TheInter-IC(I
2
C)busisatwo-wireserialinterface
developedbyPhilips/Signetics.Thespecificationsup-
portsdatatransmissionupto400Kbps.
TheI
2
Cinterfaceemploysacomprehensiveprotocolto
ensurereliabletransmissionandreceptionofdata.
Whenthebusisactive,onedeviceistheMaster
(generatestheclockandthehandshakingsignals),
whilealltheotherdevicesareSlaves.Thecurrentbus
Mastercanbothread-fromandwrite-toanyoftheSlave
unitsbyaddressingthemindividually.OnaMulti-Mas-
terbustheMastersfollowanarbitrationschemeto
ensurethatthebusisnotcorrupted.
EachdeviceattachedtotheI
2
Cbusisassigneda
uniqueaddress.WhenaMasterwishestoinitiatea
datatransfer,itfirsttransmitstheaddressofthedevice
thatitwishesto“talk”to.Alldevices“listen”toseeifthis
istheiraddress.Withinthisaddress,abitspecifies
whethertheMasterwishestoread-fromorwrite-tothe
Slavedevice.
Theoutputstagesofeachdeviceonthebus,attached
totheclock(SCL)anddata(SDA)lines,musthavean
open-drainoropen-collectorinordertoperformthe
wired-ANDfunctionofthebus.Externalpull-up
resistorsareusedtoensureahighlevelwhenno
deviceispullingthelinedown.Theonlylimitationon
thenumberofdevicesthatmaybeattachedtothebus
isthemaximumbusloadingspecification.Forcomplete
busspecifications,refertoPhilips/Signeticsdocument
“TheI
2
C-busandHowtoUseIt”(www.semiconduc-
tors.philips.com).MUseoftheSSPModuleintheI2CMulti-MasterEnvironmentAN578INITIATINGANDTERMINATINGAuthor:ScottFinkMicrochipTechnologyInc.DATATRANSFERDuringtimesofnodatatransfer(idletime),boththeINTRODUCTIONSCLandSDAlinesarepulledhigh.AMasterdevicewhichwishestotakecontrolofthebusmustrstgen-TheInter-IC(I2C)busisatwo-wireserial
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