3.4 MVB (IEC 61375): a fieldbus case study

3.4 MVB (IEC 61375): a fieldbus case study
Industrial Automation Automation Industrielle Industrielle Automation 3.4 MVB (IEC 61375): a fieldbus case study Prof. Dr. H. Kirrmann ABB Research Center, Baden, Switzerland

Outline 1. Applications in rail vehicles 2. Physical layer 1. Electrical RS 485 2. Middle-Distance 3. Fibre Optics 3. Device Classes 4. Frames and Telegrams 5. Medium Allocation 6. Clock Synchronization 7. Fault-tolerance concept 8. Integrity Concept 9. Summary

Summary MVB is a field bus for time-critical, cyclical data transmission operating on the principle of source-addressed broadcast on different media, twisted wire pair and optical fibers. MVB is an IEC standard since (IEC 61375) for use in railways as a vehicle bus and as a train bus for closed train sets by the IEC Technical Committee 9. MVB is also an IEEE standard (IEEE 1473-T). MVB is also used outside of railways in applications such as industrial automation, printing, metals and minerals, power plants and electrical substations.

Multifunction Vehicle Bus in Locomotives
standard communication interface for all kind of on-board equipment radio power line cockpit Train Bus diagnosis Vehicle Bus brakes power electronics motor control track signals data rate 1'500'000 bits/second delay 0,001 second medium twisted wire pair, optical fibres number of stations up to 255 programmable stations up to 4095 simple sensors/actuators

Multifunction Vehicle Bus in Coaches
passenger doors information light Train Bus Vehicle Bus air conditioning power seat reservation brakes covered distance: > 50 m for a 26 m long vehicle < 200 m for a train set diagnostics and passenger information require relatively long, but infrequent messages

shielded, twisted wires with transformer coupling (200 m) • ESD
Physical Media • OGF optical fibres (2000 m) • EMD shielded, twisted wires with transformer coupling (200 m) • ESD wires or backplane with or without galvanic isolation (20 m) Media are directly connected by repeaters (signal regenerators) All media operate at the same speed of 1,5 Mbit/s. devices star coupler optical links optical links rack rack twisted wire segment sensors

Application in train sets
MVB can span several vehicles in a multiple unit train configuration: Train Bus repeater node MVB devices with short distance bus devices The number of devices under this configuration amounts to 4095. MVB can serve as a train bus in trains with fixed configuration, up to a distance of: > 200 m (EMD medium or ESD with galvanic isolation) or > 2000 m (OGF medium).

Topography Bus Administrator Node Train Bus EMD Segment Device Device Device Device Terminator Repeater ESD Segment section Repeater Device Device Device OGL link Repeater ESD Segment Device Device Device Device all MVB media operate at same speed, segments are connected by repeaters.

Outline 1. Applications in vehicles 2. Physical layer 1. ESD (Electrical, RS 485) 2. EMD (Transformer-coupled) 3. OGF (Optical Glass Fibres) 3. Device Classes 4. Frames and Telegrams 5. Medium Allocation 6. Clock Synchronization 7. Fault-tolerance concept 8. Integrity Concept 9. Summary

ESD (Electrical Short Distance) RS485
Interconnects devices over short distances ( 20m) without galvanic separation Based on proven RS-485 technology (Profibus) Main application: connect devices within the same cabinet. device 1 device 2.. n-1 device N terminator/ TxS RxS TxS RxS TxS RxS terminator/ • • • biasing biasing + 5 V + 5 V Ru Ru (390) (390) Data_N Rm Rm (150 ) (150 ) Rd Data_P Rd (390 ) (390 ) equipotential line Bus_GND GND segment length

ESD Device with Galvanic Isolation

ESD Connector for Double-Line Attachment
A.Bus_GND B.Bus_GND A.Data_P A.Data_N B.Data_P B.Data_N B.Bus_5V A.Bus_5V reserved (optional TxE) 1 2 3 4 5 5 4 3 2 1 male female 6 7 8 9 9 8 7 6 Line_A Line_B Line_B Line_A Line_A Line_A cable cable Line_B Line_B 10

EMD (Electrical Medium Distance) - Single Line Attachment
• Connects up to 32 devices over distances of 200 m. • Transformer coupling to provide a low cost, high immunity galvanic isolation. • Standard 120 Ohm cable, IEC line transceivers can be used. • 2 x 9-pin Sub-D connector • Main application: street-car and mass transit

EMD Device with Double Line Attachment
Bus_Controller transceiver A transceiver B A.Data_P A.Data_N B.Data_P B.Data_N 1 A1 B1 B2 A2 Connector_1 Connector_2 1 1 A1. Data_P B1. Data_P B2. Data_N A1. Data_N A1. Data_N B1. Data_N B2. Data_P A1. Data_P Line_A Line_A Line_B Line_B Carrying both redundant lines in the same cable eases installation it does not cause unconsidered common mode failures in the locomotive environment (most probable faults are driver damage and bad contact)

EMD Connectors for Double-Line Attachment
terminator connector 5 9 4 8 3 7 2 6 1

EMD Shield Grounding Concept
Shields are connected directly to the device case Device cases should be connected to ground whenever feasible

OGF (Optical Glass Fibre)
Covers up to 2000 m Proven 240µm silica clad fibre Main application: locomotive and critical EMC environment

OGF to ESD adapter Double-line ESD devices can be connected to fibre-optical links by adapters

Repeater: the Key Element
A repeater is used at a transition from one medium to another. (redundant) bus bus administrator slave slave slave slave repeater administrator encoder decoder ESD segment EMD segment (RS 485) decoder encoder (transformer-coupled) The repeater: • decodes and reshapes the signal (knowing its shape) • recognizes the transmission direction and forward the frame • detects and propagates collisions

Repeater internals duplicated segment Line_A Line_B repeater decoder encoder decoder Line_A direction (single-thread recogniser optical link) decoder encoder decoder Line_B (unused for single- thread) recognize the transmission direction and forward the frame within 3 µs (~500m cable back and forth). decode and reshape the signal (using a priori knowledge about its shape and encoding) jabber-halt circuit to isolate faulty segments with continuous sender. detect and propagate collisions (which also occur when senders answer on both sides with no overlap) increase the inter-frame spacing to avoid overlap of master and slave frame (race condition) can be used with all three media (OGF, EMD, ESD) appends the end delimiter in the direction fibre to transformer, remove it the opposite way suppress overshoot when the transformer side is not terminated handles redundancy (transition between single-thread and double-thread) – option.

Outline 1. Applications in vehicles 2. Physical layer 1. Electrical RS 485 2. Middle-Distance 3. Fibre Optics 3. Device Classes 4. Frames and Telegrams 5. Medium Allocation 6. Clock Synchronization 7. Fault-tolerance concept 8. Integrity Concept 9. Summary

They do not require a micro-controller.
Class 1 Device used for MVB A B board bus bus controller analog or binary MVB RS 485 address input/ redundant drivers/ output bus pairs (ESD) receivers register clock device status (monomaster) Class 1 or field devices are simple connections to sensors or actuators. They do not require a micro-controller. They do not participate in message data communication. The Bus Controller manages both the input/output and the bus.

Class 2 and higher devices have a processor and may exchange messages
Class 2-3 Device A B used for MVB private RAM application processor traffic store EPROM MVB redundant bus bus pairs (ESD) controller shared RS 485 clock local RAM drivers/ receivers local device input/ status output Class 2 and higher devices have a processor and may exchange messages Class 2 devices are configurable I/O devices (but not programmable) The bus controller communicates with the application processor through a shared memory (traffic store), which holds typically 256 ports.

Class 4-5 Device Class 4 devices present the functionality of a Programming and Test station Class 4 devices are capable of becoming Bus Administrators. To this effect, they hold additional hardware to read the device status of the other devices and to supervise the configuration. They also have a large number of ports (4096), so they can supervise the process data transmission of any other device. Class 5 devices are gateways with several link layers (one or more MVB, WTB). The device classes are distinguished by their hardware structure.

MVBC - bus controller ASIC
duplicated 12 bit device address electrical or optical CPU parallel bus to traffic store transmitters A Manchester 16x16 Clock, Main Tx buffer and CRC Timers & Control Sink Time A19..1 address encoder Unit Supervision B JTAG interface D15..0 data A DUAL 16x16 Manchester Rx buffer Class 1 Traffic Store logic Control and CRC control & Arbiter decoders B duplicated electrical or optical receivers • Automatic frame generation and analysis • Bus administrator functions • Adjustable reply time-out • Bookkeeping of communication errors • Up to 4096 ports for process data • Hardware queuing for message data • 16KByte.. 1MByte traffic store • Supports 8 and 16-bit processors • Freshness supervision for process data • Supports big and little endians • In Class 1 mode: up to 16 ports • 24 MHz clock rate • Bit-wise forcing • HCMOS 0.8 µm technology • Time and synchronization port • 100 pin QFP

Bus Interface The interface between the bus and the application is a shared memory, the Traffic Memory, where Process Data are directly accessible to the application. Application Traffic Store processor Logical Ports process data (256 typical) base for Process data 6 bus management ports messages packets 8 physical and ports bus supervision 2 message ports bus controller MVB

The Manchester-coded frame is preceded by a Start Delimiter containing
Manchester Encoding data 1 2 3 4 5 6 7 8 clock frame signal 9-bit Start Delimiter with non-Manchester sequence frame data 8-bit check end sequence delimiter The Manchester-coded frame is preceded by a Start Delimiter containing non-Manchester signals to provide transparent synchronization.

Different delimiters identify master and slave frames:
Frame Delimiters Different delimiters identify master and slave frames: Master Frame Delimiter 1 2 3 4 5 6 7 8 start bit active state idle state Slave Frame Delimiter 1 2 3 4 5 6 7 8 start bit active state idle state This prevents mistaking the next master frame when a slave frame is lost.

MVB distinguishes two kinds of frames:
Frames Formats MVB distinguishes two kinds of frames: master frames issued by the master 9 bits 4 12 8 MSD = Master Start Delimiter (9 bits) (33 bits, 22 us) CS = Check Sequence (8 bits) MSD F address CS F = F_code (4 bits) slave frames sent in response to master frames 9 16 bits 8 (33 bits, 22 us) SSD data CS SSD = Slave Start Delimiter (9 bits) 9 32 bits 8 (49 bits, 32.7 us) SSD data CS 9 64 bits 8 (81 bits, 54 us) SSD data CS 9 64 bits 8 64 bits 8 (153 bits, 102 us) SSD data CS data CS 9 64 bits 8 64 bits 8 64 bits 8 64 bits 8 (297 bits , 198 us) SSD data CS data CS data CS data CS useful (total) size in bits

propagation delay (5 µs/km)
Media Distance Limits The distance is limited by the maximum allowed reply delay of 42,7 µs between a master frame and a slave frame. repeater repeater master remotest data source cable delay for 2000m: 10 µs repeater delay: 2 x 5 µs total: ( ) x 2 = 40 µs. repeater delay master frame propagation delay (5 µs/km) max repeater delay t_ms t_source t_ms < 42,7µs slave frame The reply delay time-out can be repeater delay raised up to 83,4 µs for longer t_s distances (with reduced troughput). t_sm next master frame time distance

Telegrams are distinguished by the F_code in the Master Frame
Telegram formats Process Data Master Frame (Request) Slave Frame (Response) F = port dataset 0..7 address 4 bits 12 bits time 16, 32, 64, 128 or 256 bits of Process Data Message Data 256 bits of Message Data Master Frame F = source destination source prot size FN FF ON OF MTC transport data 12 device device ocol device 4 bits 12 bits time decoded final node by final function hardware message origin node tranport Supervisory Data origin function control Master Frame Slave Frame F = port 8-15 address 4 bits 12 bits 16 bits time Telegrams are distinguished by the F_code in the Master Frame

Principle of Source-addressed broadcast
Phase1: The bus master broadcasts the identifier of a variable to be transmitted: subscribed subscribed device device subscribed devices bus master devices sink source sink sink (slaves) bus variable identifier Phase 2: The device which sources that variable responds with a slave frame containing the value, all devices subscribed as sink receive that frame. subscribed subscribed device device subscribed devices bus devices master sink source sink sink (slaves) bus variable value

Decoupling the bus and application processes
cyclic cyclic cyclic cyclic algorithms algorithms algorithms algorithms cyclic application application application application poll 1 2 3 4 bus source master port Ports Ports Ports Ports Poll Traffic List Stores sink sink port port bus bus bus bus bus controller controller controller controller controller bus port address port data The bus traffic and the application cycles are not synchronised. The bus master sends the variable identifiers according to their individual period. Bus and applications interface through a shared memory, the traffic store*. *Verkehrsspeicher

and asynchronous access by both the bus and the application.
Traffic Memory Bus and application are (de)coupled by a shared memory, the Traffic Memory, which is not a simple dualport RAM, but a structure that guarantees exclusive and asynchronous access by both the bus and the application. Application Processor Associative Traffic Memory memory Process Data Base two pages ensure that read and write can occur at the same time Bus Controller bus

Restriction in simultaneous access
starts ends time writer reader 1 error ! (slow) reader 2 page0 traffic store page1 page 1 becomes valid page 0 becomes valid • there may be no semaphores to guard access to a traffic store (real-time) • there may be only one writer for a port, but several readers • a reader must read the whole port before the writer overwrites it again • therefore, the processor must read ports with interrupt off.

Operation of the traffic memory
In content-addressed ("source-addressed") communication, messages are broadcast, the receiver select the data based on a look-up table of relevant messages. For this, an associative memory is required. Since address size is small (12 bits), the decoder is implemented by a memory block: port index table storage processor page 0 page 1 1 data(4) 2 data(4) data(5) 4 1 data(5) data (4094) 5 2 data (4094) data(4092) 6 data(4092) 12-bit Address 7 voids voids 4091 4092 4 4093 4094 3 4095 bus

F_code Summary Master Frame Slave Frame F_code address request source
size response destination 16 1 single 32 all 2 logical Process_Data device 64 Process_Data devices 3 subscribed 128 (application subscribed 4 as 256 -dependent) as 5 reserved source - sink 6 reserved - 7 reserved - 8 all devices Master_Transfer Master 16 Master_Transfer Master 9 device General_Event >= 1devices 16 Event_Identifier Master 10 device reserved - - 11 device reserved - - 12 device Message_Data single device 256 Message_Data selected device 13 group Group_Event >= 1devices 16 Event_Identifier Master 14 device Single_Event single device 16 Event_Identifier Master 15 device Device_Status single device 16 Device_Status Master or monitor

The Master performs four tasks:
Master Operation The Master performs four tasks: 1) Periodic Polling of the port addresses according to its Poll List 2) Attend Aperiodic Event Requests 3) Scan Devices to supervise configuration 4) Pass Mastership orderly (last period in turn) basic period basic period sporadic phase sporadic phase periodic super- event periodic super- event visory phase visory phase phase phase phase phase 1 2 3 4 5 6 7 SD ? ? ? ? 1 2 8 9 SD ? ? ? ? EV 1 2 time guard phase guard phase The Administrator is loaded with a configuration file before becoming Master

Response at human speed: > 0.5 s Response in 1..200 ms
Bus Traffic State Variable Messages State of the Plant Events of the Plant Response at human speed: > 0.5 s Response in ms ... commands, position, speed • Diagnostics, event recorder • Initialisation, calibration Periodic Transmission On-Demand Transmission Spurious data losses will be compensated at the next cycle Flow control & error recovery protocol for catching all events Basic Period Basic Period Periodic Data event time Sporadic Data

A basic period is divided into a periodic and a sporadic phase.
Medium Access basic period basic period periodic sporadic periodic sporadic phase phase phase phase 1 2 3 4 5 6 ? ? ? ? 1 2 7 8 9 10 ? ! ? ? 1 2 3 time events ? events ? guard event guard time data time individual period A basic period is divided into a periodic and a sporadic phase. During the periodic phase, the master polls the periodic data in sequence. Periodic data are polled at their individual period (a multiple of the basic period). Between periodic phases, the Master continuously polls the devices for events. Since more than one device can respond to an event poll, a resolution procedure selects exactly one event.

Bus Administrator Configuration
period 0 period 1 period 2 period 3 period 4 1 ms 1 ms 1 ms 1 ms 4 ms Tspo Tspo Tspo Tspo 1 2.0 4.0 1 2.1 4.1 1 2.0 8.2 1 2.1 1 2.0 4.0 time 2 ms cycle 2 begin of turn 2 ms The Poll List is built knowing: • the list of the port addresses, size and individual period • the reply delay of the bus • the list of known devices (for the device scan • the list of the bus administrators (for mastership transfer)

Poll List Configuration
The algorithm which builds the poll table spreads the cycles evenly over the macroperiod

Event Resolution (1) To scan events, the Master issues a General Event Poll (Start Poll) frame. If no device responds, the Master keeps on sending Event Polls until a device responds or until the guard time before the next periodic phase begins. A device with a pending event returns an Event Identifier Response. If only one device responds, the Master reads the Event Identifier (no collision). The Master returns that frame as an Event Read frame to read the event data

start poll and parameter setup
Event Resolution (2) If several devices respond to an event poll, the Master detects the collision and starts event resolution arbitration round start poll and parameter setup individual poll event reading group poll Fcode9 Fcode13 Fcode13 Fcode13 Fcode14 Fcode12 Fcode12 any? C xxx1 C xx11 N x101 C 0101 A A D telegram time collision silence collision valid event frame The devices are divided into groups on the base of their physical addresses. The Master first asks the devices with an odd address if they request an event. • If only one response • If there is no response, • If collision keeps on, the comes, the master returns the master asks devices master considers the 2nd that frame to poll the event. with an even address. bit of the device address.

Event Resolution (3) Example with a 3-bit device address: 001 and 101 compete width of start arbitration group general poll address silence xxx n = 0 collision no event xx0 xx1 n = 1 collision silence x00 silence x10 x01 silence x11 n = 2 collision collision 000 100 010 110 001 101 011 111 individual poll event read EA EA EA EA EA EA EA EA even devices odd devices time

Time Distribution At fixed intervals, the Master broadcasts the exact time as a periodic variable. When receiving this variable, the bus controllers generate a pulse which can resynchronize a slave clock or generate an interrupt request. Application processor 1 Application processor 2 Application processor 3 Bus master Int Req Int Req Int Req Periodic list Slave clock Slave clock Slave clock Ports Ports Ports Master clock Bus controller Bus controller Bus controller Bus controller MVB Sync port address Sync port variable

Slave Clock Synchronization
Master clock Slave clock Slave clocks Slave clocks MVB 1 MVB 2 Bus administrator 1 Bus administrator 2 Slave devices Synchronizer The clock does not need to be generated by the Master. The clock can synchronize sampling within 100 µs across several bus segments.

Fault-tolerance Concept
Transmission Integrity MVB rather stops than provides false data. The probability for an undetected transmission error (residual error rate) is low enough to transmit most safety-critical data. This is achieved through an extensive error detection scheme Transmission Availability MVB continues operation is spite of any single device error. In particular, configurations without single point of failure are possible. This is achieved through a complete duplication of the physical layer. Graceful Degradation The failure of a device affects only that device, but not devices which do not depend on its data (retro-action free). Configurability Complete replication of the physical layer is not mandatory. When requirements are slackened, single-thread connections may be used and mixed with dual-thread ones.

Basic Medium Redundancy
The bus is duplicated for availability (not for integrity) address data control parallel bus logic send register receive register bus controller encoder selector signal quality report decoder decoder A B A B transmitters receivers bus line B bus line A A frame is transmitted over both channels simultaneously. The receiver receives from one channel and monitors the other. Switchover is controlled by signal quality and frame overlap. One frame may go lost during switchover

The physical medium may be fully duplicated to increase availability.
Medium Redundancy The physical medium may be fully duplicated to increase availability. Principle: send on both, receive on one, supervise the other B A A B device device repeater repeater optical link A optical link B device device repeater repeater electrical segment X electrical segment Y Duplicated and non-duplicated segments may be connected

Double-Line Fibre Layout
star coupler A opto links A device rack copper bus A A A B B copper bus B Bus Administrator redundant opto links B Bus Administrator star coupler B The failure of one device cannot prevent other devices from communicating. Optical Fibres do not retro-act.

Total or partial redundancy ?
not redundant APL APL APL APL Traffic Store Traffic Store Repeater Traffic Store Traffic Store Phy Phy Phy Phy Phy Phy Phy Phy Phy totally redundant

A centralized bus master is a single point of failure.
Master Redundancy A centralized bus master is a single point of failure. To increase availability, the task of the bus master may be assumed by one of several Bus Administrators The current master is selected by token passing: token passing current bus master bus bus bus administrator administrator administrator 1 2 3 Bus slave slave slave slave slave slave slave device device device device device device device If a bus administrator detects no activity, it enters an arbitration procedure. If it wins, it takes over the master's role and creates a token. To check the good function of all administrators, the current master offers mastership to the next administrator in the list every 4 seconds.

Mastership transfer state machines
INIT get next administrator in the list token passing STANDBY_MASTER (entering this state resets T_standby) yes master list or basic period exhausted ? no T_standby valid Master_Frame inquire status no no mastership offered to me ? status request to me ? FIND_NEXT status (AX, MAS, ACT) status response T_find_next am I configured (ACT = 1) ? no valid next master ? yes mastership reject no yes mastership accept mastership offer INTERIM_MASTER REGULAR_MASTER master collision or resign mastership response T_interim end of turn remote accept ? report error no yes

Transmission Integrity (1)
Manchester II encoding Double signal inversion necessary to cause an undetected error, memoryless code Clock Data 1 1 1 1 Frame violations Line Signal Start Delimiter Manchester II symbols 2) Signal quality supervision Adding to the high signal-to-noise ratio of the transmission, signal quality supervision rejects suspect frames. 125ns 125ns 125ns reference BT = bit time = 666 edge ns BT0.5 time BT1.0 BT1.5

3) A check octet according to TC57 class FT2 for each group of up to 64 bits, provides a Hamming Distance of 4 (8 if properties of Manchester coding are considered): -15 (Residual Error Rate < under standard disturbances) Master Frame size in bits 9 4 12 8 MD = Master frame Delimiter 16 data bits (33bits) = 22 us MSD F address CS CS = Check Sequence 8 bits useful (total) size in bits Slave Frame 9 16 8 16 data bits (33bits) = 22 us, poll = 67 us SSD 2 bytes CS SD = Slave frame Delimiter 9 32 8 32 (49) = 33 us, poll = 78 us SSD 4 bytes CS 9 64 8 64 (81) = 54 us, poll = 99 us 128 (153 bits) = 102 us, poll = 147 us 256 (297 bits) = 198 us, poll = 243 us (worst-case response = 43 us) SSD 8 bytes CS DATA 64 repeat 1, 2 or 4 x

4) Different delimiters for address and data against single frame loss: respond within respond within 1.3 µs < t < 4.0 µs 4 µs < t <1.3 ms ms sm MSD ADDRESS a CS SSD DATA (a) CS MSD ADDRESS b CS time t mm 1,3 ms 5) Response time supervision against double frame loss: > 22 µs > 22 µs MSD ADDRESS a CS SSD DATA (a) CS MSD ADDRESS b CS SSD DATA (b) CS time accept if 0.5µs < t_mm < 42.7 µs 6) Configuration check: size at source and sink ports must be same as frame size.

Safety Concept Data Integrity Very high data integrity, but nevertheless insufficient for safety applications (signalling) Increasing the Hamming Distance further is of no use since data falsification becomes more likely in a device than on the bus. Data Transfer • critical data transmitted periodically to guarantee timely delivery. • obsolete data are discarded by sink time supervision. • error in the poll scan list do not affect safety. Device Redundancy Redundant plant inputs A and B transmitted by two independent devices. Diverse A and B data received by two independent devices and compared. The output is disabled if A and B do not agree within a specified time. Availability Availability is increased by letting the receiving devices receive both A and B. The application is responsible to process the results and switchover to the healthy device in case of discrepancy.

redundant, integer output
Integer Set-up poll A B A B time individual period Bus Administrator redundant vehicle bus (for availability only) input output devices devices A B A B confinement application fail-safe responsibility comparator and enabling spreader device logic (application dependent) redundant input redundant, integer output

Integer and Available Set-up
poll A B A B time individual period redundant redundant bus bus administrator administrator redundant vehicle bus (for availability) input output devices devices A B A B A B A B comparator C C and enabling logic confinement A switchover logic or B spreader device comparator (application (application dependent) dependent) redundant input available and integer output

Summary Topography: bus (copper), active star (optical fibre) Medium: copper: twisted wire pair optical: fibres and active star coupler Covered distance: OGF: 2000 m, total 4096 devices EMD: 200 m copper with transformer-coupling ESD: 20 m copper (RS485) Communication chip dedicated IC available Processor participation none (class 1), class 2 uses minor processor capacity Interface area on board 20 cm2 (class 1), 50 cm2 (class 2) Additional logic RAM, EPROM , drivers. Medium redundancy: fully duplicated for availability Signalling: Manchester II + delimiters Gross data rate 1,5 Mb/s Response Time typical 10 µs (<43 µs) Address space 4096 physical devices, 4096 logical ports per bus Frame size (useful data) 16, 32, 64, 128, 256 bits Integrity CRC8 per 64 bits, HD = 8, protected against sync slip

Software: Link Layer Interface
Real-Time Protocols Link Layer Interface Upper Link Layer LP LM LS process message supervisory management station data data data Traffic Store slave master Lower Link Process Data polling Layer Message Data telegram arbitration Supervisory Data handling mastership transfer frame coding Physical Layer

Available Components Bus Controllers: BAP 15 (Texas Instruments, obsolete) MVBC01 (VLSI, in production, includes master logic MVBC02 (E2S, in production, includes transformer coupling) – exists as VHDL Repeaters: REGA (in production) MVBD (in production, includes transformer coupling) – exists as VHDL Medium Attachment Unit: OGF: fully operational and field tested (8 years experience) ESD: fully operational and field tested (with DC/DC/opto galvanic separation) EMD: lab tested, first vehicles equipped Stack: Link Layer stack for Intel 186, i196, i960, 166, 167, Motorola 68332, under DOS, Windows, VRTX,... Tools: Bus Administrator configurator Bus Monitor, Download, Upload, remote settings

Comparison MVB (IEC 61375) vs Fieldbus (IEC 61158-2) Frames
Preamble Start Delimiter PhSDU End Delimiter Spacing 1 1 1 1 1 N+ N- 1 N+ N- Data FCS 1 N+ N- N+ N- 1 1 v v v v 16 bits MVB frame Start Delimiter 8 bits End Delimiter N- N+ 1 N- N+ 1 1 1 Data FCS v v Master Frame N+ N- N+ N- Data FCS v v Slave Frame IEC frames have a lesser efficiency (-48%) then MVB frames To compensate it, a higher speed (2,5 Mbit/s) would be needed, which reduces the covered distance without repeaters fro copper wiring.

Throughput (raw data) and comparison with IEC field busses
transmission delay [ms] 0.9 0.8 IEC 1,0 Mbit/s 0.7 1,5 Mbit/s 0.6 0.5 0.4 0.3 IEC 2,5 Mbit/s 0.2 0.1 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 dataset size in bits

Operation: What would a faster bus bring ?
20 Mbit/s 24 Mbit/s - short 24 MBit/s - far 12 Mbit/s - short 10 Mbit/s 12 Mbit/s - far 1.5 Mbit/s - short 1.5 Mbit/s - far 1.0 Mbit/s 16 32 64 128 256 512 1024 2048 4096 frame size [bits] 0.2 Mbit/s A faster bus makes only sense with longer frames, i.e. coarser granularity of exchanged data. With a frame size of 256 bits, 1.5 Mbit/s is optimal.

3.4 MVB (IEC 61375): a fieldbus case study

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