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1、SynchronousResets?AsynchronousResets?Iamsoconfused!HowwillIeverknowwhichtouse?CliffordE.CummingsDonMillsSunburstDesign,Inc.LCDMEngineeringABSTRACTThispaperwillinvestigatetheprosandconsofsynchronousandasynchronousresets.Itwillthenlookatusageofeachtypeofresetfollowedbyrecommendationsforproperusa
2、geofeachtype.Thispaperwillalsodetailaninterestingsynchronizationtechniqueusingdigitalcalibrationtosynchronizeresetremovalonamulti-ASICdesign.1.0resets,Resets,RESETS,andthenthere’sRESETSOnecannotbegintoconsideradiscussionofresetusageandstyleswithoutfirstsalutingthemostcommonresetusageofall.This
3、undesiredresetoccursalmostdailyinsystemsthathavebeentested,verified,manufactured,andintegratedintotheconsumer,education,government,andmilitaryenvironments.Thisresetfollowswhatisoftencalled“TheBlueScreenofDeath”resultingfromsoftwareincompatibilitiesbetweentheOSfromacertainsoftwarecompany,thesof
4、twareprogramstheOSisservicing,andthehardwareonwhichtheOSsoftwareisexecuting.Whybeconcernedwiththeseannoyinglittleresetsanyway?Whydevoteawholepapertosuchatrivialsubject?AnyonewhohasusedaPCwithacertainOSloadedknowsthatthehardwareresetcomesinquitehandy.Itwillputthecomputerbacktoaknownworkingstate
5、(atleasttemporarily)byapplyingasystemresettoeachofthechipsinthesystemthathaveorrequireareset.ForindividualASICs,theprimarypurposeofaresetistoforcetheASICdesign(eitherbehavioral,RTL,orstructural)intoaknownstateforsimulation.OncetheASICisbuilt,theneedfortheASICtohaveresetappliedisdeterminedbythe
6、system,theapplicationoftheASIC,andthedesignoftheASIC.Forinstance,manydatapathcommunicationASICsaredesignedtosynchronizetoaninputdatastream,processthedata,andthenoutputit.Ifsynciseverlost,theASICgoesthrougharoutinetore-acquiresync.IfthistypeofASICisdesignedcorrectly,suchthatallunusedstatespoint
7、tothe“startacquiringsync”state,itcanfunctionproperlyinasystemwithouteverbeingreset.AsystemresetwouldberequiredonpowerupforsuchanASICifthestatemachinesintheASICtookadvantageof“don’tcare”logicreductionduringthesynthesisphase.Itistheopinio
