Environmental Engineering Reference
In-Depth Information
provides guaranteed message latency, has message oriented addressing identifiers
and a scalable fault tolerance over single or dual channels. The physical layer (OSI
layer 1) includes an independent bus guardian for error containment while sup-
porting bus speeds up to 10 Mb/s. The basic features of FlexRay are
Scalable synchronous and asynchronous data transmission
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High net data rate of 5 Mb/s with a gross data rate of up to 10 Mb/s
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Deterministic data transmission, guaranteed message latency and jitter
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Fault tolerant and time triggered services in hardware versus software
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Fast error detection and signalling, supports redundant channels
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Fault tolerant, synchronous, global time base
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Bus Guardian error containment at the physical layer (electronic or optical)
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Arbitration free transmission
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Supports all popular network configurations (bus, star, multiple star)
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FlexRay is not TTP/C, but it has some features of TTP/C such as time division
multiple access (TDMA) bus access scheme. The message format of FlexRay
consists of a static header plus a 246 byte dynamic frame lengths containing
membership and acknowledgement fields.
FlexRay is one of many in-vehicle protocols either in use or proposed for data
communications. Table 4.24 provides a listing of some of the more popular and
open system protocols. There are other, proprietary protocols in existence, but only
open architectures are of future interest.
Table 4.24 In-vehicle network data protocols
Data protocol
Applications
Media
Data rate (maximum)
Bluetooth
Control
Wireless
750 kb/s
CAN
Control
Twisted pair
1 Mb/s
D2B
Audio/video
Fibre optic
12 Mb/s
DSI
Sensor multiplexing
2 wires
5 kb/s
FlexRay
Safety and mobility
2 wires
10 Mb/s
IEEE-1394
Multimedia
6 wire twisted pairs
200 Mb/s
J1850 PWM
Control
2 wires
41.6 kb/s
J1939
Control
Twisted pair
1 Mb/s
LIN
Control
1 wire
20 kb/s
MOST
Multimedia
Fibre optic
25 Mb/s
TTP
Real time control
2 channels
5 Mb/s (10 Mb/s optical)
Bus loading on conventional vehicles will continue to increase. In hybrid
propulsion systems, the demand for more functionality automatically increases the
network traffic since more torque sources must be managed in addition to the
internal combustion engine and transmission. With CAN protocols network access
is on demand, and it becomes a real issue when several modules contend for
the bus, each with high priority messages. Once agreement is reached to regulate
