COP888EB datasheet(30/75 Pages) NSC

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Frame Formats (Continued)

DATA FIELD

The Data field consists of the data to be transferred within a

data frame. It can contain 0 to 8 bytes and each byte con-

tains 8 bits. A remote frame has no data field.

CRC FIELD

The CRC field consists of the CRC sequence followed by the

CRC delimiter. The CRC sequence is derived by the trans-

mitter from the modulo 2 division of the preceding bit fields,

starting with the SOF up to the end of the data field, exclud-

ing stuff-bits, by the generator polynomial:

χ15 + χ14 + χ10 + χ8 + χ7 + χ4 + χ3 +1

The remainder of this division is the CRC sequence transmit-

ted over the bus. On the receiver side the module divides all

bit fields up to the CRC delimiter, excluding stuff-bits, and

checks if the result is zero. This will then be interpreted as a

valid CRC. After the CRC sequence a single “recessive” bit

is transmitted as the CRC delimiter.

DS012837-21

DS012837-22

A remote frame is identical to a data frame, except that the RTR bit is “recessive”, and there is no data field.

IDE = Identifier Extension Bit

The IDE bit in the standard format is transmitted “dominant”, whereas in the extended format the IDE bit is “recessive” and the id is expanded to 29 bits.

r = recessive

d = dominant

FIGURE 19. CAN Data Transmission Frames

COP888EB Datasheet(PDF) 30 Page - National Semiconductor (TI)

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