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1、Electricboilertemperaturesystem1.MCUAmicrocontroller(orMCU)isacomputer-on-a-chip.Itisatypeofmicroprocessoremphasizingself-sufficiencyandcost-effectiveness,incontrasttoageneral-purposemicroprocessor(thekindusedinaPC).Themajorityofcomputersystemsinusetodayareembedde
2、dinothermachinery,suchastelephones,clocks,appliances,vehicles,andinfrastructure.Anembeddedsystemusuallyhasminimalrequirementsformemoryandprogramlengthandmayrequiresimplebutunusualinput/outputsystems.Forexample,mostembeddedsystemslackkeyboards,screens,disks,printer
3、s,orotherrecognizableI/Odevicesofapersonalcomputer.Theymaycontrolelectricmotors,relaysorvoltages,andreadswitches,variableresistorsorotherelectronicdevices.Often,theonlyI/Odevicereadablebyahumanisasinglelight-emittingdiode,andseverecostorpowerconstraintscanevenelim
4、inatethat.Incontrasttogeneral-purposeCPUs,microcontrollersdonothaveanaddressbusoradatabus,becausetheyintegratealltheRAMandnon-volatilememoryonthesamechipastheCPU.Becausetheyneedfewerpins,thechipcanbeplacedinamuchsmaller,cheaperpackage.Integratingthememoryandotherp
5、eripheralsonasinglechipandtestingthemasaunitincreasesthecostofthatchip,butoftenresultsindecreasednetcostoftheembeddedsystemasawhole.(EvenifthecostofaCPUthathasintegratedperipheralsisslightlymorethanthecostofaCPU+externalperipherals,havingfewerchipstypicallyallowsa
6、smallerandcheapercircuitboard,andreducesthelaborrequiredtoassembleandtestthecircuitboard).Thistrendleadstodesign.Amicrocontrollerisasingleintegratedcircuit,commonlywiththefollowingfeatures:centralprocessingunit-rangingfromsmallandsimple4-bitprocessorstosophisticat
7、ed32-or64-bitprocessorsinput/outputinterfacessuchasserialports(UARTs)otherserialcommunicationsinterfaceslikeI²C,SerialPeripheralInterfaceandControllerAreaNetworkforsysteminterconnectperipheralssuchastimersandwatchdogRAMfordatastorageROM,EPROM,EEPROMorFlashmemoryfo
8、rprogramstorageclockgenerator-oftenanoscillatorforaquartztimingcrystal,resonatororRCcircuitmanyincludeanalog-to-digitalconverters.Thisintegrationdrastic
