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Manual_CANopen_StrainLink_EN_V3_05.doc
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The figure below shows the structure of a Standard Frame according to the CAN 2.0A standard.
1
11
1
1
1
4
0…64
15
1
1
1
7
3
S
ta
rt
o
f
F
ra
m
e
(
S
O
F
)
Id
e
n
ti
fi
e
r
R
T
R
*
ID
E
*
*
r0
D
L
C
D
A
T
A
E
n
d
o
f
F
ra
m
e
(
E
O
F
)
In
te
rm
is
s
io
n
(
IF
S
)
*
RTR = 0 => Data Frame
RTR = 1 => Remote Frame
** IDE = 0 => 11Bit Identifier
IDE = 1 => 29 Bit Identifier
A
C
K
recessive
dominant
C
R
C
CAN Data Frame
•
Start of Frame: dominant (logical 0), used for synchronization
•
Identifier: information for the receiver and priority information for bus arbitration
•
RTR: recessive, differentiates between the data frame (dominant) and the data request frame
(recessive)
•
IDE: Identifier Extension
•
r0: reserved
•
DLC: contains length information for the following data
•
DATA: contains the data of the frame
•
CRC: marks the error code for the preceding data. The CRC checksum is used for detecting errors.
•
ACK: contains an acknowledgment from other receivers upon correct reception of the message
•
EOF: marks the End of Frame (7 recessive bits)
•
IFS: marks the intermission frame space, the time for transmitting a correctly received frame.
4.2.4
Bitwise bus arbitration
During the arbitration phase, it is determined which of the messages undergoing simultaneous arbitration has
the highest priority. The message having the lowest value for the message identifier has the highest priority.
The arbitration phase comprises the transmission of the message identifier and the RTR bit (Remote
Transmission Request bit). If a network node detects a dominant bus level (logical 0) although it connected a
recessive level (recessive bit) itself, it stops transmission immediately and transitions to the receiver state
because, in this case, a message with a higher priority was obviously transmitted at the same time.