Specifications

Message Objects
10-9 CAN Controller Module
10.3 Message Objects
CAN allows messages to be sent, received, and stored by using data frames.
Figure 10–4 illustrates the structure of the data frames with extended and
standard identifiers.
Figure 10–4. CAN Data Frame
S
O
F
Standard Identifier
11 bit
Extended Identifier
18 bit
DLC
Data
Byte 0
S
R
R
I
D
E
R
T
R
r
1
r
0
C
R
C
A
C
K
E
O
F
Data
Byte 1
Data
Byte 6
Data
Byte 7
. . .
S
O
F
Standard Identifier
11 bit
DLC
Data
Byte 0
I
D
E
R
T
R
r
0
C
R
C
A
C
K
E
O
F
Data
Byte 1
Data
Byte 6
Data
Byte 7
. . .
Data frame contains:
- SOF: Start of Frame – signifies the start of frame.
- Identifier:
J Message priority – determines the priority of the message when two or
more nodes are contending for the bus.
J Message filtering – determines if a transmitted message will be re-
ceived by CAN modules.
- RTR: Remote Transmission Request bit – differentiates a data frame from
a
remote frame .
- SRR: Substitute Remote Request bit – this bit occupies the position as
RTR would in a standard frame.
- IDE: Identifier Extension bit – differentiates standard and extended
frames.
- r0, r1: reserved
- DLC: Data Length Code – denotes the number of bytes (0 to 8) in a data
frame.
- Data: Four 16-bit words are used to store the (maximum) 8-byte data field
of a CAN message.