field bus
TRANSCRIPT
Seite 1
Prof. Dr. Egon Sommer
MUAS
1
Fieldbuses in Cars and IndustryProf. Dr. Egon Sommer
MUAS
Table of Content
1. What is a Fieldbus ?
2. Some Basics of Fieldbuses
3. CAN Bus
4. Application in Cars
5. EtherCat
Seite 2
Prof. Dr. Egon Sommer
MUAS
1. Where does the word „Field“ come from ?
The outside area of such a plant is called the „Field“
The first buses should connect sensors and actors in such applications
Prof. Dr. Egon Sommer
MUAS
1. Development of control systems
Computer
Bus
MCs
Today
Central-Computer
Process I/O
Yesterday
Field
Substitute many cables with only one (or two) wires !
Transport Information in a serial way = serial bus
Process I/O
Seite 3
Prof. Dr. Egon Sommer
MUAS
1. Definition of Fieldbus
A Fieldbusis a serial bus that is optimized for
real-time data transfer between field devices*
serial bus: information is time multiplexed
real-time: cycle times from 100us to about 50ms
data transfer: packets from 1 to 250 Byte
*field device: sensors, actors, microcomputers
Prof. Dr. Egon Sommer
MUAS
Market share Europe (2001)
53,6
10,38,4
8,1
6,1
3,8
3,5
2,5
5,8
Profibus
FF
Interbus
Modbus
ASI
Devicenet
CAN
Ethernet
others
Seite 4
Prof. Dr. Egon Sommer
MUAS
-> 2. Basics
1. What is a fieldbus ?
2. Basics of Fieldbuses
3. CAN Bus
4. Application in Cars
5. EtherCat
Prof. Dr. Egon Sommer
MUAS
Requirements for Fieldbuses
length 100m to few km -> long distance
short latency -> real-time
Data rates from 0,1 to 100 MBit/s
Low error rates (10 –9) -> low disturbance
Low-priced connecting components
Easy adaptation to topology of plant
Seite 5
Prof. Dr. Egon Sommer
MUAS
serial buses
with media wireless
radio
infrared
power line
twisted pair
coax cable
fiber optic
Media for Serial BusesProf. Dr. Egon Sommer
MUAS
Electro Magnetic Interference
Twisted pair and differential evaluation of the signal is insensitive to electromagnetic interference (RS485)
If EMI hits the bus, both bus lines are affected in the same way, which leaves the differential signal unaffected
BusBUS_L
BUS_H
EMI
Node CNode A Node BV
t
U diff
BUS_H
BUS_L
Shielding the bus presents further improvement
Seite 6
Prof. Dr. Egon Sommer
MUAS
Classification using Media Access
serial buses
time multiplex frequency multiplex
several membersper channel
one memberper channel
asynchronoustransmission
synchronoustransmissionwith centralController
controlledaccess
randomaccess
central allocation decentral allocation carrier sensewith collision-detection
carrier sensewith collision-avoidance
Prof. Dr. Egon Sommer
MUAS
Media access (MAC) - Methods
How can several devices share a common medium ?
Only one station is allowed to transmit at a time !
Master/Slave
Token Passing
Carrier Sense Multiple Access / Collision Detection
Time Distributed Multiple Access
Seite 7
Prof. Dr. Egon Sommer
MUAS
-> 3. CAN Bus
1. What is a fieldbus ?
2. Basics of Fieldbuses
3. CAN Bus
4. Application in Cars
5. Example EtherCat
Prof. Dr. Egon Sommer
MUAS
Media access (MAC) und Addressing
CAN Bus
Access
Master/Slave
Token-passing
CSMA/CA = collision avoidance
TDMA
Address
Destination Address
Source Address
Seite 8
Prof. Dr. Egon Sommer
MUAS
CAN-BUS: Addressing
Source Addressing
ID = Identifier = Message Number Station Number
ID (11 bit) Information (64bit) broadcast broadcast
Prof. Dr. Egon Sommer
MUAS
CAN-BUS: Media Access (Arbitration)
• bitwise, lowest message-ID wins
CSMA/CA = collision avoidance
Bus
C
B
A
Sampling
time
• zero is dominant
! Identifiers must be unique !
Seite 9
Prof. Dr. Egon Sommer
MUAS
CAN Baud Rate vs. Bus Length
max 1Mbit/s for 40m length
max 1000m length with 50 kBit/s
Figure valid for
wire
40 100 1000 10,000
CAN Bus length [m]
0 10 200
1000
500
10
5
Bit Rate
[kbps]20
50
200
100
Each Bit must be stable at all stations before sampling !
=> Speed is slow for big distance
Prof. Dr. Egon Sommer
MUAS
Cables (equivalent circuit diagram)
∆R ∆L
∆G ∆C
∆∆∆∆R = resistance ΩΩΩΩ/m
∆∆∆∆C = capacity pF/m
∆∆∆∆L = inductance nH/m
∆∆∆∆G = conductance between wires mS/m
ZR j L
G j C
L
C=
+
+≈
∆ ∆
∆ ∆
∆
∆
ω
ω
with ∆∆∆∆R, ∆∆∆∆G = 0;
vL C r
=∗
≈1 1
∆ ∆ ε
( )[ ]T C l R R l Ri l= ∗ ∗ + ∗∆ ∆ ||
Ri resistance of source (transmitter)
Rl resistance of load (receiver)
Characteristic impedance Velocity of propagation
Time constant
! Cable constants ∆∆∆∆R ,∆∆∆∆C and length limit speed of CAN !
Seite 10
Prof. Dr. Egon Sommer
MUAS
CAN data transfer
Receiving
Device
CAN Data Link
LayerID + DataCAN Data Link
LayerID + data...
Transmitting
Device
CAN Physical
Layer
CAN Physical
LayerCAN_L
CAN_Hrecessive recessive
dominant
Application
LayerApplication
LayerData Objects
Without a higher layer protocol, CAN only provides a reliable way to share “short” data (8 Byte) with all connected nodes
Prof. Dr. Egon Sommer
MUAS
CAN Protocol format
Version 2.0A 11Bit ID - Version 2.0B 29 Bit ID
Seite 11
Prof. Dr. Egon Sommer
MUAS
Basic CAN Implementation
Only basic functions regarding the filtering and managing of CANmessages are implemented in hardware which can result in a high CPU load
Should only be used in CANs with very low baud rates and/or very few messages
Host
CPU
CPU load
low high
RxTx
Status/Control
Registers
Receive
Buffer(s)
CAN
Protocol
Controller
AcceptanceFiltering
Bus Inte
rfaceCAN
Bus HostInter-
face
Transmit
Buffer(s)
Prof. Dr. Egon Sommer
MUAS
Full CAN Implementation
Host CPU
CPU load
low high
Status/ControlRegisters
MessageObject 1
CAN
Protocol
Controller
AcceptanceFiltering
HostInter-
face
Message
Object 2
MessageObject n
...
ReceiveBuffer(s)
CAN
Bus
Bus Inte
rface
Extensive filtering possibilities, more time before CPU needs toreact: leads to lower CPU load
Message Objects store all message information (e.g. identifier /data bytes)
Seite 12
Prof. Dr. Egon Sommer
MUAS
CAN Applications
CAN in industrial automation
Excellent way of connecting all kinds of automation equipment (control units, sensors and actuators)
Used for initialization, program and parameter up-/download, exchange of rated values / actual values, diagnosis etc.
Machine control (printing machines, paper- and textile machines etc.): Connection of the different intelligent subsystems
CAN in medical equipmentComputer tomographs, X-ray machines, dentist & wheel chairs
CAN in building automationHeating, air conditioning, lighting, surveillance etc.
Elevator and escalator control
Prof. Dr. Egon Sommer
MUAS
-> 4. Application in Cars
1. What is a fieldbus ?
2. Basics of fieldbuses
3. CAN Bus
4. Application in Cars
5. EtherCat
Seite 13
Prof. Dr. Egon Sommer
MUAS
Example BMW Series 7
4 different buses with about 70 microcomputers !
Prof. Dr. Egon Sommer
MUAS
Features BMW
Rear Mirrors
Steering Wheel
safety system with 10 airbags
DSC
Seite 14
Prof. Dr. Egon Sommer
MUAS
CAN Buses in the VW Phaeton
CAN 1 - Drive System
500 kBit/s
CAN 2 - Comfort System
100 kBit/s
CAN 3 - Infotainment
100 kBit/s
Prof. Dr. Egon Sommer
MUAS
Can-Bus Drive
Seite 15
Prof. Dr. Egon Sommer
MUAS
Can-Bus ComfortProf. Dr. Egon Sommer
MUAS
Can-Bus Infotainment
Can-Bus Comfort
Seite 16
Prof. Dr. Egon Sommer
MUAS
Can-Bus - Total network
Can-Bus Comfort
3 buses with about 45 microcomputers !
Prof. Dr. Egon Sommer
MUAS
-> 5.EtherCat
1. What is a fieldbus ?
2. Basics of fieldbuses
3. CAN Bus
4. Application in Cars
5. EtherCat
Seite 17
Prof. Dr. Egon Sommer
MUAS
What is Ethercat?
Master/Slave network with real-time features
Ethernet physical layer
Ethernet-(or UDP-)frame with own protocol
Standard network adapter for master – slaves need special hardware
Virtual shared memory
Distributed clocks with precise synchronization
Prof. Dr. Egon Sommer
MUAS
Topology: flexible tree structures
network topology almost
arbitrary
minimal cable length
cost-effective and flexible
extendable anywhere
Seite 18
Prof. Dr. Egon Sommer
MUAS
Protocol supports topology recognition
Simplified setup
User guidance at errors
topology recognition is pre-requisite for propagation delay measurement
K1 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 K2 18 19 20 21 22
K3 23 24 25 26 27 28 29 30 31 32 33 K4 34 35 36 37 38
39
40K5 41 42 43
K6 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
59 60
61
62 63 64 65 66
coupler detects and
reports branch
Prof. Dr. Egon Sommer
MUAS
EtherCAT Distributed Clocks
EtherCAT Clock Master generates system time
Time value is distributed by broadcast mechanism
Local time is latched at reception of system time
Slave clocks are adjusted accordingly Synchronisation in the nanosecond range!
M S
S
S S S S S
S
∆t
Seite 19
Prof. Dr. Egon Sommer
MUAS
Frame Format
Standard ISO/IEC 8802.3 Frame Format
Ether-Type: 88A4, publicly assigned by IEEE
EtherCAT/UDP: with Routing and for Socket Interface Implementation
UDP Port: 34980 = 0x88A4, registered with IANA
DA SA TypePreFrame HDR FCS
Ethernet Header ECAT Enet
(6) (6) (2)(8) (2) (4)
HDR
IP
(20)
HDR
UDP
(8)
EtherCAT HDR Data
EtherCAT HDR Data
EtherCAT Telegram EtherCAT Telegram
(10) (34….1488) (10) (34….1444)(2) (2)
CT
R
CT
R
DA SA TypePreFrame HDR FCS
Ethernet Header ECAT Enet
(6) (6) (2)(8) (2) (4)
EtherCAT HDR Data
EtherCAT HDR Data
EtherCAT Telegram EtherCAT Telegram
(10) (34….1488) (10) (34….1444)(2) (2)
CT
R
CT
R
Prof. Dr. Egon Sommer
MUAS
Pass-through telegram access saves time
Data is modified and/or added whiletelegram passes through
vomMaster
fromMasterto Master
Seite 20
Prof. Dr. Egon Sommer
MUAS
EtherCAT: random Address-Mapping via FMMU
FMMU: Fieldbus Memory Management Unit
• Process data of Ethernet Terminals can be assigned to Sub-telegrams randomly
• Data of Sub/telegrams can be assigned to logical process image randomly
logic
al pro
cess im
age:
up t
o
4 G
Byte
0
23
2Telegram structure
Ethernet HDR HDR 1 Data 1 HDR 2 Data 2 HDR n Data n CRC
SubTelegram 1
Sub-Telegram 2
Sub-Telegram n
Prof. Dr. Egon Sommer
MUAS
EtherCat-Highlights
Network process image: 4 Gigabyte
Node process image: 2 Bit to 64 Kbytes
Address assignment: freely configurable
Address selection for nodes: automatically via software
Optimized protocol directly in Ethernet frame
Protocol implemented completely in hardware
For routing and socket interface: UDP datagram
Telegram data exchange during pass-through at full speed
Distributed Clock for precise synchronization
Time Stamp Data Types for resolution in nanoseconds
0
23
2
Seite 21
Prof. Dr. Egon Sommer
MUAS
Prof. Dr. Egon Sommer
MUAS
The End
Thank you for your attention !
Muchas gracias !
Questions ?
Preguntas ?