nec协议
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nec协议
篇一：necprotocolnec协议
necprotocol
tomyknowledgetheprotocolidescribeherewasdevelopedby nec.iveseenverysimilarprotocoldescriptionsontheinte rnet,andtheretheprotocoliscalledjapaneseFormat.
idoadmitthatidontknowexactlywhodevelopedit.whatidok nowisthatitisusedinmylateVcRproducedbysanyoandwasma rketedunderthenameofFisher.necmanufacturedtheremote controlic.
thisdescriptionwastakenfromtheVcRsservicemanual.tho sewerethedays,whenservicemanualswerefulledwithusefu linformation!
Features
8bitaddressand8bitcommandlengthaddressandcommandare transmittedtwiceforreliabilitypulsedistancemodulati oncarrierfrequencyof38khzbittimeof1.125msor2.25ms modulation
thenec
protocoluses
pulsedistance
encoding
pulseisofathebits.each
560μ
slong38khzcarrierburst(about21cycles).alogical"1"ta kes2.25mstotransmit,whilealogical"0"isonlyhalfoftha t,being1.125ms.therecommendedcarrierduty-cycleis1/4 or1/3.
protocol
thepictureaboveshowsatypicalpulsetrainofthenecproto col.withthisprotocolthelsbistransmittedfirst.inthis caseaddress$59andcommand$16istransmitted.
amessageisstartedbya9msagcburst,whichwasusedtosetth egainoftheearlieriRreceivers.thisagcburstisthenfoll owedbya4.5msspace,whichisthenfollowedbytheaddressan dcommand.addressandcommandaretransmittedtwice.these condtimeallbitsareinvertedandcanbeusedforverificati onofthereceivedmessage.thetotaltransmissiontimeisco nstantbecauseeverybitisrepeatedwithitsinvertedlengt h.ifyourenotinterestedinthisreliabilityyoucanignore theinvertedvalues,oryoucanexpandtheaddressandcomman dto16bitseach!
acommandistransmittedonlyonce,evenwhenthekeyonthere motecontrolremainspressed.every110msarepeatcodeistr ansmittedforaslongasthekeyremainsdown.thisrepeatcod eissimplya9msagcpulsefollowedbya2.25msspaceanda560μsburst.
extendednecprotocol
thenecprotocolissowidelyusedthatsoonallpossibleaddr esseswereusedup.bysacrificingtheaddressredundancyth eaddressrangewasextendedfrom256possiblevaluestoappr oximately65000differentvalues.thiswaytheaddressrang ewasextendedfrom8bitsto16bitswithoutchanginganyothe rpropertyoftheprotocol.thecommandredundancyisstillp reserved.thereforeeachaddresscanstillhandle 256differentcommands.
keepinmindthat256addressvaluesoftheextendedprotocol areinvalidbecausetheyareinfactnormalnecprotocoladdr esses.wheneverthelowbyteistheexactinverseofthehighb yteitisnotavalidextendedaddress.
externallinks
examplecommands
thetablebelowliststhemessagessentbytheremotecontrol ofmylateFisher530VcR(itserveduswellduringits20years longlife).
篇二：红外遥控协议分析之：nec协议
红外遥控编码传输协议
生产厂家对红外遥控的编码做了严格的规范，目前国内