Image Processing Reference
In-Depth Information
computational power, small amount of memory, low-cost oscillator). Typical applications involving
these networks include controlling doors (e.g., door locks, opening/closing windows) or controlling
seats (e.g., seat position motors, occupancy control). Besides cost considerations, a hierarchical com-
munication architecture, including a backbone such as CAN and several subnetworks such as LIN,
enables reducing the total traffic load on the backbone.
Both LIN and TTP/A are master-slave networks where a single master node, the only node that has
to possess a precise and stable time base, coordinates the communication on the bus: a slave is only
allowedtosendamessagewhenitispolled.Moreprecisely,thedialogbeginswiththetransmission
bythemasterofa“commandframe”thatcontainstheidentiierofthemessagewhosetransmission
is requested. The command frame is then followed by a “data frame” that contains the requested
message sent by one of the slaves or by the master itself (i.e., the message can be produced by the
master).
13.2.3.1 LIN Network
LIN (see Refs. [,]) is a low-cost serial communication system used as SAE class A network,
where the needs in terms of communication do not require the implementation of higher-bandwidth
multiplexing networks such as CAN. LIN is developed by a set of major companies from the auto-
motive industry (e.g., DaimlerChrysler, Volkswagen, BMW, and Volvo) and is already widely used in
production cars.
The LIN specification package (LIN version . []) includes not only the specification of the
transmission protocol (physical and DLLs) for master-slave communications, but also the specifica-
tion of a diagnostic protocol on top of the DLL. A language for describing the capability of a node (e.g.,
bit-rates that can be used, characteristics of the frames published, and subscribed by the node, etc.)
and for describing the whole network is provided (e.g., nodes on the network, table of the transmis-
sions' schedule, etc.). hese description language facilitates the automatic generation of the network
configuration by software tools.
A LIN cluster consists of one “master” node and several “slave” nodes connected to a common bus.
For achieving a low-cost implementation, the physical layer is defined as a single wire with a data rate
limitedtokbit/sduetoEMIlimitations.hemasternodedecideswhenandwhichframeshallbe
transmitted according to the schedule table. The schedule table is a key element in LIN; it contains
the list of frames that are to be sent and their associated frame-slots thus ensuring determinism in the
transmission order. At the moment a frame is scheduled for transmission, the master sends a header
(a kind of transmission request or command frame) inviting a slave node to send its data in response.
Any node interested can read a data frame transmitted on the bus. As in CAN, each message has to
be identified: distinct message identifiers are available. Figure . depicts the LIN frame format
and the time, termed a “frame-slot,” during which a frame is transmitted.
Frame-slot
Frame
Interframe
space
Response
space
Header
Response
...
Protected
identifier
Break
Sync
Data1
Data2
DataN
Checksum
FIGURE .
Format of the LIN frame. A frame is transmitted during its frame-slot, which corresponds to an entry
of the schedule table. (From Navet, N., Song, Y.Q., Simonot-Lion, F., and Wilwert, C.,
Proc. IEEE
., (), , .
With permission.)
