerisonandthefrontpanelswitchesareenabled.
At6 o'clock,thecomputerison,butthefrontpanelswitchesare
disabled.Inthisposition,thekeymayberemoved.
Withthepowerswitchon,thePowerindicatorshouldlightshowing
thatthecomputercircuitryisreceivingoperatingvoltagefromthe
powersupply.IfthePowerindicatordoesnotlight,turnoffthepower
switchandcheckthepowercordandfuse.
HeadLoadLight
DisketteSlot
DoorTab
Label
Figure1-2InsertingtheDiskette
248067A '5

B.InitializingBASIC.Whenthepoweristurnedon,BASICis
loadedintomemoryautomatically.Whenithasbeenloaded,BASICprints
MEMORYSIZE?
ontheterminaltobegintheinitializationdialog.Thisquestionasks
theoperatortospecifytheamountofmemorytobeusedbyBASICprograms.
Typinga numberandcarriagereturnreservesthatnumberofbytes.Typing
justa carriagereturndirectsBASICtouseallavailableread/write
memory.BASICnowprints
LINEPRINTER?
Theoperatortypesa letterandcarriagereturntoindicatethetype
ofprinterinuseasfollows:
LetterPrinter
0= LP80
C= C700
Q= Q70
Ifnoprinterisconnected,anyofthelettersmaybetyped.Ifthe
responseisnot0,C orQ,however,BASICasksLINEPRINTER?again.
BASICnowasks
HIGHESTDISKNUMBER?
Ina systemwith1 disk,thehighestnumberis0.With2 disks,the
highestnumberis1.Typingjusta carriagereturnisequivalentto
typing0.
NowBASICasksthenumberofdiskdatafiles(randomaccessand
sequential)tobeopenatonetime:
HOWMANYDISKFILES?
Theoperatorrespondswiththenumberofdiskdatafilesexpectedtobe
openatanyonetime.BASICthen-prints
HOWMANYRANDOMFILES?
Hereagain,theoperatorrespondswiththenumberofrandomaccessfiles
expectedtobeopenatanyonetime.
NowBASICisinitializedandprintsthefollowingmessages:
ALTAIRMINI-DISKBASIC
REVISION4.1JULY1977
COPYRIGHT1977BYMITS,INC.
6 248067A

OK
BASICisnowreadyforuse.
Atanytime,BASICmaybereloadedsimplybymomentarilydepressing
theSTARTswitch.
C.InitializingNewDiskettes.BecausetheBASICcodetakesup
somuchdiskettespace,itissuppliedona "writeprotected"diskette.
ThismeansthatnoprogramsordatamaybesavedontheBASICdiskette.
InadditiontoBASIC,theBASICdisketteincludestwoprograms,
PIPandSTARTREK,whichareavailabletousers.Beforetheycanberun,
theBASICdiskettemustbemounted(seesectionD below).Sincethe
BASICdisketteiswriteprotected,mountingitcausesa DISKI/OERROR,
butthereadingprocessisnotaffected.
Thedesiredprogrammaynowbereadfromthediskandloadedinto
memory.Todothis,typethefoilowingcommand:
LOAD"<programname>",<disknumber>
where<programname>isthenameofthedesiredprogramand<disknumber>
m
isthenumberofthediskdriveintowhichtheBASICdiskwasinserted
(usuallyzero).
ToavoidinadvertantdamagetotheBASICdisk,typethefollowing
command:
UNL0AD<disknumber>
where<disknumber>isthe.drivenumberthatappearedintheLOADcommand
above.
NowtheBASICdiskettemayberemovedandanotherdisketteinserted
intothedriveandmounted.
Theprogrammaybesavedonthenewdiskettebytypingthefollowing
command:
SAVE"<programname>",<disknumber>
where<disknumber>isthenumberofthediskdriveintowhichthenew
diskettewasinserted.
Subsequenttosavingtheprogram,itmayberunbytypingthefollowing
comnand:
RUN"<programname^^diskrrumber>
where<disknumber>isthenumberofthediskdriveintowhichthediskette
bearingtheprogramwasinserted.
248067A 7

CAUTION
DonotattempttowriteprogramsordataontotheBASIC
diskette.ThiscanresultinFILELINKERRORSthatcanmake
theBASICdisketteunusable.Beforewritinganythingondisk,
unloadandremovetheBASICdiskette.
Ifthediskettehasneverbeenuseditmustbeinitializedbefore
itcanbeused.Thisisdonebytypingthefollowingcommand:
DSKINI<disknumber>
wheredisknumberisthenumberofthediskdriveonwhichtheblank
disketteisloaded.TheDSKINIcommandmarksallthesectorsonthe
disketteasbeingempty.BASICreadsthesemarkstodeterminesector
boundaries.
CAUTION
Onlynew,blankdiskettesneedtobeinitialized.
UsingDSKINIona diskettethatcontainsfilesdestroys
allthefiles.DISKINIshould,therefore,beusedwith
extremecaution.TheDSKINIprocesstakesabout2 minutes
perdiskette.Whenitisfinished,BASICprintsOK.
D.MountingDiskettes.Toreadya disketteforreadingorwriting,
typethe foil owingcommand:
MOUNT<disknumber>
Omittingthedisknumbercausesalldisksinthesystemtobemounted.
Aftera fewseconds,BASICprints
OK
toindicatethatthediskisreadyforuse.
Beforeremovinga mounteddiskfroma drive,typethefollowing
command
UNLOAD<disknumber>
Omittingthedisknumberunloadsallmounteddisks.
8 248067A

E,DisketteSpecificationsandCare.The8800Tsmanddmuse
51/411,hard-sectoreddiskettes.DiskettesareavailablefromMITS(Part
number102501)ormaybepurchasedfromanyAltairComputerCenter.
Thenotchonthesideofthedisketteengagesa switchinthe
drivewhichenablesthewritecircuitry.Coveringthenotchwitha
pieceoftapemakeswritingonthedisketteimpossible.TheBASIC
disketteisprotectedinthismanner.
CAUTION
UnprotectingtheBASICdiskettecancausedestruction
oftheBASICinterpreter.DONOTremovetheBASIC
disketteprotectiontab.
Severalhandlingprecautionswillmaximizethelifeandusefulness
ofdiskettesanddrives. \
1.Returndiskettestotheirstorageenvelopeswhentheyarenot
inuse.Donotleavetheminthedrive.
2.Keepdiskettesawayfrommagneticfields.Fieldsmaybe
causedbyfluorescentlights,transformersorlargepieces
ofmagnetizablematerials.
3.Markthediskettelabelonlywithfelttippen.Donotuse
ballpointpenorpencil.
4.Keepdust,andotherparticulatematterawayfromdiskettes.
5.Keepdiskettesawayfromexcessivesunlightandheat.
6.Nevertouchthediskettesurface(throughtheheadaccess
window)orattempttocleanit.
F.MiscellaneousInformation.SincetheaddressoftheMini-Disk
controlleristhesameasthestandardsizefloppydiskcontroller
(88-DCDD)thestandardsizediskdrivesmaynotbeusedinthe8800T-sm
or-dmsystem.
AtimingcircuitintheMiniDiskControllerturnsoffthedrive
motor6.4secondsafterthelastaccessoperationtominimizedrive
wear.
248C67A 9

1-3,UsingthisDocumentationPackage
Theremainderofthedocumentationinthispackagecontainsreference
materialforoperatingandmaintainingthecomponentsofthesystem.
Threecommonlyencounteredsituationswhichrequiretheuseof
thisreferencematerialare1)expansionofthesystemmemory,2)adding
ormodifyinginput/outputperipheralequipmentand3)addingspecial
purposePROMfunctions.Theproceduresformakingthesemodifications
aresketchedbelowalongwithreferencestomoredetailedinformation.
Thereferencesareeithertothemanualsortothepagenumbersinthis
documentationpackageinwhichtheinformationmaybefound.
NOTE
Beforeworkingontheinsideofthecomputercasemake
surethepowerisoffandthepowercorddisconnectedfromthe
line.
Toremovethecasecover,removethetwoboltsintheupper
cornersofthebackpanel.Thenslidethecoverbackandlift
itoff.
Toremovea card,pullstraightuponbothendsofthe
card.Carefullyremoveanycableconnectorswhentheboardis
free.
Toinserta card,connectthenecessarycablesandposition
theboardsotheedgeconnectorisdownandthecomponentside
oftheboardistotherightasviewedfromthefrontofthe
unit.Insertthecardintothecardguidesandslideit
straightdownuntilitmakescontactwiththeconnectoratthe
bottomoftheslot.Applyfirm,steadypressuretotheupper
edgeofthecarduntiltheboardseatsintheconnector.The
topedgeshouldbeflushwiththetopofthecardguides.
A.ExpandingMemory.Systemmemoryexpansionisaccomplishedby
addingmemoryboardsorreplacingthemwithboardsofhighercapacity.
Usethefollowingproceduretomakethesechanges:
248C67A20