msm9225 Oki Semiconductor, msm9225 Datasheet - Page 46

• Manufacturer Part Number: msm9225
• Description: Can Controller Area Network Controller
• Manufacturer: Oki Semiconductor

PROTOCOL
The CAN (Controller Area Network) is a high-speed multiplexed communication protocol
designed to perform real-time communication inside an automobile. CAN specifications are
broadly classified into two layers, the physical layer and the data link layer. The data link layer
consists of logical link control and medium access control.
The configuration of each layer is listed below.
Protocol Mode Function
(1) Standard format mode
(2) Extended format mode
Message Format
CAN protocol messages have the following 4 types of frames.
* In a wired-OR logic circuit, the stronger value is defined as "dominant" and the weaker value
¡ Semiconductor
as "recessive". In figures hereafter, dominant (abbreviation: D) = 0, and recessive (abbreviation:
R) = 1.
2032 types of identifiers can be set in this mode.
Since the identifier is 11 bits, 2032 types of messages can be handled.
2032 ¥ 2
In the standard format mode, the identifier is 11 bits. However, in the extended format mode,
the identifier is extended to 29 bits (11 + 18).
If the SRR and IDE bits of the arbitration field are both "recessive", the mode changes to the
extended format mode.
If remote frames for an extended format mode message and a standard format message are
transmit simultaneously, the node that transmit the extended format message will change to
the receive state.
(1) Data frame
(2) Remote frame
(3) Error frame
(4) Overload frame : frame that is output when the receive side has not completed preparing
18
types of identifiers can be set in this mode.
Lower
Upper
: transmit data frame
: transmit request frame from the receive side
: frame that is output when an error is detected
for reception
Application layer (not including object)
Data link layer
• Logical link control (LLC): message and status handling
• Medium access control (MAC): as per protocol
Physical layer: signal level and bit representation
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