protocol modbus

8/3/2019 Protocol MODBUS

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GIAO THC MODBUSV GIAO TIP PC PLC DNG TH VIN MODBUS

Modbus la mot giao thc do hang Modicon (sau nay thuoc

AGE va Schneider Automation) phat trien.

Modbus mo ta qua trnh giao tiep gia mot bo ieu khien

vi cac thiet b khac thong qua c che yeu cau/ap ng.V ly do n gian nen Modbus co anh hng tng oi

manh oi vi cac he PLC cua cac nha san xuat khac.


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Trong moi PLC ngi ta co the tm thay mot tap hp con

cac dch vu a a ra trong Modbus. ac biet trong cac he

thong thu thap d lieu va ieu khien giam sat (SCADA),

Modbus hay c s dung tren cac ng truyen RS232/485ghep noi noi tiep gia cac thiet b d lieu au cuoi

(PLC, PC, RTU)


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I./ C che giao tiep Cac cong Modbus chuan tren cac bo ieu khien cua

Modicon cung nh mot so nha san xuat khac s dung giao

dien noi tiep RS232/485. Cac bo ieu khien nay co the

c noi mang trc tiep hoac qua Modem.

Cac tram Modbus giao tiep vi nhau qua c che chu/t

(master/slave), trong o ch mot thiet b chu co the chu

ong gi yeu cau, con cac thiet b t se ap ng bang

d lieu tra lai hoac thc hien mot hanh ong nhat nhtheo nh yeu cau.


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I./ C che giao tiep(tt) Cac thiet b chu thong thng la cac may tnh ieu

khien trung tam hoac cac thiet b lap trnh, trong khi cac

thiet b t co the la PLC hoac cac bo ieu khien so

chuyen dung khac Mot tram chu co the gi thong bao yeu cau ti mot so

tram t nhat nh, hoac gi thong bao ong loat

(broadcast) ti tat ca tram t.


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I./ C che giao tiep(tt) Ch trong trng hp nhan c nhan c yeu cau rieng,

cac tram t mi gi thong bao ap ng tra lai tram

chu.

Trong mot thong bao yeu cau co cha a ch tram nhan,ma ham dch vu ben nhan can thc hien, d lieu i kem

va thong tin kiem loi.


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I./ C che giao tiep(tt) V du trong giao tiep tay oi (peer to peer), moi bo ieu

khien co the ong vai tro la chu hoac t trong cac lan

giao dnh (mot chu ky yeu cau ap ng) khac nhau. Mot

tram co the cung mot luc co quan he logic vi nhieu oi

tac, v vay no co the ong thi ong vai tro la chu va

t trong cac giao dch khac nhau.


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Chu trnh yeu cau ap ng


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Thong bao yeu cau

Mot thong bao yeu cau bao gom cac thanh phan sau:

a ch tram nhan yeu cau (0 247), trong o 0 la a ch

gi hang loat.

Ma ham goi ch th hanh ong tram t can thc hien

theo yeu cau. V du, ma ham 03 yeu cau tram t oc noi

dung thanh ghi lu tr va tra lai ket qua.


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Thong bao yeu cau(tt)

D lieu cha trong thong tin bo sung ma tram t can cho

viec thc hien ham c goi. Trong trng hp oc thanh

ghi, d lieu nau chi ro thanh ghi au tien va so lng cac

thanh ghi can oc. Thong tin kiem loi giup tram t kiem tra o ven toan

cua noi dung thong bao nhan c.


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Thong bao yeu cau(tt)

Thong bao ap ng cung bao gom cac thanh phan giong nh

thong bao yeu cau.a ch ay la cua chnh tram t a thchien yeu cau va gi lai ap ng. Trong trng hp bnh thng,

ma ham c gi nguyen nh trong thong bao yeu cau va d lieu

cha ket qua thc hien hanh ong, v du noi dung hoac trang thai

thanh ghi. Neu xay ra loi, ma ham trong thong bao ap ng c

sa e ch th ap ng la mot thong bao loi, con d lieu mo

ta chi tiet loi xay ra. Phan kiem loi giup tram chu xac nh ro

o chnh xac cua noi dung thong bao ap ng nhan c t tram

t.


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II./ Che o truyen(tt) oi vi cac thiet b ghep noi qua mang Modbus chuan, co

the s dung mot trong hai che o truyen la ASCII hoac

RTU.

Ngi s dung chon mot trong hai che o theo y muon,cung cac tham so truyen thong qua cong noi tiep nh toc

o truyen, parity chan/le, vvChe o truyen cung nh cac

tham so phai giong nhau oi vi tat ca cac thanh vien

cua mot mang Modbus.


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II.1./ Che o ASCII Moi byte trong thong bao c gi thanh hai ky t ASCII 7

bit, trong o moi ky t bieu dien mot ch so hex. u

iem cua che o nay la no cho phep mot khoang thi

gian trong toi a mot giay gia hai ky t ma khong gayra loi. Cau truc mot ky t khung gi i c the hien

nh sau:

Start 0 1 2 3 4 5 6 P Stop


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II.1./ Che o ASCII(tt)Moi ky t bao gom :

1 bit khi au (Startbit).

7 bit bieu dien mot so hex cua byte can gi di dang ky

t ASCII (0 9 va A F), trong o bit thap nhat c gi i

trc.

1 bit parity chan/le, neu s dung parity.

1 bit ke thuc (Stopbit) neu s dung parity hoac 2 bit ketthuc neu khong s dung parity.


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II.2./ Che o RTU Khi cac thiet b trong mot mang Modbus chuan at che o

RTU (Remote Terminal Unit), moi byte trong thong bao c

gi thanh mot ky t 8 bit. u iem chnh cua che o nay

so vi che o ASCII la hieu suat cao hn. Tuy nhien, moithong bao phai c truyen thanh mot dong lien tuc.

Cau truc mot ky t khung gi i c the hien nh sau:

Start 0 1 2 3 4 5 6 7 P Stop


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II.2./ Che o RTU(tt)Moi ky t bao gom :

1 bit khi au (Startbit).

8 bit cua byte thong bao can gi, trong o bit thap nhat

c gi i trc

1 bit parity chan/le, neu s dung parity.

1 bit ke thuc (Stopbit) neu s dung parity hoac 2 bit ket

thuc neu khong s dung parity.


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III.1 Khung ASCII Trong che o ASCII, mot thong bao bat au vi dau (:),

tc ky t ASCII 3A, va ket thuc bang hai dau quay lai xuong dong (CRLF), tc hai ky t ASCII 0D va 0A. Moi

byte trong thong bao c truyen i bang hai ky t ASCII, v

vay cac ky t c phep xuat hien trong cac phan con

lai cua khung la 0-9 va A-F.

Khi

ua ch M

hmD liu M

CRCKtthc

: 2 k t 2 k t N k t 2 k t CR+LF


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III.1 Khung ASCII(tt)


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III.1 Khung ASCII(tt)

Moi thiet b tham gia mang co trach nhiem lien tuc theo

doi ng truyen va phat hien s xuat hien cua hai dau

cham. Khi dau hai cham nhan c th hai ky t tiep theo

se mang a ch cua thiet b c yeu cau nhan thong

bao hoac thiet b a gi thong bao ap ng. Khoangcach thi gian toi a cho phep gia 2 ky t trong mot

thong bao la mot giay. Neu vt qua gia tr nay, ben

nhan se coi la loi.Khung ASCII s dung phng phap LRC

(Longitudinal Redundancy Check) e cho viec kiem loi


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phng phap LRC

Cch tnh CHECK-SUM (LRC) ca ch ASCII bo m tnh nguyn vn ca dliu truyn i:

Ta tnh tng ca cc byte bt u t ADRtrong khung truyn cho n byte d liu cuicng trong khung truyn sau ly b 2.


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phng phap LRC(tt)

V d : mun c lin tc 8 Word t a ch0614H ca PLC c a ch l 01H


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phng phap LRC(tt)

LRC = (01H+03H+06H+14H+00H+08H) (vly b 2)= DA

Suy ra

PCPLC

: 01 03 06 14 00 08 DA CR LF


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phng phap LRC(tt)


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PLC sau khi nhn c s truyn ngc limy tnh chui sau

PLCPC

: 01 03 10 00 01 00 02 00 03 00 04 00 05 0006 00 07 00 08 C8 CR LF


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III.2./ Khung RTU

Trong che o RTU, mot thong bao bat au vi mot

khoang trong yen lang toi thieu la 3.5 thi gian ky t.

Thc te, ngi ta chon thi gian o bang so nguyen lan

thi gian ky t, nh c bieu th bang day (----) hnhdi ay. O au tien c truyen se la 8 bit a ch, sau

o en 8 bit ma ham, mot so byte tuy y d lieu va cuoi

cung la thong tin kiem loi CRC (Cyclical Redundancy Check).


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III.2./ Khung RTU(tt)

Sau khi truyen ky t cuoi cung cua ma CRC, khung thong

bao cung phai ket thuc bang mot khoang trong yen lang

toi thieu la 3.5 thi gian ky t, trc khi bat au mot

thong bao mi. Thc chat, khoang trong ket thuc cuamot khung thong bao cung co the chnh la phan khi

au bat buoc cua thong bao tiep theo.


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Khac vi che o ASCII, toan bo khung thong bao RTU

phai c truyen thanh mot dong lien tuc. Neu mot

khoang trong lien tuc ln hn 1.5 thi gian ky t xuat

hien trc khi truyen xong toan bo khung, thiet b se huybo thong bao cha ay u o va cho rang byte tiep theo

se la a ch cua mot thong bao mi.


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III.2./ Khung RTU(tt) a ch

Phan a ch trong mot khung thong bao bao gom hai ky t (ASCII)hoac tam bit (RTU). Cac gia tr a ch hp le nam trong khoang 0 247,

trong o a ch 0 danh rieng cho gi thong bao hang loat en cac tram

t. Neu Modbus c s dung tren cac mang khac, co the phng thc gi

ong loat khong c ho tr, hoac thay the bang mot phng phap khac.

Mot thiet b chu s dung o a ch e ch nh thiet b t nhan

thong bao yeu cau. Sau khi thc hien yeu cau, thiet b t a a ch mnh

vao khung thong bao ap ng, nh vay thiet b chu co the xac nh thiet

b t nao a tra li. Trong mot mang Modbus chuan ch co mot tram chu

duy nhat, v the o a ch khong can thiet phai cha ca a ch tram gi

va nhan.


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Ma hamGiong nh a ch, phan ma ham trong mot khung

thong bao bao gom hai ky t (ASCII) hoac tam bit (RTU).

Cac gia tr hp le nang trong khoang t 1-255, trong o

cac ma ham trong thong bao yeu cau ch c phep t 1

127. Tuy nhien, hau het cac thiet b ch ho tr mot

phan nho so ham tren va mot so ma ham c d tr

cho sau nay. Mot so ham tieu bieu c liet ke trongBang 3.1


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Khi mot thong bao gi t thiet b chu en thiet b t,

ma ham ch nh hanh ong ma thiet b t can thc

hien. Khi thiet b t tra li, no cung dung chnh ma

ham o trong thong bao ap ng bnh thng. Trongtrng hp xay ra loi, ma ham tra lai se la ma ham

trong yeu cau vi bit cao nhat c at bang 1 va thanh

phan d lieu se cha thong tin chi tiet ve loi xay ra.

Thong tin loi gi ve c bieu dien Bang 3.2

Mot so ham thong dung c cac bo ieu khien


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Mot so ham thong dung c cac bo ieu khien

Modicon ho tr.


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Thong bao loi c gi tra ve t thiet b t


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D lieuTrong mot thong bao yeu cau, noi dung phan d lieu

noi len chi tiet hanh ong ben nhan can thc hien. V du

trong mot yeu cau oc cac thanh ghi th phan d lieu chathong tin ve a ch thanh ghi au tien, so lng cac thanh

ghi can oc va chieu dai thc te cua chnh phan d lieu.


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Trong trng hp bnh thng, phan d lieu trong

thong bao ap ng se cha ket qua cua hanh ong a

thc hien, v du noi dung cac thanh ghi a oc.

Neu xay ra loi, phan d lieu cha ma ngoai le, nho ma thiet b chu xac nh hanh ong tiep theo can

thc hien. Lu y rang, mot so ham khong oi hoi tham

so, v vay phan d lieu co the trong.


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Tnh CRC cho ch RTU:

To mt thanh ghi 16 bit v ly gi tr lFFFF. Gi thanh ghi ny l CRC

Thc hin ly XOR 8bit u tin ( 1 byte) ca

thng ip vi byte thp ca thanh ghi CRC16 bit trn Di sang phi 1 bit ( chia cho 2) . Thm s 0

vo MSB v kim tra LSB Nu LSB =0 th thc hin li bc 3 ( di

tip) v Nu LSB=1 thc hin lnh XOR vi40961 ( A001H )


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Tnh CRC cho ch RTU(tt):

Thc hin li bc 3 v 4 cho n khi dchc 8 ln . Lc ny th byte 8 bit cthc hin xong

Thc hin li bc 2 n 5 cho cc byte tiptheo ca thng tin gi i.Lm cho n khithc hin xong tt c byte

Ni dung cui cng ca thanh ghi CRC chnh

l gi tr CRC Khi t CRC vo d liu truyn i th byte

thp truyn trc v byte cao truyn sau.


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IV./ Th vien giao thc Modbus Nhng th vien lenh cua STEP 7-Micro/WIN lam cho viec

giao tiep vi cac thiet b Modbus chu de dang hn bang

cach them vao cac chng trnh con va ngat a c thiet

ke ac biet cho viec giao tiep Modbus. Vi lenh ModbusSlave, ta co the thiet lap S7-200 hoat ong nh mot thiet b

Modbus RTU slave va giao tiep vi cac thiet b Modbus chu.


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IV./ Th vien giao thc Modbus(tt) Ta co the tm thay nhng lenh nay trong th muc Libraries

cua tap lenh STEP 7-Micro/WIN. Khi ta chon lenh MudbusSlave, mot hay nhieu chng trnh con lien quan c t ong

them vao project.


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Nhng yeu cau cho viec s dung giao thc Modbus: S dung port 0 cho viec giao tiep.

Khi port 0 c s dung cho giao tiep Modbus , no khong the c s dung

cho bat c muc ch nao, bao gom ca viec giao tiep vi STEP 7-Micro/WIN.

Giao tiep Modbus anh hng en tat ca cac vung nh SM lien quan en

giao tiep Freeport qua Port 0.

Giao tiep Modbus s dung 3 chng trnh con va 2 ngat.

Giao tiep Modbus s dung 1857 byte chng trnh cho nhng lenh Mudbus Slave

va cac chng trnh con ho tr.

Bien s dung cho giao tiep Modbus oi hoi 779 khoi byte cua vung nh V.

a ch bat au cua vung nay c nh ngha bi ngi s dung va c

danh rieng cho cac bien cua Modbus.


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Cach s dung nhng lenh giao tiep Modbus : Chen lenh MBUS_INT vao chng trnh va ch can thc thi no trong mot chu

ky quet. Ta co the s dung lenh MBUS_INT e thiet lap hoac thay oi cac

thong so giao tiep Modbus.

Khi lenh MBUS_INT c chen vao th rat nhieu chng trnh con va ngat an

c t ong them vao chng trnh.

Ta phai ch ra a ch bat au cua 779 byte lien tiep cua vung V cho viec

giao tiep Modbus.

at lenh MBUS_SLAVE vao chng trnh. Lenh nay c goi moi chu ky

quet e phuc vu bat c yeu cau nao ma no c nhan.

Noi cap truyen thong gia Port ttren S7-200 va thiet b Modbus chu.


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Cc m hm cho PLC


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V.1./ a ch Modbus a ch Modbus thng c viet t 5 en 6 ky t gia tr

gom loai d lieu va khoang trong. Ky t th nhat hoacth hai xac nh loai d lieu, ky t cuoi th t chon loaid lieu cho phu hp. a ch cua thiet b Modbus chu(Modbus master ) phai ung vi chc nang (Function), ach con lai th c ho tr bi Modbus t (Modbus Slave).


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V.1./ a ch Modbus(tt) 000001 en 000128 la a ch ngo ra Q0.0 - Q15.7

010001 en 010128 la a ch ngo vao I0.0 - I15.7

030001 en 030032 la thanh ghi ngo vao Analog AIW0 -

AIW62

040001 en 04xxxx la thanh ghi Holding cua bo nh V (V

memory)

h d h


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Bang a ch ModBus va a ch tng ng cua CPU S7 200 c

Modbus tro en :

a ch Modbus a ch CPU S7-200

000001 Q0.0

000002 Q0.1

000003 Q0.2

... ... 000127 Q15.6

000128 Q15.7

010001 I0.0

010002 I0.1

010003 I0.2


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a ch Modbus a ch CPU S7-200

... ...

010127 I15.6

010128 I15.7

030001 AIW0

030002 AIW2

030003 AIW4


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a ch Modbus a ch CPU S7-200 ... ...

030032 AIW62

040001 Hold Start hay (VW0)

040002 HoldStart+2 hay (VW2) 040003 HoldStart+4 hay (VW4)

... ...

04xxxx HoldStart+2 x(xxxx-1) hay

(VW2*(xxxx-1))

V 2 /


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V.2./ Lenh MBUS_INIT

V 2 /


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V.2./ Lenh MBUS_INIT(tt)

V 2 /


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Lenh MBUS_INIT dung e cho phep va khi tao hoac

khong giao tiep Modbus. Trc khi lenh MBUS_SLAVE co

the dung th lenh MBUS_INIT phai c thc thi khong co

loi (Error). Lenh nay c hoan thanh th bit Donec setngay lap tc trc khi tiep tuc lenh ke tiep. Lenh c

thc thi trong moi vong quet th ngo vao EN la ON.

V 2 /


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Thong so set toc o Baund la :1200, 2400, 4800, 9600, 19200,

38400, 57600, hay 115200. Thong so Parity c set phu hp vi parity cua modbus

chu (Modbus master). Gom co cac gia tr sau : 0-no parity

1-odd parity

2-even parity

V 2 /


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Delay m rong chuan Modbus trong ieu kien het thi gian ket thuctin nhan, bang cach them vao so mili giay cua khoang thi gian

nay. Gia tr tieu bieu cho thong so nay la 0 oi vi mang co day,

neu ta s dung nhng Modem co the sa loi th set Delay t 50 en

100 ms. Gia tr cua Delay co the t 0 ti 32767 ms.

MaxIQ la set nhng so cua I va Q e a ch Modbus 00xxxx va01xxxx tai gia tr t 0 128. Gia tr 0 khong the oc hay viet en

ngo vao va ngo ra, ta co the lay gia tr MaxIQ la 128.

V 2 /


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MaxAI la set nhng so thanh ghi ngo vao la word (AI) e a chModbus 03xxx tai gia tr t 0 32. So 0 khong c phep oc ngo

vao analog.

Gia tr MaxAI c chon nh sau :

Chon so 0 cho CPU 221

Chon so 16 cho CPU 222

Chon so 32 cho CPU 224, 226, va 226XM MaxHold : set so cua thanh ghi word holding trong vung nh V en a

ch Modbus 04xxxx. V du : e Modbus chu truy cap 2000 bytes cua

vung nh V, ta set MaxHold la 1000 words (holding register : thanh ghiholding)

V 2 / h


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HoldStart la a ch bat au cua thanh ghi holding (holdingregister) trong vung nh V. Gia tr nay c set trong VB0, do

o HoldStart c set a ch VB0 (&VB0). Mat khac, a

ch vung nh V ac trng cho a ch khi au cua thanh

ghi holding cho phep VB0 c dung mot ni nao khactrong d an (Project). Modbus chu truy cap vao vung nh V

bat au tai HoldStart. Khi lenh MBUS_INIT hoan tat ngo

vao Done se len ON.


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V.3./ Lenh MBUS_SLAVE


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V.3./ Lenh MBUS_SLAVE(tt) Lenh MBUS_SLAVE c s dung e phuc vu yeu cau t

Modbus chu (Modbus master), va c thc thi trong moi chu

ky vong quet e kiem tra va ap ng yeu cau cua

Modbus. Lenh c thc thi trong moi vong quet th ngo

vao EN la ON. Lenh MBUS_SLAVE khong co thong sovao.

Ngo ra Done la ON khi lenh MBUS_SLAVE ap ng yeucau cua Modbus. Va ngo ra Done la OFF neu khong co

yeu cau e thc thi.

V / L h h h M db Sl


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V.4./ Loi thc thi giao thc Modbus Slave

protocol modbus

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