thiet_ke_mang_rs485

8/7/2019 Thiet_ke_mang_rs485

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ti: NGHIN CU V THIT K MNG RS 485 Trang:1

GII THIU TI

Ngy nay vi tc pht trin nhanh ca cng ngh vi in t k thut

truyn thng v cng ngh phn mm. Trong nhng nm gn y to ra s

chuyn bin c bn trong hng i,m c ng dng thc trin trong i sng,

trong khoa hc k thut m cng ngh vi x l em n.V d nh iu khin mt

to nh, cc thit b sinh hot, t ng bo chy ...v..v

Trong lnh vc t ng ho cng nghip t n gin iu khin trc tuyn

trn mt n v x l cho ti kt hp ca nhiu vi x l iu khin mt hthng phc tp.Vy vi em l sinh vin ca nghnh t ng iu khin vi ti

c giao l "Nghin cu v thit k mng RS485" ng dng vo thc t cho

cng vic chuyn mn, em s i su vo pht trin v ng dng mng RS485

phc v cho cng vic chuyn mn ca em (ni ring) v trong nghnh cng

nghip (ni chung).

Vi ti c giao l nghin cu v thit k mng RS485 ng dng cho

ti y l dng phng php Master v Slave (ch v t) ti pht tringm:

1. Trm ch ( Master ) v hai trm t (Slave ).

2. Trm t 1 dng iu khin Led thng qua ng truyn RS 485.

3. Trm t 2 cng ging nh trm t1 nhng c thm iu khin ng c.

- ng truyn RS485 l chun giao tip ni tip bt ng b cn bng

s dng in p chnh lch i xng gia hai u dy dn. Dng mng Half -

Duplex (bn song cng) tc l ti mt thi im bt k trn dy truyn ch c thl mt thit b hoc l truyn hoc l nhn.

- RS 485 cho php 32 b truyn trn Bus to thnh mng cc b (mng

Lan ).


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PHN I

C SL THUYT

Chng I: CH TRUYN TI

I:Truyn bit song song v truyn bit ni tip.

1: Truyn bit song song :

- Phng php truyn bit song song c dng ph bin trong cc bus ni

my tnh, bus gi liu, bus a ch,bus iu khin, tc truyn ti ph thuc vo

s cc knh dn hay chnh l rng ca bus song song.

VD: 8 bit, 16 bit, 32 bit hay 64 bit.

- Phng php truyn ny ch hn ch khong cch nh, c yu cu rt

cao v thi gian v tc truyn .

2: Truyn bit ni tip :

- Vi phng php ny tng bit c chuyn i mt cch tun t qua mt

ng truyn duy nht, tc bit v th hn ch, nhng cch thc hin li n

gin, tin cy ca d liu cao. Tt c cc mng truyn thng u s dng

phng php ny .

II: Truyn ng b v khng ng b.

- S phn bit gia ch truyn ng b v khng ng b ch lin quan

ti phng thc truyn bit song song, vn t ra y l ng b ho gia bn

gi v bn nhn d liu .

- Trong ch truyn ng b cc i tc truyn thng lm vic theo cng

mt nhp, tc vi cng tn s v lch pha c nh c th quy nh mt trm c


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vai tr to nhp v dng mt ng dy ring mang nhp ng b cho cc trm

khc .

- 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 hoc 8

bit gi l k t, cc k t c chuyn i vo cc thi im khng ng u. V

vy cn thm 2 bit nh du khi u v kt thc cho mi 1 k t.

III: Truyn mt chiu, hai chiu ton phn v gin on.

- Mt ng truyn d liu hoc lm vic theo ch hai chiu ton phn

hoc hai chiu gin on .

- Trong ch truyn mt chiu, thng tin ch c truyn i theo mt

chiu, mt trm ch c th ng vai tr hoc bn pht hoc bn nhn thng tin

trong sut qu trnh giao tip.

- Ch truyn hai chiu gin on cho php mi trm c th tham gia

gi hoc nhn thng tin nhng khng cng mt lc, nh vy m thng tin c

trao i theo c hai chiu lun phin trn cng mt ng truyn vt l.

- Vi ch truyn hai chiu ton phn mi trm u c th gi v nhn

thng tin cng mt lc. Phngphp ny s dng hai ng truyn ring bit cho

thu v pht .

IV: Truyn ti di c s, truyn ti di mang v truyn ti di

rng.

1: Truyn ti di c s :

- Mt tn hiu mang mt ngun thng tin c th biu din bng tng ca

nhiu dao ng c tn s khc nhau nm trong mt phm vi hp c gi l di

tn c s hay di hp. Tn hiu c truyn i cng chnh l tn hiu c tao ra


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sau khi m ho bit. Mi thnh vin trong mng phi phn chia thi gian s

dng ng truyn v trong mt nhp ch c th truyn i mt bt .

2: Truyn ti di mang :- Trong mt s trng hp di tn c s khng tng thc trong mi

trng lm vic .

VD: Tn hiu c tn s, c th bc x nhiu nh hng ti cc thit b

khc hoc ngc li b cc thit b khc gy nhiu. khc phc tnh trng ny ta

s dng tn hiu mang di tn ny ln hn nhiu so vi tn s nhp, d liu cn ti

s dng kim ch tn s, bin pha tn hiu mang, bn nhn s thc hin qu

trnh gii iu ch phc hi thng tin ngun .

3: Truyn ti di rng :

- Mt tn hiu c th cha ng nhiu ngun thng tin khc nhau, bng

cch s dng kt hp mt cch thng minh nhiu thng s thng tin. Sau khi nhiu

ngun thng tin khc nhau c m ha bit, mt tn hiu c to ra s dng

iu bin mt tn hiu khc thng c tn s ln hn nhiu gi l tn hiu mang,

cc tn hiu mang c iu bin c tn s khc nhau nn c th pha trn xp

chng thnh tn hiu duy nht c ph tn tri rng, tn hiu ny cui cng li c

dng iu bin mt tn hiu mang khc, tn hiu thu c t khu ny mi c

truyn i, y chnh l k thut dng knh phn tn.

V: Cu trc mng bus:

- c s dng mt ng dn chung cho h thng, cc thnh vin tham

gia vo mng c ni trc tip qua ng dn chung ny, y l mt kt cu ca

cu trc n gin c u im v mt tit kim dy dn, d lp t.

- Trong cu trc bus ny ta c th chia lm ba cu trc sau: nh c m

t hnh v 1.3 (trang bn).


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+ Daisy-chain, Trunk-line/Drop-line v Mch vng khng tch cc.

+ hai cu trc u Daisy-chain v Trunk-line/Drop-line cc thnh vin

tham gia vo mng c ni vi nhau theo cu trc ng thng bi v hai u

ca ng thng khng khp kn.

+ i vi Daisy-chain cc trm c ni theo phng php ni tip

nhau bi nhng dy dn khng ni qua on dy ph nh cu trc ca Trunk-

line/Drop-line.

+ Phng php ni mng trong cu trc ca Trunk-line/Drop-line th

ngc li so vi Daisy-chain, mi thnh vin ni mng khng ni trc tip nh

trn m phi qua mt on dy dn ph gi l Drop-Line kt ni vo bus ti

mt ng dn chnh gi l Trunk-line.

+ Mch vng khng tch cc cng tng t nh cch ni Trunk-

Line/Drop-Line, cng ni qua mt on dy dn ph Drop-Line n trc chnh

nhng khc nhau ch trc chnh khp kn thnh mt vng gi l mch vng. Tt

c c minh ha hnh v di dy.

Hnh 1 : Cu trc bus

Drop-line

Trunk-line

Drop-lineDrop-line

Cac oan day dan

Daisy-chain

Trunk-line/Drop-line

Mach vong khong tch


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- i vi h thng bus ny ngoi nhng u im n gin nh d kt ni v

nhng tnh nng u vit ca chng, bn cnh c s tin li trong vic thay th,

sa cha, thm bt mt thnh vin vo trm khng lm nh hngn h thng,

nn i vi h thng ny thng c s dng rng ri trong h thng mng iu

khin cng nghip. Bn cnh nhng u im trn vic s dng chung mt ng

truyn cng t ra mt gii php hp l, nht l s lng thnh vin ca mng

tng ln l s i hi phn chia knh truyn theo thi gian tht ph hp

trnh xung t xy ra khi nhiu trm cng thu pht mt lc, th gi l phng php

truy cp bus. Bn cnh nhng u im y cu trc bus cng c nhng khuyt im

sau:

- Mt tn hiu gii s ti tt c cc trm c mt trn mng do khng

kim sot c nu khng thc hin vic gn a ch cho trm cn truyn, trong

thc t vic gn a ch s gy ra khng t kh khn.

- Tt c cc trm u c kh nng pht cng nh lun kim tra ng truyn

xem c d liu gi cho mnh hay khng, do h thng phi thit k sao cho

ti thc hin cng vic ny mi trm, dn n s hn ch s lng thnh vin

tham gia mng.

- Chiu di dy dn cng tng i di, v vy i vi cu trc ng thng

thng xy ra phn x gia cc mi ni lm suy gim cht lng tn hiu, do

mt vn cn phi khc phc ti im ny.

- Trng hp dy dn t hay ngn mch trong phn kt ni bus ca mt

trm b h hng u dn n ngng hot ng h thng m vic nh v cng gp

nhiu kh khn.

VI: Cu trc mch vng ( tch cc):

- tm hiu cu truc ny trc ht ta kho st qua m hnh ca cu trc

bng hnh v di y.(Hnh 1)


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Hnh 2 : Cu trc mch vng.

- Cu trc mch vng tch cc l cu trc cc thnh vin tham gia vo

mng c kt ni mt cch tun t t thnh vin ny n thnh vin kia sao cho

chng lin lc vi nhau theo mt vng khp kn. Mi thnh vin t tham gia tch

cc vo vic kim sot ng truyn nhn bit mt dng d liu, v mi trm

nhn d liu t mt trm ng trc v chuyn tip cho trm ng sau n theo

mt chiu c nh hng trc cho n khi dng d liu ny tr v im xut pht

ban u t my pht dng d liu v c my ny thu nhn tr li v hy b.u im y l mi mt trm va c chc nng thu va c chc nng pht li,

do d trnh c s suy gim ca tn hiu, bi mi ln mt trm thu c th ng

thi pht li dng d liu nn c xem nh c khuch i tr li tn hiu

ban u, do i vi cu trc ny c th truyn c vi khong cch kh ln v

nhiu trm c th c kt ni hn so vi cu trc bus, mt u im na l dng

d liu c di chuyn theo mt hng nht nh, do cng l mt vn gp

phn tch cc vo vic khc phc xung t trn ng truyn, i vi kiu mch

vng c hai cu trc, l cu trc c iu khin trung tm v khng c iu

khin trung tm c minh ha hnh v trn (Hnh 2 ).

MASTER

Khong co ieu khientrung tam

Co ieu khien

trung tam


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- Vi mch vng khng c iu khin trung tm th cc thnh vin tham gia

lin kt mng l nh nhau khng c s u tin trc hay sau, do mi thnh vin

trn mng t phn chia kim sot ng dn.

- i vi mch vng c iu khin trung tm th vic kim sot ng

dn thuc trch nhim ca trm ch m nhim.

- Cu trc mch vng c xy dng trn c s ca cu trc im - im v

vy rt thch hp cho vic s dng cng c truyn thng hin i nh cp quang,

tia hng ngoi.v.v Vic gn a ch cho cc phn t trn mng cng c th do trm

ch iu khin mt cch t ng. u im tip theo l i vi cc thnh vin tham

gia ni mng mt cch tun t va thu va pht. Do vic khc phc khi c s

c xy ra trn ng truyn nh t dy, ngng mch cng tr nn d dng

xc nh, tuy nhin s hot ng ca mng c lin tc ta c th kt hp mt

ng dy d phng c m t khi qut qua nhng hnh v di y (Hnh 3 )

Hnh 3: X l s c trong mch vng.

- Trong trng hp th nht trn hnh By-pass s c ng dy gia 1 v

2 c m t nh sau: khi xy ra s c ti mt im cc trm ln cn ti im s

c t pht hin li ng truyn v chuyn mch qua ng dn ph i vng qua

By-pass s co ng day gia 1 va 2

1 28

76 5

43

au tat do s co tai tram 3

1 28

76 5

4

3


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v tr b s c. Trong trng hp trn hnh u tt do s c ti trm 3 khi mt

trm b s c cc trm ln cn t u tt qua n i vng li nh hnh v minh ha.

VII. Cu trc sao:- L cu trc m tt c cc trm tham gia vo mng phi c lin kt

qua mt mng trung tm, trm ny ng vai tr nh mt trung tm giao tip gia

cc trm, iu khin truyn thng cho ton b mng, s giao tip gia cc thnh

vin khc nhau trn mng u thng qua trm ny, nu nh trm trung tm ng

vai tr tch cc th n s kim sot ton b vic truyn thng ca mng, ngc li

chng c xem nh mt b chuyn mch thng thng cho cc trm khc bt tay

nhau. Xt v mt kin trc lin kt vt l th c xem mng nh mt lin kt

im - im thng thng, nhng v mt logic vn c th l im - nhiu im.

- Cc nhc im ca cu trc sao l:

+ Nhc im th nht l: trm trung tm i hi phic tin cy

cao, i vi trm ny n ging nh mt b no ca mng.

-Nhc im th hai l: Nu khong cch gia cc trm nh hn nhiu so

vi t cc trm n trm trung tm th qu l tn km dy dn, do i vi h

thng mng s dng trong cng nghip i khi c phn hn ch. Trn hnh di

y c th m t mt cu trc dng sau:

Hnh 4 : Cu trc hnh sao

Tram trungtam


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VIII. Cu trc cy (Tree):

- Cu trc cy cng c s dng rng ri trong k thut t ng ha cngnghip n c th c din t nh mt chui cc lin kt ng thng lin kt li

vi nhau to thnh cu trc cy. Trong trng hp ny cc phn t dng ni

cc phn t ng thng li vi nhau c ngha c bit.

- Cc phn t kt ni cc dng cu trc ng thng to thnh cu trc

dng cy c th n gin l cc b lp (Repeater) kt ni cc phn t c cng

kiu, hay l cc Router, Bridge, Gateway cho cc trng hp kt ni cho cc mng

c kiu khc nhau. Hnh v di y l m hnh mt kiu cu trc dng cy:

Hnh 5 : Cu trc cy

IX. Kin trc giao thc :

- tm hiu kin trc ca giao thc trc ht ta cn hiu khi nim dch

v truyn thng l g.

- Vy dch v truyn thng l g: L mt dch v cha cc qui tt, qui c

m cc thnh vin tham gia ni mng cn c s dng, cc dch v c s

R Repeater


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dng vi cc yu cu khc nhau nh trao i thng tin d liu, gim st thit b,

to lp cu hnh v.v Cc dch v truyn thng ny c cung cp bi cc nh cung

cp h thng truyn thng, bi phn cng hoc phn mm chuyn dng, m i

hi ngi s dng phi khai thc ph hp cho mc ch v yu cu ring ca mnh

tham gia ni mng, vic khai thc cc dch v t pha ngi s dng phi

thng qua mt phn mm giao din mng. Chng hn xy dng mt phn mm

ng dng no nh trong iu khin gim st SCADA, phn mm lp trnh vi

iu khin, phn mm lp trnh iu khin nh Delphi kt hp vi cc th vin

phn mm c sn to ra mt chng trnh ng dng truy xut d liu n cc vi

x l hay cc PLC v.v Tt c u thit lp sn trn cc cng c phn mm chuyn

dng m chng ta cn hiu v khai thc chng mt cch c mc ch cho mt yu

cu no nh trong lnh vc t ng ha chng hn th c gi l dch v

truyn thng.

- Nhng h thng truyn thng khc nhau c th qui nh mt chng ring

bit v cc yu cu dch v truyn thng ca mnh. Mt h thng truyn thng

khng nht thit phi h try cc dch v truyn thng, v d mt cng c

phn mm SCADA ta c th khai thc d liu t cc cm bin cc PLC nhng

khng nht thit phi h tr phn mm lp trnh cho PLC v phn mm ny lun i

km theo PLC khi ta c c.

- Ta cng c th phn loi dch v truyn thng theo cc cp khc nhau,

nh cc dch v s cp c th l cch to lp ngt ni ca mt phn t trn mng

thng thng, v cc dch v cp thp nh s trao i d liu ca cc phn t v

cui cng cc dch v cp cao. Mt dch v cp cao lun lun c h tr bi

dch v cp thp hn n, thc hin chc nng ca ring mnh chng hn nhto lp cu hnh h thng, hay bo co trng thi c th s dng dch v cp di

n l dch v trao i d liu thc hin, ngoi cch trao i d liu cng

cn cch to lp v ngt ni ca dch v s cp. Vic phn cp dch v truyn


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thng gp phn rt quan trng trong vic s dng dch v dn n s tin li cho

ngi s dng.

X. Giao thc:

- Trong thc tin cuc sng s giao tip gia ngi vi ngi cng t ra

mt yu cu lm sao hiu c ngn ng ca nhau, nhn bit mc ch y u

cu cng nh hnh ng trong giao tip, m rng hn vn y ta ni n s

giao tip ca my mc thit b cng cn c mt ngn ng chun g. Vy trong k

thut truyn thng cng nghip cng nh mt mng my tnh rng ln c s

giao tip nh vy th yu cu t ra l bn cung cp dch v cng nh bn s dng

dch v phi tun th nhng qui tc, th tc nht nh trong phn giao tip gia

cc phn t vi nhau. Vic tun th nhng qui tc qui c c gi l giao

thc. Vy giao thc chnh l c s cho vic s dng cc dch v truyn thng.

Mt qui nh chun giao thc bao gm cc thnh phn sau:

+ C php (Syntax): C php l mt tiu chun qui nh v cu trc ca

mt dng d liu c s dng khi trao i cho nhau trong cha ng y

cc qui nh to thnh mt gi d liu hp l, chng hn nh mt gi d liu

phi c phn thng tin hu ch gi l d liu, thng tin im n c gi l a

ch, thng tin iu khin, thng tin kim li .v.v

+ Ng ngha (Semantic): Qui nh ngha tng phn ca mt gi d liu,

nh phng php nh a ch, phng php bo ton d liu, th tc iu khin

thng tin, x l li.

+ nh thi (Timing): Qui nh v trnh t th tc giao tip, ch truynng b hay bt ng b, tc truyn .v.v

+ Vic thc hin mt dch v truyn thng trn c s ca mt giao thc

tng ng gi l x l giao thc bn gi, v gii m x l giao thc bn nhn.

Vic thc hin tng giao thc tng ng cng ging nh vic x dng cc dch


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v truyn thng theo cc cp cng c s phn chia giao thc theo tng cp v s

h tr ca cc giao thc cho nhau.

+ Giao thc cp cao gn gi vi ngui s dng v thng c thc hin

bng phn mm, mt s v d giao thc cp cao l FTP (File Transfer Protocol)

dng trong trao i file t xa, HTTP (Hypertext Transfer Protocol) dng trao

i cc trang HTML trong cc ng dng Web, MMS (Manufactoring Message

Specification) dng trong t ng ha cng nghip.

+ Giao thc cp thp gn gi vi thit b phn cng thng c thc hin

trc tip trn cc mch in t, mt s v d v giao thc cp thp nh sau:

TCP/IP (Transmission Control Protocol/Internet Protocol) c dng ph bin

trong Internet, HART (Highway Adressable Remote Transducer) dng trong iu

khin qu trnh, HDLC (High Level Data-link Control) lm c s cho nhiu giao

thc khc v UART dng trong a s cc giao din vt l ca cc h thng bus.

Hai giao thc ni sau HDLC v UART c vai tr quan trng trong truyn thng

cng nghip do c gii thiu s lc y:

+ Giao thc HDLC:

HDLC cho php ch truyn ni tip ng b hoc khng ng b. Mt bc

in hay cn gi l mt khung (Frame) c cu trc sau:

01111110 8/16 bit 8 bit n bit 16/32 bit 01111110

C a ch ieu khien D lieu FCS C

- Mi khung c m u v kt thc bng mt c hiu (Flag) vi dy bit

01111110. Dy bit ny c m bo khng bao gi xut hin trong cc phnthng tin khc qua phng php nhi bit (Bit Stuffing), tc c sau mt dy 5 bit

c gi tr 1 (11111) th mt bit 0 c b sung vo.


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- 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, n y c chiu

di l 8 hay 16 bit.

- Trong HDLC c ba lai bc in c phn bit 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)

+ Unmunbered Frames: khung b tr kim sot cc mi lin kt gia cc

trm

+ Cu trc cc thng tin iu khin c qui nh nh sau:

1 2 3 4 5 6 7 8

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

Trong cc k hiu vit tc c ngha nh sau:

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

+ N (R) : S th t khung ch nhn c chia Module cho 8

+ P/F : bit ch nh kt thc qu trnh truyn

+ S, M : Cc bit c chc nng khc

- thng tin c di bin thin, cng c th trng nu nh bc in

khng dng vo mc ch vn chuyn d liu. Sau thng tin l n dy bt kim


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li FCS (Frame Check Sequence), dng vo mc ch bo ton d liu. Tc

truyn thng tiu biu i vi HDL t 9,6 Kbit/s n 2Mbit/s.

Giao thc UART:

- UART (Universal Asynchronous Receiver/Transmitter) l mt mch vi

in t s dng rt rng ri cho vic truyn bit ni tip cng nh chuyn i song

song - ni tip gia ng truyn v bus my tnh. UART cho php la chn gia

ch truyn mt chiu, hai chiu ng b hoc hai chiu khng ng b. Vic

truyn ti c thc hin theo tng k t 7 hoc 8 bit, c b sung hai bit nh

du u cui v mt bt kim tra chn l P (Parity Bit). V d vi k t 8 bit c

minh ha di y.

Start 0 1 2 3 4 5 6 7 p Stop

0 LSB MSB 1

- Bt khi u (Start bit) bao gi cng l 0 v bit Stop (Stop bit) bao gi

cng l 1. Cc bit trong mt k t bao gi cng c truyn th t t bit thp

LSB ti bit cao MSB. Gi tr ca bit chn l P ph thuc vo cch chn:+ Nu chn parity chn, th P bng 0 khi tng s bit 1 chn.

+ Nu chn parity l th P bng 0 khi tng s bit 1 l.

-Nh tn ca n th hin, ch truyn khng ng b c s dng

y, t 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 nhn thng tin phi t chnh nhp ly mu ca mnh ng b vibn gi.


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XI. M hnh lp :

- Vic trao i thng tin trn mng i hi c mt gii php hp l, lm

sao chng c th hiu nhau bt tay nhau trong giao tip v hiu c ngha yucu thng tin, do i hi phi c s tng tt rt phc tp gia cc thnh vin

trn mng, mt yu cu tru tng kh cao gia cc thit b phn cng cng nh

phn mm, n gin thay v phi x l ton b trn mt nn tng duy nht, ta

c th chia nh cng vic thnh nhng lp v x l mt cch c lp trn nhng

lp th gi l m hnh lp.

- thc hin mt dch v truyn thng ca mt gi gi liu c gi i,

c x l qua nhiu lp bn gi v bn nhn trn c s cc giao thc qui nh

c gi l x l giao thc theo m hnh lp, mi lp y c th thc hin bng

cc chc nng ca phn cng hay phn mm. Mi mt trm c xem nh mt h

thng a tn, trong mi tn c xy dng trn c s tn trc n, s lng cc

tn cng nh tn v chc nng ca cc tn u ph thuc vo nh thit k v mc

ch ca mi tn l cung cp dch v cho tn cao hn t pha bn gi cng nh bn

nhn, d liu s c thm vo nhng thng tin h tr khi i qua x l ca tn

i vi bn gi, bn nhn s thc hin ngc li d liu c xc lp v tch ra

khi i qua cc tn x l tng ng tn , h nh v di y m t qu trnh thc

hin cc lp bn gi v bn nhn.

Hnh 6 :ng truyen vat l

N

N-1 N

N

N-1 N

D lieu

Lp N-1

Lp N

Lp N+1

D lieu

D lieu

D lieu

D lieu

D lieu


17/102


- Nguyn tc ca kin trc phn lp trong mt mng l: mi mt h thng

trong mt mng u phi c mt cu trc lp, tc l s lng lp cng nh chc

nng ca mi lp l nh nhau v l do thc hin mt thng tin trn mt mng

i hi phi c hai hay nhiu i tc tham gia, vy vic to lp mt thng tin ch

c thc hin khi cc i tc thc hin truyn thng trong cc lp tng ng, s

dng chung mt ngn ng , chung mt giao thc th c th trao i thng tin cho

nhau, nu s truyn thng c s khc bit v giao thc, chng hn nh gia hai

mng khc nhau th iu cn thit y l dng mt b chuyn i hiu c hai

giao thc nh Bridge hay Gateway. Vn mu cht y c th thc hin

c vic chuyn i l s thng nht v dch v truyn thng, xut pht t yu

cu ny ra i cc kin trc giao tip chun sau y:

XII : Kin trc tiu chun OSI :

- Nhiu nh sn xut theo m hnh ISO (International Standards

Organization) l t chc tiu chun quc t cho OSI (Open Systems

Interconnection) l kt ni cc h thng m. M hnh ny c nh ngha vo

nm 1979 gii quyt vic truyn thng gia cc thngmng khng ging nhau.

Application

Presentation

Session

Transport

Nerwort

Data link

Physical

User program

Application

Presentation

Session

Transport

Nerwort

Data link

Physical

User program

Moi trng truyen

A B

Hnh 7: Mo hnh ISO


18/102


- M hnh chun ISO nh sau: nu d liu c truyn gia hai thit b

qua mt mng chung th ta cn phi nh ngha giao thc v k thut truy cp.

Cc thng tin lin quan v d nh thit lp link cng phi c xc nh. Do t

chc chun ha quc t ISO nh ngha m hnh 7 lp nh sau:

- Cc lp 1, 2 v 4 tuyt i cn thit cho vic truyn thng tin cy, y

. Lp 1 nh ngha cc iu kin vt l nh cc mc dng in v in p.

Trong lp 2 c nh ngha c ch truy cp v a ch ca trm. iu ny bo

m ch c mt trm c th gi d liu qua mng bt c thi im n o.

- tin cy v s tng thch d liu ch c m bo bng cc chc

nng ca lp 4 lp vn chuyn. Xut pht t iu khin vn chuyn, lp vn

chuyn cng thc hin cc chc nng iu khin lun d liu, cm v ghi nhn.

- Cc link c thit lp nhm c c chc nng ny.

- Lp th 7 l lp ng dng cha cc dch v truyn thng v d c m

t hnh v di y.

- M hnh chun nh ngha cc lp m trong ngi ta nh ngha

p ng ca cc cng s truyn thng. Cc lp ny c sp xp theo lp ny trn

lp kia v lp th 7 l lp cao nht v ch nhng lp ng dng nhau truyn thng

vi nhau.

- Cch ci t cc lp ring trong trng hp thc thi khng xc nh theo

m hnh chun m ph thuc vo ci t c th. Trong nhng trng hp nh

PROFIBUS th khng s dng cc lp 3 v 6 c oc s truyn thng vi tc

cao vi kh nng thi gian thc v cc chc nng thit yu c tch hp tronglp 1, 2 v lp 7.

- ngha ca cc lp nh bn sau y:


19/102


Lp Ten goi Chc nang ac tnh

7Lp ng dung

(Application layer)

Cac chc nang ng dung

cung cap cac dch vu

truyen thong chuyen

dung

Cac dch vu

truyen thong.

V du:

Read/Write

6

Lp gii thieu

(Presentation layer)

Gii thieu d lieu

chuyen oi dang gii

thieu chuan cua he thong

truyen thong sang dang

phu thuoc thiet b.

Ngon ng thong

thng.

5Lp kiem soat noi

(Session layer)

ong bo hoa m ong va

giam sat mot phien.ieu phoi phien

4Lp van chuyen

(Transport layer)

Ket noi ngat ket noi

cac link lap lai cac

packet, sap xep th t

cac packet, ong goi.

Van chuyen

khong co li cac

goi d lieu .

3Lp mang

(Network layer)

nh a ch cua mang

khac routing, ieu khien

luon.

Truyen thong

gia hai mang

2Lp lien ket d lieu

(Data link layer)

Cac ky thuat truy cap cac

bien gii khoi d lieu,

Kiem tra CRC,

taken passing


20/102


van chuyen d lieu

khong loi, phat hien loi

x ly loi.

1Lp vat ly

(Physical layer)

Cac kha canh vat ly cua

chuyen d lieu, moi

trng truyen, toc o

baud, qui cach ky thuat

ve cac tham soien c,

va chc nang cua bus.

Cap dan

Bng 1 : nghi cc lp trong m hnh OSI

Lp vt l (Physical layer):

- Lp ny bo m cc bit c truyn qua mi trng vt l theo th t

m lp ny nhn c t lp lin kt d liu. Cc c tnh in v c cng nh

kiu cch truyn cng c nh ngha y.

+ Cc chi tit v cu trc mng nh bus, cy, sao.

+ Chun truyn dn nh RS232, RS485

+ Phng php m ha

+ Ch truyn ti

+ Cc tc truyn cho php

+ Giao din c hc nh phch cm.

+ Lp lin kt d liu (Data Link Layer):

- Trch nhim ca lp ny l truyn cc chui bit gia hai h thng. Vic

ny cng bao gm vic iu khin, vic truy cp mi trng truyn dn, bo ton


21/102


d liu, lp lin kt d liu cng bo m truy cp c quyn mi trng truyn.

Do lp ny c chia lm hai lp nh l lp iu khin truy cp mi trng

MAC (Medium Access Control), v lp iu khin logic LLC (Logic Link

Control). Trong mt s h thng, lp lin kt d liu c th m nhim thm cc

chc nng khc nh vic kim sot lu thng v ng b ha vic chuyn giao cc

khung d liu.

- thc hin chc nng bo ton d liu, thng tin nhn c t lp pha

trn c ng gi c chiu di hp l (frame). Cc khung d liu ny cha cc

thng tin b sung phc v mc ch kim li, kim sotlu thng v ng b ha.

Lp lin kt d liu bn pha nhn thng tin s da vo cc thng tin ny xcnh tnh chnh xc ca d liu, sp xp cc khung li theo ng trnh t v khi

phc li thng tin chuyn tip ln lp trn n.

+ Lp mng (Network layer):

- Lp ny c trch nhim truyn d liu gia hai thit b u cui d liu

(Data Terminal). Cc data terminal l cc my gi (pht) v my nhn (thu) d

liu m c th i qua nhiu h thng chuyn tip. - Mt h thng truyn thng din rngnh mng Internet hay mng vin

thng, l s lin kt gia cc mng hon ton c lp, mi mng u c mt

khng gian a l ring v cch xc lp a ch khc nhau, s dng cng ngh

truyn thng khc nhau. Vy mt gi d liu i t i tc ny n i tc khc ca

hai mng khc nhau c th qua nhiu ng khc nhau, thi gian khc nhau,

qung ng vn chuyn v cht lng ng truyn cng khc nhau th lp

mng ny c trch nhim tm ng i ti u nht, gii 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.


22/102


- C th nhn thy i vi lp ny khng c ngh a trong mt h thng

mng trong cng nghip sn xut, bi y khng c nhu cu trao i d liu

gia hai mng khc nhau.

- Lp vn chuyn (Transport Layer):

- Lp ny c trch nhim cung cp cho ngi s dng mt lin kt tin cy

t u ny n u kia. Khi mt gi d liu c chuyn i thnh tng gi th cn

m bo cc gi n ch v ng th t ban u. Vy chc nng ca lp vn

chuyn l cung cp dch v cho vic vn chuyn mt cch tin cy bao gm c khc

phuc li v iu khin lu thng trn mng. Nh vy m cc lp trn ch thc thi

chc nng ring ca n m khng cn quan tm n c ch vn chuyn d liu.

- thc hin vic vn chuyn mt cch hiu qu tin cy, mt gi d liu

vn chuyn c chia thnh nhng phn nh trc khi vn chuyn v c nh

du th t kim sot trc khi b sung cc thng tin kim sot lu thng.

- Do c tnh ring ca mng trong lnh vc cng nghip nn mt s nhim

v c th ca lp vn chuyn tr nn khng cn thit, v d nh vic dn knh

hay kim sot lu thng. Mt s cc ng dng cn li ca lp ny kt hp vi lpng dng tin vic thc hin cho ngi s dng chn phng php ti u nng

cao hiu sut truyn thng.

-Lp kim sot ni (Session layer):

Mt qu trnh truyn thng gia hai nt mng, chng hn nh vic trao i chng

trnh th c tin hnh qua nhiu giai on. Cng ging nh s giao tip gia hai

ngi th cng c s xp t trc. Vy gia hai i tc truyn thng cng cn cs h tr t chc lin kt. Lp ny c chc nng kim sot mi lin kt truyn

thng gia cc chng trnh ng dng, bao gm cc vic to lp, qun l v kt

thc cc ng ni gia cc ng dng i tc. V mi lin kt gia cc chng

trnh ng dng mang tnh cht logic, thng qua mt mi lin kt vt l gia hai


23/102


trm, gia hai nt mng c th tn ti song song nhiu mi lin kt logic. Thng

thng kim sot ni thuc chc nng h iu hnh. thc hin cc ng ni

gia hai ng dng i tc, h iu hnh c th to cc qu trnh tnh ton song

song. Nh vy, nhim v ng b ha cc qu trnh tnh ton ny i vi vic s

dng chung mt giao din mng cng thuc chc nng ca lp kim sot ni.

- Lp gii thiu (Presentation layer):

Trong cc h thng mng c kiu khc nhau, thng s dng cc ngn ng khc

nhau, nh s dng h iu hnh khc nhau do cch biu din d liu ca chng

cng rt khc nhau, hoc cch sp xp cc baye khc nhau trong mt kiu baye,

hoc s dng bn m khc nhau. Lp gii thiu s m nhim chc nng ny dch

nhng ngn ng khc nhau ny sang mt ngn ng chung c c php tru tng.

Vy chc nng chnh ca lp gii thiu l chuyn i cc dng d liu khc nhau

v c php thnh mt dng chun, nhm to iu kin cho cc i tc tham gia

truyn thng c th hiu c nhau mc d chng c th s dng ngn ng hon

ton khc nhau. Ni mt cch khc lp gii thiu gii phng s ph thuc ca lp

ng dng vo cc phng php biu din d liu khc nhau.- Lp ng dng (Application layer):

Lp ng dng l lp trn cng ca m hnh OSI, c chc nng cung cp dch v

cp cao trn c s ca giao thc cp cao cho ngi s dng v cc chng trnh

ng dng. Chun quan trng nht trong t ng ha l MMS (Manufacturing

Message Specification) hay gi l c t thng ip sn xut.

Cc dch v ca lp ng dng c thc hin hu ht bng phn mm. Thnhphn phn mm ny c th c tch hp sn trong cc linh kin giao din mng,

hoc di dng phn mm iu khin c th np ln khi cn thit, hoc mt th

vin cho ngn ng lp trnh chuyn dng hay ngn ng lp trnh ph thng. c

kh nng s dng cho mt chng trnh ng dng, chng hn nh iu khin c s


24/102


hay iu khin gim st, nhiu h thng cung cp dch v ny thng qua mt cc

khi hm i vi cc thit b trng thng minh , cc khi hm ny khng n

gin thun mang tnh cht dch v truyn thng, m cn tch hp c chc nng x

l thng tin thm ch c iu khin ti ch. y cng chnh l xu hng mi trong

vic chun ha lp ng dng cho cc h thng bus trng, hng ti kin trc

iu khin phn tn trit .

XIII . Phng php truy cp bus :

- Trong tt c cc h thng mng nh mng my tnh rng ln, hay mt

mng trong phm vi hp nh mng iu khin trong cng nghip, th bt c h

thng no cng c th s dng cu trc mng bus, nhng c bit hn l h thng

cu trc dng mng bus v mng mch vng ng vai tr rt quan trng v thng

c s dng trong h thng mng cng nghip sn xut, bi nhng u im ca

n trong t ng ha cng nghip ch l: n gin v cu trc, thch ng cho

mt mng nh v va chi ph t cho dy dn, d lp t v rt linh hot trong sn

xut.

- i vi cu trc bus v mt k thut phn chia thi gian cho knh truynl mt yu cu cao, v trong mt khong thi gian no nht nh ch c mt

trm duy nht trn mng c php tham gia truy cp bus khng th c hai trm

cng tham gia mt lc, i vi tt c cc trm cn li phi ch cho ti khi n lt

mnh, v vy i hi phi c s phn chia ng truyn mt cch hp l trnh

lng ph thi gian cng nh kh nng p ng v mt x l iu khin ca c h

thng. Trong mt mng c cu trc bus cc trm i hi phi c s phn chia nhau

thi gian truy cp bus trnh hin tng xung t tn hiu xy ra trn ng dn,dn n sai lch thng tin, ti mi thi im trn bus ch c php duy nht mt

dng d liu gi i tng ng vi iu ny cng c ngh a l c mt trm c

php gi thng tin, cn s lng cc trm mun nhn tin th khng hn ch, y l

mt trong nhng vn nh hng n nng sut ca h thng.


25/102


- i vi nhng cu trc dng khc nh dng mch vng, mch sao khng

phi khng c s xung t m vn xung t ny cng c th xy ra tuy khng

nh cu trc bus, v d mt cu trc vng mi trm khng phi bao gi cng

khng ch c dng d liu i qua n hon ton, hay cu trc sao phn t x l

trung tm khng ng vai tr ch ng m n c nhim v nh mt b chia tn

hiu th vn xung t vn c th xy ra, do nhng cu trc ny cng dng

phng php phn chia quyn truy cp nhng c phn n gin hn so vi mt

cu trc dng bus.

Phng php truy cp bus l mt vn ca mt h thng dng bus m i hi

phi c s hp l y, v mi phng php k thut ca mi cu trc h thngkhc nhau u c quan tm n, l mt c tnh ca kh nng hon thin h

thng. V vy i vi cu trc dng bus h thng c tnh nng hon thin th

cc c im sau y cn c p ng khi x l phng php truy cp. l

tin cy ca d liu, tnh nng thi gian thc v hiu sut s dng ng truyn.

Tnh nng thi gian thc c ngha l kh nng p ng v x l thng tin mt cch

kp thi khng c s tr hon v mt l do no khc, v d nh s chm tr v m

ng nhiu cng vic cng mt lc th c xem l thi gian khng thc, chnghn nh mt my tnh (PC) ang x l mt lnh hay ang chy mt chng trnh

m phi dng li khi c mt tnh hung mi pht sinh nh s pht hin tn hiu di

chuyn ca chut hay s tc ng ca bn phm dn n thi gian x l lnh hay

chng trnh ni trn b gin on v lc ny my tnh phi m ng cng vic

bi nhng s tc ng ny dn n thi gian b tr hon khng p ng kp thi v

c xem l thi gian khng thc.

- Hiu xut ca ng truyn l mt yu t c kh nng lm tng hoc gim

tc p ng ca mng. N l mt i lng ph thuc vo s lu thng v

phng php truy cp. Nu mt lu thng thp dn n hiu xut thp, ngc

li mt lu thng cao khng c s kim sot cng dn n n tt gy ra s gin


26/102


on lm gim hiu sut ng truyn, khai thc hiu sut ti a ta phi c

nhng phng php thch hp tm ra nhng gii php nng cao hiu xut ng

truyn trn c s phng php truy cp bus. Ta c th a ra hai phng php

truy cp l phng php tin nh v ngu nhin nh sau:

+ Phng php tin nh: trnh t truy cp bus c qui nh trc mt

cch cht ch theo mt trnh t c gim xc nh phng php truy cp

Master/Slave, hay theo s qui nh trc v thi gian TDMA hoc phng php

phn tn bi cc thnh vin Token passing.

+ Phng php ngu nhin: trong phng php ny trnh t truy cp bus

khng c s qui nh trc m hon ton xy ra mt cch t pht theo tnh cht

nhu cu ring. Khi xy ra tnh hung yu cu ca tng trm, mi thnh vin t

gim st ng truyn nu thy ng truyn rnh lp tc chim ly truy cp.

Trong phng php ny c kh nng xy ra xung t, v vy loi tr tc hi

xung t c th s dng nhng phng php nhn bit xung t nh CSMA/CD

hoc CSMA/CA. Nguyn tt hot ng ca cc phng php ny l khi nhn bit

c xung t xy ra th t nht c mt trm ngng gi tn hiu. Ta i vo tm hiu

cc phng php c th nh sau.

XIV. Phng php truy cp Master/Slave:

- Phng php truy cp Master/Slave hay cn gi l phng php Ch/ T,

y trm ch c vai tr ch ng tch cc cn cc trm t l cc phn t tiu cc

b ng, tt c cc trm t ny u chu s chi phi bi trm ch. Trm ch c

xem nh tri tim mch mu ca h thng trm ch (Master) c trch nhim ch

ng phn chia quyn truy cp bus cho cc trm t (Slave), cc trm t th ng

ch c quyn truy cp bus nhn hay gi d liu i khi nhn c s y u cu t

pha trm ch, ngc li chng phi i s yu cu t trm ch hay thc hin mt

cng vic no ca ring chng. Vy i vi trm ch c th dng phng php

kim sot ton b hot ng mng ca mnh nh phng php hi tun t


27/102


(polling) theo chu k, nh vy m d liu t trm ch c th gi n tt c cc

trm t theo mt th tc tun t mt vng lun phin trn mng, yu cu tr li

cc thng tin k thut t pha trm thay nhn nhng thng tin iu khin t pha

trm ch gi n trm t.

- m bo cho mt h thng hot ng tt. Trong mt s h thng cc

trm t hon ton chu s gim st cht ch t pha trm ch, tt c mi hot ng

ny sinh t pha cc trm t vi nhau u phi thng qua trm ch, chng hn s

trao i d liu cn thit ca hai trm t khng c thc hin bi chng m nht

thit phi c s phn b ca trm ch. Do nu hot ng giao tip theo phng

php hi tun t chu k, th nu mt yu cuc gi d liu ca mt trm tn cho trm t khc th trm ch yu cu d liu t pha trm t gi sau trm

ch gi cho trm t nhn, nh vy trm ch ng vai tr trung gian trong vic giao

tip gia hai trm t vi nhau. Do khi c yu cu trao i d liu bt thng

ca trm t ny vi trm t khc th trc ht trm t mun gi phi thng bo

yu cu ca mnh khi trm ch hi n v sau ch cho n khi c phc v.

- Trnh t th tc truy cp bus ca h thng mng no vi m hnh ch

t. Phng php truy cp cng nh cch thc truyn d liu gia cc trm u

c xy dng mt cch c qui nh c gi l tin nh hay nh trc do ngi

to lp mng to ra bng cc cng c to lp mt cu hnh ca mt mng c m

hnh mt trm ch duy nht v nhiu trm t. Thi gian cn thit trm ch hon

thnh cng vic hi tun t mt vng cng chnh l thi gian ti thiu ca mt chu

k bus. Nh vy ta cng c th tnh ton trc c mt cch tng i chc chn

ca mt chu k bus, v tt c nhng thnh vin tham gia v mt s lng ta c th

bit trc cng nh chiu di ti a ca mt khung d liu tc ng truyn

(Boud), do ta c th xc nh c chu k bus. Tc p ng ca chu k bus

chnh l mt tnh nng thi gian thc ca h thng, m tnh nng ny ng mt vai


28/102


tr quan trng trong h thng iu khin cng nghip. Ta c th m t mt m

hnh ch t (Master/Slave) qua hnh v di y:

Hnh 8 : M hnh ch t (Master/Slave).- Phng php ch t thch hp cho mt h thng iu khin. Bi l tnh

n gin kt ni, kh nng thm bt s lng thnh vin v lp t. Ton b k

thut ca mng hu nh tp trung vo trm ch, cc trm t ch ng mt vai tr

nh mt thit b c th d dng thm vo hay bt i.

- Mt nhc im ca phng php ch t l phng php kim sot tp

trung bi trm ch, iu ny l mt nhc im lm gim hiu sut thng tin, khi

mt yu cu trao i d liu gia hai t pht sinh s khng c thc hin nu

khng qua trung gian trm ch. Chnh v l do ny khi xut hin mt nhu cu trao

i d liu gia hai phn t t vi nhau nh cc vi x l hay PLC nht nh phi

c thc hin vi thi gian ti thiu di hn mt chu k bus.

- khc phc tnh trng ny c th s dng mt h thng cho php cc

phn t t c th thng tin trc tip cho nhau nhng trong mt chng mc no

c kim sot nht nh c th minh ha y qua hnh v (hnh 9 ).

Master

Slave Slave Slave


29/102


Hnh 9 : M t s trao i d liu gia hai trm t.

- Vy khi c mt yu cu trao i d liu gia trm t B cho trm t A,

trong khi mt yu cu t pha trm ch yu cu tm t A nhn d liu

(Receive-Request) v trm B gi d liu (Send-Request) th trm B gi trc tip

cho trm A (Send-Data), sau khi nhn c s kt thc (Send -Completed) tpha trm B th trm A c trch nhim thng bo li (Receive -Completed) cho

trm ch nh c minh ha hnh v. Nh vy vic truy cp ng truyn cng

khng chng cho nhau m hai trm t vn thc hin trao i d liu c vi

nhau trong mt chu k bus.

- Mt nhc im th hai l: i vi phng php ny tin cy ca h

thng hon ton ph thuc vo trm ch, nu trong mt trng hp no gy s

c trm ch th ton b h thng mng ngng hot ng dn n nh hng tin

sn xut trong phm vi t ng ha cng nghip. Vy ta cn c bin php khc

phc trong trng hp ny l phng php s dng mt trm t c vai tr ng

Master Slave(A) Slave(B)

Send-Request

Send-Data

Send CompletedReceive

Completed

Receive -Request


30/102


mt trm ch khi cn thit, v d nh nu c s c xy ra th trm t ny c kh

nng thay th trm ch tm thi.

XV. Phng php TDMA:

- Phng php TDMA hay cn gi l phng php a truy cp phn chia

theo thi gian (Time Division Multiple Access), mi mt trmc phn chia mt

khong thi gian truy cp bus nht nh. Tt c cc trm trao i thng tin cho

nhau trong mt khong thi gian lun phin c cho php ca mnh, theo mt qui

c phn chia trc, vic phn chia ny c xy dng trn mt h thng mng

m ngi xy dng mng to lp ra n gi l c ch tin nh, ngha l c s sp

xp qui nh trc. y n c c im khc vi m hnh ch t ch l c th

c trm ch hoc khng c trm ch no, nu c trm ch th trm ch ny ch c

mt vai tr hn ch l mc kim sot cc trm tun th ng vai tr phn

chia thi gian ca mnh khng lm nh hng khong thi gian ca cc thnh vin

khc trn mng, v mi trm ch ng trong vai tr giao tip vi cc trm khc.

- Di y minh ha cho phng php phn chia theo thi gian TDMA

cho mt chu k bus c v hnh 10 :

1 2 N Yeu cau rieng

Hnh 10 : Chu k bus TDMA

- Nh hnh v mi khong thi gian ny tng ng dnh ring cho mttrmv mi trm ch c quyn trao i thng tin cho nhau trong khong thi gian

tng ng ca mnh c nh du t 1 n N, cc trm s trao i thng tin lun

phin sau mi thi gian N ln, khng c s u tin dnh ring cho trm no. Ngoi

nhng khong thi gian phn chia t 1 n N cn c mt khong thi gian dnh

Mot chu ky bus


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cho cc thng tin ring v mt l do no xy ra. V d nh thng tin cnh bo,

yu cu thay i cu hnh.

- i vi nguyn tc chung phn chia thi gian tng khong t 1 n N ca

TDMA th c nhng cch truy cp khc nhau nh sau: chng hn c th phn chia

theo th t truy cp bus hay phn chia theo a ch hay theo chc nng ca tng

trm, v cng c th dng phng php kt hp gia TDMA v phng php ch

t (Master/slave) nhng y c s cho php cc trm t lin lc vi nhau, trm

ch ch c vai tr gim st khong thi gian cho tng trm thch hp.

XIV. Phng php Token Passing:

- Token (th bi) l mt thng ip khng cha d liu c cu trc c bit

khc vi mt khung d liu thng thng, n c xem nh mt cha kha lun

chuyn t trm ny n tm khc trn mng, Token cho php mt trm c quyn

truy cp bus trao i thng tin gi liu trong thi gian trm nhn Token, vy

Token l mt bc thng ip ng vai tr phn chia quyn truy cp bus cho cc

trm. Nu mt trm no nhn c Token nhung khng c nhu cu truy cp

bus thi trm nhng Token li cho trm khc theo mt trnh t nht nh. Nutrnh t ny ng vi trnh t sp xp vt l trong mt mch vng (tch cc hoc

khng tch cc) ta dng khi nim Token Ring. Cn nu trnh t c qui nh ch

c tnh cht logic nh cu trc bus, v d nh theo th t a ch, ta dng khi

nim Token Bus. Trong mi trng hp u hnh thnh mt mch vng logic.

- Mt trm ang d Token chn nhng c quyn truy cp bus v gi thng

tin d liu m cn ng vai tr c bit l kim sot cc trm khc, chng hn

nh nu mt trm no c s c, i vi cc trm cn li khng gi Token cng

c kh nng tham gia kim sot, chng hn sau mt thi gian nht nh khn g

nhn c Token c th l mt hay mt s c bi trm no ang gi Token, th

lc ny mt trm m nhim chc nng to ra Token mi v tip tc lun chuyn

trn mng thay th Token c. Chnh v vy Token Passing c xp vo phng


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Token Tram4Tram2

Tram1

Tram3

Token rin

Tram 1 Tram 2 Tram 3

Tram 6Tram 5Tram 4

TokenBus

php kim sot phn tn. Do thi gian c quyn gi Token hn ch dn n vic

tnh ton c thi gian phn ng cng nh chu k bus ti a. Cc h thng s

dng phng php truy nhp ny cng c kh nng thi gian thc.

Hnh 11 : Hai dng ca phng php Token Passing

- Trong thi gian xc lp cu hnh, cc trm c th d tnh v thi gian

dng Token ca mnh, t i ti tha thun mt chu k bus thch hp tt c

cc trm u c quyn tham gia gi thng tin v kim sot hot ng truyn thng

ca mng. Vic kim sot bao gm cc vic sau:

+ Gim st Token: nu do mt li no m Token b mt hoc gia

bi, cn phi thng bo xa cc Token c v to mt Token mi.

+ Khi to Token: sau khi khi ng mt trm c trch nhim to

mt Token mi.

+ Tch trm ra khi mch vng logic: mt trm c s c phi c

pht hin v tch ra khi trnh t nhn Token.

+ B sung trm mi: mt trm mi c kt ni mng, mt trm c

c thay th hoc a tr li s dng phi c b sung vo mch vng logic

c quyn nhn Token.


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- Token Passing cng c th s dng kt hp vi phng php ch/t, trong

mi trm c quyn gi Token l mt trm ch, hay cn gi l trm tch cc.

Phng php kt hp ny cn c gi l Multi - Master. Cc trm ch ny c th

l cc b iu khin (PLC, PC), cn cc trm t (trm khng tch cc) l cc b

vo/ra phn tn, cc thit b trng thng minh.


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Chng II : CHUN TRUYN DN

- Truyn d liu ni tip, khng ng b l phng php dng ch yu

trong truyn thng cng nghip, vi phng php ny cc bit c truyn t bn

gi n bn nhn mt cch tun t trn cng mt ng truyn, cng chnh v

khng c mt ng dy ring bit mang tn hiu nhp nn vic ng b ho thuc

trch nhim bn gi v bn nhn tha thun trn c s giao thc truyn thng .

- Cc chun truyn dn TIA/EIA l hip hi xy dng v pht trin mt

s giao din cho truyn thng cng nghip, trong c c cc truyn dn ni tiptheo ngha truyn thng. Mt chun truyn dn ni tip trc ht c hiu l cc

qui nh c thng nht v giao din vt l gia cc thit b cui x l d liu v

cc thit b truyn d liu.

I: Phng thc truyn dn tn hiu:

- Tn hiu c dng truyn ti thng tin khng k ti mi trng truyn

dn th thnh phn cbn trong h thng gm c b pht v b thu, mt thit b

va c kh nng thu v pht c gi vi ci tn l (Transceiver).- C hai phng thc truyn dn tn hiu trong h thng truyn thng cng

nghip l chnh lch i xng v phng thc khng i xng.

+ Truyn dn khng i xng

Truyn dn khng i xng tn hiu s, s lin quan gia trng thi logic

ca mt tn hiu vi trng thi logic ca dy bit mang thng tin c truyn ph

thuc vo phng php m ho bit, tc l gi tr logic ca tn hiu ti mt thi

im khng nht thit phi ng nht vi gi tr logic ca bit tng ng mang

thng tin.

+Truyn dn chnh lch i xng.

Truyn dn chnh lch i xng s dng in p gia hai dy dn biu din

trng thi logic 1 v logic 0 ca tn hiu khng ph thuc vo t. Khi nim


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chnh lch i xng c th hin qua cn xng v in p ca hai dy i vi t

trong iu kin bnh thng. Mt tc ng nhiu bn ngoi s lm tng hay gim

tc thi in p c hai dy mt gi tr gn tng ng, v th tn hiu t b sai

lch. S khc nhau v in p t gia cc thit b tham gia truyn thng cng hu

nh khng b nh hng trc tip ti vic nh gi gi tr logic ca tn hiu. Mt

nguyn nhn gy nhiu khc l xuyn m cng c loi tr ng k .

- Thng thng mt tn hiu c pht i khi ti mt u dy s phn x

ngc tr li ging nh hin tng phn x nh sng khi tc truyn tng i

thp hoc dy dn tng i ngn, sao cho thi gian Tb ln hn gp nhiu ln so

vi thi gian lan truyn tn hiu Ts, tn hiu phn x s b suy gim v b trit tiu

sau mt vi ln qua li khng gy nh hng ti cht lng ca tn hiu mang bit

d liu v vy ng ta dng tr u cui hp th tn hiu ban u .

II: c im ca cc cng ngh truyn dn RS-232, RS-422,

RS485:

Thong so RS-232 RS-422 RS-423 RS-485

Chieu dai cap

Length (max)

15m

(50 ft)

1.2km

(4000ft )

1.2km

(4000ft)

1.2km

(4000ft)

Baud rate

(Toc o

Baud)

20Kbs/15m 10M bs/12m

1Mbs/120m

100Kbs/1.2km

100Kbs/9m

10Kbs/90m

1Kbs/1.2km

10Mbs/12m

1Mbs/120m

100Kbs/1.2km

Mode Unbalanced Balanced

Differential

Balanced

Differential

Balanced

Differential

Driver No. 1 1 1 32

Receiver 1 10 10 32

Logic 0 +3V - +2V->+5V +3.6V->+6V +1.5V->+5V


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>+25V

Logic 1 -3V ->-25V -2V-> -5V -3.6V ->-6V -1.5V ->-5V

Community 2V 1.8V 3.4V 1.3VCable/signal 1 2 2 2

Methode Simplex Simplex Simplex Simplex

Phng thc Half-

duplex

Full-duplex

Half-duplex

Full-duplex

Half-duplex

Full-duplex

Half-duplex

Full-duplex

Short circuitcurrent

500mA 150 mA 150mA 150 mA

Bang 1: Thong so cho 232, 422, 423, 485

III: Chun RS-232 :

- L chun ca EIA nhm nh ngha giao din vt l gia DTE v DCE (v

d nh gia mt my tnh v mt modem). Chun ny s dng u ni 25 chn,

tuy nhin ch c mt s t chn l thc s cn thit cho vic lin kt. V phng

din in, chun ny quy nh cc mc logic 0 v 1 tng ng vi cc in th

nh hn -3V v ln hn +3V. Tc ng truyn khng c vt qu 20Kbs

v khong cch nh hn 15m.

- Chun RS-232C c th chp nhnphng thc truyn song cng (Full-Duplex).

- Mt trong nhng yu cu quan trng ca RS-232C l thi gian chuyn t

mc logic ny sang mc logic khc khng vt qu 4% thi gian tn ti ca mt

bit. Gi s vi tc truyn 19200 baud th thi gian chuyn mc logic phi nh


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hn 0.04/19200 = 2.1 s. iu ny lm gii hn chiu di ng truyn. Vi tc

19200 baud ta c th truyn xa nht l 50ft (15.24m ).

- Mt trong nhng vn quan trng cn ch l khi s dng RS-232C l

mch thu pht khng cn bng (n cc), tc l tn hiu vo v ra c so vi t.

IV: RS-422A:

- Mt ci tin quan trng ca chun RS-232C l chun RS-422A. Chun

ny s dng vic truyn d liu sai lch Differential Data trn nhng ng truyn

cn bng. Mt d liu sai lch cn hai dy, mt cho d liu khng o (Non-

Inverted) v mt ng cho d liu o (Inverted). D liu c truyn trn

ng dy cn bng, thng l cp dy xon vi mt tr u cui. Mt IC li

(Driver) s bin i cc mc logic thng thng thnh mt cp tn hiu sai lch

truyn. Bn nhn s c mt mch chuyn i tn hiu sai lch thnh cc mc logic

tng ng. Cc IC li RS-422A hu ht hot ng vi ngun +5V nh cc chp

logic khc. Vi chun mi ny, tc cng nh khong cch truyn c ci

thin rt nhiu.

V: RS 485 :

- Chun RS-232 dng ng truyn khng cn bng v cc tn hiu u ly

im chun l ng mass chung, do tc truyn v khong cch truyn b

gii hn. Khi cn tng khong cch v tc truyn phng php dng hai dy tr

nn hu hiu hn v hai dy c t tnh ging nhau, tn hiu truyn i l hiu s

in p gia hai dy. Do , loi tr c nhiu chung.

- Tn hiu t my tnh theo chun RS-232 c mc in p l 12V phi i

sang mc TTL 0 -> 5V dng vi mch MAX 232, sau tn hiu n c i

sang tn hiu vi sai dng vi mch MAX 485. in p vi sai phi ln hn 200mV.Nu Vab > 200mV ta coi nh logic 1 c truyn cn nu Vab < -200mV th logic

0 c truyn.

- Truyn RS-485 l cng ngh truyn c s dng thng xuyn bi

PROFIBUS. Cc lnh vc ng dng bao gm tt c cc lnh vc m trong cn


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VI: Cch lp t RS-485:

Tt c cc thit b c ni vo cu trc Bus ti a 32 trm (Master hay

Slave) c th c ni vo mt Sement(on). Bus c kt thc bng Bus tch

cc (Active Bus Terminator) u v cui mi Segment. m bo hot ng

khng c li th c u kt thc Bus lun lun c c in.

Hnh 1 : S o mang Half_ Duplex RS485:

Hnh 2 : S o mang RS485 Full_Duplex:

MAX485

12

34

6

7RORE

DEDI

A

B

MAX485

12

34

6

7RORE

DEDI

A

B

MAX485

1 234

6 7

RO

RE

DE

DI

A B MAX485

1 234

6 7

RO

RE

DE

DI

A B

R1

120

R2

120

U4

MAX489

2

3

4

5

11

12

9

10

RO

RE

DE

DI

B

A

Y

Z

U4

MAX489

2 3 4 5

11

12

9 10

RO

RE

DE

DI

BAY ZU4

MAX489

2 3 4 5

11

12

9 10

RO

RE

DE

DI

BAY Z

R1

120

R2

120

R3

120

R4

120

U4

MAX489

2

3

4

5

11

12

9

10

RO

RE

DE

DI

B

A

Y

Z


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Trong trng hp tren 32 tram hoac e m rong mang, ngi ta s dung

cac Repeatrer e lien ket cac oan Bus rieng lai. Chieu dai toi a cua cap phu

thuoc vao toc o truyen: toc o truyen cang cao th chieu dai cap cang giam.

BAUDRATE MAX. SEGMENT

LENGTH

MAX. EXPANSION

9,6 1000 m 10000 m

19.2 1000 m 10000 m

93.75 1000 m 10000 m

187.5 1000 m 10000 m

500 400 m 4000 m

1500 200 m 2000 m

3000 100 m 1000 m

6000 100 m 1000 m

12000 100 m 1000 mToc o truyen va chieu dai cap truyen RS-485

e tang chieu dai cap truyen , ta co the dung bo Repeater nh sau:

- B Repeater hay gi l b tip sc, c chc nng lm khuch i tn hiu

d liu trn cp LAN, ta cn RS-485 Repeater khi ta mun gn hn 32 nt vo

R2

120

U1

MAX491

2

3

4

5

11

12

9

10

RO

RE

DE

DI

B

A

Y

Z

R1

120

DATA IN

DATA OUT


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mng hoc chiu di on cho php c vt qu. Ti a 9 Repeater c th c

s dng gia hai nt bt k.

- Ch l vic tng kch thc mng bng Repeater c th dn n thi

gian truyn di hn v c th k n khi ci t cu hnh mng.

VII: Topology ca mng RS-485:

- Tc truyn, ta c th chn mt trong cc tc truyn sau:

9,6 Kbps,19,2 Kbps, 45,45 Kbps, 93,75 Kbps, 187,5 Kbps, 500 Kbps, 1,5 Mbps

Cc thnh phn gn vo Bus c chia lm hai nhm:

+ Cc thnh phn c tc truyn t 9.6Kbps n ti a 1.5Mbps.

+ Cc thnh phn c tc truyn t 9.6Kbps n ti a 12Mbps.

- Gn nt: Cc nt c gn vo Bus qua cc b kt ni Bus (Bus

Connector) Bus Rerminnal hay RS485 Repeater.

Kt thc cp:

- Mi Sub Segment phi c kt thc hai u bng tng tr c tnh ca

n. B kt thc cp ny (Bus Terminator) c tch hp trong RS485 Repeater,

Bus Terminal, ILM v cc Bus Connector v c th kch hot nu cn.

- Trc khi kch hot Bus Terminal ny th phi cung cp ngun cho cc

thnh phn mng ny. Vi ccbus Terminal v cc Bus Connecter th ngun in

ny c cung cp bi DTE c kt ni, tri li RS485 Repeater, ILM v

Terminal lun c ngun in ring cho mnh.

- K thut truyn RS-485 cho php gn ti a l 32 thit b (cc DTE v cc

Repeater) trn Bus Segment. Chiu di cp ti a c cho php bi Segment ph

thuc vo tc truyn v cp LAN c s dng.


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- Mng RS-485 em thit k trong ti ny l mng bn song cng (Half-

Duplex): D liu ch i t Master n cc vi x l hay t cc vi x l n Master.

Ti mt thi im trn mng ch c mt phn t truyn v cho php cc phn t

khc c th nhn thng ip . C iu quan trng ta nn ch l vi s mch

RS-485 c thit knh trn th ch c th giao tip gia Master (PC) v cc vi

x l nhng gia cc vi x l khng th lin lc trc tip vi nhau. Chng giao

tip vi nhau nu c th thuc mt dng giao tip khc.

VIII. Cc phng thc truyn thng:

- C 3 phng php truyn c dng trong mc ch truyn thng tin:

n cng, bn song cng, v song cng. Ta s ln lt kho st cc phng php

truyn trn.

+ n cng:

ng truyn n cng c kh nng truyn d liu ch theo mt hng.

Nguyn nhn khng phi do tnh cht ca ng dy n gin, ch v mt u cui

ch c mt my pht v u cui kia cng ch c mt my thu. Cu hnh ny t

c s dng trong cc my tnh v khng c cch no my thu pht tn hiu

nhn bit ti my pht cho bit thng ip nhn ng. Pht thanh v truyn

hnh l mt trong nhng th d v n cng.

+ Bn song cng (Half-duplex Communication).

ng truyn bn song cng c th pht v nhn d liu theo c hai hng

khng ng thi. Trong sut mt cuc truyn, mt modem l my pht v modem

cn li s l my thu. V d nh mt thit b A l my pht gi d liu n thit bB l my thu, sau A v B i vai tr cho nhau, B l my pht gi tn hiu bo

d liu nhn c c li hay khng n my thu A. Nu khng c li th A v B

s li i vai tr cho nhau v A tip tc gi d liu n my thu B. Nu my thu B


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bo d liu c li th my pht A s gi li d liu c cho n khi B bo l d liu

khng c li.

Nhc im ca phng php ny l thi gian cn chuyn ng truyn

bn song cng t hng ny sang hng khc c th di gp nhiu ln thi gian

truyn mt k t. S chuyn ng ca xe trn ng ray l mt v d v phng

php ny.

- Song cng ( Full-duplex Communication):

Ngc li so vi truyn bn song cng, ng truyn song cng c kh

nng pht v nhn d liu ng thi theo c hai hng. Mt cch khi qut, ng

truyn song cng tng ng vi 2 ng truyn n cng, mt ng cho mi

hng.

- V hai ng truyn c th tin hnh song song, mt ng cho mi

hng, nn truyn song cng c th pht nhiu thng tin hn truyn bn song cng

vi cng tc truyn d liu. Truyn song cng khng mt thi gian thay i

hng truyn.

IX. Truyn thng tun t:

- Hu ht cc my tnh lu tr d liu v thao tc d liu theo cch song

song. Ngha l khi gi mt byte t b nhn ny ti b nhn khc ca my tnh, n

khng truyn tng bit mt m mt lc mt byte trn nhng cp si song song

nhau. S cc bit truyn i cng mt lc thay i ty thuc vo tng my tnh

nhng thng thng l 8 hoc bi ca 8.

- Tuy nhin vic truyn d liu t my tnh ny n my tnh hay mt thit

b khc th xy ra theo kiu tun t, ngha l d liu c gi i tng bit mt. Mt

b giao tip tun t s m nhn nhim v chuyn i d liu t song song sang

ni tip trc khi chng gi i hoc i t ni tip sang song song khi chng nhn

v.


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- C hai hnh thc truyn thng tun t: truyn thng ng b v khng

ng b.

- Truyn thng bt ng b (Asynchronous Communication): Khong thi

gian gia hai k t truyn i khng c nh, mc d khong thi gian gia hai bit

lin tip trong mt k t l khng thay i nhng khong thi gian gia hai k t

lin tip khng phi l hng s. S bin thin tc ny lm ny sinh vn l

phi lm sao my thu phn bit c gia bit 0 v khng c d liu.

- gii quyt vn trn, ngi ta pht trc tip mt bit Start ngay trc

mt k t v mt hoc hai Stop bit ngay sau mi k t c truyn i.

- kim tra li ng truyn, ngi ta s dng bit chn l (Parity bit), tc

kim tra tng s bit trong 1 byte d liu c truyn. Phng thc ny thng

c s dng trong cc my tnh PC v tnh n gin ca n. Hn ch ca phng

php ny l tc truyn thp do phi truyn thm mt s bit Start, bit Stop v bit

Parity.

- Truyn thng ng b ( Synchronous Communications):

- Phng thc truyn ny khng dng cc bit Start, Stop ng khung

mi k t m chn cc k t c bit nh SYN ( Synchronization), EOT (End Of

Transmission) hoc mt c gia cc d liu ca ngi s dng bo hiu cho

bn nhn bit rng c d liu ang n hay n.

- Truyn ng b thng c tin hnh tc di 4800bps, 9600bps

hoc thm ch cn cao hn. Trong phng php ny, mt khi ng b, cc

modem vn tip tc gi cc k t duy tr ng b, ngay c lc khng pht dliu. Mt k t "idle" c gi i khi khng c d liu pht. Trong phng php

truyn ng b khng ging nh phng php truyn bt ng b, khong thi

gian gia hai k t lun bng nhau.


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Chng III: GII THIU AVRATMEGA32

I: Gii thiu AVRATMEGA32 :

- VARATMega32 l ca cng ty Hoa K y l loi vi iu khin mi rt

mnh c rt nhiu u im so vi cc vi iu khin khc nh vi iu khin 89C5x

hay 89C5x vv

- Cng ty Atmel l nh xut hng u v vi mch (IC) l mt kin trc ph

bin ca cc b vi s l hin i .

- Kin trc RISC vi hu ht cc lnh c chiu di c nh, truy nhp b

nh np lu tr (Load-Store), v 32 thanh ghi a nng .

- Kin trc ng ng lnh kiu hai tng (Two-Stageinstructionpipeline)

cho php lm tng tc thc thi lnh .

- C cha nhiu b phn ngoi vi ngay trn chp bao gm cng I/O s, b

bin i ADC, b nh EEPROM, b nh thi, UART, b nh thi RTC, b iu

ch rng xung (PWM) vv c im ny c xem l ni bt so vi v nhiu hvi iu khin khc v trong khi nhiu b vi x l khc phi to b truyn nhn

UART hoc giao din SPI bng phn mn hay my o th trn vi iu khin

AVRATMega32 li c thc hin bng phn cng trn cc vi iu khin

AVRATMega32 tch hp sn .

II: c im chung:

- L mt vi iu khin 8 bit mnh, ch tiu cht lng cao tiu th nng

lng thp.- Kin trc RISC (Reduce Instruction Set Computer) cao cp.

- Vi 132 lnh mnh hu ht cc lnh c thc thi trong mt chu k my.

- C 32 thanh ghi 8bit a nng.

- Tc x l ln n 16 triu lnh trong 1 giy (gp 16 ln 89 C51x ) .


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III: B nh d liu v b nh trng trnh khng t mt d liu

(Nonvolatile )

- 32 Kb b nh dnh cho vic lp trnh chu c 10 ngn lp trnh/ xo

- 1024 byte EEPROM, chu c 10 ngn ln vit/ xo.

- 2 Kb SRAM.

- Ch bo mt cho chng trnh lp trnh c.

- Giao din JTAG .

IV: C nhiu thit b ngoi vi c tch hp sn.

- Hai Timer trn b m 8 bit, vi ch chia tng ring bit v ch so

snh .

- B m thi gian thc vi ch giao ng ring bit.

- Mt Timer trn b m 16 bit vi ch chia tng ring bit v ch so

snh.

- Bn knh PWM.- 8 knh, 10 bit AC.

- 8 knh bin i AC n cc.

- 2 knh bin i vi sai vi khuych i 1,1 hay 200 ln.

- Giao tip 12C.

- Ch USART lp trnh c.

- Giao din ch/t SPI.

- B Watchdog Timer lp trnh c vi dao ng ring l.- B so snh Analog trn Chip.

V: Nhng im c bit.

- T Reset khi cp ngun.

- C b giao ng RC bn trong chp.


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- Cc ngun ngt trong v ngt ngoi.

- C 6 ch ngh (Sleep): Dng (Idle), tit kim nng lng (Power save),

ngun gim (Power Down), gim nhiu khi bin i ADC ch ch (Standby ),

v ch ch m rng.

VI: S lng I/O v dng ng gi:

- C 32 ng I/O lp trnh c vi cc chc nng khc nhau.

- 40 chn kiu ng gi PDIP, 44 chn kiu TQFP, v 44 chn kiu MLF

VII: Ngun cung cp.

- T 2.5 Volt n 5.5 Volt i vi ATMega 32L

- T 4.5 Volt n 5.5 Volt i vi ATMega 32L

VIII: Thch anh dao ng:

- T 0 n 8MHz cho ATMega 32L- T 0 n 16MHz cho ATMega 32

IX: Nng lng tiu th ch giao ng 1MHz, 3 Volt, 25 0C

i vi ATMega 32L

- Ch lm vic : 1.1 mA.

- Ch dng (Idle): 0.35mA

- Ch d ngun gim < 1uA


48/102


X: H tr tt cho cc trnh bin dch bng C nh IamgeCreft C,

Code VisionAVR, IAR ...

Hnh1: S o chan cua ATMega32


49/102


Hnh 2: S khi ca ATMega32

XI: M t cc chn :

- VCC: Chn cp ngun V+

- GND: Chn cp ngun V-

- PortA (PA0..PA7): PortA c chc nng l cc u vo ca b bin i

A/D.- PortA cng c chc nng nh l mt cng xut nhp 8 bit, hai hng. Nu

chc nng bin i A/D khng c s dng th cc chn ca PortA c th c kh

nng cung cp cc in tr ko ln bn trong (c kh nng la chn cho tng bit).


50/102


Khi PortA c s dng chc nng l cc cng xut, cc b m xut nhp ca n

c mt tnh nng i xng l c kh nng ht hoc cp ngun cao.

- Khi PortA c x dng nh nhng chn (Input), chng s c kh nng

ht dng rt mnh nu nhng in tr ko xung bn trong c kch hot. Cc

chn ca PortA s trng thi Tri-Stated khi ch Reset c kch hot, thm

ch nu xung ng h b ngng.

- PortB (PB0..PB7): PortB c chc nng nh l mt cng xut nhp 8 bit,

hai hng. PortB c th c kh nng cung cp cc in tr ko ln bn trong ( c

kh nng la chn cho tng bit ). Khi PortB c s dng chc nng l cc cng

xut, cc b m xut nhp ca n c mt tnh nng i xng l c kh nng ht

hoc cp ngun cao.

Khi PortB c x dng nh nhng chn (Input), chng s c kh nng ht dng

rt mnh, nu nhng in tr ko xung bn trong c kch hot. Cc chn ca

PortB s trng thi Tri-Stated khi ch Reset c kch hot, thm ch nu

xung ng h b ngng. Ngoi ra PortB cng c chc nng c bit khc.

- PortC (PC0..PC7): PortC c chc nng nh l mt cng xut nhp 8 bit,

hai hng . PortC c th c kh nng cung cp cc in tr ko l n bn trong ( c

kh nng la chn cho tng bit ). Khi PortC c s dng chc nng l cc cng

xut, cc b m xut nhp ca n c mt tnh nng i xng l c kh nng ht

hoc cp ngun cao.

Khi PortC c x dng nh nhng chn (Input), chng s c kh nng ht

dng rt mnh, nu nhng in tr ko xung bn trong c kch hot. Cc chn

ca PortC s trng thi Tri-Stated khi ch reset c kch hot , thm ch nu

xung ng h b ngng.- Nu giao din JTAG c cho php, cc in tr ko ln trn cc chn

PC5(TDI), PC3(TMS), PC2(TCK), s c kch hot thp ch nu c reset xay ra.

Ngoi hai chc nng l xut nhp v giao din JTAG th PortC cn c cc chc

nng c bit khc.


51/102


- PortD (PD7..PD0): Cng nh PortA, PortB, PortC, PortD cng c chc

nng xut nhp tng t nh cc Port khc, ngoi ra PortD cng c chc nng l

mt giao din ni tip USART, v chn vo ca cc ngt ngoi. V chc nng

USART th s ni chi tit phn sau.

Reset: Khi mt mc in p thp c c vo c t vo chn ny ko

di hn mt thi gian ti thiu th tri thi Reset s c kch hot , thm ch1 nu

xung ng h b ngng, xung c thi gian ngn hn thi gian ti thiu khng c

m bo s pht sinh ra Reset.

XTal1: li vo ca b khuych i dao ng o v l li vo ca xung ng h

VK hot ng.

Xtal2: li ra t b khuych i o.

AVCC:l ni cung cp ngun cho b bin i A/D bn trong VK, mc d nu ta

khng s dng ch bin i A/D th ta cng nn mc chn ny ln VCC.

AREF: L chn Vref ca b bin i ADC

XII: Giao din ni tip USART.

- Tng quang giao din ni tip USART

- Giao din ni tip USART (Universal Synchronous And Asynchonous

Serial Receiver And Transmitter) l mt b truyn nhn ni tip linh ng cao

c tch hp sn trong VK c cc chc nng chnh l:

+ Ch truyn pht song cng hon chnh (cc thanh ghi truyn

nhn l nhng thanh ghi c lp vi nhau)

+ Ch truyn nhn ng bv khng ng b+ Ch hot ng ng b vi cc thit b ch t

- phn gii cao v cc tc baud.

- H tr kch thc cc khung truyn l: 5,6,7,8 hoc 9 bit d liu v mt

hay 2 bit Stop.


52/102


- T ng pht bit kim tra chn l v t kim tra chn l.

- T ng d khi d liu b trn.

- T ng d li khung truyn.

- Ch lc nhiu gm li bit Start, v b lc thng thp s.

- H tr ba ngt ring bit: TX (ngt khi truyn xong), RX (ngt khi thu xong),

ngt khi thanh ghi truyn rng.

- H tr ch thng tin a VK .

- H tr tc truyn gp i ch truyn bt ng b.

Hnh 3 : S khi ca b USART

XIII: Tc baud:

Tc baud ph thuc vo tn s thch anh chun mc vo VK ta c th

s dng nhng gi tr chun gn gi tr cho thch anh ph hp vi tc baud.


53/102


Hnh 4: S khi cch pht tc baud

- Txclk: xung clock pht (tn hiu bn trong)- Rxclk: xung clock thu (tn hiu bn trong)

- Fosc: Tn s dao ng ca h thng.

- Cch thng dng nht t tc baud l ci t cc gi trtng ng

vi tc baud m ta mong mun vo thanh ghi tc baud UBRR.Bng v d

di y cho ta cc gi tr tng ng vi tc baud m ta mun t trong trng

hp s dng mt s thch anh thng dng.

Bang1: Phat toc o baud.


54/102


Bang 2 : Phat toc o baud.

Bang 3: Phat toc o baud.

XIV: B bin i ADC bn trong chp:

- Trong phn ln cc b vi iu khin AVR iu c b bin i ADC c

tch hp sn bn trong chp, y c th xem l phn ni tri hn cc vi iu khin

khc VD: nh 89C51vv.

- c im ca b bin i ADC bn trong vi iu khin ATMEGA32 :

+ phn gii ln n 10 bit .


55/102


+ Thi gian chuyn i t 13 dn 260us .

+ 8 knh bin i ADC n cc .

+ 7 knh vi sai .

+ in p bin di t 0VCC .

+ C th la chn mc Vref l 2,56 volt .

+ Hai knh nhp vo vi sai vi ch la chn b khuych i l 10x n

200x .

+ H tr ngt khi hon thnh vic bin i ADC .

+ H tr ch gim nhiu .

Hnh 5: S o khoi bo bien oi ADCtrong vi ieu khien ATMega32 .


56/102


PHN II

THIT K V THI CNGI: Mch ngun :

Hnh 1: S ngun n p 5V.

Dng IC n p 3 chn 78xx loi ny cho ra in p c nh c ch ra

bng hai s cui ca IC. V d 7805 n p 5V, 7812 (+12V), 7815 (+15V), 7824

(+24V); u ra thng thng mc thm t C = 0,1 uF ci thin qu trnh qu

v d cho in tr ra ca mch nh.

Hnh 1: Mch hin th Led

8055V

0,117 35 V

LED

R3

R

0

VCC

Q1A

3

1

2


57/102


II: Mch hin th Led:

hin th trng thi nhn c ca cc Vi iu Khin ta x mch hin thbi cc Led c mc vo mch nh hnh trn. Khi c tn hiu kch vo cc B

Transistor lm cho Transistor dn, lc ny dng in chy t Vcc qua mi ni CE

qua R3 qua Led v xung mas lm cho Led sng.

Ta c:

Vcc = 5V;

Vce = 0,2V;

Vled = 0,7V; dng chy qua Led ti a l: Iled = 15mA;T s mch ta c :

Vcc = Vce + Vled + R3* Iled;

R3* Iled = Vcc -Vce -Vled

III: IC MAX RS485 :

Hnh 3: S o chan Max 485

Ngun 5volt .

Chun EIA .

Tc truyn d liu 5mb/s .

Bo v nhit v ngn mch .

Thi gian tr khi truyn l 10ns v nhn l 20ns .


58/102


ChanTen Chc nang

IP/SO MAX

1 3

RO Ngo ra bo thu :

Neu A > B la200mV, RO la cao.

Neu A < B la 200mV , RO la thap.

2 4

/RE Cho phep ngora bo thu :

RO c cho pheo khi /RE la thap.

RO la tr khang cao khi /RE la cao.

3 5

DE Cho phep ngo ra lai :

Cac ngo ra lai A va B c cho phep khi DE cao.

Cac ngo ra lai A va B la tr khang cao khi DE thap.

Neu nhng ngo ra lai c cho phep th tng ngo co chc

nang nh lacac ng lai.

Khi chung la tr khang cao, chc nang cua chung nh la

cac ng thu cua bo thu neu /RE la thap.

4 6

DI Ngo vao bo lai :

DI thap th A thap va B cao

DI cao th A cao va B thap.

5 7 GND Noi mass.

6 8 A Ngo vao vo thu va ngo ra bo lai eu khong ao.

7 1 B Ngo vao bo thu va ngo ra bo lai eu ao.

8 2 Vcc Nguon cung cap dng 4.75V 5.25VVcc


59/102


Chc nang cua cac ng ieu khien :

Truyen :

Tn hieu vao Tn hieu ra

/RE DE DI B A

X 1 1 0 1

X 1 0 1 0

0 0 X High Z High Z

1 0 X High Z High Z

Nhan:

Tn hieu vao Tn hieu ra

/RE DE A-B R

0 0 mV200 1

0 0 mV200 0

0 0 Ngo vao h

mach

1

1 0 X High Z

IV: MASTER V SLAVE :

Phng php truy cp cho h thng mng ca ti ny. Theo hng php

Master/ Slave th: trm ch (Master) c trch nhim ch ng trong vic phn chia


60/102


quyn truy cp bus cho h thng, c bit trnh s xung t khi c hai trm t

cng pht d liu ln ng truyn mt lc y l mt im yu c th lm mt d

liu c gi, hay c th lm sai lch ni dung .

+ Trm ch Master c trch nhim phn chia quyn truy cp bus cho trm

t.

+ Trm ch c th dngphng php hi tun t n cc trm t.

+ Cc trm t ng vai tr th ng, ch c quyn truy cp khi nhn c

yu cu t trm ch.

+ Cc trm t s gi d liu ln ng truyn v trm ch khi c yu cu,ngc li thc thi cng vic ca ring mnh cho n khi trm ch hi tip sau mi

chu k.

+ Tt c cc trm t khng c quyn lin lc vi nhau.

Da vo cc tnh cht ny ta xy dng phng php ch t (Master/ Slave)

. m bo ti mt thi im ch c mt trm t duy nht tc cc Vi X

L c quyn truy cp bus, vic ny c m nhim bi trm ch (Master) phi cmt phng php iu khin cc trm t thch hp, mt khc tt c cc trm t

nhn d liu t ( Master) gi i, hay truyn d liu v cho (Master) u ph thuc

vo cc lnh nhn c t (Master). thc hin nhng yu cu ny th i hi

trm ch phi c k thut qun l ng truyn, cng nh p ng ng tnh cht

ca phng php ch t (Master/ Slave) . nh hnh 4 :


61/102


MASTER

Rs485

SALAVE SALAVE

. . .

Hnh 4: S o khoi mang RS485

V: Trm ch (Master ) :

- Dng vi s l ATMega32 :

- Port A t PA0 - PA7 dng xut gi tr hin th Led.

- Port B t PB1 - PB5 iu khin qut Led, PB6 v PB7 c

dng hin th Led cho ng c, PB0 c ni vi chn s 2 v

chn s 3 ca 485, mc ch iu khin vic truyn nhn d liu.

- Port C t PC0 - PC7 dng sut ra iu khin phm theo

phng php ma trn , c bn hng bn ct .

- PC0- PC3 s dng lm hng .

- PC4 -PC7 s dng lm ct .

-Chn Reset ni ngun VCC, qua b t .

- Port PD0 v PD7 s giao tip ni tip. Trong chn PDO l

chn RXD tc l chn nhn d liu ca Port ni tip, chn PD1 l

chn TXD tc l chn truyn d liu ca Port ni tip. Hai chn ny

c ni RS485 tng ng vi chn RXD c ni vi chn s 1 l


62/102


chn R ca Max 485, chn TXD c ni vi chn s 4 l chn D ca

Max 485 c th hin hnh 5:

T

1 s

C

Q5

U2

ATMega32

30

31

10

11

9

12

13

1

15

161718192021

32

2223242526272829

4039283736353433

876543232

AVCC

GND

VCC

GND

RESE

XTAL2

XTAL1

PB0

PD1(TXD)

PD2PD3PD4PD5PD6PD7

PD0(RXD)

PC0PC1PC2PC3PC4PC5PC6PC7

PA0PA1PA2PA3PA4PA5PA6PA7

PB7PB6PB5PB4PB3PB2PB1AREF

Q5

Enter

2

. . . . .

3

VCC

4

VCCC1

VCC

5

6

C2C

MAX485

6

7

23

8

4

5

1

A

B

REDEV

CC

DGND

R

7

Q5 Q5

VCC

8

VCC

9

Q5

0

r

Y1

R4

R N

Hnh 5: S thit k trm ch (Master )

Phng php truyn nhn d liu ca master :

Trm ch gi i mt khung d liu gm cc byte sau :

Dc (a ch ), byte Dl ( d liu ), c lnh truyn v nhn ( R , S ), byte ng c

C (a ch ) Byte u tin byte ny l byte a ch nhn din ..

L (lnh ) Byte th hai l Byte lnh gm hai lnh, l yu cu nhn d

liu hay yu cu gi d liu v master .DL (d liu ) Byte th ba l Byte d liu.

Byte th 4: l byte iu khin ng c nu trm c ng c hoc byte thm

vo cho khung d liu 4 byte i vi trm khng c ng c.


63/102


Bt u

Khi ng Port nitip.

t tc baud.

Qut Led.

Qut phm 4

Kim tra b mnhn

Nhn khung dliu gm 4 byte

X l khung dliu

Rx Counter < 4

Rx Counter = 4

Gi khung d liugm 4 byte

Kt thc

Byte = 4

Hnh 6: Lu gii thut Master


64/102


VI: Khi qut v cc trm t :

- Gm c mt trm ch (Master ) v hai trm t ( Slave).

- Cc Vi X L (cc trm) ly Byte u tin hay gi l byte a ch so snh

vi a ch ca mnh nu ng th x l tip cc Byte cn li, nu khng th b

khung truyn va nhn c v i nhn khung tip theo

- Nu ng l a ch ca mnh th Vi X L kim tra Byte lnh nu l lnh

nhn th

Vi X L nhn Byte th ba lm Byte d liu i vi trm c a chi l 8 th byte

th 4 l byte iu khinng c, i vi trm c a ch l 4 th byte th 4 l byte

thm vo cho khung d liu (khung d liu l 4 byte).

- Nu l lnh gi :

Nu l lnh gi th vi s l kim tra d liu ca mnh v gi khung d liu

v cho trm ch thng qua ng truyn RS485

Vy theo phng php ny ti mt thi im ch c mt Vi X L truy cp

ng truyn gi d liu v cho trm ch, khi Vi X L nhn c lnh, i

vi cc Vi X L cn li khng c xc nh a ch th b khung v thc thi

cng vic ca ring chng khng truy cp ng truyn, vy khng th xy ra hin

tng ti mt thi im c hai hay nhiu trm t cng truyn d liu ln ng

truyn, do khng th c xung t xy ra y. Ton b h thng c trm

ch quon l v ch c trm t no c yu cu gi d liu th mi c quyn truy

cp bus .


65/102


VII: Trm t 1( a ch 4 )

S mch in c th hin hnh 8 trm ny th n gin d liu

nhn c t trm ch gi ti v so snh vi a ch ca mnh l 4 nu ng thxc nh byte th hai l lnh g nu l lnh nhn th n ly byte d liu l byte th

3 ng thi a gi tr ny ra Prot A. Nu l lnh gi th n c gi tr ca Port A

hin c ca n v gi gi tr ny v cho trm ch. Di y l s mch c

th hin hnh 8: V l gii tht c th hin hnh 9:

R4

R

U2

ATMega32

30

31

10

11

9

12

13

1

15

1617

18192021

32

2223242526272829

403928373635

3433

32

8765432

8765432

AVCC

GND

VCC

GND

RESE

XTAL2

XTAL1

PB0

PD1(TXD)

PD2

PD3PD4PD5PD6PD7

PD0(RXD)


PA0PA1PA2PA3PA4

PA5PA6PA7

AREF

PB7PB6PB5PB4PB3PB2PB1


Y1

VCC

C

VCC

VCC

MAX485

6

7

23

8

4

5

1

A

B

REDEV

CC

DGND

R

C1

C2C


66/102


Hnh 8: S o thiet ke tram (Slave 1 )

Hnh 9: Lu gii thut Trm 1

Bt u

Khi ng Port nitip.

Nhn khung d liu4 byte

Kim tra a ch Sai

Nhn byte d liu,lm d liu

Gi khung d liu

Kt thc

Kim tra lnh(2 lnh RS)

ng


67/102


VIII: Trm Slave (trm t 2 ) :

Cng dng vi s l ATMega32 c thit k phn cng gn ging nh

trm 1. Khc ch l c thm phn ng c. Phn mm c lp trnh thu

nhn v x l d liu t trm ch gi n v c hin th cc trng thi nhn

c bi cc LED. Ngoi ra ta cn c mch iu ng c trn trm ny, v c

iu khin trc tip bi trm ch. khi trm t ny nhn c lnh iu khin t

trm ch gi ti, mch iu khin ng c hot ng nh sau :

Khi nhn c lnh kch khi ng ng c theo chiu thun t trm ch

(Master), th trm t kch hot chn PC1 lm cho Q3 dn in ng thi Q2 cng

c in (v Q2 v Q3 trng thi lun lun dn ) nn dng in qua ng c n

D1 qua Q3 v Mass, (trong mch Q2, Q1 lun dn bo ha). Khi c lnh khi

ng theo chiu ngc li theo yu cu ca trm ch, th lc ny chn PC0 c

kch hot, dng in chy t Q1 qua ng c, n D2 qua Q4 v Mass, lc n y

dng chy qua ng c theo chiu ngc li do ng c c khi ng theo

chiu ngc li.Cng dng bn byte :

- C (a ch )

- L (lnh )

- DL (d liu )

- ( ng c )


68/102


R4

R

Q2

R5R

Q1

D1

DIODE

R

U2

ATMega32

30

31

10

11

9

12

13

1

15

161718192021

32

2223242526272829

4039283736

353433

8765432

32

AVCC

GND

VCC

GND

RESE

XTAL2

XTAL1

PB0

PD1(TXD)

PD2PD3PD4PD5PD6PD7

PD0(RXD)


PA0PA1PA2PA3

PA4PA5PA6PA7


AREF

B

A R2R

C1

Q2

VCC

VCC

C2C

C

Y1

B

R

DC. .

MAX485

6

7

23

8

4

5

1

A

B

REDEVC

C

DGND

R

D2

DIODE

A

Q3

VCC

VCC

VCC

R1R

Hnh 10: S o thiet ke tram (salave 2 )


69/102


Hnh 11: Lu gii thut Trm t 2

Bt u

Khi ng Port nitip.

Nhn khung d liu4 byte

Kim tra a chSai

Nhn byte d liuv byte ngc

Gi khung d liu

Kt thc

Nhn R

Kim tra lnh(2 lnh RS)

ng

S (Lnh gi)


70/102


CHNG TRNH VIT CHO CC TRM

Tram chu Master.

This program was produced by theCodeWizardAVR V1.24.7d ProfessionalAutomatic Program Generator Copyright 1998-2005 Pavel Haiduc, HP InfoTech s.r.l.http://www.hpinfotech.come-mail:[email protected] :

Version :Date : 6/3/2006Author : F4CGCompany : F4CGComments:Chip type : ATmega32Program type : ApplicationClock frequency : 4.000000 MHzMemory model : SmallExternal SRAM size : 0

Data Stack size : 512*****************************************************/#include #include #define RXB8 1#define TXB8 0#define UPE 2#define OVR 3#define FE 4#define UDRE 5

#define RXC 7#define FRAMING_ERROR (1


71/102


char rx_buffer[RX_BUFFER_SIZE];#if RX_BUFFER_SIZE


72/102


#endif// USART Transmitter buffer#define TX_BUFFER_SIZE 8char tx_buffer[TX_BUFFER_SIZE];

#if TX_BUFFER_SIZE


73/102


unsigned char j,k,chuso[4],bay[8],tr,i,ma[4],n,p,bd,x,tam1,tam2,tam3;unsigned char nhan0,nhan1,nhan2,nhan3,z,nt,truyen=1,nhan,ks;void main(void){

// Declare your local variables here// Input/Output Ports initialization// Port A initialization// Func7=In Func6=In Func5=Out Func4=Out Func3=In Func2=In Func1=Out Func0=Out// State7=T State6=T State5=1 State4=1 State3=T State2=T State1=1 State0=1PORTA=0x33;DDRA=0xFF;// Port B initialization// Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=Out Func0=Out// State7=T State6=T State5=T State4=T State3=T State2=T State1=1 State0=1

PORTB=0x03;DDRB=0xFF;// Port C initialization// Func7=Out Func6=Out Func5=Out Func4=Out Func3=Out Func2=Out Func1=OutFunc0=Out// State7=0 State6=0 State5=0 State4=0 State3=0 State2=0 State1=0 State0=1PORTC=0x01;DDRC=0xFF;// Port D initialization// Func7=In Func6=In Func5=In Func4=In Func3=In Func2=In Func1=In Func0=In

// State7=T State6=T State5=T State4=T State3=T State2=T State1=T State0=TPORTD=0x00;DDRD=0x00;// Timer/Counter 0 initialization// Clock source: System Clock// Clock value: Timer 0 Stopped// Mode: Normal top=FFh// OC0 output: DisconnectedTCCR0=0x00;TCNT0=0x00;OCR0=0x00;// Timer/Counter 1 initialization// Clock source: System Clock// Clock value: Timer 1 Stopped// Mode: Normal top=FFFFh// OC1A output: Discon.// OC1B output: Discon.// Noise Canceler: Off


74/102


// Input Capture on Falling Edge// Timer 1 Overflow Interrupt: Off// Input Capture Interrupt: Off// Compare A Match Interrupt: Off

// Compare B Match Interrupt: OffTCCR1A=0x00;TCCR1B=0x00;TCNT1H=0x00;TCNT1L=0x00;ICR1H=0x00;ICR1L=0x00;OCR1AH=0x00;OCR1AL=0x00;OCR1BH=0x00;

OCR1BL=0x00;// Timer/Counter 2 initialization// Clock source: System Clock// Clock value: Timer 2 Stopped// Mode: Normal top=FFh// OC2 output: DisconnectedASSR=0x00;TCCR2=0x00;TCNT2=0x00;OCR2=0x00;

// External Interrupt(s) initialization// INT0: Off// INT1: Off// INT2: OffMCUCR=0x00;MCUCSR=0x00;// Timer(s)/Counter(s) Interrupt(s) initializationTIMSK=0x00;// USART initialization// Communication Parameters: 8 Data, 1 Stop, No Parity// USART Receiver: On// USART Transmitter: On// USART Mode: Asynchronous// USART Baud rate: 9600UCSRA=0x00;UCSRB=0xD8;UCSRC=0x86;UBRRH=0x00;


75/102


UBRRL=0x19;// Analog Comparator initialization// Analog Comparator: Off// Analog Comparator Input Capture by Timer/Counter 1: Off

ACSR=0x80;SFIOR=0x00;// Global enable interrupts#asm("sei")

rx_counter=0;rx_buffer[1]=0;

rx_buffer[2]=0;rx_buffer[3]=0;rx_buffer[4]=0;rx_buffer[5]=0;

rx_buffer[6]=0;rx_buffer[7]=0;chuso[0]=32;chuso[1]=32;chuso[2]=32;j=0;k=0;z=0;

while (1){

// Place your code heredelay_ms(10);UCSRB=0x00;

if (truyen==1){

for ( i=0; i


76/102


if ((z!=1) & (n==17)){

chuso[j]=126;

ma[j]=0;delay_ms(100);j++;

}if ((z!=1) & (n==18))

{

chuso[j]=18;ma[j]=1;delay_ms(100);

j++;}if ((z!=1) & (n==20)){

chuso[j]=61;ma[j]=2;delay_ms(100);j++;

}if ((z!=1) & (n==24))

{chuso[j]=109;ma[j]=3;delay_ms(100);j++;}

if ((z!=1) & (n==40)){chuso[j]=75;ma[j]=4;delay_ms(100);j++;}

if ((z!=1) & (n==36)){chuso[j]=103;ma[j]=5;delay_ms(100);


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j++;}

if ((z!=1) & (n==34)){

chuso[j]=119;ma[j]=6;delay_ms(100);j++;}

if ((z!=1) & (n==33)){chuso[j]=76;ma[j]=7 ;delay_ms(100);

j++;}

if ((z!=1) & (n==72)){chuso[j]=127;ma[j]=8;delay_ms(100);j++;}

if ((z!=1) & (n==68))

{chuso[j]=111;ma[j]=9;delay_ms(100);j++;}

if ((z==1) & (n==130)){chuso[j]=103;ma[j]=4;delay_ms(100);j++;}

if ((z==1) & (n==66)){chuso[j]=95;ma[j]=8;delay_ms(100);


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j++;}

}//for ( i=0; i


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}if (z==1)// chu lenh (L).{PORTB=0x01;

DDRB=0xff;PORTA=178;delay_ms(1);}

if(z==2)//du lieu (DL){PORTB=0x01;DDRB=0xff;PORTA=121;delay_ms(5);

PORTB=0x02;DDRB=0xff;PORTA=50;delay_ms(5);}if (z==3) //dong co (D){PORTB=0x01;DDRB=0xff;PORTA=121;

delay_ms(1);if ((chuso[0]==18)&&(chuso[1]==126))bay[3]=1;if ((chuso[0]==18)&&(chuso[1]==18))bay[3]=2;if ((chuso[0]==126)&&(chuso[1]==126))bay[3]=0;tr=1;

}else{bay[3]=255;tr=1;

}// doan chuong trinh tinh gia tri cua bay.if ((tam1!=32)&&(tam2==32)&&(tam3==32)&&(bd==1)&&(k


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chuso[0]=32;chuso[1]=32;chuso[2]=32;j=0;

z++;k++;bd=0;}if ((tam1!=32)&&(tam2!=32)&&(tam3==32)&&(bd==1)&&(k


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putchar(bay[1]);putchar(bay[2]);

putchar(bay[3]);delay_ms(10);

UCSRB=0x00;delay_ms(10);UCSRB=0x90;

PORTB=0;delay_ms(100);

z=0;k=0;tr=0;bd=0;

} //ket thuc truyen}//fi truyen// doan nhanif (rx_counter>=4){

truyen=0;nhan=1;nhan0=getchar();

nhan1=getchar();

nhan2=getchar();nhan3=getchar();nt=nhan2;

PORTA=nt;DDRA=0xFF;

PORTB=2;rx_counter=0;rx_buffer[1]=0;

rx_buffer[2]=0;rx_buffer[3]=0;rx_buffer[4]=0;rx_buffer[5]=0;

rx_buffer[6]=0;rx_buffer[7]=0;

UCSRB=0x00;

} // ket thuc nhanPORTC=0;

thiet_ke_mang_rs485

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