Wilamowski B.M., Irwin J.D. The Industrial Electronics Handbook. Second Edition: Industrial Communication Systems

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Communication Aspects of IEC 61499 Architecture 55-7

55.3 Logic Encapsulated in Basic FB

Let.us.consider.in.more.detail.how.the.logic.is.programmed.in.FBs..We.use.as.example.the.basic.FB-type.

LIGH

.tha

.enc

apsulates

.the.beh

avioral

.log

.of.a.sing

.fou

r-lamp

.LED.sec

tion.

According

.to.IEC.6149

.basic.FBs.are.den

.by.thei

.inte

rface

.(i.e

.inpu

.and.outp

.even

.and.data.

vari

ables),

.inte

rnal

.vari

ables,

.algo

rithms,

.and.a.stat

.mach

ine

.call

.exec

ution

.cont

rol

.char

.(ECC

Figu

.55.4.show

.the.ECC.of.the.LIGH

.FB.as.seen.in.FBDK

.In.the.le.pane

.one.sees.also.the.list.of.

eigh

.alg

orithms

.(IN

IT,

.…,.SET

_4,

.SET

_1).

.algo

rithms

.are.invo

ked

.in.the.acti

ons

.asso

ciated

.with.the.stat

.of.ECC..Init

ially,

.ECC.is.in.a.

spec

ically

.desig

nated

.star

.stat

.in.our.case.this.is.WAIT.stat

.in.the.midd

le.

.For.exam

ple,

.in.the.case.

of.INIT.inpu

.even

.the.ECC.will.“jum

p”

.into.stat

.INIT

.exec

ute

.the.rst.acti

on,

.consi

sting

.in.call

ing

algo

rithm

.with.name.INIT

.then.exec

ute

.the.seco

.acti

on,

.consi

sting

.in.call

ing

.algo

rithm

.CLEA

.and.

emit

ting

.of.out

put

.eve

.INI

TO,

.and.the

.wil

.ret

urn

.to.the.WAI

.sta

te.

Algorithms

.can.be.prog

rammed

.in.die

rent

.prog

ramming

.lang

uages.

.For.exam

ple,

.it.is.expe

cted

.that.

the.PLC.pro

gramming

.lan

guages

.of.IEC.613

31-3

.sta

ndard

.[19

]

.may.be.use

.amo

.oth

ers.

55.4 Extension

Now.let.us.consider.one.possible.functional.extension.of.our.sample.system.that.justies.the.distribution.

of.the.appl

ication

.acro

.seve

ral

.comp

uting

.devic

es.

.Assu

.that.in.addit

ion

.to.the.prev

iously

.cons

idered

con

guration

.in.Figu

.55.2

.we.add.two.butt

ons

.for.incr

easing/decreasing

.the.spee

.of.the.movi

.ligh

a.nume

ric

.disp

lay

.indi

cating

.the.curr

ent

.freq

uency

.of.the.ligh

.upda

te,

.and,.most.impo

rtantly,

.one.more.

sect

ion

.of.LEDs,.so.the.ligh

.will.“jum

p”

.from.one.LED.sect

ion

.to.anot

her,

.as.show

.in.Figu

.55.5

FIGURE 55.4 ECC.of.the.FB-type.LIGHTS.

55-8 Industrial Communication Systems

START

COLD

INIT

EO0

EO1

INITO

INIT

REQ

CHOICES

OUT

INITO

IND

INITO

INIT

START

STOP

INITO

INIT INITO

INIT

INITO

INIT INITO

CNF

IND

OUT

REQ

NEW

REQ REQ

REQ

LEDS1

MODE

LED3

LED2

LED1

LED0

LED3

LED2

LED1

LED0

LED3

LED2

LED1

LED0

BITN

CNF

INIT INITO

REQ

LEDS2

CNF

REQ CNF

CNF

OUT

DIV2

MUL2

TYPE

IVAL

LABEL0

LABEL

“RUN”

“STOP”

“UP”

“TIME”

“FLASH_ALL, CHASE_UP, CHASE_DOWN”

t#250ms

“DOWN”

LABEL1

WARM

STOP

E_RESTART

E_SWITCH

PUSH_BUTTON

DOWN

KNOB

FREQ

MEMT

CURFREQ

E_CYCLE

MODE

Decentralized logic

SWITCH3

PERIODIC

LOGIC1

LOGIC2

LIGHTS

MODE

LED3

LED2

LED1

LED0

BITN

LIGHTS

MODE

TIME

START

CPU

Controller

Added physical components

STOP

LED3 LED2 LED1 LED0 LED3 LED2 LED1 LED0

ALL

CHS_UP

CHS_DOWN

LED_HM1

NUM_DISP

SWITCH2

RUNSTOP

RS_GATE

FIGURE 55.5 New.system.with.added.peripherals.

Communication Aspects of IEC 61499 Architecture 55-9

 e.logic.and.modes.of.operation.of.the.new.system.shall.remain.the.same.. e.changes.to.the.FB.

model.will.closely.follow.the.changes.introduced.into.the.physical.system..For.each.new.peripheral.ele-

ment,

.we.haveadded.a.new.FB.. ere.is.only.one.extra.FB.FREQ.not.corresponding.to.any.physical.com-

ponent.

. is.block.implements.a.global.variable.storing.the.current.ashing.frequency.value.

.frequency.is.set.by.the.time-setting.knob.and.can.be.changed.(increased.or.decreased).as.a.result.

of.pressing.buttons.“+”.and.“−.”. e.current.ashing.frequency.value.is.passed.to.the.numeric.display.

and.to.the.“pulse”.generator.in.the.FB.PERIODIC.

.is.interesting.that.we.did.not.need.to.change.the.logic.at.all!.We.just.added.one.more.FB.LOGIC2.

and.“cascaded”.it.aer.LOGIC1..When.the.running.light.reaches.the.rightmost.or.lemost.position.at.

the.LED.block,.it.“jumps”.to.the.next.LED.block..For.that,.the.event.output.CR.of.one.block.is.connected.

to.the.event.input.NEW.of.the.other.

Similar

.to.the.rst.version.of.the.system,.the.extended.system.can.be.easily.simulated.by.substituting.

FBs.interfacing.physical.peripheral.devices.by.the.FBs.imitating.this.on.screen.

55.5 Distribution

IEC.61499.implies.a.two-stage.design.process..First,.an.application.is.created.as.a.network.of.FBs..At.

this.stage,.communication.between.FBs.is.abstract,.implemented.via.event.and.data.ow.arcs..Second,.

the.application.can.be.distributed.across.several.devices.as.illustrated.in.Figure.55.6.. e.connections.

Application

FB2

FB3

FB1

FB2

FB1

FB2

Device border

crossing points:

here Communication

Function Blocks

for inter-device

communication

are to be inserted

FB3

Device 1

Network

Device 2

FB3

Publish

FB1

FIGURE 55.6 Distribution.of.the.application.across.two.devices:.the.connections.between.blocks.which.are.mapped.

to.the.same.device.are.preserved.. e.connections.crossing.the.device.boundaries.are.appended.by.communication.

FBs..(From.Vyatkin,.V.,.IEC 61499 Function Blocks for Embedded Control Systems Design,.Instrumentation.Society.of.

America,.Research.Triangle.Park,.NC,.2007.)

55-10 Industrial Communication Systems

between.blocks.which.are.mapped.to.the.same.device.are.preserved.. e.connections.crossing.the.device.

boundaries.are.appended.by.communication.FBs.

55.6 Communication FBs

In.IEC.61499,.communication.is.implemented.via.a.particular.case.of.service.interface.FBs.called.CIFBs..

 e.standard.explicitly.refers.to.two.generic.communication.patterns:.PUBLISH/SUBSCRIBE.for.uni-

directional

.transactions.and.CLIENT/SERVER.for.bidirectional.communication.. ese.patterns.can.be.

adjusted.to.a.communication.mechanism.of.a.particular.implementation..Otherwise,.providers.of.com-

munication

.hardware/soware.can.specify.their.own.patterns.if.they.dier.from.the.above-mentioned.

ones..Figure.55.7.illustrates.the.generic.PUBLISH.and.SUBSCRIBE.FBs.performing.unidirectional.data.

transfer.via.a.network.

.PUBLISHER.serves.for.publishing.data.SD_1,.…,.SD_m.that.come.from.one.or.more.FBs.in.

theapplication..It.is,.therefore,.initialized/terminated.by.the.application..Upon.a.request.event.fromthe.

application.at.the.REQ.event.input,.the.data.that.need.to.be.published.are.sent.by.the.PUBLISHER.viaan.

implementation-dependent.network..When.this.is.done,.the.PUBLISHER.informs.the.publishing.appli-

cation

.via.the.event.output.CNF.

.SUBSCRIBER.FB.is.initiated.by.the.application.. e.application.reads.the.data.RD_1,.…,.RD_m..

Normal.data.transfer.is.initiated.by.the.sending.application.via.the.REQ.input.event.to.the.PUBLISHER..

 is.is.illustrated.in.Figure.55.8.by.means.of.time-sequence.diagrams.. e.PUBLISHER.sends.the.data.

and.triggers.the.IND.event.at.the.outputs.of.the.SUBSCRIBER.to.notify.the.reading.applications.that.

new.values.of.data.are.available.at.the.RD_1,.…,.RD_m.outputs.of.the.SUBSCRIBER.. e.reading.appli-

cation

.can.notify.the.SUBSCRIBER.by.the.RSP.event.that.the.data.have.been.received.

55.7 Communication Using Services of Internet Protocol Suite

 e. generic. communication. patterns. of. the. standard. were. further. specied. in. the. “IEC. 61499.

Compliance. Prole. for. Feasibility. Demonstrations”. [1]. for. implementations. using. services. of. the.

Internet.protocol.suite.

INIT

REQ RSP

INIT

QI QI QO

IND

INITO

STATUS

RD_1

RD_m

...

PARAMS

Network

PARAMS

SD_1

SD_m

...

CNF

STATUS

PUBLISH_m

SUBSC RIBE_m

INITO

FIGURE 55.7 Publish.and.subscribe.CIFBs.

Communication Aspects of IEC 61499 Architecture 55-11

Provisions.of.the.compliance.prole.were.implemented,.for.example,.in.FBDK.[2].as.the.pairs.of.

PUBLISH_n/SUBSCRIBE_n.and.CLIENT_n_m/SERVER_n_m.FBs.. e.PUBLISH/SUBSCRIBE.com-

munication

.is.implemented.using.services.of.the.universal.datagram.protocol.(UDP).. e.communica-

tion

.is.essentially.unreliable.and.multicast.. e.CLIENT/SERVER.communication.is.implemented.via.

the.transfer.control.protocol.(TCP)..It.is.point-to-point.and.reliable.

Using

.this.library.of.communication.FBs,.a.user.can.develop.distributed.applications.communi-

cating

.via.local.networks.(Ethernet).and.even.via.the.Internet..The.specifics.of.the.implementation.

imply.the.addressing.schema..The.communication.FBs.have.input.parameter.IDs,.which.are.set.as.

follows.

.PUBLISH/SUBSCRIBE.communication.pattern.assumes.that.there.could.be.many.subscribers.

for.one.(or.even.several).publisher(s).as.illustrated.in.Figure.55.9.. is.communication.pattern.is.imple-

mented

.in.FBDK.using.the.multicast.services.of.the.UDP.

.PUBLISH.block.has.to.have.an.ID.that.follows.the.rules.for.Internet.multicast.addresses..In.gen-

eral,

.an.Internet.address.consists.of.four.numbers.in.the.interval.0-255;.for.example,.124.11.2.1..( e.

multicast.addresses.are.in.the.interval.224.0.0.0.through.239.255.255.255,.but.the.range.of.addresses.

between.224.0.0.0.and.224.0.0.255,.inclusive,.is.reserved.for.system.purposes.).In.the.example,.the.ID.of.

the.PUBLISHER.(located.in.Device.1).is.225.0.0.1:1204.(where.225.0.0.1.is.an.IP.address.for.that.multi-

cast

.group.and.1204.is.a.unique.port.number.selected.in.Device.1).. e.ID.of.the.publisher.completely.

identies.the.multicast.group.

Any

.SUBSCRIBE.block.located.in.a.device.on.the.same.network.segment.as.the.PUBLISH.can.receive.

the.published.data.if.it.has.the.same.ID.as.the.PUBLISH.. e.published.data.will.be.received.by.both.

subscribers.located.in.Device.2.and.Device.3.

.CLIENT_SERVER.communication.is.point-to-point.(i.e.,.only.one.client.can.send.and.receive.

data.to/from.one.server).. e.addressing.is.illustrated.in.Figure.55.10.. e.SERVER,.which.is.located.

in.Device.2,.has.ID.that.refers.to.the.address.of.the.host.device.(localhost).and.adds.there.a.unique.(for.

that.device).port.number.. e.CLIENT,.located.in.Device.1,.has.an.ID.that.is.composed.of.two.parts:.IP.

address.of.the.server’s.device.and.the.same.port.number.as.used.in.the.SERVER’s.ID.

INIT(+)

INITO(+)

REQ(+)

CNF(+)

IND(+)

RSP(+)

SD_1, ..., SD_m

RD_1, ..., RD_m

INITO(+)

PARAMS

normal_service_establishment

normal_data_transfer

SUBSCRIBERPUBLISHER

FIGURE 55.8 Communication.establishment.and.normal.data.transfer.sequence.

55-12 Industrial Communication Systems

INIT

INITO

Device 1

Device 2

Device 3

Different addresses of devices

Same address of the multicast group

REQ

147.11.22.3:1501

225.0.0.1:1204

147.11.22.4:1499

147.11.22.5:1499

MGR_ID

SD_1

SD_2

INIT

RSP

QO QO

STATUS

RD_1

RD_2

SUBSCRIBE_2 SUBSCRIBE_2

INITO

IND

CNF

PUBLISH_2

FIGURE 55.9 Multicast.communication.over.a.local.network.implemented.using.PUBLISH_2.and.SUBSCRIBE_2.FBs.

Communication Aspects of IEC 61499 Architecture 55-13

55.8 adding Distribution and Communication

to the Sample System

In.this.section,.we.see.how.distribution.and.communication.can.be.added.to.our.extended.example.

from.Figure.55.5..Assume.that.the.peripherals.are.grouped.into.three.networking.devices.as.shown.in.

Figure.55.11.. ere.are.two.LED.panels.(LED1.and.LED2),.one.of.which.(LED1).has.increase–decrease.

speed.buttons.and.control.panel.(device.panel).for.setting.parameters.of.the.running.lights.process..

 e.devices.are.connected.by.two.dierent.networks:.LED1.and.LED2.with.a.DeviceNet.segment,.while.

Panel.and.LED1.with.Ethernet.

 ese

.physical.connections.need.to.implement.the.logical.connection.between.the.devices.that.can.

be.dierent.. us,.LED2.and.panel.have.no.direct.physical.connection,.but.information.ow.from.Panel.

to.LED2.is.required.

.terms.of.IEC.61499,.network.topology.of.this.system.can.be.described.within.a.simulation.system.

conguration.as.shown.in.Figure.55.12.. e.system.conguration.is.supposed.to.produce.on-screen.

simulation.of.our.system;.that.is.why.three.devices.have.type.“FRAME_DEVICE.”

.FB.application.capturing.the.behavior.logic.of.this.system.is.exactly.the.same.as.was.seen.in.Figure.

55.8..Applying.the.mapping.technique.for.distribution.of.our.application.across.these.three.devices,.we.

obtain.the.system.conguration.with.explicit.communication.as.shown.in.Figure.55.13.

.communication.FBs.SEND/RCV.used.in.the.distributed.version.of.our.system.implement.the.

point-to-point.communication.model.. ey.are.similar.to.PUBLISH/SUBSCRIBE,.with.the.only.dif-

ference

.that.multicast.is.not.supported..We.also.assume.that.if.the.ID.parameter.is.le.blank,.then.the.

compiler.inserts.the.instance.name.as.the.ID,.and.each.ID.uniquely.belongs.to.a.pair.of.SEND.and.

RCV.FBs..( is.way.of.addressing.is.implemented.for.the.local.communication.FBs.PUBL/SUBL.in.

FBDK/FBRT.)

 ere

. are. two. modications. of. the. SEND/RCV. FBs,. one. for. communication. over. MODBUS.

protocol.and.the. other.for. communication. in.DeviceNet. using.the.CIP.. e.latter.FBs.are. called.

CIP_SEND_n/CIP_RCV_n.

INIT

Device 1 Device 2

147.11.22.4:2048

Localhost:2048

153

MGR_ID

147.11.22.3:1501

147.11.22.4:1499

Same ID

as the server

has:

Different addresses of devices

REQ

INIT

RSP

CLIENT_2_1

SD_1

SD_2

INITO

CNF

INITO

IND

RD_1

STATUS

SERVER_1_2

RD_1

RD_2

STATUS

FIGURE 55.10 Point-to-point. bidirectional. communication. implemented. using. SERVER_1_2. and.

CLIENT_2_1.FBs.

55-14 Industrial Communication Systems

CPU

START

STOP

MODE

TIME

All

CHS_UP

CHS_DOWN

CPU

LED3 LED2 LED1 LED0 LED3 LED2 LED1 LED0

DeviceNet

Device: LED1

Device: LED2

Information ow between the devices

LED1

LED2

Panel

Device: Panel

EtherNet

FIGURE 55.11 Distributed.conguration.of.the.“running.lights”.system.(le).and.information.ow.between.the.devices.

Communication Aspects of IEC 61499 Architecture 55-15

55.9 Internals of Communication FBs: Modbus

Modbus.(described.in.Chapter.4.12.of.this.Handbook.and.in.[20–24]).is.one.of.the.many.communica-

tion

.proto

cols

.that.may.be.used.for.tran

sferring

.even

.and.data.over.a.netw

ork.

.As.this.proto

col

.is.

base

.on.a.remo

.memo

.data.mode

.whic

.is.acce

ssed

.and.upda

ted

.using.the.clie

nt–server

.inte

rac-

tion

.mode

.it.is.natu

rally

.impl

emented

.in.IEC.6149

.as.CLIE

.and.SERV

.comm

unication

.serv

ice

inte

rface

.FBs.ill

ustrated

.in.Fig

ure

.55.

14.

.Modb

.proto

col

.incl

udes

.thre

.versi

ons,

.name

.RTU,.ASCI

.and.TCP.. e.rst.two.use.a.dif-

erent

.meth

.of.byte.enco

ding

.on.the.same.physi

cal

.medi

.(RS23

.or.RS48

5),

.whil

.the.last.tran

smits

the.mess

ages

.over.TCP/

.conn

ections.

.Due.to.thes

.vari

ations

.of.the.proto

col,

.one.SERV

.and.one.

CLIE

.FB.typ

.are.nee

ded

.for.eac

.ver

sion.

.des

cription

.of.a.typ

ical

.dat

.and.eve

.tra

nsfer

.seq

uence

.is.as.fol

lows:

•

. e.devi

.cont

aining

.the.RCV.FB.(the.serv

.devi

ce)

.init

ializes

.this.serv

.(INI

T+

.even

.i.e.,.

INIT.even

.with.QI.inpu

.set.to.TRUE

)

.whil

.simul

taneously

.prov

iding

.con

guration

.para

meters.

For.the.TCP.versi

on,

.thes

.consi

.of.the.loca

.IP.addr

esses

.and.port.numbe

.on.whic

.it.will.lis-

.awai

ting

.for.the.arri

val

.of.conn

ection

.requ

ests

.from.clie

nts.

.For.the.RTU.and.ASCI

.versi

ons,

the.para

meters

.are.the.iden

tication

.of.the.hard

ware

.inte

rface

.(e.g

.the.seri

.port

)

.to.use.as.well.

as.the.seri

.line.para

meters

.(bau

.rate

.numbe

.of.star

.and.stop.bits

.numbe

.of.bits

.and.pari

ty).

All.ver

sions

.als

.req

uire

.an.add

itional

.par

ameter,

.the.Mod

bus

.dev

ice

.ID.

•

. e.device.containing.the.SEND.(client.device).initializes.this.client.(INIT+.event)..Required.

para

meters

.incl

ude

.the.seri

.line.inte

rface

.deta

ils

.(for.RTU.and.ASCI

.vers

ions)

.and.the.Modb

devi

.ID.of.the.remo

.serv

.with.whic

.it.will.comm

unicate.

.For.the.TCP.vers

ion,

.the.IP.addr

ess

FIGURE 55.12 e.network.topology.of.our.system.described.as.a.part.of.distributed.system.conguration.of.

IEC.614

99.

55-16 Industrial Communication Systems

COLD

INIT

REQ

LABEL1

LABEL0

“RUN”

“STOP”

“TIME”

“UP”

“DOWN”

“TIME”

“FLASH_ALL, CHASE_UP, CHASE_DOWN”

t#250ms

INITO

INIT

LABEL

INITO

IND

INITINITO

IND

INIT INITO

IND

INIT INITO

INIT

NEW

REQ

MODE

INITO

CNF

IND

RD_1

INIT INITO

IND

LABEL

INIT

REQ

DIV2

MUL2

REQ

START

STOP

SD_1

CHOICES

TYPE

IVAL

TYPE

IVAL

INITO

EO0

EO1

CNF

INIT

REQ

INITO

CNF

INIT

REQ

INITO

CNF

IND

INIT INITO

REQ

CNF

REQ

CNF

REQ

ID ID

SD_1

INIT INITO

CNF

REQ

INIT INITO

CNF

LED3

LED2

LED1

LED0

BITN

LED3

LED2

LED1

LED0

BITN

INIT

NEW

REQ

MODE

INITO

CNF

INIT

REQ

INITO

CNF

INIT

REQ

LED3

LED2

LED1

LED0

LED3

LED2

LED1

LED0

INITO

INIT INITO

CNF

REQ

INIT INITO

CNF

REQ

INIT INITO

IND

INIT INITO

IND

INIT

REQ

INITO

INIT INITO

CNF

IND

CNF

OUT

WARM

STOP

E_RESTART

START

COLD

WARM

STOP

COLD

WARM

STOP

E_RESTART

START

PULSE1 CR2

COM _MODE1

LOGIC2

LEDS2

CR1

CIP_SEND_0

LED_HMI

LIGHTS

CIP_RCV_0

CIP_RCV_1

DOWN

MOLFREQ

PULSE

PULSE1

CR1

LOGIC1

CR2

LEDS1

LED_HMI

LIGHTS

CIP_SEND_0

CIP_RCV_0

COM_MODE

COM_MODE1

CIP_SEND_1

DIV FREQ

PUSH_BUTTON

RUNSTOP

RS_GATE

Device: PANEL

Device: LED1

Device: LED2

Legend:

Cummunication over DeviceNet Cummunication over TCP/IP

E_SWITCH

FREQ

DIVFREQ

MULFREQ

RCV0

CURFREQ

PERIODIC

PULSE

SEND0

SEND_0

RCV_0

RCV_1

RD_1

E_CYCLE

MODE

COM_MODE

SEND_1

SWITCH3

NUM_DISP

MEMT

KNOB

SWITCH2

FIGURE 55.13 Application.is.mapped.on.three.devices.and.communication.FBs.are.inserted.