Giao Trinh Mang Cong Nghiep_2

8/2/2019 Giao Trinh Mang Cong Nghiep_2

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B mn CNK tng Gio trnh: Kthut thng tin cng nghip

Chng 1: MU

1.1 Mng truyn thng cng nghip l g?

Ngy nay vi s pht trin mnh m ca ngnh cng nghip, i hi phi c s ci

tin v p dng cng ngh mi vo trong qu trnh sn xut nhm nng cao hiu qusn xut. Mt trong nhng gii php tt nht, l p dng quy trnh t ng ha vosn xut. Cc dy chuyn sn xut khng th hot ng c lp m cn phi c s linkt vi nhau to nn mt m hnh thng nht. S kt ni cc thit b cng nghip vi nhau to thnh mt h thng mng v c gi l mng cng nghip.

Mng cng nghip hay mng truyn thng cng nghip l mt khi nim ch cc hthng mng truyn thng s, truyn bit ni tip, c s dng ghp ni cc thit bcng nghip.

phn bit r mng cng nghip v cc h thng mng khc ta c th a ra bngso snh sau

Bng 1.1: So snh mng cng nghip v cc h thng mng khc

Mng cng nghip Cc h thng mng vin thng

- Phm vi a a l hp

- i tng l cc thit b cng nghip

- Dng thng tin l s liu

- K thut truyn d liu theo ch bitni tip

- n gin

- Phm vi a l rng, s lng thnh vintham gia ln

- i tng l c con ngi v thit btrong con ngi l ch yu

- Dng thng tin bao gm ting ni, hnhnh, vn bn

- Cng ngh phong ph

- Phc tp

T ta c th kt lun mng cng nghip thc cht l mt dng c bit ca mngmy tnh, c th so snh vi mng my tnh thng thng nhng im ging nhau vkhc nhau nh sau:

K thut truyn thng s hay truyn d liu l c trng chung ca c hai h

thng mng. Trong nhiu trng hp, mng my tnh c s dng trong cng nghip ccoi l mt phn trong m hnh phn cp ca mng cng nghip.

Yu cu tnh nng thi gian thc, tin cy v kh nng tng thch trong mitrng cng nghip ca mng cng nghip cao hn so vi mng my tnh thngthng, mng my tnh thng i hi ch bo mt cao hn.

Mng my tnh c phm vi tri rng rt khc nhau, c th ch nh nh mngLAN cho mt nhm cc my tnh hoc rt ln nhmng Internet.

Mng my tnh c th s dng gin tip mng truyn thng truyn d liucn mng cng nghip thng c tnh cht c lp, phm vi hot ng tngi hp.

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S khc nhau trong phm vi v mc ch s dng gia cc h thng mng truynthng cng nghip vi cc h thng mng vin thng v mng my tnh dn n skhc nhau trong cc yu cu k thut cng nhkinh t.

V d: Do yu cu kt ni nhiu mng my tnh khc nhau cho nhiu phm vi ngdng khc nhau nn kin trc, giao thc mng my tnh ph thng thng phc tphn so vi kin trc giao thc mng cng nghip. i vi cc h thng truyn thngcng nghip, c bit l cp di th cc yu cu v tnh nng thi gian thc, khnng thc hin n gin, gi thnh h lun c t ln hng u.

1.2 Phn loi v c trng cc h thng mng cng nghip

sp xp phn loi v phn tch c trng ca cc h thng mng cng nghip, tada vo m hnh phn cp cho cc cng ty, x nghip sn xut. Vi m hnh ny ccchc nng c phn thnh nhiu cp khc nhau c m t trong hnh v sau:

iu hnhsn xut

iu hnhQu trnh

iu khin

Chp hnh

QL

Hnh 1.1 : M hnh phn cp chc nng cng ty sn xut cng nghip

Cng cp di th cc chc nng cng mang tnh cht c bn hn v i hi yucu cao hn v nhanh nhy, thi gian phn ng. Mt chc nng cp trn c thchin da trn cc chc nng cp di, tuy khng i hi thi gian phn ng nhanh nh cp di, nhng ngc li lng thng tin cn trao i v x l li ln hn nhiu. Cth coi y l m hnh phn cp chc nng cho c h thng t ng ha ni chungcng nh cho h thng truyn thng ni ring ca mt cng ty.

Tng ng vi nm cp chc nng l bn cp ca h thng truyn thng. T cpiu khin gim st tr xung thut ng "bus" thng c dng thay th cho "mng"vi l do phn ln cc h thng mng pha di u c cu trc vt l hoc logic theokiu bus

M hnh phn cp chc nng s tin li cho vic thit k h thng v la chn thitb. Trong thc tng dng, s phn cp chc nng c th khc mt cht so vi trnhby, ty thuc vo mc t ng ha v cu trc h thng c th. Trong nhngtrng hp ng dng n gin nhiu khin trang thit b dn dng (my git, tlnh, iu ha...), s phn chia nhiu cp c th hon ton khng cn thit. Ngc litrong tng ha mt nh my hin i nhin nguyn t, xi mng, lc du, ta c

th chia nh hn na cc cp chc nng tin theo di.Bus trng, bus thit b

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Bus trng (fieldbus) l mt khi nim chung c dng trong cc ngnh cngnghip ch bin ch cc h thng bus ni tip, s dng k thut truyn tin s ktni cc thit b thuc cp iu khin (PC, PLC) vi nhau v vi cc thit bcp chphnh, hay cc thit b trng. Cc chc nng chnh ca cp chp hnh l o lng,truyn ng v chuyn i tn hiu trong cc trng hp cn thit. Cc thit b c khnng ni mng l cc vo/ra phn tn (distributed I/O) cc thit bo lng (senser,tranducer, transmitter) hoc cc cp chp hnh (actuator, value) c tch hp kh nngx l truyn thng. Mt s kiu bus trng ch thch hp ni mng cc thit b cm

bin v ccu chp hnh vi cc biu khin, cng c gi l bus chp hnh/cmbin.

Trong cng nghip ch to (tng ha dy chuyn sn xut, gia cng, lp rp)hoc mt s lnh vc ng dng khc nh tng ha ta nh, sn xut xe hi, khinim bus thit bli c s dng ph bin. C th ni, bus thit b v bus trng cchc nng tng ng, nhng do nhng c trng ring bit ca hai ngnh cngnghip, nn mt s tnh nng cng khc nhau. Tuy nhin, s khc nhau ny ngy cng

trnn khng r rt, khi m phm vi ng dng ca c hai loi u c mrng van cho sang nhau. Trong thc t, ngi ta cng dng chung mt khi nim l bustrng.

Do nhim v ca bus trng l chuyn d liu ln cp iu khin x l vchuyn quyt nh iu khin xung cc c cu chp hnh, v vy yu cu v tnhnng thi gian thc c t ln hng u. Thi gian phn ng tiu biu nm trong

phm vi t 0,1 ti vi miligiy. Trong khi , yu cu v lng thng tin trong mtbc in thng ch hn ch trong khong mt vi byte, v vy tc truyn thngthng ch cn phm vi Mbit/s hoc thp hn. Vic trao i thng tin v cc binqu trnh ch yu mng tnh cht nh k, tun hon, bn cnh cc thng tin tham s

ha hoc cnh bo c tnh cht bt thng.Cc h thng bus trng c s dng rng ri nht hin nay l PROFIBUS,

ControlNet, INTERBUS, CAN, WordFIP, P-NET, Modbus v gn y phi k tiFoundation Fielfbus, DeviceNet, AS-i, EIB v Bitbus l mt vi h thng bus cm

bin/chp hnh tiu biu c th nu ra y.Bus h thng, bus iu khin

Cc h thng mng cng nghip c dng kt ni cc my tnh iu khin vcc my tnh trn cp iu khin gim st vi nhau c gi l bus h thng (systembus) hay bus qu trnh (process bus). Khi nim sau thng c dng trong lnh vc

iu khin qu trnh. Qua bus h thng m cc my tnh iu khin c th phi hphot ng, cung cp d liu qu trnh cho cc trm k thut v trm quan st (c thgin tip thng qua h thng qun l csd liu trn cc trm ch) cng nh nhnmnh lnh, tham siu khin t cc trm pha trn. Thng tin khng nhng c traoi theo chiu dc, m cn theo chiu ngang. Cc trm k thut, trm vn hnh v cctrm ch cng trao i d liu qua bus h thng. Ngoi ra cc my in bo co v lutr d liu cng c thc kt ni qua mng ny.

Ch phn bit gia cc khi nim bus trng v bus h thng khng bt buc nms khc nhau v kiu bus c s dng, m mc ch s dng hay ni cch khc l thit bc ghp ni. Trong mt s gii php, mt kiu bus duy nht c dng

cho chai cp ny.i vi bus h thng, ty theo lnh vc ng dng m i hi v tnh nng thi gian

thc c c t ra mt cch ngt ngho hay khng. Thi gian phn ng tiu biu nm

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trong khong mt vi trm miligiy, trong khi lu lng thng tin cn trao i ln hnnhiu so vi bus trng. Tc truyn thng tiu biu ca bus h thng nm trong

phm vi t vi trm Kbit/s n vi Mbit/s.Khi bus h thng chc s dng ghp ni theo chiu ngang gia cc my tnh

iu khin, ngi ta dng khi nim bus iu khin. Vai tr ca bus iu khin l phc

v trao i d liu thi gian thc gia cc trm iu khin trong mt h thng c cutrc phn tn. Bus iu khin thng thng c tc truyn khng cao, nhng yu cuv tnh nng thi gian thc thng rt kht khe.

Do cc yu cu v tc truyn thng v kh nng kt ni d dng nhiu loi mytnh, hu ht cc bus h thng thng dng u da trn nn Ethernet, v d IndustrialEthernet, Fieldbus Foundations High Speed Ethernet (HSE), Ethernet/IP, bn cnh

phi kn PROFIBUS- FMS, ControlNet v Modbus Plus.Mng x nghip

Mng x nghip thc cht l mt mng LAN bnh thng c chc nng kt ni ccmy tnh vn phng thuc cp iu hnh sn xut vi cp iu khin gim st. Thng

tin c a ln trn bao gm trng thi lm vic ca cc qu trnh k thut, cc ginmy cng nh ca h thng iu khin tng, cc s liu tnh ton, thng k v din

bin qu trnh sn xut v cht lng sn phm. Thng tin theo chiu ngc li l ccthng s thit k, cng thc iu khin v mnh lnh iu khin. Ngoi ra thng tincng c trao i mnh theo chiu ngang gia cc my tnh thuc cp iu hnh snxut, v d h trkiu lm vic theo nhm, cng tc trong d n, s dng chung ccti nguyn ni mng (my in, my ch...).

Khc vi cc h thng bus cp di, mng x nghip khng yu cu nghim ngt vtnh nng thi gian thc. Vic trao i d liu khng din ra nh k, nhng c khi vis lng ln n hng Mbyte. Hai loi mng c dng ph bin cho mc ch ny lEthernet v Token-Ring. Trn csgiao thc chun nh TCP/IP v IPX/SPX.

Mng cng tyMng cng ty nm trn cng trong m hnh phn cp h thng truyn thng ca mt

cng ty sn xut cng nghip. c trng ca mng cng ty gn vi mng vin thnghoc mt mng my tnh din rng nhiu hn trn cc phng din phm vi v hnhthc dch v, phng php truyn thng v cc hnh thc dch v, phng php truynthng v cc yu cu v k thut. Chc nng ca mng cng ty l kt ni cc my tnhca cc vn phng ca cc x nghip, cung cp cc dch v trao i thng tin ni b vvi cc khch hng nh th vin in t, thin t, hi tho t xa qua in thoi,

hnh nh, cung cp dch v truy cp Internet v thg mi in t... Hnh thc t chcghp ni mng cng nh cc cng nghc p dng rt a dng ty thuc vo u tca cng ty. Trong nhiu trng hp, mng cng ty v mng x nghip c thc hin

bng mt h thng mng duy nht v mt vt l, nhng chia thnh nhiu phm vi vnhm mng lm vic ring bit.

Mng cng ty c vai tr nh mt ng cao tc trong h thng h tng cstruynthng ca mt cng ty, v vy i hi v tc truyn thng v an ton, tin cy c

bit cao, Fast Ethernet, FDDI, ATM l mt vi v d cng ngh tin tin c p dngy trong hin ti v tng lai.

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Chng 2: CSK THUT

2.1 Cc khi nim cbn

2.1.1 Thng tin, dliu v tn hiu

Thng tin: Thng tin l mt khi nim tru tng, n phn nh thc ti khch quan,cho chng ta hiu bit, nhn thc c thgii khch quan. Thng tin l mt trongnhng khi nim quan trng nht trong khoa hc k thut, cng ging nh vt cht vnng lng. Cc u vo v u ra ca mt h thng k thut ch c th l vt cht,nng lng hoc thng tin.

Mt h thng x l thng tin hoc l mt h thng truyn thng, hoc l mt h

thng k thut ch quan tm ti u vo v u ra l thng tin. Tuy nhin a s cc hthng k thut thng c cc u vo v u ra hn hp (vt cht, nng lng vthng tin).

Thng tin l cscho s giao tip. Thng qua vic giao tip v cc i tc c thmhiu bit ln nhau hoc v cng mt vn , mt s kin hoc mt h thng.

Dliu

Thng tin l mt i lng tru tng, v vy cn c biu din di mt hnhthc khc. Kh nng biu din thng tin rt a dng. Dng biu din thng tin phthuc vo mc ch, tnh cht ca ng dng. c bit, thng tin c thc m t, hay

ni cch khc l c "s lng ha" bng d liu c th lu tr v x l bng mytnh. TRong trng hp ta ni rng thng tin c s ha s dng hm nh phn.Khi d liu chnh l phn thng tin hu ch c biu din bng cc dy bit {0,1}.

Trong thc t, cc khi nim x l thng tin v x l d liu, truyn ti thng tin vtruyn ti d liu hay c dng vi cc ngha tng t, ta cn phn bit r rnggia thng tin v d liu. V d, hai tp d liu khc nhau c th m t cng mt nidung thng tin. Ngc li, hai tp d liu ging nhau c th mang nhng thng tinkhc nhau, ty theo cch m t. Ta c th so snh quan h gia d liu v thng tin viquan h trong ton hc gia s v ngha s dng n.

Theo ngha th hai, d liu c hiu l phn biu din thng tin hu dng (thngtin ngun) trong mt bc in. Tuy nhin, cn c vo ng cnh c th m ta khng snhm ln gia hai cch s dng thut ng ny.

Lng thng tin

Thng tin chnh l s xa b tnh bt nh, v d mt s khng nh v mt s kinc xy ra hay khng, mt cu tr li ng hay sai. Mc ca s xa b tnh bt nhny - hay ni cch khc, gi tr v s hiu bit mt ngun thng tin mang li - cgi l lng thng tin. Chnh v d liu l mt dng biu din thng tin c th x lc trong my tnh, nn lng thng tin cng c o bng n v d liu. Trongtrng hp thng tin v s khng nh ng/sai, r rng ch cn 1 bit biu din, hayni cch khc lng tin bng 1 bit. biu din cc k t trong bng gm c 256 kt ta cn 8 bit cho mi ch ci..

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Tn hiu

Vic trao i thng tin hay d liu ch c th thc hin c nh tn hiu. C thnh ngha, tn hiu l din bin ca mt i lng vt l cha ng tham s thngtin/d liu v c th truyn dn c. Theo quan im ton hc th tn hiu c coi lmt hm ca thi gian. Trong cc lnh vc k thut, cc loi tn hiu thng dng l :

quang, in, kh nn, thy lc v m thanh.Cc tham s sau y thng c dng trc tip, gin tip hay kt hp biu th

ni dung thng tin:

Bin (in p, dng..)

Tn s, nhp xung, rng xung, sn xung

Pha, v tr xungTa c th phn loi tn hiu da theo tp hp gi tr ca tham s thng tin hoc datheo din bin thi gian thnh nhng dng sau:

Tng t: Tham s thng tin c th c mt gi tr bt k trong mt khongno

Ri rc: Tham s thng tin ch c th c mt s gi tr (ri rc) nht nh.

Lin tc: Tn hiu c ngha ti bt k thi im no trong mt khong thigian quan tm. Ni theo ngha ton hc, mt tn hiu lin tc l mt hm lintc ca bin thi gian trong mt khong xc nh.

2.1.2 Truyn thng, truyn dliu v truyn tn hiu

Giao tip v truyn thng

Giao tip hay truyn thng l mt qu trnh trao i thng tin gia hai ch th vinhau, c gi l cc i tc giao tip, theo mt phng php c quy nh trc.i tc ny c thiu khin i tc kia, hoc quan st trng thi ca i tc. Cc itc giao tip c th l ngi hoc h thng k thut - tc l cc thit b phn cng (itc vt l) hoc cc i tc phn mm (i tc logic). Trong trng hp sau, khi nimtruyn thng thng c s dng thay cho khi nim giao tip. Tuy nhin khi nimgiao tip c ngha bao trm hn. Trong phm vi ti liu ny ch cp ti h thngtruyn thng cng nghip, nn cc i tc thun ty l cc thit b, h thng k thut,nn hai thut ng giao tip v truyn thng c s dng vi ngha tng ng.

thc hin vic giao tip hay truyn thng ta cn cc tn hiu thch hp, c th l

tn hiu tng t hay tn hiu s. S phn bit gia tn hiu v thng tin dn ti sphn bit gia x l tn hiu v x l thng tin, gia truyn tn hiu v truyn thng.C th s dng cc dng tn hiu rt khc nhau truyn ti mt ngun thng tin, cngnh mt tn hiu c th mang nhiu ngun thng tin khc nhau.

Trn cscc dng tn hiu khc nhau, ngi ta c th phn bit cc kiu giao tipnh sau:

Giao tip ting ni

Giao tip hnh nh

Giao tip vn bn

Giao tip d liuChnh v d liu l mt dng biu din thng tin s dng m nh phn, truyn ti

thng tin s dng tn hiu s cng c gi l truyn d liu. C th ni truyn d liu

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l phng php truyn thng duy nht gia cc my tnh trong mng my tnh. Ngynay k thut s cng c p dng rng ri trong vic truyn ti ting ni, hnh nh vvn bn, v vy truyn d liu ng vai tr quan trng hng u.

S phn bit gia tn hiu s v tn hiu tng t ph thuc vo ngha ca tham sthng tin m tn hiu mang. S phn bit gia phng php truyn tn hiu s dng

k thut s (gi tt l truyn tn hiu s) vi cc phng php truyn tn hiu truynthng cng tng t nh vy. Trong cc h thng truyn thng cng nghip hin i tach quan tm ti truyn tn hiu s, hay ni cch khc l truyn d liu. Cc chungiao tip trong cc h thng ny cng l cc chun giao tip s.

M ha/Gii m

Thng tin cn trao i gia cc i tc cn c m ha trc khi c mt hthng truyn dn tn hiu chuyn ti pha bn kia. Trong thut ng truyn thng, mha ch qu trnh bin i ngun thng tin (d liu) cn trao i sang mt chui tnhiu thch hp truyn dn. Qu trnh ny t nht gm hai bc: m ha ngun vm ha ng truyn.

Trong qu trnh m ha ngun, d liu mang thng tin thc dng hay d liu ngunc b xung cc thng tin ph tr cn thit cho vic truyn dn, v da ch bnnhn v bn gi, kiu d liu, thng tin tm kim li... D liu trc khi gi i cng cth phn chia thnh nhiu gi d liu bc in ph hp vi phng php truyn, nnli tng hiu sut ng truyn, hoc m ha bo mt. Nh vy lng thng tincha ng trong mt tn hiu s nhiu hn lng thng tin thc dng cn truyn ti

i tc

truyn thng

M ha/Gii m

M ha/Gii m

H thng truyn dn tn hiu

i tc

truyn thng

Hnh 2.1: Nguyn tc cbn ca truyn thng

Sau khi c m ha ngun, m ha ng truyn l qu trnh to tn hiu tngng vi cc bit trong gi d liu hay bc in theo mt phng php nht nh phhp vi ng truyn v k thut truyn. Trong truyn thng cng nghip, m hang truyn ng ngha vi m ha bit,bi tn hiu do khu m ha tng bit to racng chnh l tn hiu c truyn dn. i vi cc h thng truyn thng khc, qutrnh m ha ng truyn c th bao hm vic iu bin tn hiu v dn knh, cho

php truyn cng mt lc nhiu ngun thng tin v truyn tc cao. Vic dn knhc th thc hin theo phng php phn chia tn s, phn chia thi gian hoc phnchia m.

Trong mt tn hiu c truyn ti i, cn c mt phng php bn nhn phnbit gii hn gia cc bit d liu ni tip nhau, qu trnh gi l phng php ngb ha. thc hin c cng vic ny mt cch n gin, tn hiu thng c

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pht theo mt nhp u n, mi nhp ng vi 1 bit. Trong qu trnh ngc li vi mha lgii m, l qu trnh chuyn i cc tn hiu nhn c thnh dy bit tngng v sau x l, loi b thng tin b xung ti to thng tin ngun.

iu chv iu bin tn hiu

iu chv iu bin l hai khi nim c dng vi ngha rt gn nhau. iu ch

c hiu l qu trnh to mt tn hiu trc tip mang tham s thng tin, th hin quabin , tn s hoc pha, trong tham s thng tin c th ly mt gi tr bt k. Mttrng hp c bit ca iu ch l khi n c dng vo mc ch truyn d liu vtham s thng tin ch c th ly hai gi tr logic 1 v 0, ngi ta dng khi nim mha bit nh gii thiu trn. iu ch cn tm thy ng dng trong cc b chuyni D/A, cc b to xung (iu ch rng xung, iu ch m xung).

Khc mt cht, iu bin ch qu trnh dng tn hiu mang thng tin iu khin,bin i cc tham s thch hp ca mt tn hiu th hai (tn hiu mang). Mc ch cbn ca iu bin l s dng mt tn hiu mang c mt di tn khc thc hinphng php dn knh phn chia tn s, hoc trnh truyn dn di tn csd bnhiu. i khi ranh gii phn bit gia iu ch v iu bin cng khng hon tonr rng, v vy trong thc t khi nim th nht thng c s dng chung cho c haitrng hp. Trong ting anh ngi ta s dng mt thut ng chung l modulation, tuynhin ty theo ng cnh m c hiu theo hai ngha khc nhau.

Tc truyn v tc bit

Thi gian cn truyn mt tp d liu, v d mt k t, ph thuc vo hai yu tl tc baudv phng php m ha bit. Tc baud c nh ngha l s ln tnhiu thay i gi tr tham s thng tin (v d bin ) trong mt giy v c n v l

Baud. Do hu ht cc h thng truyn d liu hot ng theo nhp tun hon, tc

baud tng ng vi tn snhp ca h thng thu pht. Cng cn lu rng, i vinhiu phng php m ha bit, tn hiu khng bt buc phi thay i trng thi trongmi nhp, v th khi nim tc baud khng hon ton chnh xc. Thay vo , ngita s dng cc khi nim tc truyn hay tc bit.

Tc truyn hay tc bit c tnh bng s bit d liu c truyn i trong mtgiy, tnh bng bit/s hoc bps (bit fer second).Nu tn s nhp c k hiu l f n s

bit c truyn i trong mt nhp l n, s bit c truyn i trong mt giy s lv=f*n. Nh vy, c hai cch tng tc truyn ti l tng tn s nhp hoc tng s

bit truyn i trong mt nhp. Nu mi nhp ch c duy nht mt bit c truyn i thv=f. Nh vy, chi vi cc phng php m ha bit s dng hai trng thi tn hiu,v trng thi tn hiu thay i lun phin sau mi nhp th tc bit mi tng tngtc baud, hay 1 baud tng ng 1 bit/s.

Cn phn bit gia tc truyn thng tin hu ch v tc truyn thng tin tngth. Mt thng tin cn truyn i (thng tin hu ch) s m ha ngun, tc c nggi v b xung cc thng tin ph trcn thit cho vic truyn ti (overhead). V vytc truyn thng tin tng th c th ln hn rt nhiu so vi tc truyn thnghu ch, ph thuc vo h thng truyn thng. Thc t, tc truyn thng hu ch rtkh xc nh c mt cch chnh xc.

Thi gian bit/Chu k bit

Trong vic phn tch nh gi tnh nng thi gian ca mt h thng truyn thng ththi gian bit l mt gi tr hay c dng. Thi gian bithay chu k bitc nh ngha

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l thi gian trung bnh cn thit chuyn mt bit, hay chnh bng gi tr nghch oca tc truyn ti:

TB= 1/v

TB=1/f, trng hp n=1

Thi gian lan truyn tn hiu

Thi gian lan truyn tn hiu l thi gian cn mt tn hiu pht ra t mt u dylan truyn ti u dy khc, ph thuc vo chiu di dy v cu to dy dn. Tc lan truyn tn hiu chnh l tc truyn sng in t. Tuy nhin, trong mi trngkim loi hoc si quang hc, gi tr ny s nh hn tc truyn sng in t hay tc nh sng trong mi trng chn khng. Ta c:

TS= l/(k*c), viTSl thi gian lan truyn tn hiu; l l chiu di dy dn,c l tc nh sng trong chn khng (300.000.000m/s) vk biu th h s gim tc , c tnh theo cng thc

1k

= , vi l hng sin mi ca lp cch ly

i vi cc loi cp c lp bc cch ly l Polyethylen vi hng sin mi =2.3,ta c h s . H s cng ng vi mi trng truyn l cp quang hc vthng c dng mt cch tng qut tnh ton gi tr tng i ca thi gian lantruyn tn hiu trong nhiu php nh gi. Nh vy T

0.67k

Ss ch ph thuc vo chiu didy dn:

TS(giy) = l (mt)/300.000.000

Lu rng, thi gian lan truyn tn hiu khng c quan h trc tip vi tc truyn thng. Tuy nhin, tnh nng thi gian ca mt h thng truyn khng ph thucvo hai tham s ny, trong khi mt s phng php truyn thng i hi s trao irng buc gia chng. V d, ta khng thng thi tng chiu di dy dn v tc truyn thng mt cch ty .2.1.3 Tnh nng thi gian thc

Tnh nng thi gian thc l mt trong nhng c trng quan trng nht i vi cch thng tng ha ni chung v cc h thng bus trng ni ring. S hot ng

bnh thng ca mt h thng k thut lm vic trong thi gian thc khng ch phthuc vo chnh xc, ng n ca cc kt quu ra, m cn ph thuc vo thi

im a ra kt qu. Mt h thng c tnh nng thi gian thc khng nht thit phi cphn ng tht nhanh, m quan trng hn l phi c phn ng kp thi i vi cc yucu, tc ng bn ngoi. Nh vy, mt h thng truyn thng c tnh nng thi gianthc phi c kh nng truyn ti thng tin mt cch tin cy v kp thi vi cc yu cuca i tc truyn thng. Tnh nng thi gian thc ca mt h thng iu khin phntn ph thuc rt nhiu vo h thng bus trng c dng.

m bo tnh nng thi gian thc, mt h thng bus phi c nhng c imsau :

nhanh nhy: Tc truyn thng hu ch phi nhanh p ng nhu

cu trao i d liu trong mt gii php c th. Tnh tin nh : Don trc c v thi gian phn ng tiu biu v thi

gian phn ng chm nht vi yu cu ca tng trm.

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tin cy, kp thi :m bo tng thi gian cn cho vic vn chuyn dliu mt cch tin cy gia cc trm nm trong mt khong xc nh.

Tnh bn vng : C kh nng x l s c mt cch thch hp khng gyhi thm cho h thng.

R rng, kh nng tha mn yu cu v thi gian thc ph thuc vo bi ton ng

dng c th. Mt mng cng nghip c tnh nng thi gian thc khng c ngha l sthch ng vi mi ng dng i hi yu cu v thi gian thc. Nhim v ca ngitch hp h thng l phi la chn v thit k mt gii php thch hp tha mn yucu ny trn csphn tch cc tnh nng k thut lin quan, di iu kin rng bucl gi thnh chi ph.

2.2 Ch truyn ti

Ch truyn ti c hiu l phng thc cc bit d liu c chuyn gia cci tc truyn thng. Nhn nhn t cc gc khc nhau ta c th phn bit cc chtruyn ti nh sau :

Truyn bit song song hoc truyn bit ni tip Truyn ng b hoc truyn khng ng b

Truyn mt chiu hay n cng (simplex), hai chiu ton phn, hai chiung thi hay song cng (duplex, full-duplex) hoc hai chiu gin on hay

bn song cng (half-duplex)

Truyn ti di cs, truyn ti di mang v truyn ti di rng.2.2.1 Truyn bit song song v truyn bit ni tip

Truyn bit song song

Phng php truyn bit song song c dng ph bin trong cc bus ni b camy tnh nh bus a ch, bus d liu v bus iu khin. Tc truyn ti ph thucvo s cc knh dn, hay cng chnh l rng ca mt bus song song, v d 8 bit, 16

bit, 32 bit hay 64 bit. Chnh v nhiu bit c truyn i ng thi, vn ng b hati ni pht v ni nhn tn hiu phi c gii quyt. iu ny gy trngi ln khikhong cch gia cc i tc truyn thng tng ln. Ngoi ra, gi thnh cho cc bussong song cng l mt yu t dn n phm vi ng dng ca phng php truyn nych hn chkhong cch nh, c yu cu rt cao v thi gian v tc truyn.

Truyn bit ni tip

Vi phng php truyn bit ni tip, tng bit c chuyn i mt cch tun t quamt ng truyn duy nht. Tuy tc bit v th m b hn ch, nhng cch thc hinli n gin, tin cy ca d liu cao. Tt c cc mng truyn thng cng nghip us dng phng php truyn ny.

100101

11

10010111

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Hnh 2.2 : Truyn bit song song v truyn bit ni tip

Mt mng truyn thng cng nghip c nhim v kt ni cc thit b k thut ckh nng x l thng tin hay ni cch khc l x l d liu. Nhng thit b d tnti di dng ny hay dng khc cng u l nhng my tnh, c b vi x l v hthng bus ni b song song. V vy, c th dng phng php truyn ni tip, ta

cn cc b chuyn i gia bus song song v ni tip c minh ha trong hnh diy.

Song song

Ni tip

Song song

Ni tip

M ha/Gii m M ha/Gii m

Knh truyn dn

Hnh 2.3 :Nguyn tc truyn bit ni tip

2.2

ruyn thng lm vic theo cng mt nhp, th quy nh mt trm c vai tr to nhpng b cho cc trm khc. Bin php kinh

t

nho

Asynchronous

Reciver/Transmiter) thng dng dng bc in 11 bit bao gm 8 bit k t, hai bt khi v 1 bit k i chn l.

.2 Truyn ng b v truyn khngng b

S phn bit gia truyn ng b v khng ng b ch lin quan ti phng thctruyn bit ni tip. Vn t ra y l vic ng b ha gia bn gi v bn nhnd liu, tc l vn lm th no bn nhn bit khi no mt tn hiu trn ngtruyn mang d liu gi v khi no khng.

Trong ch truyn ng b, cc i tc ttc l cng tn s v lch pha cnh. Cv dng mt ng dy ring mang nhp

hn l dng mt phng php m ha bit thch hp bn nhn c th ti to nhpng b t chnh tn hiu mang d liu. Nu phng php m ha bit khng cho php

nh vy, th c th dng k thut ng gi d liu v b xung mt dy bit mang thngtin ng b ha vo phn u mi gi d liu. Lu rng, bn gi v bn nhn ch ct ng ng b trong khi trao i d liu.Vi ch truyn khng ng b, bn gi v bn nhn khng lm vic theo mt

nhp chung. D liu trao i thng c chia thnh tng nhm 7 bit hoc 8 bit, gi lk t. Cc k t cn c chuyn i vo nhng thi im khng ng u, v vy cnthm hai bit nh du khi u v kt thc cho mi k t. Vic ng b ha cthc hin vi tng k t. V d, cc mch UART (Universal

u v kt thc im tra l

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2.2 hiu v truyn hai chiu

t ng truyn d liu c th lm vic di ch mt chiu, hai chiu tonph c hai chiu gin on. Ch truyn ny t ph thuc vo tnh cht vt l cam uyn dn, m ph thuc vo phng php truyn dn tn hiu, chuntruyn dn (RS-232, RS-422, RS-485,...) v vo cu hnh ca h thng truyn dn.

rong ch truyn mt chiu, thng tin chc chuyn i theo 1 chiu, mt trmch ng va ng tin (receiver)trn sut qu trnh y tnh s dngch

u im ca ch ny l khngc tht c tc truyn tng

b pht v b thu, thut ng nhn to transceiverc ghpv receiver. Trong khi b pht lm vic th b thu phi ngh v

ng

p vi cu trc mch vng v cu trc hnh

.3 Truyn mt c

Mn hoi trng tr

T c th i tr hoc bn pht (transmitter) hoc bn nhn th

giao tip. C th nu mt vi v d trong k thut m truyn ny nh bn phm, chut hoc mn hnh vi my tnh. Cc h thng pht

thanh v truyn hnh cng l nhng v d tiu biu. Hin nhin, ch truyn mtchiu hu nh khng c vai tr quan trng i vi mng cng nghip.

a. Simplex

b. Half-duplex

c. Duplex

Hnh 2.4: Truyn simplex, hafl-duplex v duplex

Ch truyn hai chiu gin on cho php mi trm c th tham gia gi hoc nhnthng tin, nhng khng cng mt lc. Nh vy thng tin c trao i theo c haichiu

B pht B thu

B thu pht B thu pht

B thu pht B thu pht

10110101

10110101

10110101

10110101

lun phin trn cng mt ng truyn vt l.i hi cu hnh h thng phc tp lm, trong khii cao. Mt trm c ct hai chtransmitter

c li. Do c tnh ny, ch truyn hai chiu gin on ch thch hp vi kiulin kt im - nhiu im cng nh kiu nhiu im - im, hay ni cch khc lthch hp vi cu trc bus. Trong mt h thng bus, trm no cng c quyn pht nncn mt phng php phn chia thi gian - tc phng php truy nhp bus - trnh

xung t tn hiu. Trong khi mt trm pht th tt c cc trm khc phi c gitrng thi thu nhn tn hiu. Ch truyn y c s dng ph bin trong mng cngnghip, v d chun RS-485.

Vi ch truyn hai chiu ton phn mi trm u c th gi v nhn thng tincng lc. Thc cht ch ny ch khc vi ch hai chiu gin on ch phi sdng hai ng truyn ring bit cho thu v pht, tc l khc cu hnh truyn thng.D dng nhn thy, ch truyn hai chiu ton phn ch thch hp vi kiu lin ktim - im, hay ni cch khc l thch hsao.

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2.2.4 Truyn ti di cs, di mang v di rng

Truyn ti di cs

Mt tn hiu mang mt ngun thng tin c th biu din bng tng ca nhiu giaong c tn s khc nhau nm trong mt phm vi hp, c gi l di tn cshaydi hp. Tn hiu c truyn i cng chnh l tn hiu c to ra sau khi m ha bit,

hoc nm trong mt khong hp no , ty thuc vo phngphp m

thng tin duy nht, mi thnh vin trongm

y, ngi ta s dng mt tn hiu khc - gi l tn hiu mang, c tn s nmtro

nhiu ngun thng tin khc nhau c m ha bit, mi tn hiu c toiu bin mt tn hiu khc, thng c tn s ln hn nhiu, gi l tn

hi

hn s thchi

nn c tn s cnh ha bit. V d c th quy nh mc tn hiu cao ng vi bit 0 v mc tn hiu

thp ng vi bit 1. Tn s ca tn hiu thng nh hn, hoc cng lm l tng ngvi tn s ca nhp bus. Tuy nhin, trong mt nhp (c th tng ng hoc khngtng ng vi chu k ca tn hiu), ch c th truyn i mt bit duy nht. C nghal, ng truyn ch c th mang mt knh

ng phi phn chia thi gian s dng ng truyn. Tc truyn ti tuy c bhn ch, nhng phng php ny d thc hin v tin cy, c dng ch yu trong cch thng mng truyn thng cng nghip.

Truyn ti di mangTrong mt s trng hp, di tn c s khng tng thch trong mi trng lm

vic, v d tn hiu c cc tn s ny c th bc x nhiu nh hng ti hot ng cacc thit bin t khc, hoc ngc li b cc thit b khc gy nhiu. khc phctnh trng n

ng mt di tn thch hp - gi l di mang. Di tn ny thng ln hn nhiu so vitn s nhp. D liu cn truyn ti s dng iu ch tn s, bin hoc pha ca tnhiu mang. Bn nhn s thc hin qu trnh gii iu ch hi phc thng tin ngun.Khc vi truyn ti di rng nu di y, truyn ti di mang ch p dng cho mtknh truyn tin duy nht, ging nh truyn ti di cs.

Truyn ti di rng

Mt tn hiu c th cha ng nhiu ngun thng tin khc nhau bng cch s dngkt hp mt cch thng minh nhiu thng s thng tin. V d mt tn hiu phc tp cth tng hp bng phng php xp chng t nhiu tn hiu thnh phn c tn s khcnhau mang cc ngun thng tin khc nhau.

Sau khira s dng

u mang. Cc tn hiu mang c iu bin c tn s khc nhau, nn c th phatrn, xp chng thnh mt tn hiu duy nht c ph tn tri rng. Tn hiu ny cuicng li c dng iu bin mt tn hiu mang khc. Tn hiu thu c t khuny mi c truyn i. y chnh l k thut dn knh phn tn trong truyn tithng tin, nhm mc ch s dng ng truyn hiu qu hn. Pha bn n

n vic gii iu bin v phn knh, hi phc cc tn hiu mang cc ngun thng tinkhc nhau.

Phng thc truyn ti di rng v k thut dn knh c dng rng ri trong ccmng vin thng bi tc cao v kh nng truyn song song nhiu ngun tin. Tuynhin, v c im phm vi mng, l do gi thnh thc hin v tnh nng thi gian,truyn ti bng rng cng nh k thut dn knh hu nh khng ng vai tr g trong

cc h thng truyn thng cng nghip.

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2.3 C

Cu trthnh phthut, tro c khi tm hiu v cc cu trc thngdng n

Lin ktLin k

thng. vi nhau y tnh iu khin,cc b trng h

Khi ntruyn thhay mt t trm, nn quan h gia cc i tc ny ch

ma

hn bit cc kiu lin kt sau y:

c giao tip theo chiu ngc li t trm t ti trm chc thc hin theo kiu im - im. Xt v mt vt l, nhiu i

c mt i tc no cng c quyn pht v bt c trm no cng nghe c.

tt c cc kiu lin kt nhtr

u trc mng Topology

c mng lin quan ti t chc v phng thc phi hp hot ng gia ccn trong mt h thng mng. Cu trc mng nh hng ti nhiu tnh nng kng c tin cy ca h thng. Tr

tro g mng truyn thng cng nghip, ta a ra mt snh ngha sau:

t (link) l mi quan h vt l hay logic gia hai hoc nhiu i tc truyni vi lin kt vt l, cc i tc chnh l cc trm truyn thngc lin kt

qua mt mi trng vt l. V d cc th ni mng trong m x l truyn thng cc PLC hoc cc b lp u l cc i tc vt l. Trong

p ny, tng ng vi mi nt mng ch c mt i tc duy nht.im lin kt logic c th c hiu theo hai ngha. Th nht, mt i tc

ng khng nht thit b phn cng, m c th l mt chng trnh h thngchng trnh ng dng trn m

ng tnh cht logic. Nh vy, tng ng vi mt i tc vt l thng c nhiu itc logic, cng nh nhiu mi lin kt logic c xy dng trn csmt mi lin ktvt l. Theo ngha th hai, mc d bn thn cc i tc vn l cc thit b phn cng,nhng quan h ca chng v mt logic hon ton khc vi quan h v mt vt l.

C th p

Lin ktim - im (poit to- poit) Mt s mi lin kt ch c hai i tngtham gia. Nu xt v mt vt l th vi mi ng truyn ch ni c haitrm vi nhau. xy dng mt mng truyn thng trn csny s cnnhiu ng truyn ring bit.

Lin ktim - nhiu im (multi-drop) Trong mt mi lin kt c nhiu itc tham gia, tuy nhin ch mt i tc cnh duy nht (trm ch) c khnng pht trong khi nhiu i tc cn li (cc trm t) thu nhn thng tincng mt lc. Vic chtc c thc ni vi nhau qua mt cp chung duy nht.

Lin kt nhiu im (multipoint) Trong mt mi lin kt c nhiu i tctham gia v c th trao i thng tin qua li t do theo bt k hng no. Bt

Cng nh kiu lin kt im - nhiu im, c th s dng mt cp duy nht

ni mng gia cc i tc.Mt h thng truyn thng khng nht thit phi h trn. ng nhin, kh nng lin kt im - nhiu im bao hm kh nng lin kt

im - im cng nh lin kt nhiu im bao hm hai kh nng cn li. Kh nng linkt nhiu im l c trng ca mng truyn thng cng nghip.

Topology

Topology l cu trc lin ktca mt mng, hay ni cch khc chnh l tng hpca cc lin kt. Topology c th hiu l cch xp xp, t chc v mt vt l camng, nhng cng c th l cch xp xp logic ca cc nt mng, cch nh ngha v

t chc logic cc mi lin kt gia cc nt mng. Tuy hai khi nim topology v cutrc mng khng hon ton ging nhau, trong thc t chng c dng vi ngha

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tng ng. Trong phm vi ti liu ny chng ta s s dng thut ngh cu trcmng.2.3

trong cu trc bus: daisy-chain;truck-line/drop-line v mch vng khng tch cc. Hai cu hnh u cng c u cu trcng thng,bi hai u ng truyn khng khp kn.

Vi daisy-chain, mi trm c ni mng trc tip ti gi i on dy dn,khng qua mt on dy ni ph no, ngc li, trong cu hnh truck-line/drop line,mi trm c n nhnh (drop-line) ,cn mch vng kh c cht ch khc vi truck ngtruyn c khp kn.

Bn cnh vic tit kim dy dn th tnh n gin, d thc hin l nhng u imchnh ca cu trc bus, nh vy m cu trc ny ph bin nht trong cc h thngmng truyn thng cng nghip. Trng hp mt trm khng lm vic (do hng hc,do ct ngun...) khng nh hng ti phn cn li ca mng. Mt s h thng cn cho

php tch mt trm ra khi mng hoc thay th m vnhot ng bnh thng.

Tuy nhin vic dng chung ng truyn dn i hi mt phng php phn chiai gian s dng thch hp trnh xung t tn hiu - gi l phng php truy nhpi trnghay truy nhp bus c thc hin nh sau: ti

mt thi im nht nh ch c gi tn hiu, cn ccth

.1 Cu trc bus

Trong cu trc n gin ny, tt c cc thnh vin ca mng u c ni trc tipvi mt ng dn chung. c im cbn ca cu trc bus l vic s dng chung

ng truyn duy nht cho tt c cc trm, v th tit kim c cp dn v cng lpt.

C th phn bit ba kiu cu hnhxp vo ki

ao l ca ha

n ng trc (truck-line)-line/drop line ch

i qua mt ngng tch cc th

t trm trong khi c h thng

thm . Nguyn tc truyn thng

c mt thnh vin trong mng nh vin khc ch c quyn nhn.

Cc dy dn

truck-line

drop-line

a. daisy-chain b. truck-line/drop-line

c. mch vng khng tch cc

Hnh 2.5: Cc cu trc dng bus

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Ngoi vic cn kim sot truy nhp mi trng, cu trc bus c nhng nhc imsau:

Mt tn hiu gi i c th n tt c cc trm v theo mt trnh t khng

hi hn ch s trm

Trong trng hp dy dn bt, hoc do ngn mch trong phn kt i bus thng. Vic

nh v li y c

Mt sCAN,

2.3.2 u

rc v chuyn tip sang trm ln cn ng sau. Qu trnh ny clp li ti khi d liu quay trv trm gi, n sc hy b.

u im cbn ca mng cu trc theo kiu ny l mi mt nt ng thi c th lmt b khuych i. do vy khi thit k mng theo kiu cu trc vng c th thc hinvi khong cch v s trm rt ln. Mi trm c kh nng va nhn va pht tn hiucng mt lc. Bi mi thnh vin ngn cch mch vng ra lm hai phn v tn hiu chc truyn theo mt chiu, nn bin php trnh xung t tn hiu thc hin n gin

hn.

kim sot c, v vy phi thc hin phng php gn a ch (logic) theokiu th cng cho tng trm. Trong thc t, cng vic gn a ch ny gy ra

khng t kh khn. Tt c cc trm c kh nng pht v lun lun "nghe" ng dn phthin mt thng tin c phi gi cho mnh hay khng, nn phi c thit ksao cho ti vi s trm ti a. y chnh l l do ptrong mt on mng. Khi cn mrng mng, phi dng thm cc b lp.

Chiu di dy dn thng tng i di v vy i vi cu trc ng thngxy ra hin tng phn x ti mi u dy lm gim cht lng tn hiu. khc phc vn ny, ngi ta chn hai u dy bng hai tru cui. Vics dng hai tru cui cng lm tng ti ca h thng.

ca mt trm b hng u dn n ngng hot ng ca c hng gp rt nhiu kh khn.

Cu trc ng thng, lin kt a im gy kh khn trong vic p dng cccng ngh truyn tn hiu mi nh s dng cp quang.v d mng cng nghip tiu biu c s dng cu trc bus l PROFIBUS,

orldFIP, Foundation Fieldbus, LonW Works, AS-i v Ethernet.

C trc mch vng (tch cc)

Cu trc mng vng c thit k sao cho cc thnh vin trong mng c ni t

im ny ti im kia mt cch tun t trong mt mch vng khp kn. Mi thnh vinu tham gia tch cc vo vic kim sot dng tn hiu. Khc vi cu trc ngthng, y tn hiu c truyn i theo mt chiu quy nh. Mt trm nhn c dliu t trm ng t

Master

a. Khng c iu khin trung tm b. C iu khin trung tm

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Hnh 2.6: Cu trc mch vng

Vi kiu mch vng khng c iu khin trung tm, cc trm u bnh ng

da imch

by-pass. Trongtrng hp th hai, khi mt trm b hng, hai trm ln cn s tu tt, chuyn sangcu hnh ging nh daisy-chain.

nh nhau trong quyn nhn v pht tn hiu. Nh vy vic kim sot ngdn s do cc trm t phn chia.

Vi kiu c iu khin trung tm, mt trm ch sm nhim vai tr kim

sot vic truy nhp ng dn.C trn cslin kt

tn hiu- im, v vy thch hp

nh cp quang, tia hngu trc mch vng thc cht

o vic s dng cc phng tin truyn hin ingoi,... Vic gn a ch cho cc thnh vin trong mng cng c th do mt trm chthc hin mt cch hon ton tng cn c vo th t sp xp vt l ca cc trmtrong mch vng.

b.u tt do scti trma. By-pass scng dy

Hnh 2.7: Xl sctrong mch vngpMt u im tip theo ca cu trc mch vng l kh nng xc nh v tr xy ra s

c, v dt dy hay mt trm khng lm vic. Tuy nhin, s hot ng bnh thngca mng trong trng hp ny ch c th tip tc vi mt ng dy d phng nhFDDI.

Thit b Thit b

B chuyn mchby-passa. Trc khi xy ra sc b. Sau khi xy ra sc

Hnh 2.8: Sdng b chuyn mch by-pass trong mch vng

Trong trng hp th nht, cc trm ln cn ti im xy ra s c s t pht hin ling dy v tng chuyn sang ng dy ph, i vng qua v tr b li (by-pass).

ng cong in nt m biu din mch kn sau khi dng bin php

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Mt k thut khc c p dng t tr c b chuynmch by-pass tng. Mi trm th i m b chuynmch ny. Trong trng hp s c xy ra, b chuyn mch s tng pht hin vngn mch, b qua thit bc ni mng qua n.

Cu trc mch vng c s dng trong mt s h thng c tin cy cao nh

INTERBUS, Token-Ring (IBM) v c bit l FDDI.2.3.3 Cu trc hnh sao

Cu trc hnh sao l mt cu trc mng c mt trm trung tm quan trng hn tt ccc nt khc, nt ny siu khin hot ng truyn thng ca ton mng. Cc thnhvin khc c kt n nhau qua trm trung tm. Tng t nh cu trcmch vng, c th nhn thy y kiu lin kt v mt vt l l im - im. Nutrm trung tm ng vai tr tch cc n c thm ng nhim v kim sot ton b

c truyn thng ca mng, cn nu khng s ch nh mt b chuyn mch.Mt nhc im ca cu trc hnh sao l s m trung tm s lm t lit ton

b cc hot ng truyn thng trung tm thng phi c phn bit hai loi trm trung tm: trm tch cc v trm th

. ngn thng khng th trnh khi phi dng cu trc ny. i

v

x l sit b s

c ti mc u v

m l dng cch vng nh

i gin tip vi

vi

ctrtrong mng. V vy trm

tin cy rt cao. Ngi tang. Mt trm thng ch c vai tr trung chuyn thng tin, trong khi mt trm tch

cc kim sot ton b cc hot ng giao tip trong mng.Mt nhc im tip theo ca cu trc hnh sao l tn dy, nu nh khong cch

hn khong cch gia chng n trm trung tmtrung bnh gia cc trm nhnhin, trong cc h thng vi

i mng truyn thng cng nghip, cu trc hnh sao tm thy trong cc phm vi nh,v d cc b chia, thng dng vo mc ch mrng cu trc khc. Lu rng trongnhiu trng hp mt mng cu trc hnh sao v mt vt l li c cu trc logic nh

mt h bus, bi cc trm vn c th t do lin lc nh khng c s tn ti ca trmtrung tm. Chnh cc h thng mng Ethernet cng nghip ngy nay s dng ph bincu trc ny kt hp vi k thut chuyn mch v phng php truyn dn tc cao.2.3.4 Cu trc cy

Cu trc cy thc cht khng phi l mt cu trc cbn. Mt mng c cu trc cychnh l s lin kt ca nhiu mng con c cu trc ng thng, mch vng hoc hnhsao. c trng ca cu trc cy l s phn cp ng dn. chia tng trc racc ng nhnh, c th dng cc b ni tch cc (Active couple), hoc nu mun tngs trm cng nh phm vi ca mt mng ng nht c th dng cc b lp (repeater).

Trong tr

ng hp cc m

ng con ny hon ton khc lo

i th ph

i dng t

i cc b

linkt mng khc nh bridge v router v gateway. Mt s h thng cho php xy dng

cu trc cy cho mt mng ng nht l LonWork, DeviceNet, AS-i.

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b ni b lp b ni sao

b ni vng

Hnh 2.9: Cu trc cy

2.4 Ki

thng, kin trc giao thc m hiup trong h thng. t

v

n cc nhim v khc nhaunh nh v tham s ha thit b

trngcp h thcc dch n mm giao din mng, to lp ngi mc ciPLC,

ph th g

thng, kin trc giao thc m hiup trong h thng. t

v

n cc nhim v khc nhaunh nh v tham s ha thit b

trngcp h thcc dch n mm giao din mng, to lp ngi mc ciPLC,

ph th g

n trc giao thcthc

i vi micc dch v cn

i vi micc dch v cn

h thng truynh thng truyn l cscho vic tl cscho vic tg nh hnh thc giao tii tru tng, vg nh hnh thc giao tii tru tng, v

Kin trc giao thc l mng di y.

Kin trc giao thc l mng di y.n tng vy cn c trnh by k l

2.4.1 Dch v tru

Mt h thng ng cp dch v truyn thng cho cc thnh vin thamgia ni mng. Cc dch v c dng cho vic thc hi

n tng vy cn c trnh by k l2.4.1 Dch v tru

Mt h thng ng cp dch v truyn thng cho cc thnh vin thamgia ni mng. Cc dch v c dng cho vic thc hi

yn thngyn thng

truyn thng cutruyn thng cu

trao i d liu, bo co trng thi, to lp cu h trao i d liu, bo co trng thi, to lp cu h

, gi ng trnh. Cc d ungng truyn thng thc hin bng phn cng hoc phn mm. Vic khai thcv t pha ngi s dng phi thng qua ph

, gi ng trnh. Cc d ungng truyn thng thc hin bng phn cng hoc phn mm. Vic khai thcv t pha ngi s dng phi thng qua ph

m st thit b v ci t chm st thit b v ci t ch ch v truyn thng do nh cch v truyn thng do nh c

c c chng trnh ng dng phn mm, v d chng trnh iu khin, giao diny (HMI) v iu khin gim st (SCADA) cc giao din mng ny c th

t sn trn cc cng c phn mm chuyn dng (v d phn mm lp trnh

c c chng trnh ng dng phn mm, v d chng trnh iu khin, giao diny (HMI) v iu khin gim st (SCADA) cc giao din mng ny c th

t sn trn cc cng c phn mm chuyn dng (v d phn mm lp trnhph n mm SCADA, phn mm qun l mng), hoc qua cc th vin phn mmn khc di dng cc hm dch v (v d vi C/C++, VB, Delphi, OLE/DDE).

ph n mm SCADA, phn mm qun l mng), hoc qua cc th vin phn mmn khc di dng cc hm dch v (v d vi C/C++, VB, Delphi, OLE/DDE).

Mi h thng truyn thng khc nhau c th quy nh mt chun ring v tp hpcc dch v truyn thng ca mnh. V d PROFIBUS nh ngha cc hm dch v

khc so vi InterBus hay ControlNet. Mt phn mm chuyn dng khng nht thitphi h trton b cc dch v truyn thng ca mt h thng nhng cng c th cngmt lc h tr nhiu h thng truyn thng khc nhau. V d vi mt cng c phnmm SCADA ta c thng thi khai thc d liu t cc u o hay cc PLC lin ktvi cc bus trng khc

Mi h thng truyn thng khc nhau c th quy nh mt chun ring v tp hpcc dch v truyn thng ca mnh. V d PROFIBUS nh ngha cc hm dch v

khc so vi InterBus hay ControlNet. Mt phn mm chuyn dng khng nht thitphi h trton b cc dch v truyn thng ca mt h thng nhng cng c th cngmt lc h tr nhiu h thng truyn thng khc nhau. V d vi mt cng c phnmm SCADA ta c thng thi khai thc d liu t cc u o hay cc PLC lin ktvi cc bus trng khc nhau, nhng khng cn ti dch v h tr ci t chngtrnh iu khin cho cc PLC.

C th phn loi dch v truyn thng da theo cc cp khc nhau: Cc dch v scp (v d to v ngt ni), dch v cp thp (v d trao i d liu) v cc dch v caocp (to lp cu hnh, bo co trng thi). Mt dch vcp cao hn c th s dngcc dch v cp thp th

nhau, nhng khng cn ti dch v h tr ci t chngtrnh iu khin cho cc PLC.

C th phn loi dch v truyn thng da theo cc cp khc nhau: Cc dch v scp (v d to v ngt ni), dch v cp thp (v d trao i d liu) v cc dch v caocp (to lp cu hnh, bo co trng thi). Mt dch vcp cao hn c th s dngcc dch v cp thp thc hin chc nng ca n. V d dch v to lp cu hnh hay

bo cc trng thi cui cng cng phi s dng dch v trao i d liu thc hinchc nng ca mnh. Mt khc, trao i d liu thng i hi to v ngt ni. Phn

c hin chc nng ca n. V d dch v to lp cu hnh haybo cc trng thi cui cng cng phi s dng dch v trao i d liu thc hinchc nng ca mnh. Mt khc, trao i d liu thng i hi to v ngt ni. Phn

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cp dch v truyn thng cn c ngha l to s linh hot cho pha ngi s dng.Ty theo nhu cu v tin li hay hiu xut trao i thng tin m ngi ta c thquyt nh s dng mt dch vcp no.

Vic thc hin tt c cc dch vc da trn cc nguyn hm dch v (seviceprimittive), gm c:

equest) dch v, k hiu l .req, v d l connect.req

d connect.res

nhn connect

a trn quan h gia bn cung cp dch v v bn yu cu dch v cng c th

Hnh 2.10: Dch xc nhn v dch v khng xc nhn

th

giao tip no c cn mt ngn ng chung cho cc i tc. Trong kthut truyn thng bn cung cp dch v cng nh bn s dng dch vu phi tunth th c. Giao thc chnh l cscho

M hn sau:

cu trc bc in, gi d liu dng khi trao

ng php bo ton d liu, th tcdng thng tin, x l li...

ng t nh cc dch v

Yu cu (r Ch th(indication) nhn li phc v, k hiu l .ind, v d connect.ind.

p ng (response) dch v, k kiu l .res, v

Xc nhn (confirmation) c p ng, k hiu l .con v d.con

Dphn bit gia loi dch v c xc nhn v dch v khng xc nhn. Dch v c xcnhn i hi s dng c bn nguyn hm, trong khi dch v khng xc nhn b quap ng v xc nhn.

Bn cu Bn cung Bn cu Bn cung

1: connect.reg

v c

2.4.2 Giao c

Bt c s ng

eo cc quy tc, th tc cho vic giao tip gi l giao thvic thc hin v s dng cc dch v truyn thng.

t quy chun giao thc bao gm cc thnh p

C php (syntax) quy nh vi, trong c phn thng tin hu ch (d liu) v cc thng tin b trnha ch, thng tin iu khin, thng tin kim li...

Ng ngha (semantic) quy nh ngha c th ca tng phn trong mt bcin nh phng php nh a ch, phiu khin

nh thi (timming) quy nh v trnh t, th tc giao tip, ch truyn(ng b hay khng ng b), tc truyn thng...

Vic thc hin mt dch v truyn thng trn cscc giao thc tng ng cgi x l giao thc. Ni mt cch khc, qu trnh x l giao thc c th l m ha (xl giao thc bn gi) v gii m (x l giao thc bn nhn). T

2: connect.ind3:connect.res4.connect.con

1: disconnect.reg2: disconnect.ind

a. Dch v c xc nhn b. Dch v khng xc nhn

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truyn thng, c th phn bit cc giao thc cp thp v giao thc cao cp. Cc giaoo c l c cho o cc ch v o cp v cc giao th cp t l

ch cp thp.

dng trao i cc trang HTMLtrong ) dng trong tng

Gia h r c tip bi cc mchi

a s cc thng bus trng. Giao thc ni sau HDLC v UART c

va

thc ca p s ch d ca c hp cso cc dch vGiao thc cao cp gn vi ngi s dng , thng c thc hin bng phn mm.

Mt s v d v dch v cao cp l FTP (File Transfer Protocol) dng trong trao i

file t xa, HTTP (Hyper Text Transfer Protocol)cc ng dng Web, MMS (Manufacturing Message Specificationha cng nghip.o t c cp thp gn vi phn cng thng c thc hin t

n t. Mt s v d giao thc cp thp quen thc l TCP/IP (Transmission ControlProtocol/Internet Protocol) c dng ph bin trong Internet, HART (HighwayAddressable Remote Transducer) dng trong iu khin qu trnh, HDLC (High leverData-link Control) lm cscho nhiu giao thc khc v UART dng tronggiao din vt l ca cc h

i tr quan trng trong truyn thng cng nghip v v vy c gii thiu s lc

di y.Giao thc HDLC

HDLC cho php ch truyn bit ni tip ng b hoc khng ng b. Mt bcin hay cn gi l khung (frame) c cu trc nh sau:01111110 8/16 bit 8 bit n bit 16/32 bit 01111110

C a ch iu khin D liu FCS C

Mi khung c khi u v kt thc bng mt chiu (flag) vi dy bit 01111110.

Dy bit ny

c

m bo khng bao gi

xu

t hi

n trong cc ph

n thng tin khc quaphng php nhi bit (bit stuffing), tc c sau mi dy 5 bit c gi tr 1 (11111) th

mt bit 0 li c b xung vo. a ch tip theo cha a ch bn gi v bn nhn.Ty theo cch gn a ch 4 hoc 8 bit (tng ng vi 32 hoc 256 a ch khc nhau), ny c chiu di l 8 hoc 16 bit.

Trong HDLC c ba loi bc in, c phn bit qua thng tin iu khin (8 bit), l:

Information Frames: khung thng tin (I-Format)

Supervisory Frames: Khung gim st vn chuyn d liu (S-Format)

Unnumbered Frames: Khung b trkim sot cc mi lin kt gia cc trm(U-Format).Cu trc ca thng tin iu khin c quy nh nh sau:

I-Format 0 N(S) P/F N(R)

S-Format 1 0 S P/F N(R)

U-Format 1 1 M P/F M

N(S): S th t khung c gi chia modulo cho 8

N(R): S th t khung chnhn c chia modulo cho 8P/F: Bit chnh kt thc qu trnh truynS,M: Cc bit c chc nng khc

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thng tin c di bin thin, cng c th trng nu nh bc in khng dngvo mc ch vn chuyn d liu. Sau thng tin l n dy bit kim li (FCS =

Frame Check Sequence), dng vo mc ch bo ton d liu. Tc truyn thngtiu biu i vi HDLC t 9,6 kbit/s n 2 Mbit/s.

Giao thc UART

L mt vi mch in tc s dng rt rng ri trong vic truyn bit ni tip cngnh chuy i tip gia ng truyn v bu ART cho

php l truyn mt chiu, hai chiu ng b hoc hai chiu khng ngb. Vic truyn ti c thc hin theo tng k t 7 hoc 8 bit, c b sung hai bitnh du u cui v mt bi a li chn l(Parity bit).

Start 0 1 2 3 4 5 6 7 P Stop

n i song song/na chn ch

s my tnh. U

t kim tr

0 LSB MSB 1Bit khi u (Start bit) bao gicng l 0 v bit kt thc (S cng l 1.

Cc bit t k tc truyn theo th t t bit thp (LSB) ti bit cao (MSB).Gi tr ca bit chn l P ph thuc vo cch chn :

Nu chn P P bng 0 khi tng s bit

Nu chn Parity l, th P bng 0 khi tng s bit 1 l l.Nh th hin, ch truyn khng ng bc s dng y, tc

khng c mt tn hiu ring phc v cho vic ng b ha gia bn gi v bn nhn.Da vo cc bit u cui v tc truyn thng c t trc cho c hai bn, bn

hn thng tin phi t chnh nhp ly mu ca mnh ng b vi bn gi.2.4

n thit c th tng iph yn thng trn mtmc try tng cao. t trong mt module

cc phn vic c th thc hin c lp. Trong m hnhl

top bit) bao gi

trong m

arity chn, th 1 l chn.

tn ca n

n

.3 M hnh lp

trao i d liu gia hai thit b, cc th tc, giao thc cc tp, R rng iu cn y l s cng tc ca hai i tc tru

Thay v phi thc hin tt c cc bc cn thiduy nht, c th chia nh thnh

p, cc phn vic c xp xp theo chiu dc thnh tng lp, tng ng vi cc lpdch v v lp giao thc khc nhau. Mi lp gii quyt mt nhim v r rng phc vtruyn thng. Mt dch vlp trn s dng dch v ca lp di ngay k n.

thc hin mt dch v truyn thng, mi bc in c x l qua nhiu lp trnc s cc giao dch quy nh, gi l x l theo m hnh lp. Mi lp y c th

thuc chc nng ca phn cng hoc phn mm. Cng lp cao hn th phn mmcng chim vai tr quan trng, trong khi vic x l giao thc cc lp di thngc cc vi mch in t trc tip thc hin.

Hnh sau y minh ha nguyn tc x l giao thc theo m hnh lp. ng t bngi thng tin, qua mi lp t trn xung di, mt s thng tin b tr li c gnthm vo phn d liu do lp trn a xung, gi l u giao thc (protocol header).Bn cnh , thng tin cn truyn i c thc chia thnh nhiu bc in c nh sth t, hoc mt bc in c th tng hp t nhiu ngun thng tin khc nhau. Ngita dng cc khi nim nh"ng gi dliu" hoc "to khung" ch cc thao tcny.

Mt qu trnh ngc li s din ra bn nhn thng tin. Cc phn header sc cclp tng ng c, phn tch v tch ra trc khi gi tip ln lp trn. Cc bc inmang mt ngun thng tin sc tng hp li, hoc mt bc in mang nhiu ngun

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thng tin khc nhau sc phn chia tng ng. n lp trn cng, thng tin ngunc ti to.

Vi m hnh phn lp, ngha ca giao thc mt ln na th hin r. ng nhin, thc hin truyn thng cn c hai i tc tham gia, vy phi tn ti cng mt tph

ih

g tin iu khin giao thc

ngia

p cc hm phn lp c trong hai thit b. Quan h giao tip y chnh l quan h

gia cc lp tng ng ca hai trm. Ch khi cc i tc truyn thng trong cc lptng ng s dng chung mt ngn ng, tc chung mt giao thc th mi c thtrao i thng tin. Trong trng hp khc, cn c mt phn t trung gian hiu c haigiao thc, gi chung l b chuyn i, c th l bridge hay gateway ty theo lp giaothc ang quan tm. Vn mu cht y c th thc hin c vic chuyn il s thng nht v dch v truyn thng ca cc lp tng ng trong hai h thngkhc nhau. Nu hai h thng li quy nh cc chun khc nhau v dch v th vicchuyn i rt b hn ch v nhiu khi hon ton khng c ngha. V d, mt bn

i ci t cc dch v cao cp nh ci t v kim sot chy chng trnh t xa, trongkhi bn i tc ch cung cp dch v trao i d liu thun ty th vic chuyn i

y khng c vai tr g cng nh khng th thc hin c. Tuy nhin, cng nhngdch vcp thp cng d c chi a ra mt chun thng nht cho c hai pha.

(N+1)-PDULp N+1

(N)-SDU

PDU: Protocol Data Unit - Khi d liu giao thch vSDU: Service Data Unit - Khi d liu dc

PCI: Protocol Control Imformation Thn

Hnh 2.11: Xl giao thc theo m hnh lp

2.4.4 Kin trc giao thc OSI

Trn thc t, kh c th xy dng c mt m hnh chi tit thng nht v chuo thc v dch v cho tt c cc h thng truyn thng, nht l khi cc h thng rt

a dng v tn ti c lp. Chnh v vy, nm 1983 t chc chun ha quc t ara chun ISO 7498 vi m hnh quy chiu OSI (Open System Interconnection

Reference model), nhm h trxy dng cc h thng truyn thng c kh nng tngtc.

(N)-PDU

(N-1)-SDU

N-PCI

Lp N

(N-1)-PCI

Lp N-1

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Lu rng, ISO/OSI hon ton khng phi l chun thng nht v giao thc, cngkhng phi l mt chun chi tit v dch v truyn thng. C th thy, chun nykhng a ra bt k mt quy nh no v cu trc mt bc in, cng nh khng nhngha bt c mt chun dch v c th no. OSI ch l mt m hnh kin trc phn lpvi mc ch phc v vic sp xp v i chiu cc h thng truyn thng c sn,trong c c vic so snh, i chiu cc giao thc v dch v truyn thng, cng nh

a chng vi nhau c minhng vi mi lp l mt (nhm) chc nng c

tr

cscho vic pht trin cc h thng mi.Theo m hnh OSI, chc nng hay dch v ca mt h thng truyn thng c chia

thnh 7 lp, tng ng vi mi lp dch v l mt lp giao thc. Cc lp ny c th dophn cng hoc phn mm thc hin, tuy nhin chun ny khng cp ti chi titmt i tc truyn thng phi thc hin tng lp nh th no. Mt lp trn c ththc hin dch v ca mnh trn css dng cc dch vmt lp pha di v theong giao thc quy nh tng ng. Thng thng, cc dch v cp thp do phn cng(cc vi mch in t) thc hin, trong khi cc dch v cao cp do phn mm (hiuhnh, phn mm iu khin, phn mm ng dng) m nhim.

Vic phn lp khng nhng c ngha trong vic m t, i chiu cc h thngtruyn thng, m cn gip ch cho vic thit k cc thnh phn giao din mng. Mtlp bt k trong 7 lp c th thay i trong cch thc hin m khng nh hng ticc lp khc, chng no n gi nguyn giao din vi lp trn v lp di n. V y lmt m hnh quy chiu c tnh cht dng lm tham kho. Khng phi h thng truynthng no cng thc hin y c 7 lp . V d, v l do hiu xut trao i thngtin v gi thnh thc hin i vi cc h thng bus trng thng thng ch thc hincc lp 1,2 v 7. TRong cc trng hp ny, c th mt s lp khng thc s cn thithoc chc nng ca chng c ghp vi mt lp khc (v d vi lp ng dng).

Mt m hnh quy chiu to ra csnhng khng m bo kh nng tng tc gia

cc h thng truyn thng, cc thit b truyn thng khc nhau. Vi vic nh ngha 7lp OSI a ra mt m hnh tru tng cho cc qu trnh giao tip phn cp. Nu haih thng thc hin cng cc dch v v trn c s mt giao thc ging nhau mplp, th c ngha l hai h thng c kh nng tng tc lp . M hnh OSI c thcoi nh mt cng trnh khung, h trvic pht trin v c t cc chun giao thc.

OSI v quan h giCc lp trong m hnh quy chiuha trong hnh v di y. Tng

ng cho cc dch v v giao thc.

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Chng trnh ng dng Chng trnh ng dng

Quan h giao tip logic gia cc lp

, cc lp y chnh lc

c m t s lc di y. Lu , y tn lp 5m sot ni"mc d khng hon ton chnh xc v mt

t

ng i ca d liu

Hnh 2.12: M hnh quy chiu ISO/OSI

Cn phi nhn mnh rng, bn thn mi trng truyn thng v cc chng trnhng dng khng thuc phm vi cp ca chun OSI. Nh vy

c lp chc nng trong cc thnh phn giao din mng ca mt trm thit b bao gmc phn cng ghp ni v phn mm cs. Cc mi tn nt gch chm biu hin quanh logic gia cc i tc thuc cc lp tng ng trong khi cc mi tn nt lin chng i thc ca d liu.

Chc nng ca cc lp(Secssion) c dch sang "ki

ng nhng th hin r hn v ngha ca lp ny. Trong mt s ti liu ting vitcc tc gi chn t "Phin"bi n ngn gn v st vi t nguyn bn ting anh.

Lp ng dng (Application layer)

Lp ng dng l lp trn cng trong m hnh OSI, c chc nng cung cp cc dchv cao cp (trn cscc giao thc cao cp) cho ngi s dng v cc chng trnhng dng. V d, c th sp xp cc dch v v giao thc theo chun MMS cng nhcc dn xut ca n s dng trong mt s h thng bus trng thuc lp ng dng.

Cc dch v thuc lp ng dng hu ht c thc hin bng phn mm. Thnhphn phn mm ny c thc nhng sn trong cc linh kin giao din mng, hocdi dng phn mm iu khin (drivers) c th np khi cn thit, v/hoc mt thvin cho ngn ng lp trnh chuyn dng hoc ngn ng lp trnh ph thng. ckh nng s dng d dng trong mt chng trnh ng dng (v diu khin cshoc iu khin gim st), nhiu h thng cung cp cc dch v ny thng qua cc khichc nng (function block). i vi cc thit b trng thng minh, cc khi chc

nng ny khng chn thun mang tnh cht ca dch v truyn thng, m cn tchhp c mt s chc nng x l thng tin, thm ch ciu khin ti ch. y cng

ApplicationLp ng dng

PresentationLp biu din d liu

SectionLp kim sot kt ni

TransportLp vn chuyn

etworkLp mng

Data li kli k t d liu

nLp n

Phys aLp vt

ic ll

7

6

5

4

3

2

1

Mi trng truyn thng

7

6

5

4

3

2

1

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chnh l xu hng mi trong vic chun ha lp ng dng cho cc h thng bustrng, hng ti cu trc iu khin phn tn trit .

yer)

di 2 bytec

n d liu l chuyn i cc dng biu din d liu khcng chun, nhm to iu kin cho i tc truyn thng

c

d phng php s dng m ha.N ha, th chc nng ny

khng nh k t hp thc hin

trn l ic x l giao thc. ychnh m

Lp ki m sot n

M h thnh nhiu giai on. Cng nhvi

c ng ni gia cc ng dng i tc. Cn phi nhc lirn

a hiu hnh. th

Lp biu din dliu (presentation la

Trong mt mng truyn thng, v d mng my tnh, cc trm my tnh c th ckin trc rt khc nhau, s dng cc hiu hnh khc nhau v v vy cch biu din

d liu ca chng cng c th rt khc nhau. S khc nhau trong cch biu din dliu c th l di khc nhau cho mt kiu d liu hoc cch sp xp cc byte khcnhau trong mt kiu nhiu byte hoc s dng nhiu m k t khc nhau. V d, mt snguyn c kiu Integer c th biu din bng 2 byte, 4 byte hoc 8 byte ty theo th hCPU, hiu hnh v m hnh lp trnh. Ngay c mt kiu Integer c

ng c 2 cch sp xp th t byte gi tr cao ng trc hay ng sau byte gi trthp. Mt v d khc l s khc nhau trong cch s dng bng m k t trong cc hthng vn chuyn thin t gy ra khng t rc ri cho ngi s dng thuc cc nckhng ni ting Anh. Trong khi a s cc h thng mi s dng 8 bit, th mt s hthng c ch x l c 7 bit, v vy mt s k tc m ha vi gi tr ln hn 127

b hiu sai.Chc nng ca lp biu di

nhau v c php thnh mt dth hiu c nhau mc d chng s dng cc kiu d liu khc nhau. Ni mt

cch khc, lp biu din d liu gii phng s ph thuc ca lp ng dng vo ccphng php biu din d liu khc nhau. Ngoi ra, lp ny c th cung cp mt sdch v bo mt d liu, v

u nh cch biu din d liu c thng nht, chunt thit phi tch ring thnh mt lp c lp, m c th

p ng dng n gin ha v nng cao hiu sut ca vl t c trng trong cc h thng bus trng.

i (session layer)

t qu trnh truyn thng, thng c tin hnc giao tip gia hai ngi cn c vic t chc mi quan h, gia hai i tc truyn

thng cn c s h tr t chc mi lin kt. Lp kim sot kt ni c chc nngkim sot mi lin kt truyn thng gia cc chng trnh ng dng, bao gm vic tolp, qun l v kt thc c

g, mi lin kt gia cc chng trnh ng dng mang tnh cht logic, thng qua mtmi lin kt vt l (gia hai trm, gia hai nt mng) c th tn ti song song nhiung ni logic. Thng thng, kim sot ni thuc chc nng c

c hin ng ni gia hai ng dng i tc, hiu hnh c th to ra cc qu trnhcon tnh ton song song (cnh tranh). Nh vy, nhim vng b ha cc qu trnhtnh ton ny i vi vic s dng chung mt giao din mng cng thuc chc nngca lp kim sot ni. Chnh v th, lp ny cn c tn l lp ng b ha.

Trong cc h thng bus trng, quan h ni gia cc chng trnh ng dng cxc nh sn (quan h tnh) nn lp kim sot ni khng ng vai tr g ng k. ivi mt s h thng khc, chc nng ca lp ny c y ln kt hp vi lp ngdng v l do hiu sut x l truyn thng.

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Lp vn chuyn (transport layer)

Bt k bn cht ca cc ng dng cn trao i d liu, iu cn thit l d liu phic t cy. Khi mt khi d liu c i,cn ph u n ch v theo ng trnh t ni. Chc n chuyn l cung cp cc dch v c in vn

chuyn d ch g trnh ng dng mt cch tin c c trchnhim kh iu khin lu thng. Nhvy m cc l c hinc cc ch ao cp m khng cn quan tm ti cch v d liu cth.

Cc n lp vn chuyn bao gm:

Qu n hnh t c cho cc trm s dng

i tc truyn thng qua tn hnh thc v/ho

X l li v kim sot dng thng tin, trong c c vic lp li quan h linkt v thc

Dn knh cc ngu

chc nng cn li c dn ln kt hp vi lp ng dng tin chovi

(routing) cho vic vn chuyn d liu,gi

ao i c thc hin gin tip thng qua chng trnh ng hnh OSI). Vic thc hin trao i d liu thng

qu

rao i mt cch tini m bo tt c cc gi

chuyn i thnh tng g chng c chuy

nng ca lp v ho vic thc h

liu gia ccc phc li v n y, bao gmp trn c th thc nng c n chuyn

him v c th ca

n l v t h

nh v cc c a ch

hin cc th tc gi li d liu khi cn thit

n d liu khc nhau ng b ha gia cc trm i tc.

thc hin vic vn chuyn mt cch hiu qu, tin cy, mt d liu cn chuyn ic thc chia thnh nhiu n v vn chuyn (data segment unit) c nh s th tkim sot trc khi b xung cc thng tin kim sot lu thng.

Do cc c im ring ca mng truyn thng cng nghip, mt s nhim v c thca lp vn chuyn trnn khng cn thit, v d vic dn knh hoc kim sot luthng. Mt s

c thc hin v to iu kin cho ngi s dng t chn phng n ti u v nng

cao hiu xut truyn thng.Lp mng (network layer)

Mt h thng mng din rng (v d Internet hay mng vin thng) l s lin ktca nhiu mng tn ti c lp. Mi mng ny u c mt khng gian a ch v ccch nh a ch ring bit, s dng cng ngh truyn thng khc nhau. Mt bc ini ti tc A sang i tc B mt mng khc c th qua nhiu ng khc nhau,thi gian, qung ng vn chuyn v cht lng ng truyn v th cng khc nhau.Lp mng c trch nhim tm ng i ti u

i phng s ph thuc ca cc lp bn trn vo phng thc chuyn giao d liu v

cng ngh chuyn mch dng kt ni cc h thng khc nhau. Tiu chun ti u y hon ton da trn yu cu ca cc i tc, v d yu cu v thi gian, qungng, v gi thnh dch v hay yu cu v cht lng dch v. Vic xy dng v hy

b cc quan h lin kt gia cc nt mng cng ph thuc trch nhim ca lp mng.C th nhn thy, lp mng khng c ngha i vi mt h thng truyn thng

cng nghip, bi y khng c nhu cu trao i d liu gia hai trm thuc hai mngkhc nhau, hoc vic trdng (khng thuc lp no trong m

a chng trnh ng dng xut pht t l do l ngi s dng (lp trnh) mun c skim sot trc tip ti ng i ca mt bc in m bo tnh nng thi gian thc,

ch khng mun ph thuc vo thut ton tm ng i ti u ca cc b router. Cngv vy, cc b router thng dng trong lin kt mng hon ton khng c vai tr gtrong cc h thng bus trng.

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Lp lin kt dliu (data link layer)

Lp lin kt d liu c trch nhim truyn dn d liu mt cch tin cy trong milin kt vt l, trong bao gm vic iu khin vic truy nhp mi trng truyn dnv bo ton d liu. Lp lin kt d liu cng c chia thnh hai lp con tng ngv iu khin tr i tr ng (Medium Access

Control, MAC) v lp iu khin lin kt logic ontrol, LLC). Trongmt s h thng, lp thm chc nng khc nhkim sot lu thng v ng b ha vic chuyn liu.

thc hin ch u, th lp pha trn cng gi thnh cc bc in c chiu di hp l (fram c khung d liu ny chacc thng tin b xung phc v mc ch kim li, kim lu thng v ng b ha.Lp lin kt d liu tin s da vo cc thng tin ny xc nhtnh chnh xc ca d liu, sp xp cc khung l t v khi phc lithng tin chuyn ln lp trn n.

Lp vt l (physica

Lp vt l l lp di cng trong m hnh ph ng truyn thng camt trm thit b. Lp im to n dn d liu bng

phng tin vt l. Cc y m t giao din vt l gia mt trm thit b vmi trng truyn thng:

Cc chi ti us, c

K thut truy n cp quang...)

Phng php m RZ, Manchest

Ch truyn t ng b)

n thng nm ngoiph

yu ht da trn mt vi chun v k thut cbn.

thit bo th phn giao din mng c th tch, hoc di dng mt module ring.

i hai chc nng ni trn: Lp uy nhp m

(Logical Link Cnhim thm cclin kt d liu cgiao cc khung d

c nng bo ton d li ng tin nhn c te). Csot

bn pha nhn thngi theo ng trnh

l layer)

n cp chc nny m nhquy nh

n b cng vic truy

t v cu trc mng (b

n dn (RS-485, MBP, truy

y, hnh sao...)

ha bit (N er, FSK...)

i (di rng/di mang/ng b/khng

Cc tc truyn cho php Giao din chc (phch cm, gic cm...)

Lu rng lp vt l hon ton khng cp ti mi trng truyn thng, m chni ti giao din ca n. C th ni, quy nh v mi trng truy

m vi ca m hnh OSI.Lp vt l cn c chun ha sao cho mt h thng truyn thng c s la chn

gia mt vi kh nng khc nhau. Trong cc h thng bus trng, s la chn nkhng qu ln, h

Tin trnh thc hin giao tip theo m hnh OSI c minh ha bng mt v d trao

i d liu gia mt my tnh iu khin v mt thit bo thng minh, th hin tronghnh v sau. Cc mi tn nt gch chm th hin quan h giao tip logic gia cc lptng ng thuc hai trm. Lp vt l thuc trm A c ni trc tip vi lp vt ltrm B qua cp truyn. Trong thc t, cc chc nng thuc lp vt l v lp lin ktd liu c thc hin hu ht trn cc vi mch in t ca phn giao din mng. ivi cc my tnh iu khin hoc cchp trong phn x l trung tm

Khi chng trnh iu khin trm A cn cp nht gi tro, n s s dng dch vtrao i d liu lp ng dng gi mt yu cu ti trm B. Trong thc t qu trnh

ny c th thc hin n gin bng cch gi mt hm trong th vin giao tip camng c s dng. Quan h ni gia hai trm c thit lp sn.

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My tnh iu khin(Tr

Thit bo (Trmm A) B)

CT iu khin CT iu khinLp ng dng Lp ng dng

Lp 3-6 Lp 3-6

Lp lin kt d liu Lp lin kt d liuLp vt l Lp vt lLp vt l Lp vt l

Cp truyn

Hnh 2.13: V d giao tip theo m hnh OSI

Lp ng dng bn A x l yu cu ca chng trnh iu khin v chuyn tip mlnh xung lp pha di - lp biu din d liu: Lp ny biu din m lnh thnh mt

t quy c, sau chuyn tip xung lp kim sot ni. Lpg thng tin phn bit yu cu cp nht d liu xut pht t

qu

tr

i din ra bn B. Qua lp vt l, tn hiu nhn c c gi mc khi phc. Mi lp pha trn s phn tch phn thng tin b

thc hin cc chc nng tng ng. Trc khi chuyn ln lp trnc tch ra. ng nhin, cc qu trnh ny i hi hai

lp liu bnthit b chuyn gi tro cp nht tr li trm A cng theong2.4.5 c TCP/IP

TC P u vph

dy bit c di v thkim sot ni s b xun

an h ni logic no, t qu trnh tnh ton no. Bc ny trnn cn thit khi trongmt chng trnh ng dng c nhiu qu trnh tnh ton cnh tranh (task) cn phi sdng dch v trao i d liu, v kt qu cp nht d liu phi c a tr vngni yu cu.

Khi d liu giao thc (PDU) t lp kim sot ni chuyn xung c lp vnchuyn xp xp mt knh truyn ti v m bo yu cu sc chuyn ti bn B mtcch tin cy. S dng dch v chuyn mch v tm ng i ti u ca lp mng, mts thng tin sc b sung vo bc in cn chuyn nu cn thit. Tip theo lp linkt d liu gn thm cc thng tin bo ton d liu, s dng th tc truy nhp mi

ng chuyn bc in xung lp vt l. Cui cng, cc vi mch in t di lpvt l (v d cc b thu pht RS-485) chuyn ha dy bit sang mt dng tn hiu thchhp vi ng truyn (m ha bit) gi sang bn B, vi mt tc truyn hay nicch khc l tc m ha bit theo quy c.

Qu trnh ngc lv dy bit d liu xung ca mnh tip theo, phn thng tin ny

i tc ca hai bn phi hiu c thng tin c cu trc v ngha nh th no,tc l phi s dng cng mt giao thc. Cui cng, chng trnh thu thp do nhn c tu cu v

trnh t nh trn.Kin trc giao th

P/I (Transmition Control Protocol/Internet Protocol) l kt qu nghin ct trin giao thc trong mng chuyn mch gi th nghim mang tn Apranet do

ARPA (Advanced ...) thuc b quc phng Hoa K ti tr. Khi nim TCP/IP dng ch c mt tp giao thc v dch v truyn thng c cng nhn thnh chun choInternet. Cho n nay, TCP/IP xm nhp n rt nhiu phm vi ng dng khcnhau, trong c cc mng my tnh cc b v mng truyn thng cng nghip.

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Kin trc giao thc TCP/IP v i chiu vi m hnh OSI c minh ha bi hnhv di y.

OSI TCP/IP

Lp ng dng

Lp biu din dliu

Lp ng dng

TELNET FTPSNMP SMTP

DNS

Lp kim sot niLp vn chuyn

Lp vn chuynTCP UDP

Lp Internet

ICMP IP ARP RARPLp mng

Lp lin kt dliuLp truy nhp mng

Lp vt l Lp vt l

Hnh 2.14: So snh TCP/IP v OSI

Khc vi OSI thc ra khng c mt m hnh giao thc no c cng b chnh thc

cho TCP/IP. Tuy nhin, da theo cc chun giao thc c pht trin ta c th spxp cc chc nng truyn thng cho TCP/IP thnh 5 lp c lp l lp ng dng, lpvn chuyn, lp Internet, lp truy nhp mng v lp vt l.

Nu tch ring TCP v IP th l nhng chun ring v giao thc truyn thng,tng ng vi lp vn chuyn v lp mng trong m hnh OSI. Nhng ngi tacng dng TCP/IP ch mt m hnh truyn thng, ra i trc khi c chun OSI.

Lp ng dng

Lp ng dng thc hin cc chc nng h trcn thit cho nhiu ng dng khcnh

v DNS (Domain Name Service) phc v qun l v trac

au. Vi mi loi ng dng cn mt module ring bit, v d FTP (File Transfer

Protocol) cho chuyn giao file, Telnet cho lm vic vi trm ch t xa, SMTP (SimpleMail Transfer Protocol) cho chuyn thin t, SNMP (Simple Network ManagementProtocol) cho qun tr mng

u danh sch tn v a ch Internet.

Lp vn chuyn

C chm bo d liu c vn chuyn mt cch tin cy hon ton khng phthuc vo c tnh ca cc ng dng s dng d liu. Chnh v th cch ny csp xp vo mt lp c lp tt c cc ng dng khc nhau c th s dng chung,c gi l lp vn chuyn. C th ni, TCP l giao thc tiu biu nht, ph bin nht

phc v vic thc hin chc nng ni trn. TCP h trvic trao i d liu trn csdch v c ni.

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Bn cnh TCP, giao thc UDP (User Data Protocol) cng c s dng cho lpvn chuyn. Khc vi TCP, UDP cung cp dch v khng c ni cho vic gi d lium khng m bo tuyt i n ch, khng m bo trnh tn ch ca cc gi dliu. Tuy nhin, UDP li n gin v hiu qu, chi hi mt cch x l ti thiu,v

c c nhim v tm ng i ti u.

Lp truy nhp mng

Lp truy nhp mng lin quan ti vic trao i d liu gia hai trm thit b trongcng mt mng. Cc chc nng bao gm vic kim sot truy nhp mi trng truyndn, kim li v lu thng d liu, ging nh lp lin kt d liu trong m hnh OSI.

Lp vt l

Ging nh trong m hnh OSI, lp vt l cp ti giao din vt l gia mt thitb truyn d liu (my tnh PC, PLC) vi mi trng truyn dn hay mng, trong c h n v cccm

So s a TCP/IP v OSI l mt v d lm sng t bn cht v ngha thc s

a m hnh quy chiu OSI. Trong thc t khng c mt giao thc no c gi liao thc OSI, cng khng c dch v no c gi l dch v OSI. Ta ch c th spxp giao thc n p no trong mhn

ruyn dn trong phm vi khong cch va v nh.

g dn hay phng php truy nhp bus.

vy thng c dng lm csthc hin cc giao thc cao cp theo yu cu ringca ngi s dng; Mt v d tiu biu l giao thc SNMP.

Lp Internet

Tng t nh lp mng OSI, lp Internet c chc nng chuyn giao d liu gianhiu mng c lin kt vi nhau. Giao thc IP c s dng chnh lp ny, nhci tn ca n hm . Giao thc IP c thc hin khng nhng cc thit bucui, m cn cc b router. Mt router chnh l mt thit b x l giao thc dng lin kt hai mng, c chc nng chuyn giao d liu t mt mng ny sang mt mngkhc, trong

c tnh tn hiu, c.

truyn, tc truy cu trc c hc phc cm/gic

nh gi

cg

o, dch v no thuc lp no hay tng ng vi lh quy chiu ny.

2.5 Truy nhp bus

2.5.1t vn

Trong cc h thng mng truyn thng cng nghip th cc h thng c cu trcdng bus, hay h thng bus ng vai tr quan trng nht v nhng l do sau:

Chi ph cho dy dn t D thc hin lp t

Linh hot

Thch hp cho vic tTrong mt mng c cu trc bus, cc thnh vin phi chia nhau thi gian s dng

ng tuyn dn. trnh s xung t v tn hiu gy ra sai lch v thng tin, mithi im trn mt ng dy ch duy nht mt in tn c php truyn i. Chnh vvy mng phi c iu khin sao cho ti mt thi im nht nh th ch mt thnhvin trong mng c gi thng tin i. Cn s lng thnh vin trong mng mun

nhn truyn thng th khng hn ch. Mt trong nhng vn quan trng hng unh hng ti cht lng cu mi h thng bus l phng php phn chia thi gian githng tin trn n

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L u r ng, mt s cu trc khng n xung t tn hiu cngc th xy ra, tuy khng hi cu trc mch vng, mitrm khng phi bao gi cng c kh nng khng ch hon ton tn hiu i qua n.Ha

us, "truy s" cng t c dngnh

rao i thng tin mt cch kp thi v tin cy. Cn hiu

su

m mt h thng truyn thng cn p ng mt nhu cu trao

bus c lin quan vi nhau, nhng khng mc r . Chu k bus ln m tng thi gian Tuy nhinthi gian p ng ti a c th nh hoc ln hn mt chu k bus, ph thuc vo

phng php truy nhTrong mt s h m chu k bus

khng c ngha bi cc hot ng giao tip tu kc phn tn vc thc hin theo mt lch trnh thi gian (schedule). Khi , rung l mt thngs quan trng nh gi tnh nng thi gian th c hiu l khong thigian sai lch gia thi im thc t mt trm g u so vi thi im lplch, cng nh gia thi im thc t mt tr u so vi thi immong mun tron

Hiu sut s dng ng truyn c tnh bng phn trm thi gian ng truync s dng thc s hiu qu vo vic truyn ti d liu. i lng ny ph thuc

o mt lu thng v phng php truy nhp bus. Mt lu thng thp dn nhiu sut thp, n n vn n tclu thng v lm n ti a,

phi dng bus, vn nhin nh cu trc bus. V d

y cu trc hnh sao, c th trm trung tm khng c vai tr chng m ch l bchia tn hiu nn kh nng gy xung t khng th trnh khi. Trong cc cu trc nyta vn cn mt bin php phn chia quyn truy nhp, tuy c thn gin hn so vicu trc bus. Chnh v th khi nim truy nhp mi trngcng c dng thay chotruy nhp bus. Tuy nhin, ging nh cch dng khi nim chung "bus trng" khngch dng li c ng c cc h th u trc b nhp bu hng

mt khi nim chung.Phng php truy nhp bus l mt trong nhng vn cbn i vi cc h thng

bus, bi mi phng php c nhng nh hng khc nhau ti cc tnh nng k thutca h thng. C th, ta phi quan tm ti t nht ba kha cnh: tin cy, tnh nngthi gian thc v hiu sut sdngng truyn. Tnh nng thi gian thc y lkh nng p ng nhu cu t

t s dng ng truyn l mc khc, s dng ng truyn.Ba yu t lin quan ti vic nh gi yu t tnh nng thi gian thc l thi gianp ng ti a, chu k bus v rung (Jitter). Thi gian p ng ti a i vi mttrm l thi gian ti a

i d liu ca trm vi mt trm bt k khc. R rng, thi gian p ng ti akhng phi l mt thng s cnh, m l mt hm ca di ca d liu cn trao i.Tuy vy, trong mt ng dng c th ta thng bit trc di d liu ti a cng nh di d liu tiu biu m cc trm cn trao i. Do vy, bn cnh thi gian p ngti a ngi ta cng quan tm ti thi gian p ng tiu biu.

Do c trng k thut tng ha, a s cc h thng bus c s dng lnh vc

ny lm vic theo chu k. Ch mt s cc hot ng truyn thng xy ra bt thng (vd thng tin cnh bo, d liu tham s,...), cn phn ln cc d liu c trao i nhk theo chu k tun hon ca bus. Chu k bus l khong thi gian ti thiu m sau cc hot ng truyn thng chnh lp li nh c. Trong iu khin tng, chu k busnh hng ti s chnh xc ca chu k ly mu tn hiu. Lu s khc nhau gia chuk bus v nhp bus.

C th d thy, thi gian p ng v chu kng buc thng l p ng.

p bus.thng bus, v d Foundation Fieldbus H1, khi ni

n hon theo chu

c. rung i c d li

m nhn c d lig lch trnh.

v hng ngc li mt lu thng qu cao cng dn gim hiu xut. t c hiu sut s dng ng truy

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c

xc nh r rng. Vic truy nhp bus c kim sot cht tr theo cch tp

tru

Hnh 2.15: Phn loi cc ph p bus

t tn hiu xy ra, th t nht mt trm phi ngngg

Nhvy, cc trm tc th gi cc d liu thu thp t qu trnhk

n phi tnh ton hoc th nghim tm ra cc thng s cho thit k cu hnh mng,trn csphng php truy nhp bus c p dng.

C th phn loi cch truy nhp bus thnh nhm cc phng php tin nh vnhm cc phng php ngu nhin. Vi cc phng php tin nh, trnh t truy nhp

bus c

ng mt trm ch (phng php Master/Slaver hay ch/t). Theo s quy nh trcv thi gian (phng php TDMA) hoc phn tn bi cc thnh vin (phng phptoken passing). Nu mi hot ng truyn thng c hn ch bi mt khong thigian hoc mt di d liu nht nh, th thi gian p ng ti a cng nh mt chuk bus c th tnh ton c. Cc h thng ny v thc gi l c tnh nng thigian thc.

Phng phptruy nhp bus

Truy nhp tin nh Truy nhp ngu nhin

Kim sot tp trungMaster/Slaver

TDMA

Kim sot phn tnToken Passing

Nhn bit xung tCSMA/CD

Trnh xung tCSMA/CD

ng php truy nh

Ngc li, trong cc phng php ngu nhin trnh t truy nhp bus khng cquy nh cht tr trc, m xy ra hon ton theo nhu cu ca cc trm. Mi thnhvin trong mng c th th truy nhp bus gi thng tin i bt k lc no. loi trtc hi ca vic xung t gy nn, c nhng phng php ph bin nh nhn bit xungt (CSMA/CD) hoc trnh xung t (CSMA/CA). Nguyn tc hot ng ca cc

phng php ny l khi c xungi v chmt khong thi gian no trc khi th li, mc d kh nng thnh cng

k c lc ny cng khng c m bo. Ngi ta thng coi cc h thng s dngcc phng php ny khng c kh nng thi gian thc. Tuy nhin, ty theo lnh vcng dng c th m yu cu v tnh nng thi gian thc cng khc nhau.2.5.2 Ch/t(Master/Slaver)

Trong phng php ch/t, mt trm ch (Master) c trch nhim chng phnchia quyn truy nhp bus cho cc trm t (slaver). Cc trm tng vai tr bng,ch c quyn truy nhp bus v gi tn hiu i khi c yu cu. Trm ch c th dng

n t (polling) theo chu k kim sot ton b hot ng giaophng php hi tutip ca c h thng.

thut ti trm ch (c th l mt PLC, mt PC,...) cng nh nhn cc thng tin iukhin t trm ch.

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Master

Slaver Slaver Slaver Slaver

Hnh 2.16: Phng php ch/t

Trong mt s h ng, cc tr m tkhng c quyn giao tip trc tip vi nhau, mbt c d liu cn trao i no cng phi qua trm ch. Nu hot ng giao tip din

ra theo chu k, tr

th

m ch s c trch nhim chng y trm tcn giv

y trnh tc hi c th do ngi s dng quynh tr cduy nht, t vng cng chnhl thi amt cch t y chnh l mt trong nhng yu t th hin tnh nngthi gi t

Ph gtn kml mt thiiu khn

hn c lnh kt thc t trm t2 (send_completed), trm t1 s c trch nhim thng bo ngc tr li trm ch(receive_completed). Nh vy,vic truy nhp ng truyn cng khng b chng cho ln nhau, v hai trm tvntrao i c d liu trong mt chu k bus.

u cu d liu tsau chuyn ti trm tcn nhn. Trong trng hp mt trm tcn trao i dliu bt thng vi mt trm khc phi thng bo yu cu ca mnh khi c trm chhi n v sau chc phc v.

Trnh tc tham gia giao tip, ha bng cc cng c to lp cu hnh. Trong trng hp ch c mt trm ch

thi gian cn cho trm ch hon thnh vic hi tun t mgi n ti thiu ca chu k bus. Do vy, chu k bus c th tnh ton trc c

ng i chc chn.an hc ca h thng.

n php ch/tc mt u im l vic kt ni mng cc trm tn gin, bi gn nh ton b "tr tu" tp trung ti trm ch. Mt trm ch thng li

t biu khin, v vy vic tch hp thm chc nng x l truyn thng lg kh khn.c im ca phMt nh ng php kim sot tp trung ch/t l hiu sut trao i

thng tin gia cc trm tb gim do d liu phi i quan khu trung gian l trm ch,dn n gim hiu sut s dng ng truyn. Nu hai trm tcn trao i mt bind liu n gin vi nhau (mt PLC c th l mt trm t), th trong nhng trng hpxu nht thi gian p ng vn c th ko di ti hn mt chu k bus. Mt trong cc

bin php ci thin tnh hung ny l cho php cc trm ttrao i d liu trong mtchng mc c kim sot. Tnh hung y l hai trm tmun gi d liu cho mttrm t, trong khi trm t2 li c trm ch hi ti sau trm t1. Sau khi trm chyu cu trm t1 nhn d liu v trm t2 gi d liu, trm t2 c th gi d liutrc tip ti trm t1. N

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Master Slaver 1 Slaver 2

1: receiver_request

2: send_request

3: send_data

4: send

Hnh 2.17: Ci thin trao i dliu gia hai trm t

Mt hn ch na ca phng php ny l tin cy ca h thng truyn thng phthu

nng thay th trm ch khi

vic trao i thng tin hunh c dhoc cc p gia cc thit b tc nhu cu traoi d

kim s t2.5.3 TDM

TRong DivisionMutip A

trm c th ong thi gian cho php - gil khe thi gian hay lt i gian (Time slot, Time slide) theo mt tun quy nhsn. Vic phn chi o ho ng (tinnh). Khc vi ph trm ch. Trongtr

c hon ton vo mt trm ch duy nht. Trong trng hp c s c xy ra trntrm ch th ton b h thng truyn thng ngng lm vic. Mt cch khc phc l s

ai tr gim st trm ch c c khdng mt trm tng vcn thit.

Chnh v l do nu trn, phng php ch/tchc dng ph bin trong cc hthng bus cp thp, tc l bus trng hay bus thit b, khi

h in ra gia trm ch l thit biu khin v cc trm t l thit b trngmodule vo/ra phn tn. Trong trng h

li u tr c tip, trm ch ch c vai tr phn chia quyn truy nhp bus ch khng

o ton b hot ng giao tip ca h thng.A

phng php kim sot truy nhp phn chia thi gian TDMA (Timele ccess), mi trm c phn chia mt thi gin truy nhp bus nht nh. Cc

thay nhau ln lt gi thng tin trong mt khth t

ta ny c thc hin trc khi h thng i vng php ch/t, y c th c hoc khng c

ng hp c mt trm ch th vai tr ca n ch hn chmc kim sot vic

tun thm bo ging lt thi gian ca cc trm khc. Mi trm u c kh nngm nhim vai tr chng trong giao tip trc tip vi cc trm khc.

1 2 ... N Theo yu cu

Chu k bus (chu k TDMA)

Hnh trn minh ha cch phn chia thi gian cho cc trm trong mt chu k bus.Ngoi cc lt thi gian phn chia cnh cho cc trm dng trao i d liu nh k

(nh s t 1 n N), thng cn c mt khong thi gian d tr ginh cho vic traoi d liu bt thng theo yu cu, v d gi thng tin

_complateted

5: receiver_complateted

cnh bo, mnh lnh t cuhnh, d liu tham s, setpoint...

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V nguyn tc TDMA c th thc hin theo nhiu cch khc nhau. C th phn chiath t truy nhp bus theo v tr sp xp ca cc trm trong mng, theo th ta ch.Ho

thiy thch hp cho cc ng dng thi gian thc. Trong mt s

ng c th p dng kt hp hai phng php ch/tv TDMA.2.5

kh nng tham giaki n khng c a tip, c thdo mt trm s c chc nng totoken m Chnh v vy, Token Passing c xp vo phng php kim sot phntn. Trnh t ng thi gian c quyn gi oken, t n ng v chu k

bus ti a c th tnh ton trc, do vy phng php truy nhp ny cng c coi lc tnh ti nh.

rong gian xc lp cu hnh, cc trm c th d tnh v thi gian dng tokenc mnh, t i ti tha thun mt chu k bus thch hp tt c cc trm u cquyn tha ia g hng t v ki t h n thng ca mng. Vicki sot bao gm cc cng vic sau:

c theo tnh cht ca cc hot ng truyn thng. Cng c th kt hp TDMA viphng php ch/tnhng cho php cc trm tgiao tip trc tip. C h thng li sdng mt bc in tng hp c cu trc ging nh s phn chia thi gian cctrm c thc v ghi d liu vo phn tng ng.

Cng nh phng php ch/t, chnh v tnh cht tin nh ca cch phn chiagian m phng php ntrng hp, ngi ta c

.4 Token Passing

Token l mt bc in ngn khng mang d liu, c cu trc c bit phn bitvi cc bc in mang thng tin ngun, c dng tng t nh mt cha kha. Mttrm c quyn truy nhp bus v gi thng tin i ch trong thi gian n c gitoken. Sau khi khng c nhu cu gi thng tin, trm ang c token s phi gi tip timt trm khc theo trnh t nht nh. Nu trnh t ny ng vi vi trnh t sp xpvt l trong mt mch vng (tch cc hoc khng tch cc), ta dng khi nim TokenRing (chun IEEE 802.4). Cn nu trnh t quy nh ch c tnh cht logic nhcutrc bus (v d theo th ta ch), ta ni ti Token Bus (chun IEEE 802.5). Trongmi trng hp du hnh thnh mt mch vng logic.

Hnh 2.18: Hai dng ca phng php Token Passing

Mt trm ang gi token khng nhng c quyn gi thng tin i, m cn c thc vai tr kim sot s hot ng ca mt s trm khc, v d kim tra xem c trmno xy ra s c hay khng. Cc trm khng c Token cng c

m sot, v d nh sau mt thi gian nht nh m toke,trm ang gi token c vn . Trong trng hp

i. c nh T hi gian ph

nTa

thi

m g i t in m so ot ng truym

Token

Trm 1

Trm 2Trm 1 Trm 2

Trm 3

Trm 4

Trm 5

Trm 6

Trm 3 Tr m 4 Tr m 5 Trm 6

Token

Token Ring Token Bus

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Gim st token: N do m i no m token b mt hoc gia bi, cnphi thng bo xa cc token c hoc to mt token mi.

Khi to nh c trch nhimto mt to

l mt trm ch, hay cn c gi l trm tch cc. Phngph

rong khi gia cc trm ch th quyn truy nhp bus c phn chia theo cchch ng vai tr l chy khng bt buc phi cc

php CSMA/CD, mi trm u c quyn truy nhp bus m khng cnhng php c tin hnh nh sau:

u phi t nghe ng dn (carrier sense), nu ng dn ri tn hiu) th mi c pht.

nhn c xem c xy ra xung t hay khng (collision detection)

u t l

token: Sau khi khi ng mt trm c chken mi.

Tch trm ra khi mch vng logic: Mt trm c s c phi c pht hin

v tch ra khi trnh tc nhn token. Bxung trm mi: Mt trm mi c kt ni mng, mt trm cc thay

th hoc a trli s dng phi c b xung vo mch vng logic cquyn nhn token.

c th s dng kt hp vi phng php ch/t, trong miToken Passing cngtrm c quyn gi token

p kt hp ny cn c gi l nhiu ch(Multi-Master), tiu biu trong h thngPROFIBUS. Cc trm ch ny c th l cc biu khin hoc cc my tnh lp trnh,cn cc trm t (trm khng tch cc) l cc thit b vo/ra phn tn, cc thit btrng thng minh. Mi trm ch qun l quyn truy nhp ca mt s trm t trcthuc, t

uyn token. Tuy nhin, mt trmc trm ttrc thuc.

Master Master Master MasterMaster

(1) Token Passing gia cc trm tch cc

(2) Master/Slave gia mt trm tch cc v mt s trm khng tch cc

Hnh 2.19: Truy nhp bus kt hp nhiu ch (Muti-Master)

2.5.5 CSMA/CD

CSMA/CD (Carrier Sense Mutiple Access with Collision Detection) l mt phngphp ni ting cng vi mng Ethernet (IEEE 802.3).

Nguyn tc lm vic:

Theo phngc s kim sot no, p

m Mi tr(khng c

Do vic lan truyn tn hiu cn mt thi gian no , nn vic c kh nng

hai trm cng pht tn hiu ln ng dn. Chnh v vy, trong khi pht thmi trm vn phi nghe ng dn so snh tn hiu pht i vi tn hiu

Slave Slave Slave Slave

1

2

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Trong trng hp xy ra xung t, mi trm u phi hy b bc in camnh, chmt thi gian ngu nhin v th li.

inh ha phng php CSMA/CD

y ra xung t tiu biu v cch khc phc c minh ha trnhn

gi i bng cch khng pht tip, cc trm mun nhn s khng nhn c chi

ng thi gian cha hai ln thi gian lan truyn tn hiu TS.

c

Hnh 2.20: M

Mt tnh hung xh v trn. Trm A v trm C cng nghe ng dn. ng dn ri nn A c th gi

trc. Trong khi tn hiu gi i t trm A cha kp ti nn trm C khng hay bit vcng gi, gy ra xung t ti mt im gn C. A v C s ln lt nhn c tn hiu

phn hi, so snh vi tn hiu gi i v pht hin xung t. C hai trm s hy bcin

u kt thc bc in v s coi nh bc in khng hp l. A v C cng c th gimt tn hiu "jam" c bit bo cho cc trm cn nhn bit. Sau mi trm chmt thi gian chngu nhin, trc khi th pht li. Thi gian chngu nhin ytuy nhin phi c tnh theo mt thut ton no sao cho thi gian chngn mtcch hp l v khng ging nhau gia cc trm cng ch. Thng thny l bi s c

u im ca CSMA/CD l tnh cht n gin, linh hot. Khc vi cc phng phptin nh, vic ghp thm hay bi mt trm trong mng khng nh hng g ti hotng ca h thng. Chnh v vy, phng php ny c p dng rng ri trong mngEthernet.

Nhc im ca CSMA/CD l tnh bt nh ca thi gian phn ng. Cc trm ubnh ng nh nhau nn qu trnh chmt trm c th lp i lp li, khng xc nhc tng i chnh xc thi gian. Hiu sut s dng ng truyn v th cng thp.R rng, nu nh khng kt hp thm vi cc k thut khc th phng php nykhng thch hp vi cc cp thp, i hi trao i d liu nh k, thi gian thc.

iu kin rng bu

Kh nng thc hin phng php CSMA/CD b hn ch bi mt iu kin rngbuc gia chiu di dy dn, tc truyn thng v chiu di bc in. Ch khi mttrm pht hin c xung t xy ra trong khi bc in cha gi xong mi c kh

nng hy b bc in (c th chn gin bng cch khng gi tip chiu kt thc).Cn nu bc in c gi i xo

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