Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement - Manual (Page 149)

High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
149
Control field: (Standard and extended format) The control field is made up of 6 bits in two fields. The first field is made up of 2 reserved
bits, which are transmitted as dominant bits. The second field contains 4 bits, which make up the data length code (DLC). The DLC
determines the number of data bytes in the data field of the data frame and is programmed through the use of the CAN message for-
mat registers, located in each of the 15 message centers.
Figure 19-3. Control Field
Data field: (Standard and extended format) The data field is made up of 0 to 8 bytes in a data frame and 0 bytes in a remote frame.
The number of data bytes associated with a message center is programmed through the use of the CAN message format registers,
located in each of the 15 message centers. The data field contents are saved to the respective message center. If the identifier test is
successful, no errors are detected through the last bit of the end of frame, and an error frame does not immediately follow the data or
remote frame. The data field is transmitted the least significant byte first, with the most significant bit value of each byte transmitted
first.
CRC field: (Standard and extended format) The CRC field is made up of a 15-bit code, which is the computed cyclic redundancy
check (after destuffing bits) from the start of frame, through the arbitration, control, data fields (when present), and a CRC delimiter.
The CRC calculation is limited to 127-bit maximum code word (a shortened BCH code) with a CRC sequence length of 15 bits.
Figure 19-4. CRC Field
Acknowledge (ACK) field: (Standard and extended format) The acknowledge (ACK) field is made up of 2 bits. The transmitting node
sends 2 recessive bits in the ACK field. The receiving nodes, which have received the message and found the CRC sequence to be
correct, reply by driving the ACK slot with a dominant bit. The ACK delimiter is always a recessive bit.
IDE/r1
Control Field
Data Field or
Control Field
Arbitration
Field
r0 DLC3 DLC2 DLC1 DLC0
Reserved Bits Data Length Code
CRC Field
CRC Sequence
CRC Delimiter
Data Field or
Control Field ACK Field
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