原创 CAN(CONTROLAREANET)介绍

The Controller Area Network (CAN) is a serial communications protocol which
efficiently supports distributed realtime control with a very high level of
security.
Its domain of application ranges from high speed networks to low cost multiplex
wiring. In automotive electronics, engine control units, sensors, anti-skid-
systems, etc. are connected using CAN with bitrates up to 1 Mbit/s. At the same
time it is cost effective to build into vehicle body electronics, e.g. lamp
clusters, electric windows etc. to replace the wiring harness otherwise
required.
The intention of this specification is to achieve compatibility between any two
CAN implementations. Compatibility, however, has different aspects regarding
e.g. electrical features and the interpretation of data to be transferred. To
achieve design transparency and implementation flexibility CAN has been
subdivided into different layers.
 the (CAN-) object layer
 the (CAN-) transfer layer
 the physical layer            
The object layer and the transfer layer comprise all
services and functions of the data link layer defined by the ISO/OSI model.
The scope of the object layer includes
 finding which messages are to be transmitted
 deciding which messages received by the transfer layer are actually to be used
 providing an interface to the application layer related hardware.
There is much freedom in defining object handling. The scope of the transfer
layer mainly is the transfer protocol, i.e. controlling the framing, performing
arbitration, error checking, error signalling and fault confinement. Within the
transfer layer it is decided whether the bus is free for starting a new trans-
mission or whether a reception is just starting. Also some general features of
the bit timing are regarded as part of the transfer layer. It is in the nature
of the transfer layer that there is no freedom for modifications.
The scope of the physical layer is the actual transfer of the bits between the
different nodes with respect to all electrical properties. Within one network
the physical layer, of course, has to be the same for all nodes. There may be,
however, much freedom in selecting a physical layer.
The scope of this specification is to define the transfer layer and the con-
sequences of the CAN protocol on the surrounding layers.