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DETAILEDPINDESCRIPTIONS
CPPE
CPUSB
SHDN
STBY
RCLKEN
PERST
TPS2231
TPS2236
SLVS536B–JULY2004–REVISEDJANUARY2005
alogiclowlevelonthisinputindicatesthatthecardpresentsupportspciexpressfunctions.cppeconnectsto
theauxininputthroughaninternalpullup.whenacardisinserted,cppeisphysicallyconnectedtogroundif
thecardsupportspciexpressfunctions.
alogiclowlevelonthisinputindicatesthatthecardpresentsupportsusbfunctions.cpusbconnectstothe
auxininputthroughaninternalpullup.whenacardisinserted,cpusbisphysicallyconnectedtogroundifthe
cardsupportsusbfunctions.
whenasserted(logiclow),thisinputinstructsthepowerswitchtoturnoffallvoltageoutputsandthedischarge
fetsareactivated.shdnhasaninternalpullupconnectedtoauxin.
whenasserted(logiclow)afterthecardisinserted,thisinputplacesthepowerswitchinstandbymodeby
turningoffthe3.3-vand1.5-vpowerswitchesandkeepingtheauxswitchon.ifassertedpriortothecardbeing
呈现,stbyplacesthepowerswitchinoffmodebyturningofftheaux,3.3-v,and1.5-vpowerswitches.
stbyhasaninternalpullupconnectedtoauxin.
thispinservesasbothaninputandanoutput.onpowerup,adischargefetkeepsthissignalatalowstateas
longasanyoftheoutputpowerrailsareoutoftheirtolerancerange.oncealloutputpowerrailsarewithin
容忍,theswitchreleasesrclkenallowingittotransitiontoahighstate(internallypulleduptoauxin).
ThetransitionofRCLKENfromalowtoahighstatestartsaninternaltimerforthepurposeofdeasserting
perst.asaninput,rclkencanbekeptlowtodelaythestartoftheperstinternaltimer.
becauserclkenisinternallyconnectedtoadischargefet,thispincanonlybedrivenlowandshouldnever
bedrivenhighasalogicinput.whenanexternalcircuitdrivesthispinlow,rclkenbecomesaninput;
否则,thispinisanoutput.
rclkencanbeusedbythehostsystemtoenableaclockdriver.
onpowerup,thisoutputremainsasserted(logiclevellow)untilallpowerrailsarewithintolerance.onceall
powerrailsarewithintoleranceandrclkenhasbeenreleased(logichigh),perstisdeasserted(logichigh)
afteratimedelayasshownintheparametrictable.onpowerdown,thisoutputisassertedwheneveranyofthe
powerrailsdropbelowtheirvoltagetolerance.
theperstsignalisanoutputfromthehostsystemandaninputtotheexpresscardmodule.thissignalisonly
usedbypciexpress-basedmodulesanditsfunctionistoplacetheexpresscardmoduleinaresetstate.
duringpowerup,powerdown,orwheneverpowertotheexpresscardmoduleisnotstableornotwithinvoltage
tolerancelimits,theexpresscardstandardrequiresthatperstbeasserted.asaresult,thissignalalsoserves
asapower-goodindicatortotheexpresscardmodule,andtherelationshipbetweenthepowerrailsandperst
areexplicitlydefinedintheexpresscardstandard.
thehostcanalsoplacetheexpresscardmoduleinaresetstatebyassertingasystemresetsysrst.这个
systemresetgeneratesapersttotheexpresscardmodulewithoutdisruptingthevoltagerails.thisiswhatis
normallycalleda
warm
重置.不管怎样,ina
cold
startsituation,thesystemresetcanalsobeusedtoextendthe
lengthoftimethatperstisasserted.
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