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7ConfiguringtheBoard
7.1ProgrammingandTestingConfiguration(USBCableAttached)—DefaultConfiguration
7.2ProgrammingConfiguration(USBCableAttached)
AUX
Usingexternal
3.3Vsupply
UsingonlyUSB
powersupply
7.3TestingConfigurationfromaSavedConfiguration(withUSBCableRemovedAfter
ConfiguringtheBoard
TheCDCE421EVMcanbepoweredfromtheUSBpowersupplyorfromanexternalsource.The
CDCE421EVMonlyneedsaUSBcableattachedforprogrammingpurposes;however,fortest
measurementsitisrecommendedtoalsouseanexternal3.3Vpowersupply.Testmeasurementscan
alsobetakenwithonlytheUSBsuppliedpower.NotethatbecauseofUSBpowervariance,resultsmay
degrade.ItisalsopossibletoprogramtheCDCE421andthendisconnecttheUSBcablewithminorboard
configurationchanges.Toenablepowerandprogrammingofanyofthefourblocksonthe
CDCE421EVM,therespectiveswitchmustbeturnedonasexplainedearlier.
Bydefault,theCDCE421EVMisconfiguredtooperatewiththeUSBcableattachedanda3.3Vpower
supplyaddedtoAUXVDDandGND.Inthisconfiguration,theUSBmicrocontrollerispoweredbytheUSB
port5VsupplywhiletheCDCE421ispoweredbythe3.3Vexternalsupply.Thissetupisoptimalfor
programmingtheCDCE421devicewhilealsotakingmeasurements.Thisconfigurationremovesthe
powervariationsinherentwithUSBpowersuppliesbyisolatingtheCDCE421fromtheUSBsupply.
TheCDCE421EVMcanalsousepowersuppliedthroughtheUSBcableasitssolepowersource.
However,becauseofpower-supplyvarianceintheUSBsupply,thisconfigurationisnotrecommendedfor
mostmeasurements.Usersareadvisedtoenablethissetupforsavingconfigurationsettingstothe
CDCE421andlaterpoweringthedevicefromitsinternalmemory.(Thisoptionisusefulifthereisnota
USBportavailableinalabortestarea.)Inthisconfiguration,JP1mustbemovedfromitsdefaultposition
tothenewpositionshowninFigure8.TheEnableonboardpowercheckboxmustbeselectedonthe
EVMsoftware,followedbypushingtheApplybutton(seeFigure5).
Figure8.JP1SettingforUSBProgrammingConfiguration
Programming)
WhenoperatingtheCDCE421withouttheUSBprogrammingcable(usefulinlabsettingswhereaPCis
notimmediatelyavailableatalabstation),theCDCE421EVMmustbepreprogrammedinoneofthetwo
configurationsdiscussedabove,andthenreconfiguredforexternalpowersupplyusage.
Beforemakingtheseboardmodifications,theCDCE421settingsmustbesavedwithoneofthetwoUSB
cableattachedconfigurations.TheWriteChronosSettingstoEEPROMNOLOCKINGsoftwarebutton
mustbeusedtosavetheCDCE421settingstoitsinternalEEPROM.Afterthesettingsaresaved,the
USBcablecanberemoved.Oncethecablehasbeendisconnected,JP1shouldbeintheUsingExternal
3.3VSupplyposition(asshowninFigure8).TheEVMisnowreadyforusewithouttheUSBcable
connected.TheCDCE421willalwaysstartfromitssavedconfigurationstateinthismode.
IftheCDCE421mustbeisolatedfromthemicrocontroller,theswitchcorrespondingtotheblockinuse
shouldbesettoOFFforCE_x,SDATA_x,andLVPECL_TERM_xwherexrepresentstheblockname
(seeFigure9).Thepowerlineswitchfortherespectiveblock,however,shouldremainon.Thissequence
alsoallowstheusertoremovetheUSBcablewithoutaffectingperformancewhiletheCDCE421is
poweredon.
SCAU020–March200710.9MHz–1175MHzLowPhaseNoiseClockEvaluationBoard13
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