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3.1VideoCaptureModeSelection
3.2BT.656VideoCaptureMode
3.2.1BT.656CaptureChannels
3.2.2BT.656TimingReferenceCodes
VideoCaptureModeSelection
ThevideocapturemoduleoperatesinoneoffivemodesaslistedinTable3-1.Thetransportchannel
interface(TCI)selectionismadeusingtheTCIbitinthevideoportcontrolregister(VPCTL).TheCMODE
bitsareinthevideocapturechannelxcontrolregister(VCxCTL).TheY/Cand16-bitrawcapturemodes
mayonlybeselectedforchannelAandonlyiftheDCDISbitinVPCTLisclearedto0.
Whenoperatingasarawvideocapturechannel,nodataselectionordatainterpretationisperformed.The
16-bitrawcapturemodeisdesignedtoacceptdatafromA/Dconverterswithresolutionhigherthaneight
bits(used,forexample,inmedicalimaging).
Table3-1.VideoCaptureModeSelection
TCIBitCMODEBitsModeDescription
00008-BitITU-RBT.656CaptureDigitalvideoinputisinYCbCr4:2:2with8-bitresolution
multiplexedinITU-RBT.656format.
00108-BitRawCaptureRaw8-bitdatacaptureatsamplingratesupto80MHZ.
01008-BitY/CCaptureDigitalvideoinputisinYCbCr4:2:2with8-bitresolutionon
parallelYandCb/Crmultiplexedchannels.
011016-BitRawCaptureRaw16-bitdatacaptureatsamplingratesupto80MHZ.
1010TCICapture8-bitparallelTCIcaptureatratesupto30MHZ.
TheBT.656capturemodecaptures8-bit4:2:2lumaandchromadatamultiplexedintoasingledata
stream.VideodataisconveyedintheorderCb,Y,Cr,Y,Cb,Y,Cr,etc.wherethesequenceCb,Y,Cr
referstoco-sitedlumaandchromasamplesandthefollowingYvaluecorrespondstothenextluminance
sample.Thedatastreamisde-multiplexedandeachcomponentiswritteninpackedformintoseparate
FIFOsfortransferintoY,Cb,andCrbuffersinDSPmemory.(Thisiscommonlycalledplanarformat).
InBT.656videocapturemode,databytesinwhichthe8bitsareallsetto1(FFh)orareallsetto0(00h)
arereservedfordataidentificationpurposesandconsequently,only254ofthepossible2568-bitwords
maybeusedtoexpresssignalvalue.
Indualchanneloperation,thevideoportcansupportcaptureoftwoBT.656datastreamsoroneBT.656
datastreamandonerawdatastream.Inthelattercase,theBT.656streammayoccuroneitherChannel
AorChannelB.Ineithercase,theBT.656stream(s)musthaveembeddedtimingreferencecodesand
theappropriateVCTLinputmustbeusedasaCAPENsignal.
Iftheportisconfiguredforsinglechanneloperation,capturewilltakeplaceonChannelAonly.The
unusedhalfoftheVDATAbusmaybeusedforGPIOorforanotherperipheralfunction.Forsingle
channeloperation,non-standardBT.656datastreamswithoutembeddedtimingreferencecodesare
supportedthroughtheuseofthetimingcontrol(VCTL)inputsignals.
Forstandarddigitalvideo,therearetworeferencesignals,oneatthebeginningofeachvideodatablock
(startofactivevideo,SAV),andoneattheendofeachvideoblock(endofactivevideo,EAV).
(TechnicallyeachlinebeginswiththeEAVcodeandendsjustbeforethesubsequentEAVcode.)Each
timingreferencesignalconsistsofafoursamplesequenceinthefollowingformat:FFh,00h,00h,XYh.
(TheFFhand00hvaluesarereservedforuseinthesetimingreferencesignals.)Thefirstthreebytesare
afixedpreamble.Thefourthbytecontainsinformationdefiningfieldidentification,thestateoffield
blankingandstateoflineblanking.Theassignmentofthesebitswithinthetimingreferencesignalislisted
inTable3-2.
46VideoCapturePortSPRUEM1–May2007
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