AN1105 STMicroelectronics, AN1105 Datasheet - Page 5

• Manufacturer Part Number: AN1105
• Description: ST7 PCAN PERIPHERAL DRIVER
• Manufacturer: STMicroelectronics

1.1.2 CAN in the OSI reference model
The protocol occupies parts of the two lowest levels (the physical and data link layers) of the
7-level ISO/OSI (Open System Interconnection) telecommunications reference model.
Table 1. ISO/OSI Standard Telecommunication Layers
In this reference model, the data link layer deals with physically passing data from one node to
another. It defines arbitration, message framing, error management and transmission timing
for example.
The physical layer deals with putting data on the physical network, and with taking it off. Con-
sequently, it defines signal levels and timings, as well as the transmission support (wire types,
connectors, etc.).
The CAN protocol splits the Data Link layer into Object and Transfer sublayers, corre-
sponding to the ISO/OSI Logical Link Control and Medium Access Control sublayers. The
Transfer layer is the interface between the user application and the CAN. The Object layer
Message prioritization
– The identifier of a message also indicates the priority of its carrier. During the arbitration
Error management system (See
– Detection: every node continuously monitors the bus, even if it is not concerned by the cur-
– Signalization: any node detecting an error, signals it to its peers and aborts the current
– Confinement: each node implements counters which are incremented (or decremented)
phase, a bitwise comparison of the different identifiers is performed. The message with the
higher identifier being the more urgent, it wins the arbitration and is immediately transmit-
ted.
rent transmission, to detect potential violations of the protocol.
transmission meanwhile. The sender automatically retries transmission within a certain
amount of time. Thus, the consistency of data throughout the network is preserved.
after each detection of an error (or successful operation). A defective station can then
switch itself off when its counters reach a certain value, and thus stop disturbing the bus
operations.
OSI Layer
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Presentation
“Error Management” on page
OSI Model
Application
Transport
Data Link
Network
Physical
Session
ST7 pCAN PERIPHERAL DRIVER
11)
No (User defined)
No (User defined)
No (User defined)
No (User defined)
No (User defined)
CAN Protocol
Partly
Yes
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