Train Communication Network
IEC 61375 - 3
Multifunction Vehicle Bus
This is the vehicle bus standardized in IEC 61375
for interconnecting rail vehicles
Introduction
IEC Train Communication Network
Multifunction Vehicle Bus
1
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
2
1999 September, HK
IEC 61375 Clause 3
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
data rate
delay
medium
number of stations
status
power electronics
track signals
1'500'000 bits/second
0,001 second
twisted wire pair, optical fibres
up to 255 programmable stations
up to 4095 simple sensors/actuators
> 600 vehicles in service in 1998
IEC Train Communication Network
Multifunction Vehicle Bus
motor control
3
1999 September, HK
IEC 61375 Clause 3
Multifunction Vehicle Bus in Coaches
passenger
information
doors
light
Train Bus
Vehicle Bus
air conditioning
seat reservation
covered distance:
power
brakes
> 50 m for a 26 m long vehicle
< 200 m for a train set
diagnostics and passenger information require relatively long, but infrequent messages
IEC Train Communication Network
Multifunction Vehicle Bus
4
1999 September, HK
IEC 61375 Clause 3
MVB Physical Media
• OGF
• EMD
• ESD
optical fibres
shielded, twisted wires with transformer coupling
wires or backplane with or without galvanic isolation
(2000 m)
(200 m)
(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
sensors
twisted wire segment
IEC Train Communication Network
Multifunction Vehicle Bus
5
1999 September, HK
IEC 61375 Clause 3
MVB Covered Distance
The MVB can span several vehicles in a multiple unit train configuration:
Train Bus
node
repeater
MVB
devices
devices with short distance bus
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).
IEC Train Communication Network
Multifunction Vehicle Bus
6
1999 September, HK
IEC 61375 Clause 3
MVB Topography
Bus
Administrator
Node
EMD Segment
Device
Device
Device
Train Bus
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.
IEC Train Communication Network
Multifunction Vehicle Bus
7
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
8
1999 September, HK
IEC 61375 Clause 3
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
TxS RxS
terminator/
biasing
•••
device 2.. n-1
TxS RxS
terminator/
biasing
+5V
+5V
Ru
(390)
device N
TxS RxS
Ru
(390)
Data_N
Rm
(150 )
Rd
(390 )
GND
Rm
(150 )
Rd
(390 )
Data_P
Bus_GND
equipotential line
segment length
IEC Train Communication Network
Multifunction Vehicle Bus
9
1999 September, HK
IEC 61375 Clause 3
ESD Device with Galvanic Isolation
shield connected to
connector casing
optocouplers
1
galvanic
barrier
protection
circuit
p ro te ctive e a rth
+5V el
TxF
0V el
TxS
TxF'
fem ale
TxS '
male
R xS
R xS '
+5V
RS 485
transceiver
+ V cc
1
Data
GND
power
cable
shield connected to
connector casing
IEC Train Communication Network
Multifunction Vehicle Bus
device casing
connected to
supply ground
DC/DC
converter
10
1999 September, HK
IEC 61375 Clause 3
1
2
3
4
5
5
A.Bus_5V
B.Bus_5V
B.Data_N
B.Data_P
A.Data_N
A.Data_P
B.Bus_GND
A.Bus_GND
ESD Connector for Double-Line Attachment
4
reserved
(optional TxE)
3
2
1
male
female
8
9
8
7
6
Line_A
Line_B
cable
9
Line_B
7
Line_A
6
Line_A
Line_A
Line_B
Line_B
IEC Train Communication Network
Multifunction Vehicle Bus
10
11
1999 September, HK
cable
IEC 61375 Clause 3
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 1158-2 line transceivers can be used.
• 2 x 9-pin Sub-D connector
• Main application: street-car and mass transit
device
bus
controller
transceiver
transformer
shield
bus section 2
bus section 1
IEC Train Communication Network
Multifunction Vehicle Bus
12
1999 September, HK
IEC 61375 Clause 3
EMD Device with Double Line Attachment
device
Bus_Controller
transceiver A
transceiver B
A.Data_P
A.Data_N
B.Data_P
B.Data_N
1
Connector_1
A1
B1
B2
1
A1. Data_P
A1. Data_N
A2
Connector_2
1
B1. Data_P
B1. Data_N
B2. Data_N
B2. Data_P
A1. Data_N
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)
IEC Train Communication Network
Multifunction Vehicle Bus
13
1999 September, HK
IEC 61375 Clause 3
EMD Connectors for Double-Line Attachment
cable
Connector_1 (m ale)
Zt.A
Line_A
A.Term_P
A.Term_N
male
1 A1. Data_P
6
Line_A
2 A1. Data_N
7
terminator connector
3
8
4 B1. Data_P
9
5
Line_B
9
5 B1.Data_N
4
8
shields contacts case
3
Line_B
B.Term _N
B.Term _P
7
5 B1.Data_N
9
Line_B
2
6
4 B1. Data_P
8
1
3
7
2 A1. Data_N
6
Line_A
1 A1. Data_P
Zt.B
fem ale
Connector_1 (female)
IEC Train Communication Network
Multifunction Vehicle Bus
14
1999 September, HK
IEC 61375 Clause 3
EMD Shield Grounding Concept
device
device
device
inter-section
connectors
terminator
terminator
shield
possible shield
discontinuity
device ground
device ground
inter-device
impedance
inter-device
impedance
Shields are connected directly to the device case
Device cases should be connected to ground whenever feasible
IEC Train Communication Network
Multifunction Vehicle Bus
15
1999 September, HK
IEC 61375 Clause 3
OGF (Optical Glass Fibre)
Covers up to 2000 m
Proven 240µm silica clad fibre
Main application: locomotive and critical EMC environment
Star Coupler
opto-electrical
transceiver
wired-or electrical media
to other device
or star coupler
to other device
or star coupler
fibre pair
Rack
device
device
IEC Train Communication Network
Multifunction Vehicle Bus
device
device
16
1999 September, HK
ESD segment
device
device
IEC 61375 Clause 3
OGF to ESD adapter
MVBC
TxD
RxDA
3
A.Data_P
TxE
5
RxDB
3
1
1
A.Data_P
A.5V
B.5V
A.0V
B.0V
RS-485 transceiver
fibre-optical transceivers
to star coupler A
to star coupler B
from star coupler A
from star coupler B
Double-line ESD devices can be connected to fibre-optical links by adapters
IEC Train Communication Network
Multifunction Vehicle Bus
17
1999 September, HK
IEC 61375 Clause 3
MVB Repeater: the Key Element
A repeater is used at a transition from one medium to
another.
bus
administrator
slave
slave
repeater
encoder
decoder
(RS 485)
slave
decoder
encoder
ESD segment
slave
(redundant)
bus
administrator
EMD segment
(transformer-coupled)
The repeater:
• decodes and reshapes the signal (knowing its shape)
• recognizes the transmission direction and forward the frame
• detects and propagates collisions
IEC Train Communication Network
Multifunction Vehicle Bus
18
1999 September, HK
IEC 61375 Clause 3
duplicated segment
Line_A
Line_B
MVB Repeater
repeater
decoder
encoder
decoder
Line_A
(single-thread
optical link)
direction
recogniser
decoder
encoder
decoder
Line_B
(unused for singlethread)
recognize the transmission direction and forward the frame
decode and reshape the signal (using a priori knowledge about ist shape)
jabber-halt circuit to isolate faulty segments
detect and propagate collisions
increase the inter-frame spacing to avoid overlap
can be used with all three media
appends the end delimiter in the direction fibre to transformer, remove it the opposite way
handles redundancy (transition between single-thread and double-thread)
IEC 61375 Clause 3
19
IEC Train Communication Network
Multifunction Vehicle Bus
1999 September, HK
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
20
1999 September, HK
IEC 61375 Clause 3
MVB Class 1 Device
A B
board bus
bus
controller
MVB
redundant
bus pairs
(ESD)
RS 485
drivers/
receivers
analog
or
binary
input/
output
device
address
register
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.
IEC Train Communication Network
Multifunction Vehicle Bus
21
1999 September, HK
IEC 61375 Clause 3
MVB Class 2-3 Device
A B
private
RAM
application
processor
traffic store
EPROM
MVB
redundant
bus pairs
(ESD)
Bus
Controller
shared
local RAM
RS 485
drivers/
receivers
local
input/
output
device
status
• 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, the traffic store, which holds typically 256 ports.
IEC Train Communication Network
Multifunction Vehicle Bus
22
1999 September, HK
IEC 61375 Clause 3
MVB 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, 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.
IEC Train Communication Network
Multifunction Vehicle Bus
23
1999 September, HK
IEC 61375 Clause 3
MVBC - bus controller ASIC
duplicated
electrical or optical
transmitters
A
Manchester
and CRC
encoder
12 bit device address
16x16
Tx buffer
CPU parallel bus
to traffic store
Clock,
Main
Timers &
Control
Sink Time
Unit
Supervision
A19..1
address
D15..0
data
B
A
JTAG
interface
DUAL
Manchester
and CRC
decoders
16x16
Rx buffer
Class 1
logic
Traffic Store
Control
& Arbiter
control
B
duplicated electrical or
optical receivers
• Automatic frame generation and analysis
• Adjustable reply time-out
• Up to 4096 ports for process data
• 16KByte.. 1MByte traffic store
• Freshness supervision for process data
• In Class 1 mode: up to 16 ports
• Bit-wise forcing
• Time and synchronization port
IEC Train Communication Network
Multifunction Vehicle Bus
• Bus administrator functions
• Bookkeeping of communication errors
• Hardware queueing for message data
• Supports 8 and 16-bit processors
• Supports big and lirttle endians
• 24 MHz clock rate
• HCMOS 0.8 µm technology
• 100 pin QFP
24
1999 September, HK
IEC 61375 Clause 3
MVB 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
processor
Traffic Store
0..4095
Logical Ports
(256 typical)
for Process
data
process data
base
8 physical
ports
messages packets
and
bus supervision
6 bus
management
ports
bus
controller
2 message ports
MVB
IEC Train Communication Network
Multifunction Vehicle Bus
25
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
26
1999 September, HK
IEC 61375 Clause 3
MVB Manchester Encoding
data
110 100010 111110 1
clock
frame
signal
0 123 45 67 8
9-bit Start Delimiter
frame data
8-bit check
sequence
end
delimiter
The Manchester-coded frame is preceded by a Start Delimiter containing
non-Manchester signals to provide transparent synchronization.
IEC Train Communication Network
Multifunction Vehicle Bus
27
1999 September, HK
IEC 61375 Clause 3
MVB Frame Delimiters
Different delimiters identify master and slave frames:
Master Frame Delimiter
0
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
start bit
active state
idle state
Slave Frame Delimiter
0
start bit
active state
idle state
This prevents mistaking the next master frame when a slave frame is lost.
IEC Train Communication Network
Multifunction Vehicle Bus
28
1999 September, HK
IEC 61375 Clause 3
MVB Frames Formats
The MVB distinguishes two kinds of frames:
master frames issued by the master
9 bits 4
16
(33) MSD F
12
address
8
CS
MSD = Master Start Delimiter (9 bits)
CS = Check Sequence (8 bits)
F = F_code (4 bits)
slave frames sent in response to master frames
8
16 9 16 bits
SSD = Slave Start Delimiter (9
(33) SSD data CS
bits)
9
32 bits
8
32 SSD
data
CS
(49)
9
64 bits
8
64 SSD
data
CS
(81)
9
64 bits
8
64 bits
8
128 SSD
CS
CS
data
data
(153)
64 bits
8
64 bits
8 64 bits 8 64 bits 8
9
256 SSD
data
CS
data
CS data CS data CS
(297)
useful (total) size in bits
IEC Train Communication Network
Multifunction Vehicle Bus
29
1999 September, HK
IEC 61375 Clause 3
MVB 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
repeater
delay
propagation delay
(6 µs/km)
max
t_ms < 42,7µs
repeater
delay
t_source
t_ms
repeater
delay
t_s
t_sm
time
IEC Train Communication Network
Multifunction Vehicle Bus
The reply delay time-out can be
raised up to 83,4 µs for longer
distances
(with reduced troughput).
distance
30
1999 September, HK
IEC 61375 Clause 3
MVB Telegrams
Process Data
Master Frame (Request)
Slave Frame (Response)
port
address
4 bits 12 bits
F=
0..7
dataset
time
16, 32, 64, 128 or 256 bits of Process Data
Message Data
256 bits of Message Data
Master Frame
source
device
4 bits 12 bits
F=
12
destination
device
prot
ocol
decoded
by
hardware
Supervisory Data
Master Frame
port
F=
8-15 address
4 bits 12 bits
source size FN FF ON OF MTC
transport data
device
final node
final function
origin node
origin function
time
message
tranport
control
Slave Frame
16 bits
time
Telegrams are distinguished by the F_code in the Master Frame
IEC Train Communication Network
Multifunction Vehicle Bus
31
1999 September, HK
IEC 61375 Clause 3
Source-addressed broadcast
Phase1: The bus master broadcasts the identifier of a variable to be transmitted:
bus
master
subscribed
device
subscribed
device
sink
source
subscribed devices
sink
sink
devices
(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.
bus
master
subscribed
device
subscribed
device
sink
source
subscribed devices
sink
sink
devices
(slaves)
bus
variable value
IEC Train Communication Network
Multifunction Vehicle Bus
32
1999 September, HK
IEC 61375 Clause 3
Traffic Memory
The bus and the application are (de)coupled by a shared memory, the
Traffic Memory, where process variables are directly accessible to the application.
Application
Processor
Associative
memory
Traffic Memory
Process Data
Base
two pages ensure that read and
write can occur at the same time
Bus
Controller
bus
IEC Train Communication Network
Multifunction Vehicle Bus
33
1999 September, HK
IEC 61375 Clause 3
Restriction in simultaneous access
starts
t1
t2
time
ends
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.
IEC Train Communication Network
Multifunction Vehicle Bus
34
1999 September, HK
IEC 61375 Clause 3
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
processor
12-bit Address
0
1
2
4
5
0
0
0
1
2
6
7
voids
4091
4092
4093
4094
0
0
voids
0
4
0
3
4095
0
storage
page 0
page 1
data(4)
data(5)
data (4094)
data(4)
data(5)
data (4094)
data(4092)
0
data(4092)
0
bus
IEC Train Communication Network
Multifunction Vehicle Bus
35
1999 September, HK
IEC 61375 Clause 3
MVB F_code Summary
Master Frame
F_code address
0
1
2
3
4
5
6
7
logical
request
Process_Data
reserved
reserved
reserved
Slave Frame
source
size
single
device
subscribed
as
source
16
32
64
128
256
-
response
destination
Process_Data
(application
-dependent)
all
devices
subscribed
as
sink
8
all devices Master_Transfer
Master
16
Master_Transfer
Master
9
device
General_Event
>= 1devices
16
Event_Identifier
Master
10
11
12
device
device
device
reserved
reserved
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
IEC Train Communication Network
36
Multifunction Vehicle Bus
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
37
1999 September, HK
IEC 61375 Clause 3
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
sporadic phase
periodic
phase
1 2 3 4
supervisory
phase
5 6 7 SD
event
phase
? ? ? ?
basic period
sporadic phase
periodic
phase
1 2
8
supervisory
phase
9 SD
guard phase
event
phase
? ? ? ? EV
guard phase
1 2
time
The Administrator is loaded with a configuration file before becoming Master
IEC Train Communication Network
Multifunction Vehicle Bus
38
1999 September, HK
IEC 61375 Clause 3
Bus Traffic
State Variable
State of the Plant
Response in 1..200 ms
Messages
Events of the Plant
Response at human speed: > 0.5 s
... commands, position, speed
• Diagnostics, event recorder
• Initialisation, calibration
Periodic Transmission
On-Demand Transmission
Spurious data losses will be
compensated at the next cycle
Periodic Data
Flow control & error recovery
protocol for catching all events
Basic Period
Basic Period
event
time
Sporadic Data
IEC Train Communication Network
Multifunction Vehicle Bus
39
1999 September, HK
IEC 61375 Clause 3
MVB Medium Access
basic period
periodic
phase
1
2
3
4
5
basic period
sporadic
phase
6
? ?
? ?
periodic
phase
1
2
7
events ?
8
9
sporadic
phase
10
?
events ?
guard
time
!
? ?
1
2
3
time
event guard
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.
IEC Train Communication Network
Multifunction Vehicle Bus
40
1999 September, HK
IEC 61375 Clause 3
MVB Bus Administrator Configuration
period 0
period 1
1 ms
1 ms
Tspo
1 2.0
period 2
4.0
period 3
1 ms
4 ms
Tspo
1 2.1
4.1
period 4
1 ms
Tspo
1 2.0 8.2
Tspo
1 2.1
1 2.0 4.0
time
2 ms
begin of turn
cycle 2
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)
IEC Train Communication Network
Multifunction Vehicle Bus
41
1999 September, HK
IEC 61375 Clause 3
MVB Poll List Configuration
macroperiod
(8 T_bp shown, in reality 1024 T_bp)
2 BP datasets
4.2
4.0
4.2
4.0
2 BP datasets
2.1
2.0
2.1
2.0
2.1
2.0
2.1
2.0
2.1
2.0
2.1
1 BP datasets
1
1
1
1
1
1
1
1
1
1
1
p e rio d 1
p e rio d 2
p e rio d 3
p e rio d 4
p e rio d 5
p e rio d 6
p e rio d 7
0
1
8.1
p e rio d 0
4.0
p e rio d 7
8.1
b a sic p e ri o d
T_ sp o
>350µs
guard
The algorithm which builds the poll table spreads the cycles evenly over the macroperiod
IEC Train Communication Network
Multifunction Vehicle Bus
42
1999 September, HK
IEC 61375 Clause 3
MVB 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 Event Poll
(parameters and
setup)
MSD
9 EM ET
- CS
Event Identifier
Response
from slave
SSD
12
1234
Event Identifier
returned as master
frame
CS
MSD
12
Event Poll telegram
IEC Train Communication Network
Multifunction Vehicle Bus
1234
CS
Event data
SSD
xxxx
Event Read telegram
43
1999 September, HK
xxxx
CS
time
IEC 61375 Clause 3
MVB Event Resolution (2)
If several devices respond to an event poll, the Master detects the collision and
starts event resolution
start poll and
parameter
setup
any?
arbitration round
individual
poll
group poll
C
xxx1
C
xx11
N
C
x101
0101
A
event
reading
A
D
time
telegram
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
bit of the device address.
that frame to poll the event. with an even address.
IEC Train Communication Network
Multifunction Vehicle Bus
44
1999 September, HK
IEC 61375 Clause 3
MVB Event Resolution (3)
Example with a 3-bit device address: 001 and 101 compete
width of
group
address
start arbitration
general poll
silence
xxx
n=0
collision
no event
xx0
xx1
silence
x00
silence
x10
x01
n=1
collision
silence
x11
collision
n=2
collision
000
100
010
110
001
101
011
111
individual poll
EA
EA
EA
EA
EA
EA
EA
EA
event read
even devices
IEC Train Communication Network
Multifunction Vehicle Bus
odd devices
45
1999 September, HK
time
IEC 61375 Clause 3
MVB 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
Bus master
Application
processor 2
Int Req
Periodic
list
Slave
Master clock
clock
Bus controller
Ports
Application
processor 3
Int Req
Slave
clock
Bus controller
Ports
Int Req
Slave
clock
Bus controller
Ports
Bus controller
MVB
Sync port address
IEC Train Communication Network
Multifunction Vehicle Bus
Sync port variable
46
1999 September, HK
IEC 61375 Clause 3
MVB Slave Clock Synchronization
Master
Slave clock clock
Slave clocks
Slave clocks
MVB 1
Bus
administrator 1
Slave devices
Bus
administrator 2
Synchronizer
MVB 2
The clock does not need to be generated by the Master.
The clock can synchronize sampling within 100 µs across several bus segments.
IEC Train Communication Network
Multifunction Vehicle Bus
47
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
48
1999 September, HK
IEC 61375 Clause 3
MVB 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.
IEC Train Communication Network
Multifunction Vehicle Bus
49
1999 September, HK
IEC 61375 Clause 3
MVB Basic Medium Redundancy
The bus is duplicated for availability (not for integrity)
address
data
control
parallel bus logic
receive register
send register
encoder
bus controller
selector
signal quality report
decoder decoder
A
transmitters
B
A
B
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
50
IEC Train Communication Network
Multifunction Vehicle Bus
1999 September, HK
IEC 61375 Clause 3
MVB Medium Redundancy
The physical medium may be fully duplicated to increase availability.
Principle: send on both, receive on one, supervise the other
device
BA
AB
device
repeater
repeater
optical link A
optical link B
device
repeater
repeater
electrical segment X
device
electrical segment Y
Duplicated and non-duplicated segments may be connected
IEC Train Communication Network
Multifunction Vehicle Bus
51
1999 September, HK
IEC 61375 Clause 3
MVB Double-Line Fibre Layout
star coupler A
opto links A
A
B
device
rack
copper bus A
A
B
copper bus B
Bus Administrator
redundant
Bus
Administrator
opto links B
star coupler B
The failure of one device cannot prevent other devices from communicating.
Optical Fibres do not retro-act.
IEC Train Communication Network
Multifunction Vehicle Bus
52
1999 September, HK
IEC 61375 Clause 3
MVB 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
bus
administrator
1
bus
administrator
2
bus
administrator
3
current bus
master
Bus
slave
device
slave
device
slave
device
slave
device
slave
device
slave
device
slave
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.
IEC Train Communication Network
Multifunction Vehicle Bus
53
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
54
1999 September, HK
IEC 61375 Clause 3
MVB Transmission Integrity (1)
1) Manchester II encoding
Double signal inversion necessary to cause an undetected error, memoryless code
Clock
Data
1
1
0
1
0
0
0
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
edge
BT = bit time = 666
ns
time
BT0.5
BT1.0
BT1.5
IEC Train Communication Network
Multifunction Vehicle Bus
55
1999 September, HK
IEC 61375 Clause 3
MVB Transmission Integrity (2)
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 Manchester coding is considered):
-15
(Residual Error Rate < 10
under standard disturbances)
Master Frame
16 (33)
9
MSD
size in bits
4
12
F address
8
CS
MD = Master frame Delimiter
CS = Check Sequence 8 bits
useful (total)
size in bits
Slave Frame
9
16 (33)
SSD
9
32 (49)
64 (81)
128 (153)
256 (297)
SSD
9
SSD
16
8
2 bytes
CS
SD = Slave frame Delimiter
32
8
4 bytes
CS
64
8 bytes
8
CS
DATA
64
repeat 1, 2 or 4 x
IEC Train Communication Network
Multifunction Vehicle Bus
56
1999 September, HK
IEC 61375 Clause 3
MVB Transmission Integrity (3)
4) Different delimiters for address and data against single frame loss:
respond within
1.3 µs < t
< 4.0 µs
ms
MSD ADDRESS a CS
SSD
respond within
4 µs < t sm<1.3 ms
DATA (a)
CS
MSD ADDRESS b CS
time
t mm • 1,3 ms
5) Response time supervision against double frame loss:
> 22 µs
MSD ADDRESS a CS
> 22 µs
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.
IEC Train Communication Network
Multifunction Vehicle Bus
57
1999 September, HK
IEC 61375 Clause 3
MVB 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.
IEC Train Communication Network
Multifunction Vehicle Bus
58
1999 September, HK
IEC 61375 Clause 3
MVB Integer Set-up
poll
A B
time
A B
individual period
Bus
Administrator
redundant vehicle bus
(for availability only)
output
devices
input
devices
A
B
A
B
confinement
°
application
responsibility
spreader device
(application
dependent)
redundant input
IEC Train Communication Network
Multifunction Vehicle Bus
fail-safe
comparator
and enabling
logic
redundant, integer output
59
1999 September, HK
IEC 61375 Clause 3
MVB Integer and Available Set-up
poll
A B
individual period
redundant
bus
administrator
redundant
bus
administrator
redundant vehicle bus
(for availability)
input
devices
A
time
A B
B
output
devices
A
B
A
B
C
A
B
C
comparator
and enabling
logic
confinement
spreader device
(application
dependent)
A
redundant input
IEC Train Communication Network
Multifunction Vehicle Bus
switchover logic or
comparator
(application
dependent)
B
available and integer output
60
1999 September, HK
IEC 61375 Clause 3
MVB 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
IEC Train Communication Network
Multifunction Vehicle Bus
61
1999 September, HK
IEC 61375 Clause 3
MVB Summary
Topography:
Medium:
bus (copper), active star (optical fibre)
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
none (class 1), class 2 uses minor processor capacity
Processor participation
Interface area on board 20 cm2 (class 1), 50 cm2 (class 2)
RAM, EPROM , drivers.
Additional logic
fully duplicated for availability
Medium redundancy:
Manchester II + delimiters
Signalling:
1,5 Mb/s
Gross data rate
typical 10 µs (<43 µs)
Response Time
4096 physical devices, 4096 logical ports per bus
Address space
Frame size (useful data) 16, 32, 64, 128, 256 bits
Integrity
CRC8 per 64 bits, HD = 8, protected against sync slip
IEC Train Communication Network
Multifunction Vehicle Bus
62
1999 September, HK
IEC 61375 Clause 3
MVB Link Layer Interface
Real-Time Protocols
Upper Link Layer
LP
LM
LS
process
data
message
data
supervisory
data
Traffic Store
Lower Link
Layer
slave
Process Data
Message Data
Supervisory Data
Physical Layer
IEC Train Communication Network
Multifunction Vehicle Bus
telegram
handling
management
station
Link Layer Interface
master
polling
arbitration
mastership transfer
frame coding
63
1999 September, HK
IEC 61375 Clause 3
MVB Components
Bus Controllers:
BAP 15 (Texas Instruments, obsolete)
MVBC01 (VLSI, in production, includes master logic
MVBC02 (E2S, in production, includes transformer coupling)
Repeaters:
REGA (in production)
MVBD (in production, includes transformer coupling)
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
IEC Train Communication Network
Multifunction Vehicle Bus
64
1999 September, HK
IEC 61375 Clause 3
MVB Throughput (raw data)
transmission delay [ms]
0.9
IEC Fieldbus @ 1,0 Mbit/s
0.8
0.7
MVB @ 1,5 Mbit/s
0.6
0.5
0.4
0.3
IEC Fieldbus @ 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
IEC Train Communication Network
Multifunction Vehicle Bus
65
1999 September, HK
IEC 61375 Clause 3
MVB versus IEC 61158-2 Frames
IEC 61158-2 frame
Preamble
Start Delimiter
1 0 1 0 1 0 1 0 1 N+ N- 1 0 N+ N- 0
PhSDU
End Delimiter
FCS
Data
Spacing
1 N+ N- N+ N- 1 0 1 v v v v
16 bits
MVB frame
Start Delimiter
8 bits
End Delimiter
0 N- N+ 1 N- N+ 1 1 1
Data
FCS
v v
Master Frame
0 0 0 0 N+ N- 0 N+ N-
Data
FCS
v v
Slave Frame
IEC 61158 frames have a lesser efficiency (-48%) then MVB frames
To compensate it, a higher speed (2,5 Mbit/s) would be needed.
IEC Train Communication Network
Multifunction Vehicle Bus
66
1999 September, HK
IEC 61375 Clause 3
IEC Train Communication Network
Multifunction Vehicle Bus
67
1999 September, HK
IEC 61375 Clause 3