Rainbow Electronics CAN интерфейс - Manual (Page 36)

BOSCH
ROBERT BOSCH GmbH, Postfach 300240, D-7000 Stuttgart 30
Sep. 1991
Part B - page 34
1 INTRODUCTION
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 according to the ISO/OSI Reference Model:
• the Data Link Layer
- the Logical Link Control (LLC) sublayer
- the Medium Access Control (MAC) sublayer
• the Physical Layer
Note that in previous versions of the CAN specification the services and functions of
the LLC and MAC sublayers of the Data Link Layer had been described in layers
denoted as ’object layer’ and ’transfer layer’. The scope of the LLC sublayer is
• to provide services for data transfer and for remote data request,
• to decide which messages received by the LLC sublayer are actually to be accepted,
• to provide means for recovery management and overload notifications.
There is much freedom in defining object handling. The scope of the MAC sublayer
mainly is the transfer protocol, i.e. controlling the Framing, performing Arbitration, Error
Checking, Error Signalling and Fault Confinement. Within the MAC sublayer it is
decided whether the bus is free for starting a new transmission or whether a reception
is just starting. Also some general features of the bit timing are regarded as part of the
MAC sublayer. It is in the nature of the MAC sublayer 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
Introduction