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OVERSAMPLINGRATECONTROL
zeroflags(pcm1780/82)
零-detectcondition
零-flagoutputs
zeroflag(pcm1781)
hardwarecontrol(pcm1781)
pcm1780,pcm1781,pcm1782
SLES132A–MARCH2005–REVISEDAPRIL2005
thepcm1780/81/82automaticallycontrolstheoversamplingrateofthedelta-sigmad/aconverterswiththe
systemclockfrequency.theoversamplingrateissetto64×oversamplingwithan1152-f
S
,768-f
S
,or512-f
S
systemclock,to32×oversamplingwitha384-f
S
or256-f
S
systemclock,orto16×oversamplingwitha192-f
S
或者
128-f
S
systemclock.
zerodetectionforeachoutputchannelisindependentfromtheother.ifthedataforagivenchannelremainsata
0levelfor1024sampleperiods(orlrckclockperiods),azero-detectconditionexistsforthatchannel.
eachchannelhasacorrespondingzero-flagpin,zerol(pin1)orzeror(pin16).giventhatazero-发现
conditionexistsforoneormorechannels,thezero-flagpinsforthosechannelsaresettoalogic-1state.这
零-flagpinscanbeusedtooperateexternalmutecircuits,orusedasstatusindicatorsforamicrocontroller,
audiosignalprocessor,orotherdigitallycontrolledfunction.
theactivepolarityofthezero-flagoutputscanbeinvertedbysettingthezrevbitofcontrolregister22to1.这
resetdefaultisactive-highoutput,orzrev=0.
thel-channelandr-channelcommonzeroflagcanbeselectedbysettingtheazrobitofcontrolregister22
to1.theresetdefaultisforindependentl-channelandr-channelzeroflags,orazro=0.
onthepcm1782,zerolandzerorareopen-drainoutputs.
thepcm1781hasazero-flagpin,zeroa(pin16).zeroaisthel-channelandr-channelcommonzero-标记
管脚.ifthedataforl-channelandr-channelremainsata0levelfor1024samplingperiods(orlrckclock
时期),zeroaissettoalogic-1state.
thedigitalfunctionsofthepcm1781arecapableofhardwarecontrol.table2showsselectableformats,table3
showsde-emphasiscontrol,andtable4showsmutingcontrol.
table2.dataformatselection
fmt(pin1)dataformat
low16-to24-位,i
2
Sformat
high16-bitright-justified
table3.de-emphasiscontrol
demp1(pin3)demp0(pin2)de-emphasisfunction
LOWLOWOFF
lowhigh48-khzde-emphasison
highlow44.1-khzde-emphasison
highhigh32-khzde-emphasison
table4.mutecontrol
沉默的(pin4)mutestatus
LOWMuteOFF
HIGHMuteON
16
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