Juriya tashar bas ta CAN gabaɗaya 120 ohms. A zahiri, lokacin zayyana, akwai igiyoyin juriya 60 ohms, kuma akwai gabaɗaya 120Ω nodes guda biyu akan bas ɗin. Ainihin, mutanen da suka san ƙaramin bas na CAN kaɗan ne. Kowa ya san wannan.
Akwai sakamako guda uku na juriya ta tashar bas ta CAN:
1. Haɓaka ikon hana tsangwama, bari siginar babban mita da ƙananan makamashi tafi da sauri;
2. Tabbatar cewa bas ɗin ya shiga cikin sauri a cikin yanayin ɓoye, don haka makamashin capacitors na parasitic zai yi sauri;
3. Inganta ingancin siginar kuma sanya shi a kan ƙarshen bas ɗin don rage ƙarfin tunani.
1. Inganta iyawar hana tsangwama
Bus ɗin CAN yana da jihohi biyu: “bayyanannu” da “boye”. "Expressive" yana wakiltar "0", "boye" yana wakiltar "1", kuma mai karɓar CAN ya ƙaddara. Hoton da ke ƙasa wani tsari ne na tsarin ciki na CAN transceiver, da bas ɗin haɗin Canh da Canl.
Lokacin da bas ɗin ya fito fili, Q1 da Q2 na ciki suna kunna, da bambancin matsa lamba tsakanin gwangwani da gwangwani; lokacin da aka yanke Q1 da Q2, Canh da Canl suna cikin yanayi mara kyau tare da bambancin matsa lamba na 0.
Idan babu kaya a cikin motar bas, ƙimar juriya na bambancin lokacin ɓoye yana da girma sosai. Bututun MOS na ciki shine babban juriya. Tsangwama na waje kawai yana buƙatar ƙaramin ƙarfi don ba da damar bas ɗin damar shiga bayyane (mafi ƙarancin ƙarfin wutar lantarki na babban sashin transceiver. Kawai 500mv). A wannan lokacin, idan akwai tsangwama na samfuri daban-daban, za a sami sauye-sauye a cikin motar bas, kuma babu wani wuri don waɗannan sauye-sauyen da za su shafe su, kuma zai haifar da matsayi na musamman a kan bas.
Sabili da haka, don haɓaka ikon hana tsangwama na bus ɗin ɓoye, zai iya haɓaka juriya na ɗaukar nauyi, kuma ƙimar juriya tana da ƙanƙanta don hana tasirin mafi yawan kuzarin amo. Koyaya, don gujewa wuce gona da iri na bas na yanzu don shigar da bayyane, ƙimar juriya ba zata iya zama ƙanƙanta ba.
2. Tabbatar da shigar da sauri cikin yanayin ɓoye
A lokacin bayyananniyar yanayin, za a caje na'urar bas ɗin parasitic na bas ɗin, kuma waɗannan capacitors ɗin suna buƙatar fitarwa lokacin da suka dawo cikin ɓoye. Idan ba a sanya nauyin juriya tsakanin CANH da Canl ba, za a iya zubar da ƙarfin kawai ta hanyar juriya na daban a cikin mai ɗaukar hoto. Wannan impedance yana da girman gaske. Dangane da halayen da'irar tacewar RC, lokacin fitarwa zai yi tsayi sosai. Mun ƙara 220pf capacitor tsakanin Canh da Canl na transceiver don gwajin analog. Matsayin matsayi shine 500kbit/s. Ana nuna siginar igiyar ruwa a cikin adadi. Rushewar wannan sigar igiyar igiyar ruwa jiha ce mai tsayi.
Domin fitar da sauri bas capacitors parasitic capacitors da kuma tabbatar da cewa bas ɗin ya shiga cikin ɓoyayyun yanayin da sauri, ana buƙatar ɗaukar juriya tsakanin CANH da Canl. Bayan ƙara resistor 60Ω, ana nuna siginar igiyoyin a cikin adadi. Daga adadi, lokacin da za a iya komawa koma bayan tattalin arziki a bayyane zuwa 128ns, wanda yayi daidai da lokacin kafa bayyane.
3. Inganta ingancin sigina
Lokacin da siginar yana da girma a babban juzu'in juzu'i, ƙarfin siginar siginar zai haifar da siginar siginar lokacin da rashin daidaituwa ba ta dace ba; da tsarin geometric na watsa na USB giciye sashe canje-canje, da halaye na na USB za su canza sa'an nan, da kuma tunani zai haifar da tunani. Mahimmanci
Lokacin da aka nuna makamashi, nau'in igiyar igiyar ruwa wanda ke haifar da tunani an cika shi tare da nau'i na asali, wanda zai haifar da kararrawa.
A ƙarshen kebul ɗin bas, saurin canje-canje a cikin impedance yana haifar da tunanin ƙarfin sigina, kuma ƙararrawar tana haifar da siginar bas. Idan kararrawa ta yi girma sosai, zai shafi ingancin sadarwa. Za'a iya ƙara mai tsayayyar tashoshi tare da daidaitattun halayen halayen kebul zuwa ƙarshen kebul, wanda zai iya ɗaukar wannan ɓangaren makamashi kuma ya guje wa haɓakar karrarawa.
Sauran mutane sun gudanar da gwajin analog (hotunan da ni ne na kwafi), adadin matsayi ya kasance 1MBIT/s, transceiver Canh da Canl sun haɗa kusan layukan murɗi na 10m, kuma an haɗa transistor zuwa resistor 120Ω don tabbatar da lokacin juyawa na ɓoye. Babu kaya a ƙarshe. Ana nuna siginar ƙarshen siginar a cikin adadi, kuma siginar da ke tashi yana bayyana kararrawa.
Idan an ƙara resistor 120Ω a ƙarshen murɗaɗɗen layi, siginar siginar ƙarshen yana inganta sosai, kuma kararrawa ta ɓace.
Gabaɗaya, a cikin topology madaidaiciya, duka ƙarshen kebul sune ƙarshen aikawa da ƙarshen karɓa. Don haka, dole ne a ƙara juriya ɗaya tasha a duka ƙarshen kebul ɗin.
A cikin ainihin tsarin aikace-aikacen, bas ɗin CAN gabaɗaya ba cikakkiyar ƙirar bas ba ce. Sau da yawa shi ne cakudaccen tsari na nau'in bas da nau'in tauraro. Daidaitaccen tsarin bas ɗin CAN na analog.
Me yasa zabar 120Ω?
Menene impedance? A kimiyyar lantarki, ana kiran cikas ga halin yanzu a cikin da'ira sau da yawa impedance. Naúrar impedance ita ce Ohm, wanda galibi Z ke amfani dashi, wanda shine jam'i z = r+i (ωl – 1/(ωc)). Musamman, impedance za a iya raba kashi biyu, juriya (ainihin sassa) da lantarki juriya (virtual sassa). Juriya na lantarki kuma ya haɗa da ƙarfin ƙarfi da juriya na azanci. A halin yanzu da capacitors ke haifar da shi ana kiransa capacitance, kuma na yanzu da inductance ke haifarwa ana kiransa sensory resistance. Maƙasudin a nan yana nufin ƙirar Z.
Za'a iya samun ma'anar impedance na kowane kebul ta hanyar gwaje-gwaje. A gefe ɗaya na kebul ɗin, janareta na raƙuman murabba'i, ɗayan ƙarshen yana haɗe zuwa resistor mai daidaitacce, kuma yana lura da yanayin juriya ta hanyar oscilloscope. Daidaita girman ƙimar juriya har sai siginar da ke kan juriya ta kasance kyakkyawan raƙuman raƙuman ƙararrawa mara kyau: matching impedance da amincin sigina. A wannan lokacin, ana iya la'akari da ƙimar juriya daidai da halaye na kebul.
Yi amfani da igiyoyi guda biyu na yau da kullun da motoci biyu ke amfani da su don karkatar da su zuwa layukan karkatattun, kuma ana iya samun tasirin yanayin ta hanyar da ke sama ta kusan 120Ω. Wannan kuma shine juriyar juriya ta ƙarshe da ma'aunin CAN ya ba da shawarar. Don haka ba a ƙididdige shi bisa ainihin halayen katako na layi. Tabbas, akwai ma'anoni a cikin ma'aunin ISO 11898-2.
Me yasa dole in zaɓi 0.25W?
Dole ne a lissafta wannan a hade tare da wasu matsayin gazawa. All musaya na mota ECU bukatar la'akari short-circuit zuwa wuta da kuma short-circuit zuwa ƙasa, don haka mu ma bukatar mu yi la'akari da gajeren kewaye da wutar lantarki na CAN bas. Bisa ga ma'auni, muna buƙatar la'akari da gajeren kewayawa zuwa 18V. Yin la'akari da cewa CANH yana takaice zuwa 18V, halin yanzu zai gudana zuwa Canl ta hanyar juriya ta ƙarshe, kuma saboda ikon 120Ω resistor shine 50mA * 50mA * 120Ω = 0.3W. Yin la'akari da raguwar adadin a babban zafin jiki, ƙarfin juriya na ƙarshe shine 0.5W.
Lokacin aikawa: Jul-08-2023
