sercos3_en

■ Sercos is an open, international standard

■

■ Redundant data transmission ensures high machine

■

■ Complete backwards compatibility ensures that

■

■ Synchronization which is accurate to less than one micro-

■

■ Leading suppliers of automation systems back Sercos

■

tion across the whole Sercos network.

with broad product portfolios.

■ Sercos allows fail-safe communication:

■

■ Sercos technology is widely accepted in many industries,

■

Cable breaks are recognized within 25μs which means

■ More than four million real-time nodes are currently being

■

■ Robust cables made from copper or fiberglass.

■

■ Ethernet-standard IEEE 802.3 physics and protocol

■

■ Sercos energy: save energy and maximize productivity

■

Sercos – the automation bus: one of the leading bus systems for applica-

tions in industrial sectors for over 20 years. The real-time technology with

Simple

■ Sercos devices are easy to configure and put into use.

■

■ The cables are easy to connect as neither the physical

■

■ Fast and efficient data transmission allows for shorter

■

cycle times and a higher output.

its millionfold proven quality, the universal application possibilities and high

security of investments make the Ethernet system the first choice in

order of the devices nor the order of the connection to

the two Sercos ports is important.

■ Maintenance is easy because the devices and their position

■

Flexible

■ Flexible network topologies (ring, line, star/tree structures).

■

■ Comprehensive choice of device profiles for all types

■

mechanical engineering and construction.

within the topology are recognized automatically.

of automation devices.

■ Innovative communication functions, for example direct

■

■ Short running times: the summation frame procedure,

■

■ Safety functions up to SIL3 that are in accordance with

■

An efficient and deterministic communication protocol

This creates a basis upon which devices from different

tion reduces running times in the network to a minimum.

■ Safety-relevant and non-safety-relevant data is transferred

■

based on an optical transmission system not susceptible

manufacturers can be combined without any problems.

■ Configurable cycle time:The communication cycle

■

over the same cable.

to interference is the foundation for Sercos’ success;

today Sercos® is used successfully in the most varied

Today, over 4 million real-time nodes are being used on

a daily basis in over 500,000 applications.

can be set between 31.25μs and 65ms – synchronization

accuracy << 1µs.

■ Devices can securely communicate outside of network

■

boundaries thanks to CIP Safety’s routing capability.

sectors and applications. Sercos has established itself

as the de facto standard on all large automation markets

Sercos III – universal communication for distributed

Efficient

■ Hot plugging can be done without damaging real-time

■

Independent

■ Sercos technology is independent from manufacturers.

■

great demands on dynamics and precision. However,

Industrial automation requires real-time-enabled and

■ Optimized use of bandwidth through a summation frame

■

owns all rights to Sercos technology.

Sercos does not only specify a real-time-enabled com-

manufacturer-independent communication solutions.

procedure and multiplexing procedure.

■ Specifications are maintained and developed

■

munication system, but goes a lot further and specifies

over 700 standardized parameters which describe the

interaction between control systems, drives and other

Different kinds of automation devices must be able to

be easily and universally connected.The open, IEC

consistent universal bus for Ethernet-based real-time

■ All Ethernet-based protocols (including TCP/IP communica-

■

tion) can be transmitted with real-time data at the same

time using the same cable.

by a task force which covers all manufacturers.

■ All specifications are freely available.

■

■ You do not have to be a member to use Sercos technology.

■

Basic principles / concepts

Universal communication

from the office to the field level

via Ethernet

Internet

Factory network

Sercos III

+

Ethernet

Router

Service

Facility network

Control

system

Gateway Safe

I/O

Safe

drive Drive

Why Ethernet?

EEtthheerrnneett

SSeerrccooss IIIIII ++ EEtthheerrnneett

Ethernet makes it possible to have a single network infrastructure for com-

munication across all levels of the automation pyramid. The vertical integra-

tion of anything from sensors to accounting software opens up new pos-

Without particular specifications, Ethernet cannot satisfy

real-time demands and efficiency requirements in auto-

mation engineering. It is for this reason that appropriate

transmission procedures have to be defined which make

evaluate and compare how different real-time Ethernet

solutions work and what effects they produce. In the

end, an objective comparison of the solutions can only

be made when actual application scenarios are available.

sibilities for operational control. At the same time, modern Ethernet-based

networks allow for greater flexibility when installing and expanding control

topologies within the production chain when compared with conventional

the Ethernet efficient and compatible with real-time.

Such diversity in real-time Ethernet solutions available

on the market does not make it easy to keep perspec-

What is important is to understand the basic principles

of different real-time Ethernet solutions and how they

work.

Ethernet technology provides a tangible

range of benefits:

■ recognized and future-proof technology

■

■ many times higher data throughput than field buses

■

■ no proprietary hardware required

■

■ use standard readily available components such as

■

double shielded CAT5e copper cables, connectors and

controllers

■ flexible and compatible automation systems thanks to

■

international standards

■ universal IT concepts with an integrated transmission

■

medium and transmission protocol from the office to

the field level

■ can connect to global networks for diagnostics

■

and maintenance

Ethernet technology combines peripheral, driver, safety

and office communication in one common medium –

simple, economical and efficient.

?

?

?

? ?

?

FL-net

Profinet Mechatrolink III Drive-Cliq

?

JetSync

Sercos EtherNet/IP

CC-Link IE EPA

Powerlink

Vnet/IP

Varan TTEthernet

RTnet

SynUTC

HSCI

Modbus RTPS

?

PowerDNA

? Fast Track Switching

SafetyNET p Ethercat

RAPIEnet

TCnet

SynqNet AFDX

Switch with time server

RTEX

DART-EC

Compatibility of real-time Ethernet protocols

Positioning drives, frequency converters,

I/O periphery

4 – 10 ms > 4 ms

Protocol efficiency

In automation engineering, many users that each have a

always has to be transmitted long enough in advance

so that it is available to be processed when it is time for

Drives with peripherals signal processing,

high-speed I/O periphery

250 µs – 4 ms << 1 µs

low amount of data to transmit are typically connected

to each other via control and sensor/actuator levels. If

synchronization.

Central drive concepts,

highly dynamic metrology applications

31.25 µs – 125 µs << 1 µs

this process data is transmitted in individual telegrams,

an unfavorable ratio between the Ethernet overhead and

Separate clocks are also used in some real-time Ethernet

protocols to minimize jitters during cyclical transmission.

TCP

Real-time

UDP TCP UDP TCP UDP

protocol

Real-time

protocol

process is based on the transmission of a synchroniza-

tion signal which is cyclically received and analyzed by all

Cycle time

of separate clocks (IEC 61588) which are synchronized

with each other via telegrams. Separate clocks allow

Sercos mode of operation

With Sercos, real-time data is sent to IEEE 802.3 in

cyclical telegrams with Ethernet protocol type 0x88CD.

Given that additional network infrastructure compo-

nents (such as hubs or switches) are avoided, trans-

Sercos differentiates between the following

■ M/S (Master/Slave): Exchange of functional data

■

■ Master Data Telegram (MDT):The master sends

■

■ DCC (Direct Cross Communication): direct cross

■

■ AcknowledgeTelegram (AT): The slaves send their

■

tion, either between control systems or between any

– CP4), they are addressed and configured for applica-

■ SMP (Sercos Messaging Protocol):Transmitting

■

MDT and several AT are sent by the master per commu-

■ Safety: Exchange of safety-related data in a M/S

■

In order to fully meet the demands of modern industrial automation,

Sercos provides a high performance protocol. This protocol combines

nication cycle.The telegram transports data from device

to device.The relevant schedule data is read at each

device or the required status data is written in.

or DCC connection, e.g. disabling or approval signals

or other set values.

■ Sync: Cyclical synchronization trigger for precise,

■

network-wide synchronization

using Ethernet, a communication cycle is divided into

two time slots (channels). Sercos-defined real-time

for each application.

Application level

Encoder profile Safe

Motion

Drive profile Safe

Drive

I/O profile Safe

I/O

Safety

M/S SVC DCC

Sync

Ethernet application

IP

MDT

0

MDT

1

MDT

MDT

AT

AT

Ethernet

2

3

2

3

telegrams

Real-time channel (RTC) UCC

MDT

0

RTC = Real-Time Channel

UCC = Unified Communication Channel

MDT = Master DataTelegram

AT = AcknowledgeTelegram

Communication level

Hardware level

Sercos III communication controller

Duplex Fast Ethernet (100 MBit/sec)

UC Channel

Conventional Ethernet communication is synchronized

in the so-called Unified Communication Channel (UCC)

in the Sercos network, e.g. for e-mail, web services or

other proprietary and standardized Ethernet-based pro-

tocols.This channel sets itself down onto the Ethernet-

layer without tunneling and has a range of benefits:

■ it is possible to test and configure slaves even without

■

“The option to communicate di-

rectly via standard Ethernet proto-

cols using all devices even without

constant Sercos real-time communication.

makes the set-up operation easier. It also

allows us access to the device parameters

while the operation is running.”

Topology

Sercos networks consist of a master which coordinates

and at least one slave which carries out automation

functions. Generally, the devices are ordered simply and

neatly in line or ring topologies. For this purpose, each

Sercos device has two communication connections

which are connected to the previous and subsequent

device via an Ethernet cable – either using a twisted

“Sercos has a clear and robust data

structure.This increases operational

reliability and simplifies applica-

tion development.The network status is

always clear and entirely transparent. I can

make diagnoses of my plant on each net-

work node with current Ethernet diagnosis

tools.”

■ connection to other automation devices which support

■

of full duplex-enabled Ethernet technology, a logical ring

In a line topology, the master is positioned at the

■ directly addressing Sercos devices via MAC or

■

pears in a ring topology (see image).

containing data run through the slaves and are ‘looped

■ standard Ethernet devices such as laptops are

■

connected directly to Sercos devices via any free

Sercos telegrams contain a Sercos header and

a data field embedded in the Ethernet frame

Line structure

(Individual ring)

Ring structure

(Double ring)

running in both directions so that all data is guaranteed

to reach each device within the cycle independent of the

Sercos port

■ full processing power for the application because the

■

(see image below).

Master Master

order they are placed in (➝■see direct cross communica-

tion). In this way, all devices can be integrated into the

master does not have to tunnel or fragment Ethernet

packets

The Sercos header describes which phase the network

is in and the position of the MDT and AT telegrams in

the communication cycle.The MDT and AT data fields

M1 M2 M1 M2

network, even across long distances, e.g. assembly

lines, without high installation costs.

The S/IP protocol allows data to be exchanged in one

■ hot plug field: exchanges data with slaves that

■

closes to form a ring; a line is added between the last

S/IP protocol can also be used in a cyclic real-time opera-

tion. In this instance, the S/IP telegrams are transmitted

■ service channel field: total number of communication

■

channels that exchange acyclic data between master

Slave

1

Slave

2

Slave

n

Slave

1

Slave

2

Slave

n

over both ports so that the data is also analyzed in two

directions in the ring. Besides having all the benefits

with the network’s real-time process.

■ real-time data field: is used to create acyclic, cyclic or

■

Sercos-based topologies: Line and ring

redundant cabling.This means that a break in the ring

network.

Realization of a branch

via an external infrastructural component

Realization of a branch

via ports integrated in the device

Telegram length: 84 – 1538 Bytes (protocol management: 44 Bytes)

Telegram time: 6,8 – 123,1 µs

Switchboard A Switchboard A

Ethernet package

Ethernet header

Sercos III

header

Data field Checksum

Slave 3 Slave 3

Sercos III data field

Hot plug field

(new devices)

Service channel

field

Real-time data

field

Slave

1

Slave

2

TopoExtensions

Slave

1

Slave

2

TopoExtensions

Real-time data field with standard

(M/S) and lateral communication

connections (DCC)

M/S connection

device #1

M/S connection DCC connection

… device #N device #1 …

DCC connection

device #N

Device data

Standard

data

Safety data

container

Slave 4 Slave 5

Slave 4 Slave 5

Slave 9

Slave 6

Slave 4 Slave 5

Slave 4 Slave 5

Slave 9

Slave 6

can be compensated for without losing synchronization

or causing a breakdown in communication (➝■see ring

redundancy).

Single devices or machine modules can also be con-

nected to a line or ring via a branch line or a transmission

line. To achieve this, either an infrastructural component

with the appropriate branch line ports is integrated into

the network or this function is directly integrated into

the Sercos device.

“With Sercos, we can adjust the

network very easily to our cur-

rent machines and plant structure.

The fact that switches and hubs are not

required means that installation costs are

reduced and cabling is made considerably

easier.”

means that a 100m wire can be strung between two

devices.The Ethernet ports on the devices are inter-

Field bus

Slave 1

Field bus

Slave 2

…

Sercos operating principles

How it works:

Given that real-time telegrams are always processed in

two directions independent of the kind of topology, a

direct exchange of data between any given slave is en-

abled within the communication cycle (see image).This

has the advantage that data can always be transmitted

“The possibility of cross communi-

cation means that decentralized au-

tomation solutions can be installed

with minimal reaction times and a great

amount of flexibility.”

bypassing the master would compromise synchronous movements, e.g. by

corrupting gantry axes or slowing down reaction times, e.g. when transmit-

ting a trigger signal quickly. Sercos slaves can communicate via cross com-

munication directly and with a minimum of communication dead times –

Synchronization

Sercos defines how the actual value is recorded and

how valid the set value is for processes from different

products and manufacturers that are to be synchronized.

Each device receives a data telegram with a particular

“Increased accuracy of the transmis-

sion ensures that we can implement

the most challenging applications.”

this ensures unlimited real-time communication and intelligent automation

structures. Control systems use the same principle to directly

communicate with each other.

transmission time delay that is appropriate to the device.

Unlike other Ethernet bus systems, Sercos derives a

general execution time directly from the bus. The device

calibrates itself independently with the bus cycle by us-

DCC – Slave-to-Slave

C2C – Controller-to-Controller

C2C

DCC DCC

generate and adjust the internal synchronizing mecha-

nism. As a result, separate clocks are synchronized

HMI HMI HMI

Master Master Master

exactly without exchanging time data that overloads the

bandwidth.

DCC DCC

figured. Variations in the sum value can delay the stable

synchronization signal. Hence delaying the synchroniza-

independently of topology and of the quantity of devices

in Sercos networks.The process itself is quick, robust

configured operation.

be consolidated and emitted.

Polling of individual

IP packages

Sercos III

telegram

Using the described process, Sercos is able to achieve

synchronization accuracy of less than 20ns and syn-

chronicity of less than 100ns. Given that individual

transmits event-controlled results such as specific

measured data and switches outputs independent from

the cycle.This increases the stability of the process in

80%

70%

fully synchronized network structures can be formed

40%

without limiting synchronization performance. Performance

30%

Custom Ethernet protocols from office technology rely

Ring redundancy and hot plugging

on user data being sent as individual packets to each

A network in a ring topology which is safe from inter-

ference is still operative when a cable breaks or when

slaves are connected or disconnected (hot plugging) and

no interruption is caused. All devices remain connected

to the master when a cable breaks due to the additional

cable in a ring network.The Sercos connections on the

“A Sercos hardware failure or

break in a cable does not result in

a breakdown in communication.

Instead, we are able to replace defective

devices or cables while the system is in

operation, which significantly increases

machine availability.”

20%

how to use fast Ethernet bandwidth efficiently: if status

data of 4 bytes per device for 20 devices were sent indi-

Efficient use of bandwidth with Sercos

with “loop back” without causing any delay. The recon-

figuration time takes a maximum of 25μs so that at the

very most the data transmitted from one cycle is lost.

The breakage point can be located exactly and defective

cables can be simply exchanged while the operation is

running.

altogether (smallest packet size with Ethernet: 64 bytes).

However, only 80 bytes would be used productively for

the application – that’s approx. 5% of the bandwidth,

even during low-peak cycle times.

“Sercos’ efficient real-time proto-

cols result in universal, consistent

machine connection with fast reac-

tion times and great accuracy.”

Cycle time

in µs

Cyclic data

per device

in bytes

Maximum number

of devices

(without UCC)

Maximum number

of devices (with UCC,

250 Bytes = 20 µs)

Maximum number

of devices (with UCC,

1,500 Bytes = 125 µs)

Uninterrupted switching (loop back) to line

topology in the case of hot plugging oder cable break

Additional cable connects two line topologies

to create a ring topology

1,000 12 251 245 220

Function-specific profiles

Cyclic real-time data in one connection

Sercos real-time communication with stan-

dardized parameters, using the example of

the drive profile

Device description

Sercos offers the possibility to represent all types of

automation devices on the field and controlling level

in the different phases of their life cycle in a functional

and logical manner. The device description language

SDDML was developed in order to describe devices

and the provided functions for the offline configuration

Device models and profiles

and for their easy display in a generic engineering tool.

“We have made very good experi-

ences with the excellent degree of

standardization of the drive profile

whereby it was possible for us to integrate

devices of various manufacturers to our

control and to commission the machine in

a remarkably short time.

The device model from Sercos not only supports pure automation devices

but also hybrid devices which combine various applications in one device.

It is for this reason that no device profiles but, instead, function-specific

A configuration interface (SCI) determines the network

configuration and defines which slaves must be present

and which are optional.The slave devices are identified

via criteria which are described in the file. Furthermore,

profiles are defined by Sercos.

the configuration file describes the parametrization of

the individual devices by means of a generic procedure.

In addition, the parametrization of the master can be

carried out.

■ Generic device profile: functions for diagnosis and

■

figured into the real-time telegrams for cyclical transmis-

tools. It is for this purpose that device manufacturers

to maintenance

■ Drive profile: consistent and continuous functions for

■

channel or the S/IP protocol.

Manager) adjusted to the device. In this case, the DTM

of Sercos networks is quite simple.The user can focus

■ I/O profile: consistent and continuous functions for

■

application. However, an SDDML-conforming device de-

supports the user in startup and diagnostics. All devices

■ Encoder profile: consistent and continuous functions

■

Sercos device DTM by means of a generic conversion

cables or fibre optic cables. After an initialization phase,

■ Energy profile: Consistent and continuous functions

■

description may already be available as file or be directly

installed devices (hot plugging) are integrated into

No master

required for

configuration/

diagnostics

Patch or

crossover cable

Ports combinable

in any arrangement

Simple cabling of devices

in a Sercos network

Standard

IP network

Sercos III real-time network

Safety

CIP

Safety profiles

How to communicate quickly and

safely using CIP Safety on Sercos

CIP Safety on SERCOS is a protocol for transmitting safety-relevant data

via Sercos – defined in cooperation with the ODVA and certified according

Safety-relevant data is transmitted as a safety data

container.The data container is stored in the relevant

real-time device channel just like standard data – in an

MDT just as in an AT. A multiplex protocol, SMP (Sercos

Messaging Protocol), is used to transmit safety data that

A single safety protocol for Sercos,

EtherNet/IP and DeviceNet enables

our machines and systems to be

universally connected and allows safety-

related process data to be transmitted.

to IEC 61508 up to SIL3. There is no need for additional cabling for a safety

bus because signals are simply transmitted alongside other real-time data

has been scanned differently without losing bandwidth

despite there being shorter bus cycles. CIP Safety is

a network protocol for functional safety. It has been

as well as standard Ethernet in one single network simplifies handling and

reduces hardware and installation costs. Integrated safety control systems

and homogeneous safety solutions can be carried out with ease.

with a safety integrity level of 3 (SIL3) and satisfies the

IEC standard 61508 for functional safety (“functional

safety of safety-related electric/electronic/programmable

electronic systems”).

Ethernet package

Ethernet

header

Sercos III

header

Data field Checksum

With CIP Safety on Sercos, data is safely transmitted

to the same medium using the same connection as the

Safe Sercos slave devices can be connected to each

other without safety controllers and can communicate

Sercos III data field

Hot plug field

(new devices)

Service

channel field

Real-time

data field

port protocol and non-medium dependent CIP safety

protocols lies in the end devices, which allows standard

reaction times.This gives the user real flexibility when

setting up safety network architecture, when install-

Real-time data field with

standard (M/S) and lateral

communication connections (DCC)

M/S connection

device #1

M/S connection DCC connection

… …

device #N device #N

DCC connection

device #1

and safety devices to be operated simultaneously on the

same network. Safe communication is possible across

ing safety programmable controllers or when directly

transmitting safety data between sensors and actuators.

Device data with

safety data container

Standard

data

Standard

data

Safety data

container

Standard

data

Safety data

container

Standard

data

does not necessarily have to be a safety controller,

but can also route data without having to interpret it.

nication from safety devices in a subnet to/from safety

devices in another subnet is made seamlessly.

Safety data container

Safety header

Data…data Checksum Safety header Redundant

data…data

Checksum

Common network infrastructure

When the application requires a Sercos ring for redun-

dant data transmission of real-time data and therefore

The common infrastructure complements the Sercos so-

lution portfolio as, alongside the extensive Sercos prod-

Sercos III

EtherNet/IP, TCP/IP, …

Sercos III

connect and disconnect the EtherNet/IP packets into the

Sercos ring. The EtherNet/IP devices can be arranged in

the number of communication interfaces and therefore

the hardware complexity will be significantly reduced

… … … … … … …

as DLR (Device Level Ring).

increases the operating efficiency in engineering and in

the operation of the facilities.

Sercos Real-Time Channel

Ethertype= 0x88CD

Unified Communication Channel

Ethertype ≠ 0x88CD

part of the existing bandwidth is used for the real-data

exchange. Sercos needs for an application with 64 drives

only 400 microseconds and a 2 milliseconds cycle for ex-

Bus cycle (i) Bus cycle (i+1)

Sercos EtherNet/IP TCP/IP

Coexistence of Ethernet protocols on the basis of the time multiplex procedure from Sercos III

The diversification in the automation technology has made machine in-

tegration a complex and cost-intensive task. In fact, manufacturers are

increasingly using industrial Ethernet solutions. But even if the technical

ample.This means that 1.6 milliseconds are available for

the transmission ofTCP/IP and EtherNet/IP telegrams.

Since the UC Channel sits directly on the Ethernet layer,

TCP/IP and EtherNet/IP as well as other Ethernet users

can be connected to the network without any additional

hardware.Tunneling of the protocols is not required.

Even before a Sercos III communication is initiated by

the master, the network users can exchange data via

TCP/IP, EtherNet/IP and the S/IP protocol specified by

Sercos.

“The utilization of a uniform net-

work infrastructure for Sercos and

EtherNet/IP devices is an innova-

tive approach to reducing the number of

communication interfaces and therefore

the hardware complexity in machines and

facilities significantly.The continuous net-

working increases the operating efficiency

in engineering and in the operation of the

facilities.”

ing performance and real-time characteristics in a negative manner. There

is one solution for Sercos that enables the operation of EtherNet/IP, TCP/IP

and Sercos devices via a single Ethernet cable. Neither additional hardware

nor tunneling of the protocols is required for that purpose.

Dual Stack Master

work infrastructure, a Sercos master and an EtherNet/IP

scanner are required.These functionalities can also be

which are destined for other devices. In the reverse di-

rection, the device transmits incoming telegrams via the

Standard I/O Standard I/O

connected in a line topology. When the last Sercos de-

vice identifies a Sercos-unknown device on its second

which come in during the time reserved for the real-time

channel, will be retained and subsequently transmitted.

Sercos III devices Ethernet/IP devices