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3.4.2VerticalSynchronization
BT.656andY/CModeFieldandFrameOperation
Table3-6.BT.656andY/CModeCaptureOperation(continued)
VCxCTLBit
CONFRAMECF2CF1Operation
1001Continuousfield1capture.Captureonlyfield1.F1Cissetafterfield1
captureandcausesCCMPxtobeset(CCMPxinterruptcanbedisabled).The
videoportcontinuescapturingfield1fields,regardlessofthestateofF1C.
1010Continuousfield2capture.Captureonlyfield2.F2Cissetafterfield2
captureandcausesCCMPxtobeset(CCMPxinterruptcanbedisabled).The
videoportcontinuescapturingfield2fields,regardlessofthestateofF2C.
1011Reserved
1100Continuousframecapture.Capturebothfields.FRMCissetafterfield2
captureandcausesCCMPxtobeset(CCMPxinterruptcanbedisabled).The
videoportcontinuescapturingframes,regardlessofthestateofFRMC.
1101Continuousprogressiveframecapture.Capturefield1.FRMCissetafterfield
1captureandcausesCCMPxtobeset(CCMPxinterruptcanbedisabled).
Thevideoportcontinuescapturingframes,regardlessofthestateofFRMC.
(Functionsidenticallytocontinuousfield1capturemodeexcepttheFRMCbit
isusedinsteadoftheF1Cbit.)
1110Reserved
1111Reserved
Thevideoportusesacapturewindowtodeterminewhichincomingdatasamplestocaptureineachfield.
Thecapturemoduleusesaverticallinecounter(VCOUNT)totrackwhichvideolineiscurrentlybeing
received.Thelinecounteriscomparedtotheappropriatecapturewindowstart(VCYSTART1or
VCYSTART2)andstop(VCYSTOP1orVCYSTOP2)valuesforthecurrentfieldtodetermineifthecurrent
lineiswithinthecapturewindow.Inordertocorrectlyalignthecapturewindowwithinthefield,thecapture
modulemustknowwhichlineshouldcorrespondtothefirstlineofthefield,thatis,whentoresettheline
counter.Thispointmayvarydependingonthetypeofcapturebeingperformedandthesignalsavailable
forverticalsynchronization.Thevideoportallowstheverticalcounterresettriggertobedeterminedby
programmingtheEXCandVRSTbitsinVCxCTL.TheencodingofthesebitsisshowninTable3-7.Note
thatVModes2and3areonlyavailableforsinglechanneloperation(channelA).
Table3-7.VerticalSynchronizationProgramming
VCxCTLBit
VModeEXCVRSTVerticalCounterResetPoint
000FirstEAVwithV=1afterEAVwithV=0-beginningofverticalblankingperiod.
VCOUNTincrementsoneachEAV.
101FirstEAVwithV=0afterEAVwithV=1-firstactiveline.VCOUNTincrementsoneach
EAV.
210OnHCOUNTresetafterVCTL2inputactiveedge-beginningofverticalblankingor
verticalsyncperiod.(VCTL2mustbeconfiguredasverticalcontrolsignal).VCOUNT
incrementswhenHCOUNTisreset.
311OnHCOUNTresetafterVCTL2inputinactiveedge-endofverticalsyncorfirstactive
scanline.(VCTL2mustbeconfiguredasverticalcontrolsignal).VCOUNTincrements
whenHCOUNTisreset.
VMode0isusedforBT.656orY/Ccapture(withembeddedcontrol)andcorrespondstomostdigitalvideo
standardsthatnumberlinesbeginningwiththestartofverticalblanking.VMode1canalsobeusedfor
BT.656orY/Ccapturebutcountsfromthefirstactivevideoline.Thismakesfielddetectionmore
straightforwardinsomeinstances(seeSection3.4.4)andallowstheVCYSTARTnbittobesetto1,but
alsohastheeffectofassociatingverticalblankingperiodswiththeendofthepreviousfieldratherthanthe
beginningofthecurrentfield.(ThiscouldbeanissuewhencapturingVBIdata.)VCOUNToperationfor
VMode0andVMode1isshowninFigure3-4.
SPRUEM1–May2007VideoCapturePort53
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