KEELOQ跳码介绍

RemoteControlSystems

RemotecontrolviaRForIRispopularformanyappli-cations,includingvehiclealarmsandautomaticgarage

doors.Conventionalremotecontrolsystemsarebased

onunidirectionaltransmissionandhavelimitedsecu-rity.Moresophisticateddevicesbasedonbidirectional

transmissionarealsoavailablebut,becauseoftheir

highcostandcertainpracticaldisadvantages,theyare

notwidelyusedincommercialremotecontroldevices.

Thepopularunidirectionaltransmissionsystemscur-rentlyhavetwoveryimportantsecurityshortcomings:

thecodestheytransmitareusuallyfixedandthenum-berofpossiblecodecombinationsisrelativelysmall.

Eitheroftheseshortcomingscanleadtounauthorized

access.TB003AnIntroductiontoKEELOQCodeHoppingAuthor:KobusMarneweckAremotecontroltransmitterofthetypenormallyusedMicrochipTechnologyInc.invehiclesecuritysystems,isnothingbutasmallradiotransmitterthattransmitsacodenumberonacertainfrequency.ThiscodenumberisnormallygeneratedbyINTRODUCTIONanintegratedcircuitencoder.Thetransmitfrequencyisnorma