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10 th OCT 2011
10-10-2011 1
Deltastar power project services Pvt.Ltd
Name of the Trg. Prg. : Fast Track Training programme
for Experienced Engineers
on Power system Protection
Topic : arrier omm!nication "asics#
omm!nication Protocol and carrier protection
Date : $% th &T. '%$$
By : Er .R.SURENDRAN
(Former SE/P&C/TNEB)
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MODBUSMODBUS
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Introduction
• Modbus s ! "ommun"!#on $ro#o"o% dee%o$ed by Mod"on
sys#ems. 'n sm$%e #erms # s ! !y o* sendn+ n*orm!#on
be#een e%e"#ron" de"es. T,e de"e re-ues#n+ #,e
n*orm!#on s "!%%ed #,e Modbus M!s#er !nd #,e de"es
su$$%yn+ n*orm!#on !re Modbus S%!es. 'n ! s#!nd!rd
Modbus ne#or #,ere s one M!s#er !nd u$ #o 01 S%!es
e!", #, ! un-ue S%!e Address *rom 2 #o 01. T,e M!s#er
"!n !%so r#e n*orm!#on #o #,e S%!es.
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What is Modbus ® protocol?Modbus Protocol is a messaging structuredeveloped by Modicon in 1979. It is used toestablish master-slave/client-servercommunication between intelligent devices. It
is a de facto standard truly open and themost widely used networ! protocol in theindustrial manufacturing environment. It hasbeen implemented by hundreds of vendors on
thousands of different devices to transferdiscrete/analog I/" and register data betweencontrol devices
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Introduction to Modbus
• Modbus can operate using a broad range ofcommunications media.
• Serial connection are typically RS232, RS422 or RS4!
• T"#$I# net%or&, %'ic' can use a (ariety of p'ysical lin&
types e.g. )t'ernet %ireless, fibre*optic, serial +###• T'ere are t%o met'ods of data transfer
• Modbus RT- +Remote Telemetry -nit
• inary data in pac&et format
• Most common implementation
• Modbus /S"II
• #lain te0t in pac&et format +1ittle used
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Introduction to Modbus
• T'e master de(ice re5uests data from t'e sla(e• Message includes6
• Sla(e address
• 7unction codes6
• 8 9 Read a coil +e.g. Read $ %rite t'e state of a digital c'annel
• 9 Read state
• 3 9 Input register +Read a register
• 4 9 utput register +Read or %rite to a register.
• Starting address of registers to be accessed
• umber of registers
• ; bit c'ec& sum
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Introduction to Modbus
• Sla(e de(ice %ill respond only to messages directto it.
• Sla(e de(ices can 'a(e up to ;!!3! registers
• Registers can be eit'er coils +bit state or data
•
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PROTOCOL MASTER SLAVEPROTOCOL MASTER SLAVE
M#$%&'
$lave 1 $lave ( $lave n
)uestion
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Protocol master slaveProtocol master slave
Master
$lave 1 $lave ( $lave n
)uestion
'esponse
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MODBUS PROTOCOL (qery!res"onse#
M$STER
TRANSM'T RECE'3E
TRANSM'T RECE'3E
SL$%E 1
TRANSM'T RECE'3E
SL$%E 2
TRANSM'T RECE'3E
S4A3E N
Protoco& 'mit on&y one m'ster 'n nti& 2)) s&'*es wit+ seri'& inter,'ce
E'c+ ,r'me 's ' "'rtic&'r nm.er o, .ytes
E'c+ ,r'me is coe/'&, "&e moe
T+e m'ster tr'nsmit ' qestion 'n w'it ' res"onse
2 s&'*es c'nt s"e' toget+er
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2
Mo.s ,r'me strctre
Address C,e"sumD!#!Fun"#on
T,e Modbus *r!me s#ru"#ure s #,e s!me *or re-ues#s (m!s#er#o s%!e mess!+es) !nd res$onses (s%!e #o m!s#er mess!+es).
Modbus ASC''
Modbus
RTU
: CR 4F
5A /e 6D /e 6A /e
Address C,e"sumD!#!Fun"#onsi&ence si&ence
S%en"e 78 59 ",!r!"#ers
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13
$ress ,ie&$ress C,e"sumD!#!Fun"#on
3!%d s%!e de"e !ddresses !re n #,e r!n+e o* 6 ... 01 de"m!%.
T,e nddu!% s%!e de"es !re !ss+ned !ddresses n #,e r!n+e o* 2 ...
01.
3!%ue 6 s resered *or bro!d"!s# mess!+es (no res$onse).
Re-ues# :A m!s#er !ddresses ! s%!e by $%!"n+ #,e s%!e !ddress n #,e !ddress
*e%d o*
#,e mess!+e.
Res$onse :,en #,e s%!e sends #s res$onse # $%!"es #s on !ddress n #,s
!ddress *e%d
o* #,e res$onse #o %e# #,e m!s#er no ,", s%!e s res$ondn+.
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3!%d "odes !re n #,e r!n+e o* 2 ... 99 de"m!%.
Re-ues# :
T,e *un"#on "ode *e%d #e%%s #,e s%!e ,!# nd o* !"#on #o
$er*orm.
Res$onse :
For ! norm!% res$onse #,e s%!e sm$%y e",oes #,e or+n!%
*un"#on "ode.
For !n e;"e$#on res$onse #,e s%!e re#urns ! "ode #,!# s
e-u!%en# #o #,e or+n!% *un"#on "ode #, #s mos# s+n*"!n#
b# se# #o ! %o+" 2.
5nction ,ie&Address C,e"sumD!#!5nction
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1)
3!%d "odes !re n #,e r!n+e o* 6 ... 99 de"m!%.
Re-ues# :
T,e d!#! *e%d "on#!ns !dd#on!% n*orm!#on ,", #,e s%!e mus#
use #o #!e
#,e !"#on de*ned by #,e *un"#on "ode. T,s "!n n"%ude #ems %ere+s#er
!ddresses -u!n##y o* #ems #o be ,!nd%ed e#"...
Res$onse :'* no error o""urs #,e d!#! *e%d "on#!ns #,e d!#! re-ues#ed.
'* !n error o""urs #,e *e%d "on#!ns !n e;"e$#on "ode #,!# #,e
m!s#er
!$$%"!#on "!n use #o de#ermne #,e ne;# !"#on #o be #!en.
D't' ,ie&Address C,e"sumD't'Fun"#on
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16
3!%d "odes !re n #,e r!n+e o* 6 ... 99 de"m!%.
Modbus RTU uses CRC : Cy"%y"!% Redun"y C,e" ( by#e)
Modbus ASC'' uses 4RC : 4on+#udn!% Redund!n"y C,e" (2 by#es)
Re-ues# :
T,e ",e"sum s "!%"u%!#ed by #,e m!s#er !nd sends #o #,e s%!e.
Res$onse :
T,e ",e"sum s re
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Re-ues# :
5r'me eem"&e in RTU moe
Fun"#on "ode 8 65 : Re!d =o%dn+ Re+s#ers
S%!e
AddressCRC16
Frs# ord
!ddress
Fun"#on
"ode 8 65
Number o*
ords #o re!d
2 by#e 2 by#e by#es by#es by#es
Res$onse :
S%!e
AddressCRC16
Number o*
by#es re!d
Fun"#on
"ode 8 65
3!%ue o* #,e
*rs# ord
2 by#e 2 by#e by#es by#es by#es
3!%ue o* #,e
%!s# ord
by#es
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Re-ues# :
5r'me eem"&e in RTU moe
Fun"#on "ode 8 6> : r#e Sn+%e Re+s#er
S%!e
AddressCRC16
ord
!ddress
Fun"#on
"ode 8 6>
3!%ue o*
ord
2 by#e 2 by#e by#es by#es by#es
Res$onse :
S%!e
AddressCRC16
ord
!ddress
Fun"#on
"ode 8 6>
3!%ue o*
ord
2 by#e 2 by#e by#es by#es by#es
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M'in c+'r'cteristics resme
Topolog(: )!s with line terminations
*axim!m distance: +ith ,-/0 : $%%% m witho!t repeater
Data rate: From $#'%% to $$0 1"its2s
*ax. no. of devices: +ith ,-/0 : 3' master incl!ded
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*ethod of accessing the medi!m: *aster slave
Transmission method: *essaging
*ax. !sef!l data si4e: $'% words
Transmission sec!rit(: L, or ,
-tart and stop delimiters Parit( "itontin!o!s stream
M'in c+'r'cteristics resme
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*od"!s -erial line ,-/0
*&D)5- -erial line ,-/0 is a lo% cost net%or& using a master$sla(emedium access %it' a transmission speed from ,288 to ! =bits$s
$""&ic'tion
Present'tion
Session
Tr'ns"ort
:etwor
Lin
P+ysic'&
7
6
)
4
3
2
1
Master - Slave Master - Slave
Mo.s
RS485 RS485
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22
Mo.s TCP!;P
MODBUS TCP!;P uses TCP/'P !nd E#,erne# 26 Mb#/s or 266
Mb#s/s #o "!rry #,e M?DBUS mess!+n+ s#ru"#ure.
$""&ic'tion
Pr
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