Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 135)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
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The Substitution Remote Request bit is a recessive bit and is substituted for the RTR bit when using
the Extended Format.
• Identifier Extension (IDE) bit: (Extended Format)
The Identifier Extension (IDE) bit is a dominant bit in the Standard Format and a recessive bit in the
Extended Format. The IDE bit is located in the Arbitration Field in the Standard Format and is located
in the Control Field in the Extended Format.
Control Field: (Standard and Extended Format)
The Control Field is made up of six bits in two fields. The first field is made up of two reserved bits,
which are transmitted as dominant bits. The second field contains four bits that 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 Format Registers, located in each of the 15 message
centers.
Figure 19-3. CONTROL FIELD
IDE/r1
Control Field
Data Field or
Control Field
Arbitration
Field
r0 DLC3 DLC2 DLC1 DLC0
Reserved Bits Data Length Code
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 following the Data or Remote Frame. The data field is
transmitted LSB first, with the MSB 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 using the
destuffed bits in the Start of Frame, the Arbitration Field, the Control Filed, and the Data Field (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.