cp3cn17 National Semiconductor Corporation, cp3cn17 Datasheet - Page 71

• Manufacturer Part Number: cp3cn17
• Description: Reprogrammable Connectivity Processor With Can Interface
• Manufacturer: National Semiconductor Corporation

Data Length Code (DLC)
The DLC field indicates the number of bytes in the data field.
It consists of four bits. The data field can be of length zero.
The admissible number of data bytes for a data frame rang-
es from 0 to 8.
Data Field
The Data field consists of the data to be transferred within a
data frame. It can contain 0 to 8 bytes. A remote frame has
no data field.
Cyclic Redundancy Check (CRC)
The CRC field consists of the CRC sequence followed by
the CRC delimiter. The CRC sequence is derived by the
transmitter from the modulo 2 division of the preceding bit
fields, starting with the SOF up to the end of the data field,
excluding stuff-bits, by the generator polynomial:
Note:
d = dominant
r = recessive
Note:
d = dominant
r = recessive
d
d
x
15
Arbitration Field
+ x
IDENTIFIER
IDENTIFIER
28 ... 18
10 ... 0
14
11
11
+ x
Arbitration Field
10
+ x
r r
d d d
8
Control Field
LENGTH CODE
+ x
IDENTIFIER
7
17 ... 0
DATA
+ x
4
18
4
+ x
d d d
STANDARD DATA FRAME (number of bits = 44 + 8N)
Figure 15. Extended Data Frame
Figure 14. Standard Data Frame
EXTENDED DATA FRAME (number of bits = 64 + 8N)
3
Control Field
LENGTH CODE
+ 1
8
DATA
4
8N (0 < N < 8)
Bit Stuffing
Bit Stuffing
Data Field
8N (0 < N < 0)
8
71
Data Field
The remainder of this division is the CRC sequence trans-
mitted over the bus. On the receiver side, the module di-
vides all bit fields up to the CRC delimiter excluding stuff
bits, and checks if the result is zero. This will then be inter-
preted as a valid CRC. After the CRC sequence a single “re-
cessive” bit is transmitted as the CRC delimiter.
ACK Field
The ACK field is two bits long and contains the ACK slot and
the ACK delimiter. The ACK slot is filled with a “recessive”
bit by the transmitter. This bit is overwritten with a “domi-
nant” bit by every receiver that has received a correct CRC
sequence. The second bit of the ACK field is a “recessive”
bit called the acknowledge delimiter.
The End of Frame field closes a data and a remote frame. It
consists of seven “recessive” bits.
15.2.3
Data Frame
The structure of a standard data frame is shown in
Figure 14. The structure of an extended data frame is
shown in Figure 15.
8
CAN Frame Formats
8
CRC Field
CRC
15
16
CRC Field
CRC
15
16
r
r
r r
r r
r r
END OF
FRAME
r r
END OF
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FRAME
r r
r r
DS020
DS021
r r
r r