溫室大棚控制系統(tǒng)外文翻譯(編輯修改稿)
2025-09-10 11:14 本頁面
【文章內(nèi)容簡介】 18B20tofunctionwithoutalocalexternalsupply.Parasitepowerisveryusefulforapplicationsthatrequireremotetemperaturesensingorthatareveryspaceconstrained.Figure1showstheDS18B20’sparasitepowercontrolcircuitry,which“steals”powerfromthe1WirebusviatheDQpinwhenthebusishigh.ThestolenchargepowerstheDS18B20whilethebusishigh,andsomeofthechargeisstoredontheparasitepowercapacitor(CPP)toprovidepowerwhenthebusislow.WhentheDS18B20isusedinparasitepowermode,theVDDpinmustbeconnectedtoground.Inparasitepowermode,the1WirebusandCPPcanprovidesufficientcurrenttotheDS18B20formostoperationsaslongasthespecifiedtimingandvoltagerequirementsaremet(seetheDCElectricalCharacteristicsandACElectricalCharacteristics).However,whentheDS18B20isperformingtemperatureconversionsorcopyingdatafromthescratchpadmemorytoEEPROM,theoperatingcurrentcanbeashighas.Thiscurrentcancauseanunacceptablevoltagedropacrosstheweak1WirepullupresistorandismorecurrentthancanbesuppliedbyCPP.ToassurethattheDS18B20hassufficientsupplycurrent,itisnecessarytoprovideastrongpulluponthe1WirebuswhenevertemperatureconversionsaretakingplaceordataisbeingcopiedfromthescratchpadtoEEPROM.ThiscanbeacplishedbyusingaMOSFETtopullthebusdirectlytotherailasshowninFigure4.The1Wirebusmustbeswitchedtothe strongpullupwithin10μs(max) afteraConvert T[44h]orCopyScratchpad[48h]Commandisissued,andthebusmustbeheldhighbythepullupforthedurationoftheconversion(tCONV)ordatatransfer(tWR=10ms).Nootheractivitycantakeplaceonthe1Wirebuswhilethepullupisenabled.TheDS18B20canalsobepoweredbytheconventionalmethodofconnectinganexternalpowersupplytotheVDDpin,asshowninFigure5.TheadvantageofthismethodisthattheMOSFETpullupisnotrequired,andthe1Wirebusisfreetocarryothertrafficduringthetemperatureconversiontime.Theuseofparasitepowerisnotremendedfortemperaturesabove+100176。CsincetheDS18B20maynotbeabletosustainmunicationsduetothehigherleakagecurrentsthatcanexistatthesetemperatures.Forapplicationsinwhichsuchtemperaturesarelikely,itisstronglyremendedthattheDS18B20bepoweredbyanexternalpowersupply.InsomesituationsthebusmastermaynotknowwhethertheDS18B20sonthebusareparasitepoweredorpoweredbyexternalsupplies.Themasterneedsthisinformationtodetermineifthestrongbuspullupshouldbeusedduringtemperatureconversions.Togetthisinformation,themastercanissueaSkipROM[CCh]mandfollowedbyaReadPowerSupply[B4h]mandfollowedbya“readtimeslot”.Duringthereadtimeslot,parasitepowered16
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