Can Communication Protocol - Omron CJ1W-CORT21 Operation Manual

1 Features and System Configuration
1-2-1

CAN Communication Protocol

In general, the CAN communication protocol is based on the Open System Interconnection (OSI) refer-
ence model in accordance with the international standard ISO-7498 (see the following illustration).
 OSI Reference Model ISO-7498
The model defines 7 layers of communication functions, two of which (layers 1 and 2) are used in
CAN. CAN uses layers 1 and 2. Layers 3 to 7 are not defined for CAN. The application layer, OSI
layer 7, defines the interface functions for specific application areas. The User Defined CAN Unit
has a user defined application layer. The user program configures the Unit, processes received
messages, collects data to transmit and triggers the Unit to send messages. This streamlined archi-
tecture ensures fast and efficient data transmission. The application functions which are available to
the user, as well as the system and device behavior of the various CAN device types are specified in
the higher layer protocol.
To achieve design transparency and implementation flexibility, CAN has been subdivided into differ-
ent layers according to the ISO/OSI Reference Model shown below.
Layer
7
3 to 6
2
1
OSI Layer 1: Transmission Medium
ISO 11898 defines the physical layer. The CAN bus is a balanced (differential) 2-wire interface running
over either a Shielded Twisted Pair (STP), Un-shielded Twisted Pair (UTP), or ribbon cable. The bit
encoding used is Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a dif-
ferential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number
of transitions and high resistance to external disturbance.
1-6
(Application Layer)
Not Defined
(Data Link Layer)
Logical Link Control: LLC
• Acceptance filtering
• Overload notification
• Recovery Management
Medium Access Control: MAC
• Data encapsulation and decapsulation
• Frame coding, stuffing
• Medium access management
• Error detection
• Error signalling
• Acknowledgement
• Serialization, deseriliazation
(Physical Layer)
• Bit encoding/decoding
• Bit timing
• Synchronization
CJ-series User Defined CAN Unit Operation Manual for NJ-series CPU Unit (W517)
Description