Fieldbus System Details - Beckhoff Automation · Fieldbus System Details • Ethernet • Profibus...

1

Fieldbus Networks WorkshopBECKHOFF

Fieldbus System Details• Ethernet• Profibus• DeviceNet• Sercos

2


Industrial Ethernet: Overview

10... 50ms (not deterministic, single frames can be delayed much longer) Typical Cycle times

No. Prioritised Ethernet will come, but cannot be mixed with standard ethernet devices

Priorities

CRCError Detection

Ethernet: up to 1500 Bytes; process data lenght depends on protocol usedFrame Length

100m between node and hub/switchNetwork expansion

Depends on protocolNode Hierarchy

UTP/STP/POF: star topology (hubs or switches)Topology

Shielded and unshielded twisted pair, Plastic Fibre Optics (PMMA); 10/100 Mbit/s10 Mbit coax-cable is hardly in use any more

Transmission Media, Baudrate

Ethernet: physical Node Address; IP: IP-Address; TCP/UDP: port-AddressAddressing

CSMA/CD Medium Access Control Method

Has been in use for controller – controller communication for years. New: use as fieldbus replacement.

Background

3


Ethernet: Overview

Ethernet transmits pakets of 46-1500 data bytesTransmission Media (10MBit/s)

• Koax cable for bus topology (10Base5 “Thick Cable”, 10Base2 “Cheapernet”); • Fibre Optics (10BaseF) • Shielded twisted pair (STP) or unshielded twisted pair (UTP) 10BaseT for star topology

Header: Physical Addresses:• 22Bit Manufacturer ID (OUI: Organizationally Unique Identifier) and 24Bit Serial Number• further: Protocol-Info, Address type (Peer to Peer, Broad-, Multicast etc.)

Media Access Method: CSMA/CD• Advantage: no need to make each Node known to the network • Disadvantage: behavior is non deterministic• Pakets „die“, if media access failed 15 times in a row

4


Switched Ethernet Topology•Switched Ethernet (full-duplex) avoids collisions•But: still non deterministic, as switches need paket queues

Small Controller

I/O I/OENET

Modular I/O Rack

Soft PLC

Block I/O

PC w/HMI

PLC

I/OENET

I/O

Modular PLC

Block I/O

Device

ENetSwitch 10/100M Ethernet

ENET

I/O I/O

Robot

Device

Device

PC w/Config Sw

Block I/O

PC w/HMI

Block I/O

ENetSwitch

10/100M Ethernet 10/100M Ethernet

5


UDP-Hdr.(IP-Port)

UDP-Data

8 Bytes

TCP/IP Stack: Overview•TCP/IP (or UDP/IP) is embedded in Ethernet Packet•Structure supports Exchange of protocol layers

Ethernet-Header(MAC-ID)

46...1500 Bytes Ethernet-Data CRC

IP-Header(IP-Address)

IP-Data

TCP-Header(IP-Port)

TCP-Data

22 Bytes

08-0

0

PRO

T20 Bytes

20 Bytes

6


Internet Protocol (IP): Overview• Datagram with 20 Byte Header• Unsecured Data transport from a source to a destination address• Header: Addresses, Header-Checksum, Protocol infos,Time to Live, Fragmentation infos etc.• Supports Routing between networks• IP-Addresses: Network-and Host address

• Address resolutionwith ARP

version Hdr Len Service Type Total Length16bit Identification Flags 13bit Fragment Offset

8bit Time to Live 8bit Protocol 16bit Header Checksum32bit Source IP address

32bit Destination IP addressOptions (if any), padding

IP Datagramm Data (up to 65535 Bytes)

IP Header and Data CRC0800DASA

20 B

ytes

Ethernet

7


User Datagram Protocol (UDP): OverviewSimple datagram-oriented data transport, carried in IP dataNon-guaranteed delivery of data

• Packets may be delivered out of order or may not be delivered at all!

Less overhead than TCPNeeded for broadcast and multicast applicationsGood for request / response type protocols

• SNMP• TFTP• DHCP / BOOTP

16bit source port number

UDP data (theoretically up to 65507 Bytes,

typically restricted by the implementation)

UDP Header and DataIP-HDR (PROT=17)

8 By

tes 16bit destination port number

16bit UDP length 16bit UDP checksum


IP

8


Transmission Control Protocol (TCP): OverviewConnection oriented data transport, carried in IP data• Point to point between exactly two host ports

Reliable: Transfers are acknowledged, Order of sequential packets maintained

Data transferred as a stream of bytesGood for protocols needing to move streams of data

• HTTP,FTP,SMTP

Only works with unicast IP addresses• No broadcast or multicast

16bit source port number

TCP data (theoretically up to 65495 Bytes,

typically restricted by the implementation)

TCP Header and DataIP-HDR (PROT=06)

20 B

ytes

16bit destination port number

16bit TCP checksum 16bit urgent pointer


IP

32bit sequence number32bit acknowledgement number

16bit window sizeHDR LEN flags(reserved)

9


TCP: Connection

Establish: Three way handshake between two hosts• Host 1 sends SYN (synchronize) to host 2• Host 2 sends ACK to host 1 along with its own SYN • Host 1 sends ACK to host 2

Terminate: Four way handshake• Host 1 sends FIN (final) to host 2• Host 2 send ACK to host 1• Host 2 (in a separate message) sends FIN to host 1• Host 1 sends ACK to host 2

-> it takes some time to establish/terminate a connection!

10


ARP: Address Resolution Protocol TCP Address: Port Number

IPAddress

EthernetAddress: MAC-ID

MAC-ID ?

If no entry in ARP Cache

Send ARP Requestwith IP Address and MAC ID

FF FF FF FF FF FF

Communication starts

Node answers with MAC-IDand both MAC-ID and IP-Address

Number are entered in ARP Cache

11


IP Address Assignment Several Possibilities:

1. Setting by Local Software (PC) or Configuration Tool

2. DHCP (Dynamic Host Configuration Protocol) – requires configuration of DHCP Server

3. BootP (Bootstrap Protocol) – requires BootP Server

4. ARP –s (adds entry in ARP cache, can be used to assign IP-Adress to MAC-ID via network)

5. DIP-Switch (on field devices, typically only for LSB)

12


Ethernet: ProfiNetProfiNet:

• Access to Profibus Networks viaEthernet

• Protokoll: RPC (Remote ProcedureCalls) via TCP/IP or UDP/IP

• DCOM-based • DCOM will not be advanced by

Microsoft (Source: VSLive Conf.)• DCOM is not Internet-compatibel

(e.g. Firewall )• Microsofts new developments are

base on HTTP and TCP/IP, SOAP (Simple Object Access Protocol: XML based description)

• ProfiNet is not (yet): Profibus on Ethernet

• But: Real Time ProfiNet will come

13


Ethernet: IDA•Initially „Kuka and Friends“ + Jetter•Kuka meanwhile pulled out•Has selected NDDS (RTI) as Middleware, uses TCP/IP und UDP/IP•Therefore NDDS-User Schneider joined IDA•5/2000: Jetter drops VentureCom DCX and moves to NDDS •So far white papers and devicemodel finished•No final protocol solution published, no products available yet.

14


Control and Information Protocol (CIP)

Ethernet: Ethernet IP•ODVA und ControlNet International•CIP (Control and Information Protocol) on TCP/IP and UDP/IP•No data concerning real time capability available•Sample Code available•First devices are entering marketplace

SemiDevices

PneuValve

ACDrives

PositionCntrllrs

OtherProfiles

Application Object Library

Application LayerExplicit, I/O, Routing

DeviceNetDLL

Transport

ControlNetDLL

TransportFuture

encapsulation

UPD TCP

IP

DeviceNetPhysical

Layer

ControlNetPhysical

Layer

EthernetPhysical

LayerFuture

ATM, FirewireUSB, Blue Tooth

ApplicationLayer

UserLayer

Transportand Data Link

Layer

PhysicalLayer

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+ + : Memorandum Of Understanding

• IAONA (Europe + US together) becomes umbrella organisation for Industrial Ethernet

• IDA and Ethernet/IP are recognized by IAONA as de facto standards

• other groups are invited to join

• areas not covered yet („white spots“) are tackled jointly (Joint Work Groups)

• therefore: new structure of IAONA

IAONA: Industrial Automation Open Networking Alliance

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IAONA: Industrial Automation Open Networking Alliance

Technical Steering Committee

Board IAONA US Board IAONA Europe

Member IAONA US Member IAONA Europe

Joint Technical Workgroup

Chairman Joint Technical Workgroup

Chairman Joint Technical Workgroup

Chairman

2 2

PNO? FF? OMAC?

29 members 129 members

TSC tasks:

•Installs Workgroups

•Publishes Standards

•Coordinates work of the Workgroups

TSC Chairman: Peter Klüger, KukaDeputy chairman: Martin Rostan, Beckhoff

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Ethernet: Modbus TCP• Serial Modbus Protocol onTCP/IP

• Master/Slave (Polling)• Few Services, easy toimplement

• Wide spread use• Only for moderate RealTime Requirements

Transaction ID

Query message from Master

Protocol IDLengthUnit ID

Modbus fct code

Data

Transaction IDProtocol ID

LengthUnit ID

Modbus fct code

Data

Response message from Slave

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Beckhoff ADSAutomation Device Specification: • Ethernet TCP/IP for networking of control system• Not just on TCP/IP or UDP/IP: available on most field bus systems as well

PLC PLC NC Fieldbus

VB OPC DLL Ethernet

ADS Router

PLC PLC NC Fieldbus

VB OPC DLL Ethernet

ADS Router

PLC PLC NC Fieldbus

VB OPC DLL Ethernet

ADS Router

Bus Controller Bus Controller

ADS Communication Path

LAN

Fiel

dbus

PC Control System PC Control System PC Control System

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ADS Message RouterCommunicates locally, viaCOM Interface, TCP/IP orFieldbusAddresses:• Clients in public Networks

via TCP/IP• Local Networks• Clients in local Networks• Fieldbusses• Coupler in Feldbus systems• Server processes

text

User Interface

Visual C++Program

ADS DLLADS

PLCControl

ADS

SystemManager

ADS

TwinCAT ADS Message Router

PLCServer

ADS

NCServer

ADS

I/O Mapper

ADS

I/O Level

TCP/IP

Fiel

dbus

A

Fiel

dbus

B

Fiel

dbus

C

Fiel

dbus

D

Fiel

dbus

E

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ADS Protocol

ADS Data

UDP Header and DataIP-HDR)

16 B

ytes


IP

Index OffsetIndex Group

ADS Port: Target Location of DataAMS Net ID: Addresses the Device

UDP Data or TCP DataUDP or TCP Hdr

• Client / Server-Principle on TCP or UDP

• Services:

–Synchronous read/write

–asynchronous read/write

–connect (with defined Cycle Time)

–notification on change (with minimal Cycle Time)

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ModbusModbus

Ethernet: Multi-Protocol DevicesBeckhoff Ethernet I/O Devicessupport all relevant Protocols –if possible even in parallel!

EthernetEthernet

ARPARP IPIP RARPRARP

ICMPICMPOSPFOSPF

TCPTCP UDPUDP

FTPFTP HTTPHTTPBOOTPBOOTPDHCPDHCPDNSDNS

“CIP”“CIP”

SNMPSNMP

IGMPIGMPIGRPIGRP

ProfiNetProfiNetADSADS

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Beckhoff and Ethernet at work: Microsoft Headquarter Munich

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Microsoft Headquarter Munich: Details

•11 Buildings•44 Floors, 27000 m²

•11 Building Controller•164 Bus Controller (BC9000)•12000 digital I/O Points•2100 analogue I/O Points

•User Interface: Web Browser•Protocol: ADS on UDP/IP

Terminal rail 1

Terminal rail 1

Terminal rail 1

Terminal rail 1

Terminal rail 4

Terminal rail 4

Terminal rail 4

Terminal rail 4

Building 1 Building 2

Building Computer

3. Floor

2. Floor

1. Floor

Ground Floor

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0

10

20

30

40

50

60

70

80

90

100

5 10 15 20 25 30No of Nodes

Cyc

le T

ime

[ms]

Ethernet: Cycle Times

Modbus TCP: Node Response within 10..20 ms, Cycle Times 40..60 ms

Beckhoff ADS/UDP: Node Response within 1..4 ms, Cycle Times 15..25 ms

• Ethernet Cycle Time is hardly predictable.

• Depends on software runtimes (UDP + TCP) andtiming behavior of „Master“ (COTS Technology)

• 100 Mbit Switched Ethernet: almost independent of no. of nodes and of no. of bytes.

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Ethernet: Conclusions • high baudrate is not always equal to high performance• standardisation of Industrial Ethernet is not finished yet• interoperability is not guaranteed yet• its either COTS technology or hard real time • infrastructure costs (industrial components) stillsignificantly higher than with standard fieldbus systems

Therefore: Ethernet is no ideal replacement for standard fieldbus systems (yet), but a nice alternative for applications with:

- existing Ethernet infrastucture- low real time requirements

26


Profibus DP: Overview

1...3 msTypical Cycle times

2Priorities

CRC. Hamming Distance: 4 (3 Bits out of 32 (246) x 8 may change)Error Detection

0...246 Bytes. Typical: 1...32 BytesFrame Length

100 m (12 Mbaud), 200 m (1,5 Mbaud), 1200 m (93,75 kBaud). With 3 repeaters: values times 4 (segment – repeater – seg – rep – seg – rep – seg)

Network expansion

Typical: 1 Master, up to 31 slaves. With repeater: up to 126 nodes. Several masters possible.

Node Hierarchy

Electrical: bus (line) with terminating resistors; FO: ringTopology

RS485: shielded twisted pair, fibre optics (plastic); 9,6 kbit/s....12 Mbit/sTransmission Media, Baudrate

Node Addressing. Frame contains transmitter and receiver addressAddressing

Polling. If more than one master present, masters use additional token passing method

Medium Access Control Method

Profibus Sensor/Actuator derivative, initially developed by SiemensBackground

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Profibus-DP: Topology

Termination

Termination

2 3 30 31

62 61 33 32

Termination

Repeater

Repeater

* Note: Repeaters do not have a station address, but theycount towards the max. number of stations in each segment

Station 1

®

PROCESS FIELD BUS

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Profibus-DP: Termination

VP

B

A

DGND

first station

390 Ω

220 Ω

390 Ω

Bus Terminationlast station

Bus TerminationVP

B

A

DGND

Data Line B

Data Line A

B BA AStation 2 Station 3

390 Ω

220 Ω

390 Ω

®

PROCESS FIELD BUS

110 nH

110 nH

110 nH

110 nH

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Profibus-DP: Shielding/Grounding

data cable

ground cable, potential equalization

Slave Slave

Master

ground rail

data cable

ground rail ground rail

®

PROCESS FIELD BUS

Screen grounding clamp

Grounding rail close to cable lead-through

Recommended Practise

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Profibus-DP: Monomaster System

DP-Master (Class 1) Monomaster Systems achieve the shortest bus cycle timeThey consist of:

- 1 DP-Master (Class 1)- 1 to max. 125 DP-Slaves- DP-Master (Class 2) - optional

Distributed Inputs and Outputs

DP - Slaves

PROFIBUS-DP

PLC

®

PROCESS FIELD BUS

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Profibus-DP: Multi Master SystemSeveral DP-Masters

may access a DP-Slave with read functionsPROFIBUS-DP Multimaster systems consist of:

- multiple Masters (Class 1 or 2)- 1 to max. 124 DP-Slaves- max. 126 devices on the same busDP-Master

(Class 2)

DP-Master(Class 1)

DP-Master(Class 1)

distributed inputs and outputs distributed inputs and outputs

PROFIBUS-PDP - Slaves

PLC

PROFIBUS - DP

PC

CNC

®

PROCESS FIELD BUS

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Profibus-DP: Multi Master Media Access

®

PROCESS FIELD BUS

PROFIBUS

Active Stations, Master Devices

Passive Stations, Slave Devices, get polled, no direct slave to slave communication

PLCPLCPC

pollingpollingpollingpolling

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Profibus-DP: Protocol Classes

®

PROCESS FIELD BUS

Slave to Slave Communication (via Master), Equidistance (Motion Control)

DPV2

Alarm and acyclic Services (e.g. Parameter data)

DPV1

Cyclic Process Data CommunicationDPV0

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TSYN = 33 Tbit

Request

Response

TRDY

min TSDR

max TSDR

Legend: TRDY = Ready TimeTSDR = Station Response Time, typically 11 TBit

TSYN = Synchronization Time, typically 22 TBit

Master Slave

Time

Request Telegram

Response Telegram

Profibus-DP: Timing

®

PROCESS FIELD BUS

35


Profibus-DP: Calculation of Cycle TimeTMC = ( TSYN + TID1 + TSDR + Header + I x 11TBit + 0 x 11TBit ) x Slaves

TMC = Message Cycle Time in Bit TimesTID1 = Idle Time at the Master = typically 75 TBitTSDR = Station Delay Time at the Slave = typically 11TBitHeader = Telegram Overhead in Request and Response Frame = 198 TBitI = Number of Input Data Bytes per SlaveO = Number of Output Data Bytes per SlaveSlaves = Number of Slaves

PROFIBUS-DP System consisting of 1 Master and 20 Slaves eachwith 2 Byte Input and 2 Byte Output Data.TMC = ( 33 + 75 + 11 + 198 + 22 + 22 ) x 20 = 7220 TBit7220 TBit (1.5 MBaud) = (TBit = 0.66 µs) = 4.8 ms7220 TBit (12 MBaud) = (TBit = 0.83 ns) = 0.6 ms

In practice, a safety margin of approx 10 to 20% should be added for bus administration,diagnostic messages and retries (after bit errors).

Example:

®

PROCESS FIELD BUS

36

Fieldbus Networks WorkshopBECKHOFF®

PROCESS FIELD BUS

Profibus: Cycle Times

0

5

10

15

20

25

30

35

40

5 10 15 20 25 30No of Nodes

Cyc

le T

ime

[ms]

12 MBaud, 2+2 Bytes12 MBaud, 6+6 Bytes12 MBaud, 20+20 Bytes1,5 MBaud, 2+2 Bytes1,5 MBaud, 6+6 Bytes1,5 MBaud, 20+20 Bytes500 kBaud, 2+2 Bytes500 kBaud, 6+6 Bytes500 kBaud, 20+20 Bytes

37


Profibus-DP: Troubleshooting

®

PROCESS FIELD BUS

Simple test for eliminating the most common wiring errors:

• Data cable crossed over

• Open circuit of one of the data cables

• Open circuit of the cable shield

• Short circuit between the data cables

• Short circuit between data cables and cable shield

• Additional bus terminating resistors inserted unintentionally

38



®

PROCESS FIELD BUS

Test each segment after installing cables and attaching bus connectors, but:

- bus connectors must not be connected to Profibus devices- bus terminating resistors must be removed or disabled

Test equipment: 2 test connectors DB9, 1 Ohmmeter

• Connector 1 with double pole single throw switch; moving contact connected to shield (case) of the test connector. Fixed contacts connected to pin 3 (data wire B) and pin 8 (data wire A).

• Connector 2 used to connect the Ohmmeter to the bus

39



®

PROCESS FIELD BUS

Wiring Test Setup

Ω

Test Connector 1 Test Connector 2

Bus Connector Bus Connector

screen screen

8 3 38

RS 485 Segment

B

A

Bus Connectors of further stations

40



®

PROCESS FIELD BUS

Test Step 1:

TC1: first connect pin 3 and shield

TC2: measure resistance R between pin 3 and shield

If R < 10 Ω: Data B and shield connection o.k.If R = infinity: Data B or shield open circuit

Then disconnect pin 3 and shield at TC1

Resistance R now has to be infinite. If not: short circuit between data B and shield or

Data A and Data B swapped over

Ω



screen screen

8 3 38

A B A B

41



®

PROCESS FIELD BUS

Test Step 2:

TC1: connect pin 8 and shield

TC2: measure resistance R between pin 8 and shield

If R < 10 Ω: Data A and shield connection o.k. If R = infinity: Data A or shield open circuit

Then disconnect pin 8 and shield at TC1

Resistance R now has to be infiniteIf not: short circuit between data B and shield or

Data A and Data B crossed over

Ω



screen screen

8 3 38

A B A B

42



®

PROCESS FIELD BUS

Test Step 3: Bus terminating resistors

TC1: switch position is not important

TC2: measure resistance R between pin 3 and pin 8

If R = infinite: o.k., if no terminating Resistors connectedIf R = 220..230 Ω: 1 Terminating Resistor connectedIf R = 110..120 Ω: 2 Terminating Resistors connectedIf R = <110 Ω: too many Terminating Resistors

Ω



screen screen

8 3 38

A B A B

43


Profibus-DP: Installation Guidelines (RS485)

®

PROCESS FIELD BUS

inside control cabinet: in separate cable conduits or cable ways without minimum spacing requirementsoutside control cabinets: In seperate cable runs spaced at least 10cm (4‘‘) apart

- DC and AC voltages > 400 V (unshielded)- Telephone cables- For areas with explosion hazard

in separate cable conduit or cable way without minimum spacing requirements

- DC voltages from 60V... 400V (unshielded)- AC voltages from 25V... 400V (unshielded)

in the same cable conduit or cable way.- Bus signals, e.g. PROFIBUS- Data signals for PC´s, programming devices,printers etc.- Screened analog inputs- Unscreened DC voltages (<= 60V)- Screened process signals (<= 25 V)- Unscreened AC voltages (<= 25V)- Coaxial cables for monitors

must be laid...Profibus cables and cables for...

44


DeviceNet: Overview


2048Priorities

CRC, Frame Check, Bus Monitoring, Bit Stuffing, Acknowledge Check. Hamming Distance: 6 (5 Bits out of 83 may change)

Error Detection

0...8 Bytes. Longer process images are sent using segmented transferFrame Length

100 m (500 kBaud), 250 m (250 kBaud), 500 m (125 kBaud). Use of repeatersdoes not lead to longer networks, as propagation delay is the limit (not damping)

Network expansion

Typical: 1 Master, up to 63 slaves. Several masters possible (rarely used)Node Hierarchy

Electrical: bus (line) with terminating resistorsTopology

ISO 11898: shielded twisted pair; 125, 250, 500 kBit/sTransmission Media, Baudrate

Frame Addressing (CAN Identifier). Predefined Master-Slave Connection Set links Node Adresses (MAC-ID) with CAN Identifiers

Addressing

CSMA/CAMedium Access Control Method

CAN based Sensor actor bus system, initially developed by Allen BradleyBackground

45


DeviceNet (CAN): Dominant and Recessive BitsV+

bus-line

S1 S2 S3

device 1 device 2 device 3

V+ -> 1-> 0

State TableS1 0 1 0 1 0 1 0 1 0 - level is dominantS2 0 0 1 1 0 0 1 1 1 - level is recessiveS3 0 0 0 0 1 1 1 1

Bus Level 0 0 0 0 0 0 0 1

46


DeviceNet: CAN Arbitration with CSMA/CA

node 1 listening only

node 2 listening only

node 3

bus-level

Node 3 wins arbitration and transmits his data.

S RO Identifier T Control DataF 10 9 8 7 6 5 4 3 2 1 0 R Field Field1

0

1

0

1

0

1

0

47


DeviceNet: Topology

PS

Trunk Line withTerminatingResistors + (short) Drop Lines

Drop Line„Zero Drop“

node 1 . . . . . . . . node n

CAN Bus Line 120 Ω120 ΩCAN_H

CAN_L

Basic CAN Topology: ISO 11898

48


DeviceNet: Dropline Daisy-Chaining & Branching

Dropline

Tap

plug-in device connector

TapTrunk

Use inside Control Panelswhere multiple devices are clustered together

Branching Limitations20 ft max to node farthest from tapsum of cable-feet goes against dropline

budget

49


DeviceNet: Propagation Delay limits Network Length

CAN-Controller 1 CAN-Controller n

opto- opto- . . . . . . opto- opto-coupler coupler coupler coupler

transceiver 1 transceiver n

~ 50 ns

~ 100...150 ns

~ 40 ns

~ 5,5 ns/m

CAN Arbitration requires Propagation delay < Bit Time

50


DeviceNet: Drop Line + Multidrop Limitations

Bit Rate

500kbit/s250kbit/s125kbit/s

Trunk Length

(without Drops)

100m250m500m

SingleDrop

Length<5m

<10m<20m

TrunkLength

(without Drops)

66m120m310m

Trunk line

Dro

p lin

e

Trunk line

Drop line

Multiport Tap

Drop Lengths

<25m<50m

<100m

SingleDrop

Length

<1,2m<2,4m<4,8m

Trunk/Drop Topology Multiport Tap TopologyΣ

51


DeviceNet: CAN Error Detection and Recovery

1. Local or global error detected.2. An Error Flag will be transmitted (globalisation of error).3. In case of local error this Error Flag will proceed an

overlapping Error Flag followed by the Error Delimiter.4. The message will be discarded by each node.5. The Error Counters of every bus node are incremented.6. The message transmission will be repeated

automatically.

52


transmitter data data 8 bit 3 repetition

receiver 1 6 bit

receiver 2 6 bit

bus-level

The receiver 2 detects an error and makes it public to the other nodes.

DeviceNet: Globalisation of Local Errors

53


DeviceNet: Why Local Errors?

Disturbance

Disturbance

Threshold AThreshold B

Threshold

Sampling Point ASampling Point B

Sampling Point

1. Different Sampling Points in different Nodes

2. Different Switching Thresholds in different Nodes

3. Dispersion during Propagation along the Bus Line

54


DeviceNet: Error Counters and Error States

Error Active

Error Passive

REC

<= 1

27an

dTE

C <=

127RE

C >

127

or

TEC

> 12

7

TEC > 255

Reset and Configuration

Reset, Configurationand Reception of

128x11 recessiveBits

REC: Receive Error CounterTEC: Transmit Error Counter

Bus Off

Too manyErrors: Bus Off

55


DeviceNet: Multimaster and Multicast

I/O 1

PLC1 MMIPLC2

DRIVE1

DRIVE2

DRIVE3

#1

#2

• Transaction #1 - position reference from I/O Rack #1 is broadcastedto PLC1, PLC2, and the MMI at the same time• Transaction #2 - speed command is sent to all three drives at the same time• But: 99% of all DeviceNet Networks are single Master / single Cast („Group 2 Only“- Networks, where Slaves communicate with Master only)

56


DeviceNet: Polling

PLC

I/O 1 I/O 2 I/O 31,4,... 2,5,..

3,6,..

• The simplest and most understood; “polling”• The PLC or scanner is the master and I/O devices are the slaves

• The slaves speak only when spoken to• Only one master per network (“single master”)

• Most (>95%) of all DeviceNet installations work this way• Deterministic behavior, easy to configure• But: less efficient use of bandwidth than other options

57


DeviceNet: Polling Procedure with AB ScannerPo

ll R

eque

st N

ode

1

Poll

Req

uest

Nod

e 2

Poll

Req

uest

Nod

e 3

Poll

Req

uest

Nod

e 4

Poll

Req

uest

Nod

e 5

Poll

Req

uest

Nod

e 6

Poll

Res

pons

e N

ode

1

Poll

Req

uest

Nod

e 7

Poll

Req

uest

Nod

e 8

Poll

Res

pons

e N

ode

2

Poll

Res

pons

e N

ode

4

Poll

Res

pons

e N

ode

6

Poll

Res

pons

e N

ode

5

Poll

Res

pons

e N

ode

3

Poll

Res

pons

e N

ode

7

Poll

Res

pons

e N

ode

8

Poll

Req

uest

Nod

e 1

Poll

Req

uest

Nod

e 2

Poll

Req

uest

Nod

e 3

Poll

Req

uest

Nod

e 4

Interscan DelayScanner first sends all Poll Requests

Interscan delay is the time the scanner module will wait between thelast poll message request and the start of the next scan cycle.

Background poll ratio sets the frequency of poll messages to adevice in relation to the number of I/O scans. For example, if theratio is set at 10, that device will be polled once every 10 scans.

It is not possible to set a specific cycle time.

58


DeviceNet: Cyclic Data Production

PLC

I/O 1 I/O 2 I/O 3

every 500 ms

every 2000 ms

every 25 ms

• Devices report data on a user-configured time increment basis (input or output)• Cyclic Data Production is more efficient for applications with slowly changingI/O (analog)

• Network traffic is reduced• Performance is repeatable

• Can be used in Master/Slave, Peer-to-Peer, or Multimaster environments• More configuration effort than polling but better performance when the minimum required update rate for individual I/O devices can be identified

59


DeviceNet: Change of State (COS)

PLC

I/O 1 I/O 2 I/O 3

#2

#1#3

• Rather than a master going through a polling list (scanning), devices report data (input or output) on a change-of-state basis as the events happen• Change of State is more efficient for discrete applications• Network traffic is significantly reduced, performance is greatly improved

• Background heartbeat for device supervision (Network Management)• Can be used in Master/Slave, Peer-to-Peer, or Multimaster environments• Bandwidth analysis in system test phase required• in DeviceNet Change of State is always combined with Cyclic

60


DeviceNet: Calculation of Cycle TimesTMC = (I x 8 + (NRQT x TTH) + O x 8 + (NRST x TTH)) x Slaves x 100%/BL

TMC = Message Cycle Time in Bit TimesI = Number of Input Data Bytes per SlaveNRQS = No. of Request Telegrams (I=1..8:NRQS=1; 9…14:2; 15…21:3; 22…28:4 etc.)TTH = Telegram Header= 50 Tbit (including 3 Stuff Bits)O = Number of Output Data Bytes per Slave NRQS = No. of Response T. (O=1..8:NRQS=1; 9…14:2; 15…21:3; 22…28:4 etc.) Slaves = Number of SlavesBL = Busload; typical: up to 80% (for polling only)

DeviceNet System consisting of 1 Master and 20 Slaves eachwith 2 Byte Input and 2 Byte Output Data, 80% BusloadTMC = (2x8 + 50 + 2x8 + 50) x 20 x 100%/80% = 3300 TBit3300TBit (500kBaud) = (TBit = 2 µs) = 6.6 ms 3300TBit (125kBaud) = (TBit = 8 µs) = 26.4 ms

Example:

61


DeviceNet: Cycle Times I (Polling)

0

20

40

60

80

100

120

140

160

5 10 15 20 25 30No of Nodes

Cyc

le T

ime

[ms]

500 kBaud, 2+2 Bytes500 kBaud, 6+6 Bytes500kBaud, 20+20 Bytes250 kBaud, 2+2 Bytes250 kBaud, 6+6 Bytes250 kBaud, 20+20 Bytes125 kBaud, 2+2 Bytes125 kBaud, 6+6 Bytes125 kBaud, 20+20 Bytes

80% Busload

62


DeviceNet: Cycle Times II (Polling, 500 kBaud)

0

5

10

15

20

25

30

35

40

5 10 15 20 25 30No of Nodes

Cyc

le T

ime

[ms]

500 kBaud, 2+2 Bytes500 kBaud, 6+6 Bytes500kBaud, 20+20 Bytes

80% Busload

63


DeviceNet: Cycle Times III

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40 45 50

No of I/O Bytes per Slave

Cyc

le T

ime

[ms]

500 kBaud, 10 Nodes, 80% Busload

64


Network Wiring Design

Network Wiring Design Affects…• Maximum communication baudrate• Network power distribution

Network Wiring Design Goals• Control total trunk length• Control cumulative drop length

(the total length of all drop lines)

65


Network Wiring Design (continued)

Important Points:• Network trunk lines may be constructed with thick, thin or

a combination of think and thin cable according to the tables in the DeviceNet Specification – typically thin is sufficient

• The trunk line must be terminated at each end• Two terminators, no more and no less• DeviceNet differs from many other networks in that it

requires network termination for proper operation,regardless of cable length

66


Network Wiring Design (continued)

… More Important Points:• The trunkline-dropline topology guidelines must be

followed faithfully• Bending the rules will usually cause more problems

than it solves• Building trunks with thin cable has a significant impact on

network power design• Thin cable has a higher DC resistance and will

adversely affect voltage drop in the power system

67


Network Power

Network power is a new concept to most controlsystems designers• 24Vdc is supplied in the network cable

• Powers simple devices• Powers the isolated network interface in larger devices

Power System Design Goals• Deliver 11Vdc minimum at each device• Limit common mode voltage to < 5v

• Voltage drop in DC common line

68


Network Power (continued)

Power System Design Process• Determine maximum current for each device• Place one or more power supplies on the network to

ensure that:• The voltage drop in the cable between a power supply

and each station it supplies does not exceed 5Vdc• The current does not exceed the cable/connector limit

• The DeviceNet Specification provides an easy table-lookup method for power system design

69


Network Power (continued)

Important Points:• Use the maximum inrush current specification for each

device for power calculations• Minimum requirements must be guaranteed when

power is applied• Use multiple power supplies with care

• You must guarantee that the power supply common does not vary by more than 5V between any two pointsin the network

70


Grounding

Network Grounding Guidelines• Connect the DC power supply common wire and the shield

to a low-impedance ground at the power supply• If multiple power supplies are present, ground at only

the power supply closest to the middle of the network• Location of ground affects common mode voltage

• All splices and taps in the network must connect the shield as well as the signal and power lines

71


DeviceNet: Shielding/Grounding

data cableShield grounded only at one location

Slave Slave

Master

ground rail ground rail ground railR-C

Optional R-C Circuit for HF grounding

72


Testing

General Test Parameters• Do not perform these tests while the system is operating

(no communication)!• All devices installed• All power supplies turned on• Perform these tests in sequence

• Some tests assume that previous tests were successful

73


Testing (continued)

Ω

120 Ω

120 Ω

Network Termination & Signal Wires• Check the resistance from CANH to CANL at each device

• If the value is > 60 ohms, there could be a break in one of the signal wires or missing network terminator(s)

• If the value is < 50 ohms look for:- a short between the network wires, - extra terminating resistor(s), - faulty node transceiver(s)

Depending on the type of Ohmmeter it may be necessary to disconnect the nodes for this test!

74


Testing (continued)

Shield• Connect a DC ammeter (16 amps max) from DC common

to the shield at the opposite end of the network from thepower supply• There should be significant current flow• If there is no current, the shield is broken or the network

is improperly grounded • If the power supply is in the middle of the network, do

this test at each end• This test can also be performed at the end of each drop

if practical

75


Testing (continued)

Grounding• Break the shield at a few points in the network and insert a

DC ammeter• If there is current flow, the shield is connected to DC

common or ground in more than one place (ground loop)

76


Testing (continued)

Network Power - Minimum supply voltage• Measure the supply voltage at each device

• It should be > 11Vdc• If not, check for faulty or loose connectors and verify

power system design calculations by measuring current flow in each section of cable with an ampmeter

77


Testing (continued)

Network Power - Common Mode Voltage • Shield must be continuous and have no current flow in it

(tested previously)• Measure and record the voltage between the shield and

DC common at each device• The maximum difference should be < 5V between any

two devices

78


Testing (continued)

MAC ID/ Baud Rate Settings• The Network Status LED is an excellent diagnostic tool for

this purpose• The LED should be flashing green on all devices

• Solid RED indicates a communication fault (possibly incorrect baud rate) or a duplicate MAC ID (station address)

• Use a network configuration tool to perform a "network who" to verify that all stations are connected and capableof communicating

79


Diagnosing Faults

Common network problems• Faulty devices• Opens & shorts in the network wiring

• Faulty connectors or cable• Electrical interference

• Incorrect grounding or broken shield• Signal distortion & attenuation

• Incorrect termination• Failure to adhere to topology guidelines• Faulty connectors or loose terminal blocks

80


Diagnosing Faults

Problems specific to DeviceNet • Missing terminators • Excessive common mode voltage

• Excess current or cable length• Faulty connectors

• Low power supply voltage• Excess current or cable length• Faulty connectors

• Excessive signal propagation delay• Excess cable length

81


Diagnosing Faults (continued)

Low-tech Approach:• Disconnect parts of the network and watch where the fault

goes• Does not work well for problems such as excessive

common mode voltage, ground loops, electrical interference and signal distortion because disconnecting part of the network frequently solves the problem

• If the network was previously operating, ask the question "what has changed?”

82



Using an Oscilloscope:• Can be misleading since many perfectly good differential

signals look perfectly awful when viewed individually• Most network problems your are tempted to diagnose with

an oscilloscope are intermittent• Unless you are able to trigger your scope on the bad

signal you will probably spend your time looking at goodsignals

83



Your Brain is Your Best Diagnostic Tool:• Be a detective, record symptoms in detail

• Your notes are invaluable if you enlist the help of others• Look for patterns in the symptoms

• Do intermittent problems occur when other un-related equipment is in use?

• Do some nodes communicate correctly? What is the difference between the functioning nodes and the others? (proximity to the power supply, to the terminator, to the scanner)

84


DeviceNet Troubleshooting: Conclusion

The vast majority of DeviceNet network problems are user created by:• Failing to follow cable system design rules

• Missing terminators• Excessive trunk/drop length• Improper topology

• Failing to follow power system design rules• Excessive common mode voltage

85


SERCOS: Overview

0,5...2 ms, cycle times of 0,0628 ms possibleTypical Cycle times

1Priorities

CRC. Hamming Distance: 4Error Detection

Cyclic Drive Telegram: typical 4 Bytes, maximal 32 BytesFrame Length

Max. 40 m between two nodesNetwork expansion

1 Master, up to 253 slavesNode Hierarchy

RingTopology

1000 µm Plastic Optical Fibre (PMMA:Polymethylmethacrylate); 2 or 4 Mbaud, coming soon: 8 and 16 MBaud

Transmission Media, Baudrate

Node AddressingAddressing

Time Slicing MethodMedium Access Control Method

Fibre Optic Network, originally developed for Drive ControlBackground

86


SERCOS: Medium Access Control via Time Slicing

• Master calculates a time window for each slave

• In the initialization phase this timing parameter is configured on the slave

• Each Slave has an adjustable address(independent of its position within the ring)

• The Master cyclically sends a synchronization telegram “MST”

• Communication is collision free due to the fixed timeslices and synchronized communication

87


SERCOS: Communication Principle

88


SERCOS: Telegram Structure

89


SERCOS: Startup PhasesThe optical Ring is checked

OK

OK

Master identifies all Slaves

Initialisation of the SlavesTiming parameters are readCalculate Time Slice parametersDownload parameters

Everything operational

Timing is activated, further Parametrisation

10 times MST

All Slaves respond with Drive Telegram

All Values ok

Slaves check parameters

Phase 0 Reset Phase

Phase 1

Phase 2

Phase 3

Phase 4

Ring identification

Initialisation Phase(+Parameterisation)

Parametrisation Phase

Operational

OK

OK

90


SERCOS: Calculation of Cycle TimeTMC = TMST+TMDTH+2TJit+(TATH+TJit+(7+I+0)x9,6 +TMDTS ) x SlavesTMC = Message Cycle Time in Bit TimesTMST = Master Sync Telegram Time = 56,4 TBitTMDTH = Master Data Telegram Header = 44,8 TBitTJit = Jitter Time btw. two messages = 16TBit@16MBaud;8@8; typ.20@4; 40@2 TATH = Slave Telegram Header = 16TBitTMDTS = Master Data Telegram Slave Header = 38,4 TBitI = Number of Input Data Bytes per SlaveO = Number of Output Data Bytes per SlaveSlaves = Number of Slaves

SERCOS System consisting of 1 Master and 20 Slaves eachwith 2 Byte Input and 2 Byte Output Data, 4MBaudTMC = 56,4 + 44,8 + 40 + (16 + 20 + (7+2+2)x9,6 + 38,4) x 20 = 3741 TBit3741TBit (4 MBaud) = (TBit = 0.25 µs) = 0.94 ms3653 TBit (16 MBaud) = (TBit = 62.5 ns) = 0.23 ms

In practice, time for data access from PLC/NC to the master should be added (typ. 0.3ms)

Example:

91


SERCOS: Cycle Times

0

1

2

3

4

5

6

7

8

5 10 15 20 25 30No of Slaves

Cyc

le T

ime

[ms]

16MBaud, 2+2Bytes

16MBaud, 6+6 Bytes16MBaud, 20+20 Bytes

4MBaud, 2+2Bytes4MBaud, 6+6 Bytes

4MBaud, 20+20Bytes2MBaud, 2+2Bytes

2MBaud, 6+6 Bytes2MBaud, 20+20Bytes

including 0.3 ms Master Access Time

92


SERCOS: Cycle Times

120

80

40

20

10

52

3210,50,250,1250,0628

Nodes per

SERCOS interface

Fibre Optic - Ring

Datarate 16 MBit/s

Position/Velocity Control Telegram

SERCOS interface Cycle time in ms

Datenrate 4 MBit/s

Position/Velocity Control Telegram

93


SERCOS: FC750x Mastercard Facts

Baudrate 2 / 4 / 8 / 16 MBit/s

Max. No of Slaves 254 Nodes

Software support TwinCAT I/O … NCI, not without TwinCAT!

Synchronization TwinCAT Real Time

Minimal Cycle time 62,5 µs

All settings via TwinCAT

FC750x does not need an interrupt!

94


SERCOS: BK7500 Bus Coupler Facts

Baudrate 2 / 4 / 8 / 16 Mbit/s

Max. No of Devices 254 Nodes

Max. number of bytes 32 bytes input / 32 bytes output for the cyclic interface (depending on the master)

Minimal Cycle time 62,5 µs; if cycle time shorterthan K-Bus update, olddata is repeated

Settings Node AddressDistance to next node (Tx Intensity)Baud Rate

95


CANopen: Overview


2048Priorities

CRC, Frame Check, Bus Monitoring, Bit Stuffing, Acknowledge Check. Hamming Distance: 6 (5 Bits out of 83 may change)

Error Detection

0...8 Bytes. Longer process images are sent using different telegrams (PDOs)Frame Length

100 m (500 kBaud), 250 m (250 kBaud), 500 m (125 kBaud). Use of repeatersdoes not lead to longer networks, as propagation delay is the limit (not damping)

Network expansion

Typical: 1 Master, up to 63 slaves. Several masters possible (rarely used)Node Hierarchy

Electrical: bus (line) with terminating resistorsTopology

ISO 11898: shielded twisted pair; 10, 20, 50, 100, 125, 250, 500, 800, 1000 kBit/sTransmission Media, Baudrate

Frame Addressing (CAN Identifier). Predefined Master-Slave Connection Set links Node Adresses (MAC-ID) with CAN Identifiers

Addressing

CSMA/CA. Medium Access Control Method

CAN Protocol defined by CAN in Automation. Used in General Automation Applications (I/Os, Drives, etc) and in Embedded Applications

Background

CANopen

96


CANopen: Device Model

Protocol Stack

PDO ProtocolSDO ProtocolSync ProtocolTime Protocol

Emergency ProtocolNMT Protocol

Heartbeat Protocoletc.

Object Dictionary

Data TypesCommunication Objects

Application ObjectsProprietary Objects

ApplicationSoftware

Device ProfileImplementation

ProprietarySoftwareRoutines

I/OCAN

• All Parameters and Application Objects are organized in an object dictionary

• Access to these objects via service data objects (SDO) and process data objects (PDO)

CANopen

97


CANopen: Process Data Object (PDO)

Other node

PDO_1 consumerPDO_1 consumer

PDO_1 producer

PDO_1DataID

Producer/Consumer: PDO makes use of CAN broadcast mechanism

• PDOs contain real time I/O data. Contents is described in PDO Mapping Object

• Each PDO has one producer and one to many consumers

• PDO equivalent in DeviceNet: I/O messages (or implicit messaging)

CANopen

98


CANopen: PDO SchedulingPDO Trans-mission Type Internal

event1. Event- or Timer-driven producer

consumer(s)

Remote Frame2. Remotely

requested producerconsumer(s)

Sync3. Synchronous

transmission(cyclic, acyclic)

producerconsumer(s)

CANopen

99


CANopen: PDO Synchronisation

time

Sync SyncCommunication_Cycle_Period

Actuation based on COMMAND at next SYNC

CommandMessages

ActualMessages

Samples takenat SYNC for

actual message

synchronous window

length(s)CommandMessages

ActualMessages

• SYNC telegram acts as trigger for input reading and output validation

CANopen

100


CANopen: PDO Mapping

6TTTh TTh Object A

6ZZZh ZZh Object G

6YYYh YYh Object F

6XXXh XXh Object E

6WWWh WWh Object D

6VVVh VVh Object C

6UUUh UUh Object B

Object Dictionary

Object B Object DObject APDO_1

Index Sub Object contents01h

02h

03h

1ZZZh

1ZZZh

1ZZZh

6TTTh TTh 8

6UUUh UUh 8

6WWWWh WWh 16Map

ping

Obj

ect

Appl

icat

ion

Obj

ect

PDO-Length: 32 Bit

The PDO Mapping Entry in the Object Dictionary allows one to determine which Application Data is mapped in the PDOs

Beckhoff CANopen Bus Couplers generate a Default Mapping autononomously

CANopen

101


CANopen: Variable PDO Mapping

6TTTh TTh Object A

6ZZZh ZZh Object G

6YYYh YYh Object F

6XXXh XXh Object E

6WWWh WWh Object D

6VVVh VVh Object C

6UUUh UUh Object B

Object Dictionary

Object G Object EObject APDO_1

Index Sub Object contents01h

02h

03h

1ZZZh

1ZZZh

1ZZZh

6TTTh TTh 8

6ZZZh ZZh 16

6XXXh XXh 8Map

ping

Obj

ect

Appl

icat

ion

Obj

ect

Variable PDO Mapping allows one to select which Application Data is mapped in the PDOs

CANopen

102


CANopen: Service Data Objects (SDO)

SDO Server

Node n-1 OD

ODNode n OD

SDO Client

Peer-to-Peer Communication

DataID 1DataID 2

• SDOs are used to read or write data to the servers object dictionary

• Typically used acyclically, but may be used for (slow changing) process data as well

CANopen

103


CANopen: Object Dictionary Access via SDO

Index Subindex Description Value

Object Dictionary

Byte 0 Byte 1-3: Multiplexor Byte 4-7: Data

Command 16-bit-Index 8-bit 1-4 byte parameterSpecifier Subindex data

• The SDO contains the address information for the object dictionary: index and subindex

• SDO equivalent in DeviceNet: Explicit Messaging

CANopen

104


CANopen: Predefined PDO Identifiers

MasterRPDO_1_MRPDO_2_M

TPDO_1_MTPDO_2_M

RPDO_3_MRPDO_4_M

TPDO_3_MTPDO_4_M

Slave XTPDO_1_XTPDO_2_X

RPDO_1_XRPDO_2_XSlave YTPDO_1_YTPDO_2_Y

RPDO_1_YRPDO_2_Y

• Nodes derive Identifier set from their node ID

• with these identifiers Master/Slave connections are established

CANopen

105


CANopen: PDO Linking• If devices shall communicate directly (without a relaying master), Identifiers have to be adapted (configured)

• This is as well the case if several nodes shall listen to the same PDO

TPDO_1_YTPDO_2_YRPDP_1_YRPDO_2_YRPDO_3_Y

RPD

O_1

_XR

PDO

_2_X

TPD

O_1

_XTP

DO

_2_X

Device X

RPDO_1_ZRPDO_2_ZRPDO_3_ZTPDO_1_ZTPDO_2_Z

Device Z Device Y

CANopen

106


CANopen: Feature List

Medium Access (CAN Arbitration) + Topology: see DeviceNet !

Up to 512 Transmit-PDOs and up to 512 Receive-PDOs

Asynchronous and synchronous PDO transmission

One Default-Server-SDO, up to 127 Server-SDOs

Up to 128 Client-SDOs

Boot-up Message and Heartbeat Message

Emergency and SDO Abort Message

Time-stamp message

NMT Slave state machine

CANopen

107


Lightbus: Overview

1..2 ms (there are applications with 67 µs)Typical Cycle times

CDL concept allows one to distinguish 8 prioritiesPriorities

CRCError Detection

4 Bytes Process DataFrame Length

POF: 40m between two slaves; 300m with HCS FibresNetwork expansion

1 Master, up to 254 slavesNode Hierarchy

RingTopology

Plastic Fibre Optics (PMMA); 2,5 MBit/sTransmission Media, Baudrate

Node AddressingAddressing

Master/Slave (Polling) Medium Access Control Method

Developed by Beckhoff in 1989. Still one of the fastest systems aroundBackground

Lightbus

108


M1400Lightbus module, 32 x digital I/O

M2400Lightbus module, 16 x digital I/O,max. 4 x analog outputs

M3000Absolut Encoder with Lightbus interface,24 Bit, 4096 steps/revolution

M3120Lightbus module, 4 channelIncremental Encoder interface

M63xxOperating panels with Lightbus interface

BK2000Lightbus Coupler,Bus Terminals

BC2000Lightbus Controller withintegrated IEC 61131-3

AX20xx-B200Compact digitalservo drive withLightbus interface

TwinCATSoftware-PLC/NC

FC2001/02PCI inter-face card

C1220ISA inter-face card

C1300VME inter-face card

C1120S5 inter-face card

Lightbus: System Overview

Lightbus

109


Lightbus: Topologyfiber optic ring with 45m (150 ft) distance between nodes

online fiber optic media diagnosticserror location indicationsyncronization commandsNO address switch settinglogical addressing possiblevarious vendors for encoders, drives, IO devices

Lightbus

110


Lightbus:Frame Format

deterministic communication in 25µs “frames”

fastest update time 25 µs for 4 interrupt channels

7 different communication cycle times for modules down to 50µs

modules freely configurable in CDL’s (communication description lists) for communication timing

Lightbus

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