Datasheet

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3.8.5SAPInputtoSAPOutput—ProcessingFlow
TAS3108,TAS3108IA
AUDIODIGITALSIGNALPROCESSORS
SLES152BOCTOBER2005REVISEDNOVEMBER2007
AllSAPdataformatoptionsotherthanI
2
Sresultinatwo-sampledelayfrominputtooutput,asshownin
Figure3-7.IfI
2
SformattingisusedforboththeinputSAPandtheoutputSAP,thepolarityofLRCLKin
Figure3-7mustbeinverted.However,ifI
2
Sformatconversionsareperformedbetweeninputandoutput,
thedelaybecomeseither1.5samplesor2.5samples,dependingontheprocessingclockfrequency
selectedfortheaudioDSPcorerelativetothesamplerateoftheincomingdata.
TheI
2
SformatusesthefallingedgeofLRCLKtobeginasampleperiod,whereasallotherformatsuse
therisingedgeofLRCLKtobeginasampleperiod.ThismeansthattheinputSAPandaudioDSPcore
operateonsamplewindowsthatare180°outofphase,withrespecttothesamplewindowusedbythe
outputSAP.ThisphasedifferenceresultsintheoutputSAPoutputtinganewdatasampleatthemidpoint
ofthesampleperiodusedbytheaudioDSPcoretoprocessthedata.Iftheprocessingcyclecompletes
allprocessingtasksbeforethemidpointoftheprocessingsampleperiod,theoutputSAPoutputsthis
processeddata.However,iftheprocessingtimeextendspastthemidpointoftheprocessingsample
period,theoutputSAPoutputsthedataprocessedduringthepreviousprocessingsampleperiod.Inthe
formercase,thedelayfrominputtooutputis1.5samples.Inthelattercase,thedelayfrominputtooutput
is2.5samples.
Therefore,delayfrominputtooutputcanbeeither1.5or2.5sampletimeswhendataformatconversions
areperformedthatinvolvetheI
2
Sformat.However,whichdelaytimeisobtainedforaparticular
applicationisdeterminableandfixedforthatapplication,providingcareistakenintheselectionof
MCLKI/XTALIwithrespecttotheincomingsampleclock,LRCLK.
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