COP888EB Datasheet, PDF (30/75 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 8k Memory, CAN Interface, 8-Bit A/D, and USART

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
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