Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement User 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

DLC3

DLC2

DLC1

DLC0

Reserved Bits

Data Length Code

CRC Field

CRC Sequence

CRC Delimiter

Data Field or

Control Field

ACK Field

Maxim Integrated