DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

The RTR bit indicates whether the frame is a Data Frame or a Remote Frame and must be
dominant for a Data Frame.
Control FieldThe Control Field contains the Identifier Extension (IDE) bit (in an
Extended Data Frame the IDE bit resides in the Arbitration Field), a reserved bit (r0), and
the Data Length Code (DLC) bits. If the IDE bit is dominant, then the frame is a
Standard Format Data Frame, otherwise it is an Extended Format Data Frame. The
reserved bit, r0, is not used and should always be dominant. The number of bytes is
stored in the Data Length Code Field. This field typically holds values from zero to
eight. Since the field is four bits long, values greater than eight can be indicated. If the
value of the Data Length Code is greater than eight then it is assumed that the frame
contains eight bytes. Table 3.2 shows the Data Length Code and the number of data
bytes.
Table 3.2 Data Length Code Field
Number
Data Length Code (D=Dominant level, R=Recessive level)
of data bytes DLC3 DLC2 DLC1 DLC0
0 D D D D
1 D D D R
2 D D R D
3 D D R R
4 D R D D
5 D R D R
6 D R R D
7 D R R R
8 R D or R D or R D or R
Data FieldThe Data Field is the payload of the Data Frame. It contains from 0 to 8
bytes and is transmitted most significant bit first. It is the only field in the Data Frame
that does not have a fixed length.
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