RS485 l protocol quy nh v iu ch mc tn hiu trn ng truyn cn CAN l chun quy nh v gi giao thc trn ng truyn vt l. RS485 l chun dng 1 Master- nhiu Slave, CAN c th dng multi Master - multi Slave.Chng 1 Tng quan

Thc s bn khng cn bit CAN hot ng nh th no...

mt thi gian rt di s hiu nhm c bn v mng CAN (Controller Area Network) l CAN ch c s dng trong xe t. S thc l CAN t khi c gii thiu vo nm 1986 chng minh l mt cng ngh bn vng, n gin v linh hot, do vy CAN tm c hng i vo tt c cc lnh vc ng dng cn n vi x l giao tip vi nhau.

Cng vi s dng trong lnh vc t khng th ph nhn c th cc ng dng ca CAN khng ch bao gm cc nhim v t ng ha cng nghip m cn bt k ng dng no khc m iu khin phn phi (distributed control) c li th v mt h thng bus ni tip s lc bt i dy ni tha. CAN chng t c tnh u vit hn bt k mt h thng bus-trng no khc nh vo c tnh r, c kh nng to chc nng trong mt mi trng in kh khn, mc kh nng thi gian thc cao, pht hin li tuyt vi, v c kh nng khng ch li, hu nh l mu thun vi nhng c tnh ni trc y l d s dng.

Ngy nay khng c ch thch hp c bit no cho CAN, can c s dng rng ri t bt k mt ng dng no, t v tr v hng khng, hng hi, y hc ti cc gia dng nh my git, my sy v thm ch my pha c ph.

D s dng c bit hin nhin i vi k s phn mm c trch nhim pht trin ng dng dng CAN. Trong thc t th giao thc CAN ngh l qun l truyn d liu ton b bao gm c lc chn bus, pht hin li v khng ch li v.v... c thc hin trong silicon. Cc b iu khin CAN ngm nh bit lm g v lm nh th no.

K s phn mm c "ging cp" xung ch lm chc nng c bn nh nhp cc gi tr ban u, c d liu, vit d liu, kim tra tnh trng v kt qu l ch tp trung vo phn mm ng dng thc t.

Cun sch ny dnh cho nhng ngi khng sn lng phc v nhng ngi cha bit v cho nhng ngi ham mun hiu bit tm ti gii thch ti sao CAN li d s dng v cun cng l ti sao li cc k tin cy.

1.1 Mng CAN l g?

CAN vit tt ca Controller Area Network, tm dch l "mng khu vc iu khin", hay gi n gin Mng CAN, l mt cng ngh mng ghp ni tip (a serial network technology) khi ngun c thit k dng cho cng nghip xe t, c bit cc loi xe Chu u, nhng ri tr thnh mt bus (knh) ph bin trong t ng ha cng nghip cng nh cc ng dng khc. Knh d liu CAN (CAN bus) khi u c dng cho cc h thng nhng, v nh tn bao hm l mt cng ngh mng cung cp truyn thng tin nhanh chng trong cc vi iu khin theo yu cu thi gian thc ang dn thay th cho cng ngh s dng b nh cng i (Dual-Ported RAM) t v phc tp hn nhiu.

CAN l mt h thng mng hai dy, na kp v tc cao vt tri hn hn so vi cc cng ngh ni tip thng thng nh R232 lin quan n chc nng v tin cy v vic thc hin CAN mang li hiu qu hn. V d, trong khi TPC/IP c thit k chuyn ti s lng ln d liu cn CAN c thit k theo yu cu thi gian thc v vi tc truyn d liu 1 MBit/sec d dng nh bi kt ni TPC/IP 100 Mbit/sec khi CAN c thi gian phn ng ngn, d sai s ng gi, khi phc v sa cha sai s nhanh.

Nhiu nh sn xut linh kin bn dn ch yu v d nh Motorola, Philips, Intel, Infineon v nhiu hng khc bn chp CAN, v thc t rng hng triu chp CAN c dng trong xe t m bo rng gi chp r v c th s dng c lu di. Hu ht cc nh sn xut linh lin bn dn thng kt hp UART vi thit k vi x l ca h nhm h tr giao tip ni tip cho RS232/485 ngy nay ang c khuynh hng s dng CAN.

S dng mng CAN trong hu ht cc xe Chu u v quyt nh ca cc nh sn xut xe ti v xe khng chy trn ng s dng CAN dn n vic xut hin ca chp CAN vo nm 1987. Cc th trng c khi lng cao khc nh ac1c ng dng ni a v iu khin cng nghip cng gia tng s liu bn CAN v m bo s c sn ca CAN trong tng lai.

Cc mng CAN c th dng c lm h thng thng tin nhng cho vi iu khin cng nh h thng thng tin m cho cc thit b thng minh. V d mt s ngi s dng trong lnh vc cng ngh y hc la chn CAN bi v chng p ng c yu cu an ton tuyt i.

Nhng yu cu tng t phi c xem xt bi cc nh sn xut thit b khc vi an ton rt cao v yu cu tin cy (v d nh r bt, thang my, v h thng giao thng).

Mng CAN:

L mt knh giao tip d liu ni tip tch hp cao cho cc ng dng thi gian thcC hiu qu v r hn bt k mt h thng bus ni tip no khc, k c RS232 v TCP/IPD s dng hn bt k mt h thng bus ni tip no khcHot ng tc truyn d liu ti 1 MBit trn giyC kh nng hot ng trong cc mi trng in kh khnang c s dng trong nhiu ng dng t ng ha v iu khin cng nghip khc nhauL mt tiu chun quc t: ISO 11989

1.2 Tm tt lch s pht trin CAN

tng ca mng CAN c nhm k s ti GmbH Robert Bosch, c, p t u thp nin 1980s. H nghin cu th trng cho mt cng ngh bus trng mi dng trong xe t m c th cho php h a thm cc chc nng vo na. H tp trung ch yu vo h thng thng tin gia cc b iu khin in t trong xe hi ca hng Mercedes-Benz.

Bt k mt h thng bus trng (field-bus system) da trn giao tip ni tip s gim dy ni m khi u ngi ta ch xem xt n hiu qu kha cnh cnh u im. iu khin phn phi, ngha l s dng mt h thng nhiu vi x l s thng xuyn cho mt tnh nng gia tng v trong th trng gi ca chp vi iu khin gim to ln lm cho vic s dng nhiu vi x l c th thc hin c. Nhng u im khc l lm tng tin cy, v ci tin dch v v bo tr.

Tuy nhin khng c mt giao thc giao tip no c trn th trng p ng nhng nhu cu c th cho tin cy tc d d liu truyn thng tin, kt qu l h pht trin mt tiu chun ca chnh h.

S quan tm ca nh sn xut xe - Mercedes-Benz v nh sn xut linh kin bn dn - Intel - v mt s i hc khc c gip cho vic lm mng CAN thnh cng.

Tiu chun CAN u tin c gii thiu vo nm 1986 trong hi ngh Hip hi K s t (SAE = The Society of Automative Engineers) Detroi, Michigan. Chp b iu khin CAN u tin Intel 82526 v Philips 82C2000 c gii thiu nm 1987.

T n nay c nhiu nh sn xut linh kin bn dn khc quyt nh sn xut loi b iu khin CAN c lp, hoc thc hin chng trong nhng thit k chp n.

Ch : Giao thc CAN c bo v bi bng sng ch cp cho Robert Bosch GmbH. Bosch s cp giy php s dng cho cc nh sn xut v i hc. Bn c th tm thy thng tin chi tit v giy php v tin bn quyn ti a ch:

Giy php s dng CAN ca Bosch

Khng cn giy php CAN cho cc ng dng da trn cc thit b CAN do mt nh sn xut c cp giy php cung cp.

Mt bc pht trin thnh cng CAN ng k khc l s thnh lp t chc nhm cc nh sn xut v ngi s dng quc t, gi l Hi CAN t ng ha (CiA = CAN in Automation) nm 1992, hot ng ca hi ny da trn mi quan tm, tham gia v khi xng ca cc thnh vin.

Bng sau cho chng ta tm tt mt s thi im ng nghi nh trong qu trnh pht trin v thnh lp giao thc CAN:

Bng 1.2.1 Tm tt lch s CAN

1983: Bt u d n pht trin mng trn xe hi trong ni b hng Bosch1986: Chnh thc gii thiu giao thc CAN1987: Nhng chp iu khin CAN u tin xut hin nh sn xut linh kin bn dn Intle v Philips1991: Bosch xut bn thng s k thut CAN 2.01992: Thnh lp nhm cc nh s dng v sn xut CAN quc t: Hi CAN t ng ha (CiA)1992: Hi CiA xut bn giao thc Lp ng dng CAN (CAN Application Layer, CAL)1992: Nhng chic xe Mercedes-Benz u tin c trang b CAN xut hin1993: Xut bn tiu chun ISO 118981994: CiA t chc Hi ngh CAN quc t ln th nht (iCC)1994: Allen-Bradley gii thiu giao thc DeviceNet1995: Xut bn Tiu chun ISO 11898 sa i (nh dng khung m rng)1995: CiA xut bn giao thc CANopen

Ti thi im hin nay, ngnh cng nghip t vn cn ang chim u th vic bn b iu khin CAN v b iu khin chp n tch hp vi b iu khin CAN vi t sut 80%, so vi 20% cho cc ng dng khc. T l 20% tiu biu cho cc ng dng khc nhau trong cc th trng ngoi xe t.

Hnh 2: Hnh 1.2.1 Biu s CAN (triu) s dng theo thi gian

Phn tm tt lch s pht trin CAN cng gii thch phn no u th vt tri ca cc cng ty c trong lnh vc CAN, t nht s cc kinh doanh CAN cng l mt ch s u th vt tri. Cng ngh CAN, c bit l cc giao thc lp cao dng CAN nh CANopen, DeviceNet v J1939 ngy cng c chp nhn v s dng gia tng vng Bc M m ln lt c ngha l u th vt tri (p o) s khng ph thuc vo quc gia.

1.3 Cc ng dng ca CAN

Mt cu hi thng gp lin quan n lnh vc ng dng khc ngoi xe t l CAN c s dng thnh cng trong nhng lnh vc no? Trong thc t th khng ch c mt cu tr li m c rt nhiu cu tr li. Khng c ch c bit no cho CAN, m vic s dng CAN m rng vi nhiu ng dng cng nghip t hng khng v v tr, hng hi, y hc, ti cc gia dng nh my git, my sy v thm ch c my pha c ph.

u im chnh ca h thng bus trng nh CAN l lm gim dy ni t v i hi phi bo tr nhiu kh v chng c c tnh gia tng ca h thng nhiu b vi x l (thng minh phn phi). CAN c bit thch hp cho cc h thng giao tip ni tip cn la chn khi bt buc cn ti tnh nng tuyt vi ca n.

Nhng ng dng chnh dng CAN trong cc lnh vc:

Xe khchXe ti v xe butXe khng chy trn ngTu khch v tu hngH thng in t hng hiin t my bay v hng khngT ng ha nh myiu khin my cng nghipT ng ha ta nhThang my (thang nng v thang trt)Thit b ph tng y tV bt k mt lnh vc no khc...

Ch : Hu ht cc ng dng cng nghip dang dng giao thc lp cao nh CANopen hoc DeviceNet trn nh ca lp ng dng CAN (xem thm Chng 3.5 Cc giao thc lp cao). c tnh rng khong 90% ng dng cng nghip dng CANopen lin quan t nht ti iu khin chuyn ng.

H thng CISCO, mt cng ty kt mng, s dng mng CAN con thc hin vic khi ng h thng v trao i nng (hot-swapping) trn cc bc PC ln thc hin routers (cu dn). S cc im CAN lp t nm gia khong 500.000 ti 1 triu, to thnh mt trong nhng ng dng ngoi xe t ln hn.

Mt s cng ty cng ngh cao cp ni ting khc s dng CAN cho nhiu mc ch v sn phm khc nhau v d nh Hewlett-Packard, Lockhead, Boeing, NASA, v nhiu cng ty khc.

Mt th trng quan trng khc ca CAN (kt hp vi CANopen) l trang thit b y t, khi u t cc c cu phng m nh n, bn, my quay, my chp X-quang, my siu m, v hn na l cc thit b ln hn nh my qut CAT. Nhng cng ty thit b y t chnh M gm Cng ty GE Medical, Philips Medical v Siemens Medical a s dng CAN/CANopen hn bt k mt cng ngh bus-trng no khc v kt qu l h yu cu CAN/CANopen tng thch nhau gia cc nh cung cp khc nhau.

DeviceNet, mt giao thc lp trn ph bin khc dng cho t ng ha cng nghip c bit ph hp cho t ng ha nh my v c s dng rng ri trong cng nghip ha hc v bn dn (my lm bnh xp, v cc my mc r bt khc).

Chng ta hy xt mt v d in hnh:

Mt trong nhng nhim v t ng ha c nhu cu nht theo tc v chun xc l iu khin chuyn ng (motion control). S lin kt gia b x l iu khin (v d my tnh cng nghip) vi mt b iu khin chuyn ng (v tr) tch hp v mt ng c c b phn tch tch hp hoc encoder cn c dy ni m rng. Tnh hung nhanh chng tr nn ti t hn khi m nhim v yu cu s dng nhiu trc chuyn ng. Khng ch s dy dn d dng n con s hng nghn m cn tr nn kh khn gia tng khi kt ni thm nhiu b iu khin v tr, v d, mt chic my vi tnh ch c th iu tit c mt s bng giao din. Mt yu t nan gii khc l mi tnh nng ca my tnh s ch gii hn mt im no khi n n thi im phn ng cn thit dng mi b iu khin chuyn ng.

Hnh 3: Hnh 1.3.1 Mng CANopen mu

Ch thch:stepper motor controller = b iu khin ng c bcdigital I/O = giao tip vo ra sanalog I/O = giao tip vo ra tng tDC servo controller = b iu khin ng c servoswitches = cng tc chuyn mchrelays, lamps = r le, n bosensor readings = s c cm binactuator control = b chp hnh iu khin

Gii php cho vn nan gii ny l s dng iu khin phn tn (phn phi) nh trnh din trong v d trong Hnh 1.3.1. Mi thnh phn, giao din I/O s v tng t, v mi trc chuyn ng c lm mt b iu khin ring. Lin kt mng gia cc thnh phn v b iu khin chnh c thc hin bng CAN, trong trng hp thc t l CANopen. CANopen l mt giao thc lp trn, mt phn mm ph thm pha trn ca lp lin kt vt l v d liu (tham kho Chng 3.5 Cc giao thc lp trn).

Thit k ny to ra s d dng kt ni thm cc thnh phn hu nh khng gii hn mt cch d dng (CANopen c gii hn ti 125 nt, cho phn ln cc ng dng t ng ha) m khng mt i c tnh. S cc dy ni gia cc thnh phn (phn t) gim cn hai, khng ch gim gi dy ni m cn gim thi gian bo tr v dch v trong lc khi ng my hoc trong trng hp my chy c trc trc.

S bo dng cho mi thnh phn trong mng s c ci thin nh vo s kin thc t l k s ch cn cm mt b dch v (v d mt my tnh xch tay) vo ch no trong mng nhm giao tip vi bt k mt b phn no ca mng. Vic ny c th c lm ch bng mt chng trnh phn mm dch v v tt c ct nt trong mng ni cng mt ngn ng. Khng cn phi c mt chng trnh dch v ring no dnh cho mi mt b phn ring bit.

S tit kim gi thnh t vic gim dy ni s khng th tnh c ht. Minh ha v d ny nh sau: Mt nh sn xut vng Boston sn xut my mc yu cu trong bnh c ba n 5 trc v tr trn mt my v vi trm im giao din I/O. H i tu thit k my mc s dng cc cng ngh CANopen thay cho dy dn thng thng. Tit kim gi thnh trong khong 1.500 USD trn mt my. Trong thi im bn chy hng, h bn c 500 my mt nm. Bn hy lm th mt php ton...NGHIN CU V THIT K MNG CANNG DNG TRONG CNG NGHIP

Dng Hu HongLp 08DD3N, Khoa in in t

TM TTTc pht trin nhanh chng ca cng ngh vi in t, k thut truyn thng v cng ngh phn mm trong nhng nm gn y to s chuyn bin c bn trong hng i cho cc gii php t ng ha cng nghip. Xu hng phn tn, mm ha v chun ha l ba trong nhiu im c trng c s thay i ny. Nhng xu hng mi khng nm ngoi mc ch gim gi thnh gii php v nng cao cht lng h thng. S ng dng rng ri cc h thng mng truyn thng cng nghip, c bit cc h thng bus trng (field bus) l mt v d tiu biu.Mng truyn thng cng nghip khng phi l mt lnh vc k thut hon ton mi m thc cht l cc cng ngh c k tha, cht lc v pht trin t k thut truyn thng cho ph hp vi cc yu cu trong cng nghip. iu ny th hin ch, mi mt ngi hot ng trong lnh vc iu khin t ng ha u bit t nhiu v n, c th ni v n, ngay c khi cha c mt cun sch c th no v mng cng nghip, v cng ngh bus trng. T hn mt thp k nay, cng ngh bus trng tr nn khng th thiu c trong cc h thng iu khin v gim st hin i. Song, thc t ngi s dng trong cng nghip thng gp phi hng lot cc vn khc nhau, mc d rt c bn, nhng khng c cp cc ti liu thuc lnh vc mng truyn thng ph thng (v d nh mng my tnh, mng vin thng).Vn t ra trc tin khi xy dng mt gii php t ng khng cn l nn hay khng nn m l la chn h thng mng truyn thng no cho ph hp vi yu cu v nhim v ca ng dng trong thc t. V d, gii php bus trng no c th tha mn yu cu v cu trc h thng v tnh nng thi gian thc ca ng dng?Thc trng hin ti c rt nhiu h thng mng cng nghip, t mng n gin gm mt vi thit b ti cc h thng mng c quy m ln hn v cc h thng SCADA trong cc nh my x nghip. Nh ni trn, vn khng phi l nn hay khng nn xy dng h thng mng m l la chn m hnh mng thch hp cho mi nhu cu ng dng ring bit. Vit Nam, mng truyn thng cng nghip c nhng bc i r rt, v c nhng m hnh mng phong ph. Tuy nhin, h thng mng CAN (Controller Area Network) l mt h thng mng tuyt vi nhng li khng my c ph bin ti nc ta c v mt ti liu cng nh mt ng dng. Thc t th mng cng nghip nc ta u do k s nc ngoi thit k v h s dng ng dng CAN rt nhiu. ti ny s phn tch mng CAN v a ra mt vi ng dng CAN mang tnh tit kim chi ph sn xut v chi ph bo tr. Thit k mt card CAN n gin nhng y tnh nng cn thit a vo ng dng trong cng nghip.QU TRNH NGHIN CU V CC KT QU0. Tng quan

Hnh 1.1 Trc y CAN ch yu c s dng cho xe t CAN (Control Area Network) xut pht l mt pht trin chung ca hai hng Bosch v Intel phc v vic ni mng trong cc phng tin giao thng c gii thay th cch ni im im c in, sau c chun ha quc t trong ISO 11898. Trong mt s chng loi t c ln, chiu di dy dn tng cng trong cch ni im im c th ln ti hng kilomt, tnh ring khi lng dy dn cng ln ti hng trm kilogam. Ch cn quan tm ti hai yu t ny cng thy hiu qu ca vic s dng mt h thng bus trng nh CAN. Nh tc truyn dn tng i cao khong cch ngn cng nh u th mt s c tnh k thut khc m cng ngh ny thm nhp c vo mt s lnh vc t ng ha qu trnh cng nghip.Ngy nay, nhng nh sn xut linh kin bn dn nh Motorola, Philips, Intel, Atmel, Microchip, Infineon tch hp CAN vo trong cc chp bn dn ca h, v thc t chng minh iu . Atmel c c mt dng vi iu khin ring dnh cho cc ng dng v automation trong cc linh kin bn dn u tch hp CAN vo trong , gi thnh sn xut c gim xung ti mc ti thiu thay v phi dng cc chip CAN c th. Trc y cc nh sn xut chp thng hay tch hp cc chun UART vo cc thit k ca h nhm h tr cc giao tip RS232/RS485 th ngy nay cc nh sn xut ny tch hp c chun CAN vo trong cc thit k vi x l.CAN c th dng c lm h thng thng tin nhng cho vi iu khin cng nh h thng thng tin m cho cc thit b thng minh. V d mt s ngi s dng trong lnh vc cng ngh y hc la chn CAN bi v chng p ng c yu cu an ton tuyt i. V d nh h thng robots, thang my, hoc l h thng vn ti yu cu c an ton thng tin v tin cy cao.Cng ty mng my tnh ni ting khp th gii, Cisco Systems, s dng CAN cho h thng mng con trin khai v ci tin nhng tnh nng cho router m khng cn phi dng h thng. S lng CAN node m Cisco dng nm trong khong 500.000 ti 1.000.000 node, iu ny l minh chng r rng nht cho li ch ca vic s dng ng dng CAN ngoi lnh vc t ng. Ngoi Cisco ra cn c rt nhiu cc cng ty c tn tui khc s dng CAN nh HP, NASA, Boeing, Lockheed ....Mt lnh vc khc m CAN c s dng nhiu l cc trang thit b y t, t cc thit b s dng trong mt phng khm thng thng nh n v nh sng ging khm bnh, h thng camera ni soi, tia X, my siu m ... n cc trang thit b ln hn nh h thng my qut CAT. Hu ht cc bnh vin t nhn ln trn nc M bao gm lun cc bnh vin nh GE Medical, Philips Medical, u c nhu cu s dng CAN (hoc l CANopen mt chun CAN m rng).0. M hnh mng CAN thcS h thng

Hnh 5.1a S khi h thng CAN Master SlaveMi trm c mt nhim v ring bit, trm 1 x l tnh hiu ADC, trong m hnh thit k l tn hiu nhit c tr v t cm bin nhit LM35. Trm 1 hin th nhit mi trng ti thi im hin ti v hin th nhit ngay ti trm qua mn hnh LCD loi 16x2, ng thi truyn nhit thu c ln Bus CAN. Trm 2 iu khin tc ng c, tnh ton tc ng c DC v truyn tc ng c ln Bus CAN, ng thi ti trm 2 cng hin th tc ng c ln mn hnh LCD 16x2. Thit b giao tip CAN vi my tnh c thit k thn thin vi ngi s dng, c giao tip USB tc cao. Trm ny c gi l trm trung tm, trm trung tm s thu thp nhit v tc ng c truyn t trm 1 v trm 2 thng qua Bus CAN sau hin th ln my tnh. Trn my tnh c ci sn phn mm hin th tc ng c v nhit mi trng, phn mm c vit bng ngn ng Visual Basic trong mi trng .NET 2.0.Phn lp trnh my tnh s dng phn mm Visual Studio 2005 dng ngn ng Visual Basic trong mi trng .NET thit k ng dng. Phin bn Visual Studio 2005 Express c Microsoft pht hnh min ph, c ng gi theo tng ngn ng. c im ca cc phin bn ny l rt nh gn, vi hu ht cc tnh nng cn thit cho vic pht trin mt ng dng bnh thng. Nu nh b Visual Studio 2005 Professional c dung lng ln ti khong 2.5GB, khi ci cng cn rt nhiu khng gian a, th cc phin bn Express c dung lng ch khong 450MB, v yu cu dung lng a khi ci t thp hn nhiu.Gii thiu chng trnh trn my tnh:

Hnh Chng trnh trn my tnh, Form1Khi nhn nt Next s chy vo chng trnh chnh ca h thng. Chng trnh chnh gm 2 khi, khi thit lp cng serial port giao tip vi my tnh v khi vn hnh chng trnh.

Hnh Chng trnh chnh trn my tnhTrong khi COM Port, c th la chn cng COM thch hp truyn nhn tn hiu, ngoi ra, cn c th thit lp cc thuc tnh khc nhau ca cng COM nh tc Baudrate, Data Bit v Parity Bit. Khi nhn chn cng COM thc hp th h thng s c kt ni lp tc vi my tnh, biu tng kt ni s hin ln v chp tt lin tc, nt Disconnect s xut hin. Nu h thng khng kt ni c th biu tng kt ni s khng xut hin.Bn phi chng trnh s miu t h thng thit k, my tnh c kt ni vi 2 node trm thng qua CAN bus ng mu xanh l. T mi trn li c tng phn t chp hnh tng ng. Tc ng c c truyn v hin th ln chng trnh, tc ng c c iu khin bng bin tr nm trm cn li. Nhit c gim st cht ch, khi qu nhit (80 0C) th qut s c bt gim thiu lng nhit trn h thng. Khi qut c bt th biu tng qut s chp tt lin tc, ng thi xut hin cnh bo qu nhit. Node trm cng c trang b LCD gim st tc ng c v nhit h thngSau thi gian nghin cu v thi cng ba trm CAN, mt trm trung tm c kt ni vi my tnh v hai trm v tinh iu khin ng c DC c iu khin bng bin tr v thu thp nhit mi trng. Khong cch truyn gia mi trm l 8m, tc truyn 125 Kb/s, h thng lm vic bnh thng, khng h c bt k s c no. Phn giao tip vi my tnh thng qua cng USB lm cho h thng tr nn thn thin hn vi ngi dng, v hu ht cc my tnh by gi u khng c cng Serial truyn thng. Tc