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

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38-1

38.1 Introduction

Ethernet. for. control. automation. technology. (EtherCAT). [ETG04,ETG05]. is. a. high-performance.

Ether

net-based

.eld

bus

.syst

em.

.Its.main.deve

lopment

.goal.was.to.appl

.Ether

net

.to.autom

ation

.appl

cations,

.whic

.requ

ire

.shor

t-cycle

.time

.and.low-

communication

.jitt

ers.

.Ether

CAT

.is.nowa

days

.a.popu

lar

.solu

tion

.for.conn

ecting

.cont

rol

.appl

ications

.to.eld.devi

ces

.in.indu

strial

.envi

ronments,

.incl

uding

moti

on-control

.appl

ications,

.and.comm

unication

.equi

pment

.and.devi

ces

.can.be.easil

.foun

.o-t

he-

shelf

.[ES

C20].

.Ethe

rCAT

.proto

col

.is.an.open.stan

dard

.curr

ently

.mana

ged

.by.the.Ethe

rCAT

.tech

nology

.group.

(ETG

.Its.spec

ication

.has.been.rece

ntly

.inte

grated

.into.the.inte

rnational

.eld

bus

.stan

dards

.IEC.6115

[IE1

58]

.and.IEC.6178

.[IE7

84].

.Ethe

rCAT

.is.base

.on.a.mast

er/slave

.approa

.(whe

.only.one.mas-

.is.allo

wed

.in.the.netw

ork)

.and.reli

.on.a.ring.topo

logy

.at.the.phys

ical

.leve

.It.can.inte

roperate

with.both.commo

.TCP/

IP-based

.netw

orks

.and.othe

.Ethe

rnet-based

.solu

tions,

.such.as.Ethe

rNet/IP

or.PROF

Inet.

38.2 Physical Layer

 e.EtherCAT.master.processes.data.via.standard.hardware.(full-duplex.Ethernet.network.interface.

cont

rollers)

.and.dedi

cated

.sow

are

.(e.g

.Beck

ho

.Twin

CAT),

.but.it.supp

orts

.also.open.sour

.solu

tions

base

.on.Linu

x-like

.oper

ating

.syst

ems.

.On.the.cont

rary,

.purp

osely

.desig

ned

.hard

ware

.has.to.be.used.

on.slav

es.

. e.mast

.node.comp

letely

.cont

rols

.tra

.over.the.netw

ork

.by.init

iating

.all.tran

smissions.

Ever

.slav

.when.rece

iving

.a.data

gram,

.proc

esses

.it.(in.hard

ware)

.and.then.forw

ards

.it.to.the.next.

slav

.in.the.physi

cal

.ring

.Unli

.Ether

net

.swit

ches

.and.brid

ges,

.fram

.are.not.mana

ged

.acco

rding

.to.

EtherCAT

38.1. Introduction.....................................................................................38-1

38.2

. Physi

cal

.Lay

er...................................................................................38-1

38.3

. Comm

unication

.Pro

tocol...............................................................38-2

Commands

38.4. Addressing........................................................................................38-5

Physical.Addressing. •. Logical.Addressing:.FMMU

38.5. SyncManager....................................................................................38-7

38.6

. Dist

ributed

.Clo

ck............................................................................38-8

38.7

. Appl

ication

.Lay

er.............................................................................38-9

Mailbox.Services

References...................................................................................................38-10

Gianluca Cena

Istituto di Elettronica e di

Ingeg

neria

dell

’Informazione

e dell

Tele

comunicazioni

Adriano Valenzano

Istituto di Elettronica e di

Ingeg

neria

dell

’Informazione

e dell

Tele

comunicazioni

Claudio Zunino

Istituto di Elettronica e di

Ingeg

neria

dell

’Informazione

e dell

Tele

comunicazioni

38-2 Industrial Communication Systems

astore-and-forward.scheme.(i.e.,.received,.interpreted,.and.then.copied.as.process.data.at.every.connection)..

Inst

ead,

.eve

.fra

.is.pro

cessed

.on-

the-y

.at.the.dat

a-link

.lay

er.

.furt

her

.impr

ove

.comm

unication

.eci

ency,

.a.eld

bus

.memo

.mana

gement

.unit.(FMM

.is.pro-

ided

.in.each.slav

.devi

.that.read

s/writes

.port

ions

.of.data.incl

uded

.in.the.fram

.whil

.it.is.bein

forw

arded

.to.the.nex

.dev

ice.

EtherCAT

.supp

orts

.two.die

rent

.type

.of.phys

ical

.laye

.name

.Ethe

rnet

.and.EBUS

. e.form

is.used.for.conn

ecting

.to.an.exte

rnal

.Ethe

rnet

.netwo

.acco

rding

.to.IEEE.802.

.it.is.typi

cally

.used.

for.the.conn

ection

.betw

een

.the.mast

.and.the.slav

.netwo

.segm

ent.

.Inde

ed,

.an.Ethe

rCAT

.net-

.can.be.seen.as.a.sing

le,

.large

.Ethe

rnet

.devi

.that.rece

ives

.and.send

.Ethe

rnet

.fram

es.

.Howe

ver,

this.“dev

ice”

.is.not.made.up.of.a.sing

.Ethe

rnet

.cont

roller

.but.incl

udes

.a.(pos

sibly

.large

)

.numb

.of.

Ethe

rCAT

.slav

es.

Conversely,

.EBU

.can.be.use

.as.a.bac

kplane

.bus.(i.

e.,

.it.is.not.qua

lied

.for.wir

.con

nections).

.part

icular,

.EBUS.is.a.physi

cal

.laye

.desig

ned

.to.redu

.pass

-through

.dela

.insid

.the.node

.typ-

cally,

.fram

.are.only.dela

yed

.by.60÷5

.ns.[PRY

08,BEC06],

.wher

eas

.a.grea

ter

.dela

.(abo

.1.μs).is.

intr

oduced

.by.Ether

net

.inte

rfaces

.betw

een

.segm

ents.

.It.uses.the.Manc

hester

.(bip

hase

.L).enco

ding

.and.

enca

psulates

.fram

.betw

een

.star

t-of-frame

.(SOF

)

.and.end-

of-frame

.(EOF

)

.iden

tiers.

. e.begi

nning

of.a.fram

.is.den

.by.a.Manc

hester

.viol

ation

.with.posit

ive

.leve

.foll

owed

.by.a.“1”.bit,.whic

.is.also.the.

rst.bit.of.the.Ether

net

.prea

mble.

. en,.the.whol

.Ether

net

.fram

.is.tran

smitted

.(inc

luding

.Ether

net

SOF.at.the.end.of.the.prea

mble,

.up.to.the.CRC)

. e.fram

.nis

hes

.with.a.Manc

hester

.viol

ation

.with.

negative.level.followed.by.a.“0”.bit,.which.is.also.the.rst.bit.of.the.IDLE.phase..It.uses.low-voltage.dif-

erential

.signa

ling

.(LVD

S),

.and.the.data.rate.is.100.Mbps.to.acco

mplish

.the.fast.Ether

net

.spec

ication.

 e.EBU

.pro

tocol

.simp

.enc

apsulates

.Ethe

rnet

.fra

mes;

.thu

.EBU

.can.car

.any.Ethe

rnet

.fra

me.

.maxi

mum

.numbe

.of.addr

essable

.devi

ces

.is.2

.for.each.segment,.while.the.distance.between.

any.two.adja

cent

.node

.(i.e

.the.cabl

.leng

th)

.can.be.up.to.10.m.for.EBUS.and.(as.usua

.up.to.100.m.for.

Ether

net

.conn

ections.

. e.whol

.netw

ork

.size.is.prac

tically

.unli

mited

.(as,.in.theo

ry,

.up.to.2

.devices.

can.be.con

nected

.usin

.100.m.Ethe

rnet

.cab

les).

.topol

ogy

.of.a.comm

unication

.syst

.is.one.of.the.cruc

ial

.facto

.for.the.succ

essful

.appl

ication

in.autom

ation

.envi

ronments.

. e.topol

ogy

.has.signi

cant

.inu

ence

.on.cabl

ing

.eor

ts,

.diag

nostic

.fea-

ures,

.redu

ndancy

.optio

ns,

.and.hot-

plug-and-play

.feat

ures.

.Sinc

.the.star.topol

ogy

.comm

only

.used.for.

Ether

net

.lead

.to.incr

eased

.cabl

ing

.eor

.and.infr

astructure

.cost

.a.line.or.tree.topol

ogy

.is.pref

erable.

Typi

cally,

.the.slav

.node.arra

ngement

.repr

esents

.an.open.ring

.At.one.of.the.open.ends

.the.mast

devi

.send

.fram

es,

.eith

.dire

ctly

.or.via.Ether

net

.swit

ches,

.and.rece

ives

.them.at.the.othe

.end.aer.

they.hav

.bee

.pro

cessed.

.All.fra

mes

.are.rel

ayed

.fro

.eac

.sla

.to.the.nex

.one

.last.slav

.in.the.netw

ork

.retu

rns

.the.fram

.back.to.the.mast

er.

. ank

.to.the.full

-duplex

.capa

bilities

of.Ethe

rnet,

.which.uses.two.wire

-pairs

.to.carr

.out.comm

unications

.in.both.dire

ctions

.at.the.same.time

.the.

resu

lting

.topo

logy

.visu

ally

.rese

mbles

.a.phys

ical

.line

.Bran

ches,

.which.in.prin

ciple

.are.poss

ible

.anyw

here,

.can.

be.used.to.enha

nce

.the.basi

.line.stru

cture

.by.maki

.it.poss

ible

.to.set.up.tree.netw

ork

.topo

logies.

38.3 Communication Protocol

 e.EtherCAT.communication.protocol.aims.at.maximizing.the.utilization.of.the.Ethernet.bandwidth,.

than

.to.its.very.high.comm

unication

.eci

ency.

.As.ment

ioned

.abov

.the.medi

.acce

.mech

anism

(MAC

)

.is.base

.on.the.mast

er/slave

.prin

ciple,

.wher

.the.mast

.node.(typ

ically,

.the.cont

rol

.syst

em)

send

.Ether

net

.fram

.to.the.slav

.node

.over.the.physi

cal

.ring

.and.each.of.the.slav

.extr

acts

.data.from.

(and.ins

erts

.dat

.into

)

.the.pay

load

.of.the

.fra

mes.

.fram

.sent.over.the.netw

ork

.are.stan

dard

.Ethe

rnet

.fram

es,

.whos

.data.eld.enca

psulates

.the.

Ethe

rCAT

.fram

. is.one,.in.turn

.is.made.up.of.a.header.and.one.or.more.Ethe

rCAT

.data

grams

.or.pro-

ocol

.data.unit.(PDU

s),

.as.to.obta

.a.more.eci

ent

.use.of.the.larg

.Ethe

rnet

.data.eld.avai

lable.

.Ethe

rCAT

PDUs.are.pack

.toge

ther

.with

out

.inte

r-PDU

.gaps

. e.fram

.is.comp

leted

.with.the.last.Ethe

rCAT

.PDU,.

unle

.the.fram

.size.is.less.than.64.octet

.in.whic

.case.the.fram

.is.padded.to.64.octet

.in.leng

th.

.Each.

EtherCAT 38-3

EtherCAT.PDU.(that.corresponds.to.a.separate.command).contains.the.header,.data,.and.working.coun-

ter

.(WC).elds.. e.standard.Ethernet.CRC.is.used.to.check.the.integrity.of.messages.

From

.the.point.of.view.of.the.master,.the.whole.EtherCAT.segment.is.seen.as.a.single.Ethernet.device,.

which.receives.and.sends.standard.Ethernet.frames.with.the.EtherType.eld.set.to.0x88A4.to.distinguish.

it.from.other.Ethernet.frames..In.this.way,.EtherCAT.can.coexist.with.other.Ethernet.protocols.. e.last.

EtherCAT.slave.device.in.the.segment.sends.the.fully.processed.frame.back.and.the.same.occurs.for.

each.device.. is.procedure.is.based.on.the.full-duplex.mode.of.Ethernet:.both.communication.direc-

tions

.are.operated.independently..In.order.to.achieve.the.maximum.performance,.Ethernet.frames.have.

to.be.processed.on-the-y,.as.depicted.in.Figure.38.1..Slave.nodes.implemented.in.this.way.recognize.

relevant.commands.and.execute.them.accordingly.while.the.frames.are.passing.through.

.said.before,.several.EtherCAT.datagrams.can.be.embedded.within.the.same.Ethernet.frame,.each.

one.addressing.dierent.devices.and/or.memory.areas..As.shown.in.Figure.38.2,.the.EtherCAT.datagrams.

are.transported.either

. 1..Directly.in.the.data.area.of.the.Ethernet.frame.or

. 2.. Within.the.data.section.of.a.UDP.datagram.carried.via.IP

.rst.variant.is.limited.to.one.Ethernet.subnet.since.associated.frames.are.not.relayed.by.routers..

For.machine.control.applications,.this.usually.is.not.a.limitation..Multiple.EtherCAT.segments.can.be.

connected.to.one.or.several.switches.. e.Ethernet.MAC.address.of.the.rst.node.in.the.segment.is.used.

for.addressing.the.EtherCAT.segment.

.second.variant.(via.UDP/IP).implies.a.slightly.larger.overhead.(because.of.the.IP.and.UDP.head-

ers),

.but.for.less.time-critical.applications.such.as.process.control.it.enables.the.use.of.IP.routing..On.the.

master.side,.any.standard.UDP/IP.implementation.can.be.used.in.this.case.

38.3.1 Commands

Each.EtherCAT.PDU.(see.Figure.38.3).consists.of.an.EtherCAT.header,.the.data.area,.and.a.subsequent.

counter.area.(WC).

Slave 1 Slave N

Master

Ethernet HDR HDR 1 Data 1

HDR n

Data n CRCHDR 2 Data 2

Datagram 1 Datagram 2 Datagram n

FIGURE 38.1 EtherCAT.typical.topology,.with.the.“on-the-y”.frame.processing.

38-4 Industrial Communication Systems

In.particular,.each.datagram.contains.the.elds.listed.in.Table.38.1.

.parameter.“command”.encodes.the.service.command..Dierent.types.of.commands.can.be.

used.to.optimize.read.and.write.operations.on.slave.devices,.which.can.be.classied.depending.on.the.

access.type:

•

. Broadcast read/write:.All.slaves.carry.out.a.logical.“OR”.operation.of.data.of.the.memory.area.and.

data.of.the.incoming.EtherCAT.datagram,.insert.this.information.into.the.outgoing.EtherCAT.

datagram,.and.write.it.back.into.the.local.memory.area.

•

. Read, write, or read/write actions:.Exchange.of.incoming.data.and.local.data..For.read.and.write.

operations,.the.read.operation.is.performed.before.the.write.operation.

•

. Read multiple write actions.(RMW):.Addressed.slave.will.read.while.others.will.write.

.IDX.eld.is.the.identier.of.the.datagram;.it.is.le.unchanged.by.the.slaves.. e.address.eld.can.

contain.dierent.information.according.to.the.addressing.mode.chosen.(a.more.detailed.description.is.

provided.in.Section.38.4).

.parameter.LEN.shall.contain.the.size.in.byte.of.the.data.to.be.read.or.written.

Destination

address

(DA)

FCS

Source

address

(SA)

Ether

type

(ET)

Ethernet payload

6B 6B 2B 4B

Pre IFG

12B8B

(a)

FCSIP header

UDP header

UDP payload

20B 8B

Pre

Ethernet header

(b)

EtherCAT

header

EtherCAT

datagram

EtherCAT

datagram

EtherCAT

datagram

…

EtherCAT

datagram

IFG

FIGURE 38.2 EtherCAT.frame.structure.

EtherCAT

datagram

…

11 bit 1 bit 4 bit

Datagram

header

Data

Working

counter

10B 2B

(WC)

Length 0

EtherCAT

datagram

Cmd RAddress Len IRQ

8 bit

32 bit

Idx M

11 bit

1 16 bit

Position Oset

Address Oset

Logical address

16 bit

Position addressing

Node addressing

Logical addressing

EtherCAT

datagram

FIGURE 38.3 EtherCAT.datagram.structure.

EtherCAT 38-5

 e.eld.C.is.used.in.the.case.of.a.network.with.a.link.failure.between.two.slaves;.a.frame.currently.

trav

eling

.thro

ugh

.the.part.of.the.ring.on.the.isol

ated

.side.of.the.netw

ork

.migh

.star

.circ

ulating.

.Inde

ed,

each.slav

.has.a.mech

anism

.call

.loop

-back

.func

tion

.that.forw

ards

.Ether

net

.fram

.to.the.next.inte

nal

.port.if.eith

.ther

.is.no.link.at.a.port.or.the.port.is.not.avai

lable.

. is.feat

ure

.is.need

.to.crea

the.ring.on.the.last.slav

. us,.to.prev

ent

.an.endl

ess

.fram

.from.circ

ulating,

.a.slav

.with.no.acti

.link.

thro

ugh

.the.mas

ter

.has.to.do.the.fol

lowing:

•

. If.the.cir

culating

.bit.of.the.Ethe

rCAT

.dat

agram

.is.0,.set.the.cir

culating

.bit.to.1.

•

. If.the.cir

culating

.bit.is.1,.do.not.pro

cess

.the.fra

.and.des

troy

.it.

.spe

cies

.whe

ther

.or.not.the.Ethe

rCAT

.PDU.is.the.onl

.one.in.the.fra

me.

.impo

rtant

.mech

anism

.is.base

.on.the.IRQ.eld

.Ether

CAT

.even

.requ

ests

.are.used.to.info

the.Ether

CAT

.mast

.of.slav

.even

ts.

. e.Ether

CAT

.even

.requ

est

.regi

ster

.is.combi

ned

.using.a.logi

cal

.AND.oper

ation

.with.a.pred

ened

.Ether

CAT

.even

.mask.regi

ster.

. is.one.is.used.for.sele

cting

.the.

inte

rrupts

.whic

.are.rele

vant

.for.the.Ether

CAT

.mast

er.

. e.resu

lting

.bits.are.then.combi

ned

.with.the.

Ether

CAT

.IRQ.eld.pres

ent

.on.the.inco

ming

.data

gram

.with.a.logi

cal

.OR.oper

ation

.and.writ

ten

.into.

the.Ether

CAT

.IRQ.eld.of.the.outg

oing

.data

gram.

.It.is.wort

.noti

.that.the.mast

.is.not.able.to.dis-

inguish

.whi

.sla

ve(s)

.was

/were

.ori

ginating

.an.int

errupt.

Finally,

.proc

ess

.data.that.can.be.read.or.writ

ten

.are.plac

.in.the.DATA.eld

.In.the.case.a.slav

.is.

writ

ing

.info

rmation

.in.the.data.eld

.it.must.reco

mpute

.and.modi

.the.CRC.eld.at.the.end.of.the.

packet.to.make.it.correct.for.next.slaves.

.last.eld.is.the.WC.. is.eld.is.used.to.coun

.the.numbe

.of.devi

ces

.that.were.succ

essfully

addr

essed

.by.an.Ether

CAT

.data

gram.

.Each.addr

essed

.slav

.incr

ements

.the.WC.in.hard

ware.

.Beca

use

each.data

gram

.has.an.expe

cted

.WC.valu

.comp

uted

.by.the.mast

er,

.the.vali

.proc

essing

.of.data

grams

can.be.chec

ked

.by.comp

aring

.the.rece

ived

.WC.with.the.expe

cted

.valu

. e.WC.is.incr

eased

.if.at.leas

one.byte

/bit

.of.the.data.eld.was.succ

essfully

.read.and/

.writ

ten.

.Comp

lex

.oper

ations

.like.RMW.com-

ands

.are.trea

ted

.like.eith

.a.read.or.a.writ

.comm

and,

.depe

nding

.on.the.addr

ess

.matc

hing

.mech

nism

.des

cribed

.abo

ve.

38.4 addressing

Dierent.addressing.modes.are.supported.for.accessing.slaves,.as.shown.in.Figure.38.3.. e.header.

with

.the.Ether

CAT

.PDU.cont

ains

.a.32.bit.addr

ess,

.whic

.is.used.for.both.physi

cal

.node.addr

essing

and.log

ical

.add

ressing.

TABLE 38.1 EtherCAT.Datagram.Format

CMD Unsigned8 EtherCAT.command.type

IDX Unsigned8 Index

.for.identic

ation

.of.dup

licates(lost)

.dat

agrams

Address DWORD Address

.(aut

oincrement,

.congure

.sta

tion

.address,.

or.logica

.address,.see.Sec

tion

.38.4)

LEN Un

signed11 Length

.of.the.DAT

.eld

R 3

.bit R

eserved

.0x00

C 1

.bit Cir

culating

.fram

0x00:

.Fram

.is.not.circu

lating

0x01:

.Fram

.has.circu

lated

.once

.bit 0x00:.Las

.Eth

erCAT

.PDU.in.Eth

erCAT

.fram

0x01:

.Eth

erCAT

.PDU.in.Eth

erCAT

.fram

.fol

lows

IRQ WORD External

.Eth

erCAT

.even

.req

uest

.regi

sters

.of.all.

slav

.comb

ined

.wit

.a.logica

.OR

TA OctetString

.LEN Da

WC WORD Working

.count

38-6 Industrial Communication Systems

38.4.1 Physical addressing

In.the.physical.addressing.scheme,.the.32.bit.address.eld.within.each.EtherCAT.PDU.is.split.into.a.16.

bit.sla

.dev

ice

.add

ress

.and.a.16.bit.phy

sical

.add

ress

.wit

hin

.the.sla

.dev

ice,

.thu

.lea

ding

.to.2

.slave.

dev

ice

.add

resses,

.eac

.one.wit

.an.ass

ociated

.16.bit.loc

.add

ress

.spa

ce.

.With.dev

ice

.add

ressing,

.eac

Ethe

rCAT

.PD

.un

iquely

.ad

dresses

.on

.sin

gle

.sl

ave

.de

vice.

.mod

.is.mos

tly

.sui

table

.for.tra

nsferring

.par

ameterization

.inf

ormation

.for.dev

ices.

. er

.are.two.

di

erent

.dev

ice

.add

ressing

.mec

hanisms,

.nam

ely,

.posi

tion

.add

ressing

.and.nod

.add

ressing.

. er

.is.als

a.th

ird

.mo

.fo

.br

oadcast

.me

ssages.

Now

.let.us.con

sider

.the.nod

.add

ressing

.mod

.(al

.de

ned

.as.con

gured

.sta

tion

.add

ress);

.bec

ause

Ethe

rCAT

.sla

ves

.can.hav

.up.to.two.con

gured

.sta

tion

.add

resses

.(if.thi

.fun

ctionality

.is.ena

bled),

.the.

add

ress

.may.be.eit

her

.assi

gned

.by.the.mas

ter

.(co

ngured

.sta

tion

.add

ress)

.or.rea

.fro

.the.int

ernal

EEP

ROM

.th

.ca

.be.ch

anged

.by.th

.sl

ave

.ap

plication

.(c

ongured

.st

ation

.al

ias

.ad

dress).

.fo

llowing

.ad

dressing

.al

ternatives

.ar

.av

ailable:

•

Pos

ition address/autoincrement address:

.Posi

tion

.add

ressing

.is.use

.to.add

ress

.eac

.sla

.dev

ice

via.its.phy

sical

.posi

tion

.wit

hin

.the.seg

ment.

.Eac

.sla

.dev

ice

.inc

rements

.the.16.bit.add

ress

.el

as.the.dat

agram

.tra

nsits

.thr

ough

.the.sla

.dev

ice;

.the.dev

ice

.whi

.rec

eives

.a.fra

.wit

.an.

add

ress

.e

.wi

.va

lue

.0.is.th

.on

.be

ing

.ad

dressed.

. i

.me

ans

.th

.e

.co

ntains

.th

.ne

ga-

tive

.posi

tion

.of.the.sla

.in.the.loo

.(th

.mas

ter

.posi

tion

.is.mar

ked

.“0”

.Due.to.the.mec

hanism

emp

loyed

.to.upd

ate

.thi

.add

ress

.whi

.the.fra

.is.tra

versing

.the.nod

.the.sla

.dev

ice

.is.sai

to.hav

.an.auto

increment

.add

ress.

.Posi

tion

.add

ressing

.sho

uld

.be.use

.dur

ing

.the.sta

rt-up

.pha

of.the.Ethe

rCAT

.sys

tem

.onl

.to.sca

.the.el

dbus;

.it.can.be.ado

pted

.occ

asionally

.to.det

ect

.new

att

ached

.sla

ves

.bec

ause

.it.can.cau

.pro

blems

.if.loo

.are.clo

sed

.tem

porarily

.due.to.lin

.pro

blems.

•

Nod

e address/congured station address and congured station alias:

.In.thi

.cas

.the.sla

ves

.are.

add

ressed

.via.con

gured

.nod

.add

resses

.assi

gned

.by.the.mas

ter

.dur

ing

.the.dat

a-link

.sta

rt-up

pha

se.

. is.ens

ures

.tha

.eve

.if.the.seg

ment

.topo

logy

.is.cha

nged

.or.dev

ices

.are.add

.or.rem

oved,

the.sla

.dev

ices

.can.sti

.be.add

ressed

.via.the.sam

.con

gured

.add

resses.

.Nod

.add

ressing

.is.

typ

ically

.us

.fo

.re

gister

.ac

cess

.to.in

dividual

.an

.al

ready

.id

entied

.de

vices.

•

Bro

adcast:

.Eac

.Ethe

rCAT

.sla

.is.add

ressed.

.Bro

adcast

.add

ressing

.is.use

.for.ini

tialization

.of.all.

sla

ves

.an

.fo

.ch

ecking

.th

.st

atus

.of.al

.sl

aves

.if.th

.ar

.ex

pected

.to.be.id

entical.

Each

.sla

.dev

ice

.has.a.16.bit.loc

.add

ress

.whi

.is.add

ressed

.via.the.os

.el

.of.the.Ethe

rCAT

dat

agram.

38.4.2 Logical addressing: FMMU

Using.the.datagram.structure.described.above,.several.EtherCAT.devices.can.be.separately.addressed.

via.a.sing

.Ethe

rnet

.fra

me,

.eac

.one.by.mea

.of.one.Ethe

rCAT

.dat

agram,

.whi

.lea

.to.a.sign

icant

imp

rovement

.of.the.sys

tem

.ban

dwidth.

.How

ever,

.for.sma

ll-size

.inp

.ter

minals,

.for.exa

mple,

.wit

.2.bit.

inp

.dev

ices

.tha

.map.pre

cisely

.2.bit.of.use

.dat

.the.ove

rhead

.of.a.sing

.Ethe

rCAT

.com

mand

.mig

be.ex

cessive.

.FMM

.les

sens

.thi

.pro

blem,

.and.the.ava

ilable

.uti

lization

.rat

.is.mor

.tha

.90%

—even

.for.

dev

ices

.wit

.onl

.2.bit

.of.use

.dat

.as.men

tioned

.bef

ore.

.Sim

ilar

.to.the.mem

ory

.man

agement

.uni

(MM

Us)

.in.mod

ern

.pro

cessors,

.the.FMM

.con

verts

.a.log

ical

.add

ress

.into.a.phy

sical

.one.via.an.int

er-

nal

.tab

le.

. e.FMM

.is.int

egrated

.in.the.Ethe

rCAT

.sla

.arc

hitecture

.and.ena

bles

.ind

ividual

.add

ress

map

ping

.for.eac

.dev

ice.

.In.con

trast

.to.pro

cessor-internal

.MMU

.tha

.typ

ically

.map.com

plete

.mem

ory

pag

es,

.the.FMM

.als

.sup

ports

.bit

-wise

.map

ping.

. is.ena

bles,

.for.exa

mple,

.the.2.bit

.of.an.inp

.ter

minal

.to.be.ins

erted

.ind

ividually

.any

where

.wit

hin

.a.log

ical

.add

ress

.spa

ce.

.If.an.Ethe

rCAT

.com

mand

.is.

sent.to.rea

.or.wri

.a.cer

tain

.mem

ory

.are

.ins

tead

.of.add

ressing

.a.par

ticular

.Eth

erCAT

.dev

ice,

.the.2.bit.

inp

.ter

minal

.ins

erts

.its.dat

.at.the.rig

.pla

.wit

hin

.the.dat

.are

.In.the.sam

.way

.oth

.ter

minals

EtherCAT 38-7

that.are.addressed.in.the.FMMU.also.insert.their.data,.so.FMMUs.allow.to.use.logical.addressing.for.

data.segments.that.span.several.slave.devices:.one.command.addresses.data.within.several.arbitrarily.

distributed.slaves,.as.shown.in.Figure.38.4.. e.access.type.supported.by.an.FMMU.is.congurable.to.

be.read,.write,.or.read/write..Conguration.of.the.FMMU.entities.is.performed.by.the.master.device.and.

transferred.to.the.slave.devices.during.the.data-link.start-up.phase..For.each.FMMU.entity,.the.follow-

ing

.items.are.congured:.a.logical,.bit-oriented.start.address,.a.physical.memory.start.address,.a.length,.

and.a.type.that.species.the.direction.of.the.mapping.(input.or.output)..When.an.EtherCAT.datagram.

with.logical.addressing.is.received,.the.slave.device.checks.whether.one.of.its.FMMU.entities.exhibits.an.

address.match..If.appropriate,.it.inserts.data.at.the.associated.position.of.the.data.eld.into.the.datagram.

(read.operation).or.extracts.data.from.the.associated.position.(write.operation).

38.5 SyncManager

EtherCAT.provides.a.mechanism.to.synchronize.slave.memory.access..Because.the.memory.of.a.slave.

can.be.used.for.exchanging.data.between.the.master.and.the.local.application.without.any.restrictions,.

some.problems.can.arise..First.of.all,.data.consistency.is.not.guaranteed,.and.a.mechanism.like.sema-

phores

.has.to.be.implemented.for.exchanging.data.in.a.coordinated.way..Moreover,.both.master.and.

slave.applications.have.to.access.the.memory.in.order.to.know.when.the.memory.is.no.longer.used.on.

the.other.side.

 us,

.SyncManager.enables.consistent.and.secure.data.exchanges.between.the.EtherCAT.master.and.

the.local.application,.generating.interrupts.to.inform.both.sides.of.changes..It.is.organized.in.channels,.

and.each.channel.denes.a.consistent.area.of.the.memory.

.SyncManager.system.is.congured.by.the.EtherCAT.master.. e.communication.direction.is.con-

gurable,

.as.well.as.the.communication.mode.(buered.mode.and.mailbox.mode).. e.SyncManager.

system.uses.a.buer.located.in.the.memory.area.for.exchanging.data.and.controls.the.access.to.this.buer..

All.accesses.to.the.buer.begin.from.the.start.address,.otherwise.the.access.is.denied..Aer.the.access.to.

Slave 1 Slave N

Master

Ethernet HDR

HDR 1 Data 1 HDR n Data n

CRC

Data n

Data 1

Logical memory: up to 4 GB

Datagram 1 Datagram n

FIGURE 38.4 FMMU.mapping.example.

38-8 Industrial Communication Systems

the.start.address,.the.whole.buer.can.be.accessed,.either.as.a.whole.or.in.several.strokes..A.buer.access.

nis

hes

.by.acces

sing

.the.end.addr

ess.

Two

.com

munication

.mod

.are.sup

ported

.by.Syn

cManagers:

•

Bue

red mode.

. e.inte

raction

.betw

een

.the.prod

ucer

.and.the.cons

umer

.of.data.is.unco

rrelated,

and.each.enti

.can.perf

orm

.the.acce

.at.any.time

.alwa

.prov

iding

.the.cons

umer

.with.the.new-

.data

.In.the.case.the.bue

.is.writ

ten

.fast

.than.it.is.read.out,.old.data.are.drop

ped.

. e.bu-

red

.mode.is.typi

cally

.used.for.cycl

.proc

ess

.data

. e.mech

anism

.is.also.know

.as.thre

e-buer

mode.beca

use

.thre

.bue

.of.iden

tical

.size.are.used

.One.bue

.is.allo

cated

.to.the.prod

ucer

.(for.

writ

ing),

.one.bue

.to.the.cons

umer

.(for.read

ing),

.and.a.spar

.bue

.help

.as.inte

rmediate

.store

Reading.the.last.byte.or.writing.the.last.byte.results.in.an.automatic.buer.exchange.

•

Mail

box mode.

. e.mail

box

.mode.impl

ements

.a.hand

shake

.mech

anism

.for.data.exch

ange,

.so.that.

no.data.will.be.lost

.One.enti

.lls.data.in.and.cann

.acce

.the.area.unti

.the.othe

.enti

.read

out.the.data

.At.rst

.the.prod

ucer

.writ

.to.the.bue

.and.lock

.it.for.writ

ing

.unti

.the.cons

umer

has.read.it.out..Aer

ward,

.the.prod

ucer

.has.writ

.acce

.agai

.whil

.the.bue

.is.lock

.for.the.

cons

umer.

. e.mai

lbox

.mod

.is.typ

ically

.use

.for.app

lication

.lay

.(AL

)

.pro

tocols.

38.6 Distributed Clock

An.important.mechanism.present.in.the.EtherCAT.protocol.is.the.distributed.clock.synchronization.

that.enab

les

.all.devi

ces

.(mas

ter

.and.slav

es)

.to.shar

.the.same.syst

.time.with.a.prec

ision

.smal

ler

.than.

1.μs..In.this.way,.all.devi

ces

.can.be.sync

hronized,

.and.cons

equently,

.slav

.appl

ications

.are.sync

hronized

as.wel

.Mai

.fea

tures

.of.thi

.mec

hanism

.are

•

. Gene

ration

.of.syn

chronous

.out

put

.sign

als

•

. Prec

ise

.tim

.sta

mping

.of.inp

.eve

nts

•

. Sync

hronous

.dig

ital

.out

put

.upd

ates

•

. Sync

hronous

.dig

ital

.inp

.sam

pling

Typically,

.the.cloc

.refe

rence

.(sys

tem

.time

)

.is.the.rst.slav

.with.dist

ributed

.cloc

.capa

bility

.aer.the.

mast

.with

.one.segm

ent.

. is.syst

.time.is.used.as.the.refe

rence

.cloc

.to.sync

hronize

.the.DC.slav

cloc

.of.othe

.devi

ces

.and.of.the.mast

.itse

lf.

. e.prop

agation

.dela

ys,

.loca

.cloc

.sour

.dri

.and.

loca

.cloc

.ose

.are.take

.into.acco

unt

.for.the.cloc

.sync

hronization.

.All.sett

ings

.are.done.duri

.the.

cloc

.syn

chronization

.pro

cess

.mad

.of.thr

.ste

ps:

. 1..Prop

agation delay measurement:

. e.mast

.send

.a.sync

hronization

.data

gram

.at.cert

ain

.inte

vals

.(as.requ

ired

.in.orde

.to.avoi

.the.slav

.cloc

.dive

rging

.beyo

.appl

ication-specic

.limi

ts),

and.each.slav

.store

.the.time.of.its.loca

.cloc

.twic

e—once

.when.the.mess

age

.is.rece

ived

.and.once.

when.it.is.sent.back.(rem

ember

.Ether

CAT

.has.a.ring.topol

ogy).

. e.mast

.read

.all.time.stam

and.comp

utes

.the.prop

agation

.dela

.betw

een

.all.slav

es.

.It.is.wort

.noti

.that.cloc

.are.not.

sync

hronized

.for.the.dela

.meas

urement,

.and.only.loca

.cloc

.valu

.are.used

.So.the.prop

agation

dela

.cal

culation

.is.bas

.on.rec

eive

.tim

.di

erences.

. 2.. Ose

t compensation to reference clock (system time):

.Beca

use

.the.loca

.time.of.each.devi

.is.a.free.run-

ing

.cloc

.that.has.not.the.same.time.as.the.refe

rence

.cloc

.a.comp

ensation

.mech

anism

.is.nece

ssary.

To.achie

.the.same.abso

lute

.time

.all.devi

.die

rence

.betw

een

.the.refe

rence

.cloc

.and.ever

.slav

devi

ce’s

.cloc

.is.comp

uted

.by.the.mast

er.

. en.the.ose

.time.is.writ

ten

.to.a.spec

ic

.slav

.regi

ster

“sys

tem

.time.ose

t.”

.Each.slav

.comp

utes

.its.loca

.copy.of.the.syst

.time.usin

.its.loca

.time.and.the.

loca

.ose

.valu

.More

over,

.smal

.ose

.erro

.are.elimi

nated

.by.the.dri.comp

ensation.

. 3..Dri

compensation to reference clock:

.Aer.the.dela

.time.betw

een

.the.refe

rence

.cloc

.and.the.

slav

.cloc

.has.been.meas

ured,

.and.the.ose

.betw

een

.both.cloc

.has.been.comp

ensated,

.the.

natu

ral

.dri.of.ever

.loca

.cloc

.has.to.be.comp

ensated

.by.a.time

-control

.loop

. is.mech

anism

read

justs

.the.loc

.clo

.by.reg

ularly

.mea

suring

.the.di

erences.

EtherCAT 38-9

38.7 application Layer

 e.EtherCAT.state.machine.is.responsible.for.the.coordination.of.master.and.slave.applications.at.start-up.

and.during.operation.

State

.changes.are.typically.initiated.by.requests.of.the.master.. ey.are.acknowledged.by.the.local.appli-

cation

.aer.the.associated.operations.have.been.executed..Unsolicited.state.changes.of.the.local.applica-

tion

.are.also.possible..Simple.devices.without.a.microcontroller.can.be.congured.to.use.EtherCAT.state.

machine.emulation.. ese.devices.simply.accept.and.acknowledge.any.state.change.automatically.

.state.machine.is.controlled.and.monitored.using.some.registers.present.on.the.slave.. e.master.

requests.state.changes.by.writing.to.the.AL.control.register.. e.slave.indicates.its.state.writing.in.the.AL.

status.register.and.puts.possible.error.codes.into.the.AL.status.code.register.

.shown.in.Figure.38.5,.there.are.four.basic.states.an.EtherCAT.slave.shall.support,.plus.one.optional.state:

•

. Init

•

. Pre-operational

•

. Safe-operational

•

. Operational

•

. Bootstrap.(optional)

All

.state.changes.are.possible.except.for.the.“Init”.state.and.for.the.“Pre-operational”:.for.the.former.

the.only.possible.transition.is.the.one.to.the.“Pre-operational”.while.for.the.latter.there.is.no.direct.state.

change.to.“Operational.”

State

.changes.are.normally.requested.by.the.master.. e.master.requests.a.write.to.the.AL.control.

state.change..If.the.requested.state.change.failed,.the.slave.also.responds.by.setting.an.error.ag.

.Bootstrap.state.is.optional,.and.there.is.only.a.transition.from.or.to.the.Init.state.. e.only.pur-

pose

.of.this.state.is.to.download.the.device’s.rmware..In.the.Bootstrap.state,.the.mailbox.is.active.but.

restricted.to.the.le.access.over.EtherCAT.service.(FoE).protocol.

38.7.1 Mailbox Services

Another.important.characteristic.of.EtherCAT.is.the.possibility.to.feature.multiprotocol.capability,.

consolidating.high-.or.same-level. protocols.in.a.standardized.mailbox..In.particular,.the.following.

capabilities.are.supplied:

•

Ethernet over EtherCAT (EoE):.tunnels.standard.Ethernet.frames.over.EtherCAT

•

CANopen over EtherCAT (CoE):. access. to. CANopen. devices. and. their. objects,. with. also. an.

optional.event-driven.PDO.(process.data.object).message.mechanism

Init

Pre-operational

Operational

Safe-operational

Bootstrap

(optional)

FIGURE 38.5 EtherCAT.state.machine.

38-10 Industrial Communication Systems

• File access over EtherCAT (FoE):.download.and.upload.of.rmware.and.other.les

•

Ser

vo drive over EtherCAT (SoE):

.ac

cess

.to.se

rvo

.pr

ole

.id

entier

.(I

DN)

.EoE.and.FoE.pro

tocols

.pro

vide

.opt

ions

.for.int

egrating

.a.Web.serv

.usi

.sta

ndard

.IP-

based

.pro

to-

cols

.suc

.as.TCP

/IP,

.UDP

/IP,

.and.all.hig

her

.pro

tocols

.based.on.the

.(HT

TP,

.FTP

.SNM

.etc

.).

.For.exa

ple,

.Eth

erCAT

.can.use.a.mech

anism

.in.whi

.the.Eth

ernet

.dat

agrams

.are.tun

neled

.and.rea

ssembled

.in.a.

asso

ciated

.dev

ice,

.bef

ore

.bei

.rel

ayed

.as.com

plete

.Eth

ernet

.dat

agrams.

. is.pro

cedure

.doe

.not.res

trict

the.ach

ievable

.cyc

.tim

.sin

.the.fra

gments

.can.be.opt

imized

.acco

rding

.to.the.avai

lable

.ban

dwidth.

Another

. imp

ortant

. asp

ect

. for. a. el

dbus

. sys

tem

. is. to. sup

port

. com

munication

. pro

tocols

. use

for.com

patibility

.and.ec

ient

.dat

.exc

hange

.bet

ween

.a.con

troller

.and.a.dri

ve;

.for.the

.pur

poses,

EtherCAT.uses.well-known.and.established.technologies..Indeed,.the.“CANopen.over.EtherCAT”.

(CoE

)

.pro

tocol

.ena

bles

.the.com

plete

.CANo

pen

.pro

le

.fam

ily

.to.be.use

.via.Eth

erCAT.

. e.SDO.

(se

rvice

.dat

.obje

ct)

.pro

tocol

.is.use

.dir

ectly,

.so.tha

.exi

sting

.CANo

pen

.sta

cks

.can.be.le.pra

ctically

unc

hanged.

. e.pro

cess

.dat

.are.org

anized

.in.PDO

.whi

.are.tra

nsferred

.usi

.the.ec

ient

.sup

port

of.Eth

erCAT.

.Mor

eover,

.opt

ional

.ext

ensions

.are.de

ned

.tha

.li.the.8.byt

.lim

.and.ena

ble

.com

plete

rea

dability

.of.the.obje

.lis

Another

.pro

tocol

.sup

ported

.is.the.“Se

rvo

.pro

le

.ove

.Ethe

rCAT”

.(So

E).

. is.cap

ability

.ena

bles

.the.

pro

ven

.ser

.pro

le,

.whi

.is.spe

cialized

.for.dem

anding

.dri

.tec

hnology,

.to.be.use

. e.ser

.ser

vice

cha

nnel,

.and.the

refore

.acc

ess

.to.all.par

ameters

.and.fun

ctions

.resi

ding

.in.the.dri

ve,

.is.map

ped

.to.the.

Ethe

rCAT

.ma

ilbox.

references

[BEC06].Becko.Automation.GmbH,.EtherCAT.per.Motion.Control,.presented.at.MOTION.CONTROL.

for

.ilB2B.i

.Bolog

na,

.Ita

ly,

.Feb

ruary

.23,.2006,.[Online],.avai

lable:

.htt

p://www.ilb2b.it/mc4_2006/

atti/BECKHOFF.pdf

[ESC20]

.Har

dware

.Dat

.She

.ESC20.Sla

.Con

troller,

.[Online],.avai

lable:

.Bec

kho

.websi

.htt

p://www.

beckho.com/

[ETG04]

.ETG.1000.4:.Dat

.link.pro

tocol

.spe

cication,

.avai

lable

.on.Eth

erCAT

.Tec

hnology

.Gro

up:

.htt

p://

www.ethercat.org/

[ETG05]

.ETG.1000.5:.App

lication

.lay

.serv

ice

.denitio

.avai

lable

.on.Eth

erCAT

.Tec

hnology

.Gro

up:

htt

p://www.ethercat.org/

[IE158]

. Int

ernational

. Elec

trotechnical

. Commi

ssion,

. Ind

ustrial

. communic

ation

. netw

orks—Fieldbus

spe

cications—Part

. 3-12:. Dat

a-link

. lay

.serv

ice

. denitio

n—Part

.4-12:. Dat

alink

. lay

. pro

tocol

spe

cication—Type

.12.elem

ents,

.IEC.61158-3/4-12.(Ed

.1.0).

[IE784]

.IEC.61784-2,.Ind

ustrial

.communic

ation

.netw

orks—Proles—Part

.2:.Addit

ional

.eldb

.pro

les

for.re

al-time

.net

works

.ba

sed

.on.ISO/IEC.8802-3.

[PR

Y08]

. Prytz,. G.,. A. perf

ormance

. ana

lysis

. of. Eth

erCAT

. and. PRO

FINET

. IRT,. IEEE In

ternational

Conference on Emerging Technologies and Factory Automation, 2008 (ETFA 2008),

. Ham

burg,

Germ

any,

.Sep

tember

.15–18,.2008,.pp

.408–415.