Rainbow Electronics CAN интерфейс - Manual (Page 40)

BOSCH
ROBERT BOSCH GmbH, Postfach 300240, D-7000 Stuttgart 30
Sep. 1991
Part B - page 38
The scope of this specification is to define the Data Link Layer and the consequences
of the CAN protocol on the surrounding layers.
Messages
Information on the bus is sent in fixed format messages of different but limited length
(see section 3: Message Transfer). When the bus is free any connected unit may start
to transmit a new message.
Information Routing
In CAN systems a CAN node does not make use of any information about the system
configuration (e.g. station addresses). This has several important consequences.
System Flexibility: Nodes can be added to the CAN network without requiring
any change in the software or hardware of any node and application layer.
Message Routing: The content of a message is named by an IDENTIFIER. The
IDENTIFIER does not indicate the destination of the message, but describes the
meaning of the data, so that all nodes in the network are able to decide by
Message Filtering whether the data is to be acted upon by them or not.
Multicast: As a consequence of the concept of Message Filtering any number of
nodes can receive and simultaneously act upon the same message.
Data Consistency: Within a CAN network it is guaranteed that a message is
simultaneously accepted either by all nodes or by no node. Thus data
consistency of a system is achieved by the concepts of multicast and by error
handling.
Bit rate
The speed of CAN may be different in different systems. However, in a given system
the bit-rate is uniform and fixed.
Priorities
The IDENTIFIER defines a static message priority during bus access.
Basic Concepts