The PS2 Mouse Interface.docx

The PS2 Mouse Interface.docx

《The PS2 Mouse Interface.docx》由会员分享，可在线阅读，更多相关《The PS2 Mouse Interface.docx（16页珍藏版）》请在冰点文库上搜索。

ThePS2MouseInterface

ThePS/2MouseInterface

Source:

http:

//www.Computer-Engineering.org

Author:

AdamChapweske

LastUpdated:

04/01/03

LegalInformation:

Allinformationwithinthisarticleisprovided"asis"andwithoutanyexpressorimpliedwarranties,including,withoutlimitation,theimpliedwarrantiesofmerchantibilityandfitnessforaparticularpurpose. 

Thisarticleisprotectedundercopyrightlaw. Thisdocumentmaybecopiedonlyifthesource,author,date,andlegalinformationisincluded.

Abstract:

ThisarticleattemptstoexplaineveryaspectofthePS/2mouseinterfaceincludingthephysicalandelectricalinterface,low-levelprotocol,modesofoperation,commands,andextensions. AllcodesamplesinvolvingthemouseencoderarewritteninassemblyforMicrochip'sPICmicrocontrollers. Allcodesamplesrelatedtotheauxiliarydevicecontroller（keyboardcontroller）arewritteninx86assembly

GeneralDescription:

TherearemanytypesofpointingdevicesavailableformodernPCs,includingmice,trackballs,touchpads,electronicwhiteboards,etc. Virtuallyallofthesepointingdevicescommunicatewithacomputerusingoneoftwointerfaces:

UniversalSerialBus（USB）orthePS/2MouseInterface. Seethefollowingtableforacomparison:

USB（v1.1）

 PS/2MouseInterface

NumberofDevicesSupported

Upto127

One

MaximumDataRate

12Mbps

40kbps

Power（max）

5V@500mA

5V@100mA

Hot-Pluggable?

Yes

No

Documentation

Well-documented:

http:

//www.usb.org

Out-of-print

（IBMTechReference）

OlderpointingdeviceinterfacesincludetheAppleDesktopBus（ADB）,RS-232serialport,andthebusmouseinterface. Theseareobsoleteandarenotcoveredinthisarticle.

ThePS/2mouseinterfaceoriginallyappearedinIBM's"PersonalSystem/2"computersinthelate80's. Itstillremainsawidely-supportedinterfaceforthesakeofconstantlymaintainingbackwardcompatibility. However,USBhasquicklycaughtontheselastfewyearsandwilleventuallyreplacethePS/2mouseinterfaceentirely.

ThePS/2mouseinterfaceusesabidirectionalserialprotocoltotransmitmovementandbutton-positiondatatothecomputer'sauxiliarydevicecontroller（keyboardcontroller）. Thecomputer,inturn,maysendanumberofcommandstothemousetosetthereportrate,resolution,resetthemouse,disablethemouse,etc. Thecomputeralsoprovidesthemousewithanoverload-protected5Vpowersupply.

ElectricalInterface/Protocol:

ThePS/2mouseusesthesameprotocolasthePS/2keyboard（akaATkeyboard）. Clickherefordetailedinformationonthisprotocol.

Inputs,Resolution,andScaling:

ThestandardPS/2mouseinterfacesupportsthefollowinginputs:

X（right/left）movement,Y（up/down）movement,leftbutton,middlebutton,andrightbutton.Themousereadstheseinputsataregularfreqencyandupdatesvariouscountersandflagstoreflectmovementandbuttonstates. TherearemanyPS/2pointingdevicesthathaveadditionalinputsandmayreportdatadifferentlythandescribedinthisdocument. OnepopularextensionIcoverlaterinthisdocumentistheMicrosoftIntellimouse,whichincludessupportforthestandardinputsaswellasascrollingwheelandtwoadditionalbuttons.

Thestandardmousehastwocountersthatkeeptrackofmovement:

theX-movementcounterandtheY-movementcounter. These are9-bit2'scomplementvaluesandeachhasanassociatedoverflowflag. Theircontents,alongwiththestateofthethreemousebuttons,aresenttothehostintheformofa3-bytemovementdatapacket（asdescribedinthenextsection.） Themovementcountersrepresenttheamountofmovementthathasoccurredsincethelastmovmentdatapacketwassenttothehost（ie,theydonotrepresentabsolutepositions.）

Whenthemousereadsitsinputs,itrecordsthecurrentstateofitsbuttonsandchecksformovement.Ifmovementhasoccurreditincrements（for+Xor+Ymovement）ordecrements（for-Xor-Ymovement）itsXand/orYmovementcounters.Ifeitherofthecountershasoverflowed,itsetstheappropriateoverflowflag.

Theparameterthatdeterminestheamountbywhichthemovementcountersareincremented/decrementedistheresolution.Thedefaultresolutionis4counts/mmandthehostmaychangethatvalueusingthe"SetResolution"（0xE8）command.

Thereisaparameterthatdoesnoteffectthemovementcounters,butdoeseffectthereported

（1）valueofthesecounters. Thisparameterisscaling. Bydefault,themouseuses1:

1scaling,whichhasnoeffectonthereportedmousemovement. However,thehostmayselect2:

1scalingbysendingthe"SetScaling2:

1"（0xE7）command. If2:

1scalingisenabled,themousewillapplythefollowingalgorithmtothecountersbeforesendingtheircontentstothehost:

MovementCounter

ReportedMovement

0

0

1

1

2

1

3

3

4

6

5

9

N>5

2*N

MovementDataPacket:

ThestandardPS/2mousesendsmovement/buttoninformationtothehostusingthefollowing3-bytepacket（4）:

Byte1 

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

Yoverflow

Xoverflow

Ysignbit

Xsignbit

Always1

MiddleBtn

RightBtn

LeftBtn

Byte2

XMovement

Byte3 

YMovement

Themovementcountersare9-bit2'scomplementintegers,wherethemostsignificantbitappearsasasignbitinByte1ofthemovementdatapacket.Thesecountersareupdatedwhenthemousereadsitsinputandfindsmovementhasoccurred.Theirvalueistheamountofmovementthathasoccurredsincethelastmovementdatapacketwassenttothehost（ie,afterapacketissenttothehost,themovementcountersarereset.）Therangeofvaluesthatcanbeexpressedbythemovementcountersis-255to+255.Ifthisrangeisexceeded,theappropriateoverflowbitisset.

AsImentionedearlier,themovementcountersareresetwheneveramovementdatapacketissuccessfullysenttothehost.Theyarealsoresetafterthemousereceivesanycommandfromthehostotherthanthe"Resend"（0xFE）command.

ModesofOperation:

Datareportingishandledaccordingtothemodeinwhichthemouseisoperating. Therearefourstandardmodesofoperation:

∙Reset-ThemouseentersResetmodeatpower-uporafterreceivingthe"Reset"（0xFF）command. 

∙Stream-Thisisthedefaultmode（afterResetfinishesexecuting）andisthemodeinwhichmostsoftwareusesthemouse. IfthehosthaspreviouslysetthemousetoRemotemode,itmayre-enterStreammodebysendingthe"SetStreamMode"（0xEA）commandtothemouse. 

∙Remote-Remotemodeisusefulinsomesituationsandmaybeenteredbysendingthe"SetRemoteMode"（0xF0）commandtothemouse. 

∙Wrap-Thismodeisn'tparticularlyusefulexceptfortestingtheconnectionbetweenthemouseanditshost. Wrapmodemaybeenteredbysendingthe"SetWrapMode"（0xEE）commandtothemouse. ToexitWrapmode,thehostmustissuethe"Reset"（0xFF）commandor"ResetWrapMode"（0xEC）command. Ifthe"Reset"（0xFF）commandisrecieved,themousewillenterResetmode. Ifthe"ResetWrapMode"（0xEC）commandisreceived,themousewillenterthemodeitwasinpriortoWrapMode.

（Note:

Themousemayalsoenter"extended"modesofoperation,asdescribedlaterinthisdocument. However,thisisnotafeatureofthestandardPS/2mouse.）

ResetMode:

Themouseentersresetmodeatpower-onorinresponsetothe"Reset"（0xFF）command.Afterentringthismode,themouseperformsadiagnosticself-testreferredtoasBAT（BasicAssuranceTest）andsetsthefollowingdefaultvalues:

∙SampleRate=100samples/sec

∙Resolution=4counts/mm

∙Scaling=1:

1

∙DataReportingDisabled

ItthensendsaBATcompletioncodeofeitherAAh（BATsuccessful）orFCh（Error）.Thehost'sresponsetoacompletioncodeotherthanAAhisundefined.

FollowingtheBATcompletioncode（AAhorFCh）,themousesendsitsdeviceIDof00h.Thisdistinguishesitfromakeyboard,oramouseinanextendedmode.IhavereaddocumentssaythingthehostisnotsupposedtotransmitanydatauntilitreceivesadeviceID. HoweverI'vefoundthatsomeBIOS'swillsendthe"Reset"commandimmediatelyfollowingthe0xAAreceivedafterapower-onreset.

AfterthemousehassentitsdeviceIDtothehost,itwillenterStreamMode. Notethatoneofthedefaultvaluessetbythemouseis"DataReportingDisabled". Thismeansthemousewillnotissueanymovementdatapacketsuntilitreceivesthe"EnableDataReporting"command.

StreamMode:

Instreammode,themousesendsmovementdatawhenitdetectsmovementorachangeinstateofoneormoremousebuttons.Themaximumrateatwhichthisdatareportingmayoccurisknownasthesamplerate. Thisparameterrangesfrom10samples/secto200samples/sec.Itsdefaultvalueis100samples/secandthehostmaychangethatvaluebyusingthe"SetSampleRate"command. Streammodeisthedefaultmodeofoperationfollowingreset.

RemoteMode:

Inthismodethemousereadsitsinputsandupdatesitscounters/flagsatthecurrentsamplerate,butitdoesnotautomaticallyissuedatapacketswhenmovementhasoccured. Instead,thehostmustpollthemouseusingthe"ReadData"command. Uponreceivingthiscommandthemousewillsendasinglemovementdatapacketandresetitsmovementcounters.

WrapMode:

Thisisan"echoing"modeinwhicheverybytereceivedbythemouseissentbacktothehost.Evenifthebyterepresentsavalidcommand,themousewillnotrespondtothatcommand--itwillonlyechothatbytebacktothehost.Therearetwoexceptionstothis:

the"Reset"commandand"ResetWrapMode"command.Themousetreatstheseasvalidcommandsanddoesnotechothembacktothehost.

IntellimouseExtensions:

Apopularextensiontot