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SPI总线A/D接口及程序设计12位，4通道串行总线A/D转换器ADS7841同步三线串行接口SPI总线标准应用领域芯片内部结构PINCONFIGURATIONSPINDESCRIPTIONS（1）PINDESCRIPTIONS（2）MAINELECTRICALCHARACTERISTICS:+5VTHEORYOFOPERATION(1)THEORYOFOPERATION(1)FIGURE1:BASICOPERATIONOFTHEADS7841.FIGURE2.SIMPLIFIEDDIAGRAMOFTHEANALOGINPUT.ANALOGINPUTREFERENCEINPUT(1)REFERENCEINPUT(2)REFERENCEINPUT(3)REFERENCEINPUT(4)FIGURE3.CONVERSIONTIMING,24-CLOCKSPERCONVERSION,8-BITBUSINTERFACE.NODCLKDELAYREQUIREDWITHDEDICATEDDIGITALINTERFACE(1)DIGITALINTERFACE(2)DIGITALINTERFACE(3)FIGURE3.CONVERSIONTIMING,24-CLOCKSPERCONVERSION,8-BITBUSINTERFACE.NODCLKDELAYREQUIREDWITHDEDICATEDCONTROLBYTE控制字节TABLEIV.DESCRIPTIONSOFTHECONTROLBITSWITHINTHECONTROLBYTE.TheMODEbitandtheMODEpinworktogethertodeterminethenumberofbitsforagivenconversion.IftheMODEpinisLOW,theconverteralwaysperformsa12-bitconversionregardlessofthestateoftheMODEbit.IftheMODEpinisHIGH,thentheMODEbitdeterminesthenumberofbitsforeachconversion,either12bits(LOW)or8bits(HIGH).TheSGL/DIFbitcontrolsthemultiplexerinputmode:eithersingle-ended(HIGH)ordifferential(LOW).Insingle-endedmode,theselectedinputchannelisreferencedtotheCOMpin.Indifferentialmode,thetwoselectedinputsprovideadifferentialinput.SeeTablesIandIIandFigure2formoreinformation.Thelasttwobits(PD1-PD0)selectthepowerdownmode,asshowninTableV.IfbothinputsareHIGH,thedeviceisalwayspoweredup.IfbothinputsareLOW,thedeviceentersapower-downmodebetweenconversions.Whenanewconversionisinitiated,thedevicewillresumenormaloperationinstantly—nodelayisneededtoallowthedevicetopowerupandtheveryfirstconversionwillbevalid.读取AD转换结果流程程序举例（1）写一个字节程序举例（2）读一个字节
