DS80C390_00 Datasheet, PDF (132/155 Pages) Dallas Semiconductor – High-Speed Microcontroller User’s Guide Supplement

Frame Types
DS80C390 High-Speed Microcontroller User’s Guide Supplement
The CAN 2.0B protocol specifies two different message formats, the standard 11-bit (CAN 2.0A) and the
extended 29-bit (CAN 2.0 B), and four different Frame Types for CAN Bus communications.
The Standard Format seen below makes use of an 11-bit identifier.
Figure 16- 1 CAN 2.0A Format
Arbitration Field
Control Field Data Field
CRC Field
ACK End of
Bus
Field Frame ^INTER Idle
S
O
R
11-bit Identifier _T
I
D
r
0
F
RE
DLC
0 to 8 Bytes
15-bit CRC
The Extended Format seen below makes use of a 29 bit identifier.
Figure 16- 2 CAN 2.0B Format
Arbitration Field
Control
ACK End of
Bus
Field ^{Data Field CRC Field Field} Frame ^{INTER Idle}
S
O
S
11-bit Identifier _R
I
D
18-bit Identifier
R
T
rr
10
F
RE
R
DLC 0 to 8 Bytes ^{15-bit CRC}
The four different Frame Types for CAN Bus communications are the Data Frame, the Remote Frame,
the Error Frame and the Overload Frame.
Data Frame:
The Data Frame is formulated to carry data from a transmitter to a receiver. The preceding two figures are
examples of data frames in the standard and extended formats. The Data Frame is composed of seven
fields. These include the Start of Frame, Arbitration Field, Control Field, Data Field, CRC Field,
Acknowledge Field and an End of Frame. A description of these fields follows.
Start of Frame - SOF: (Standard and Extended Format)
The Start of Frame is a dominant bit which signals the start of a Data or Remote Frame. The dominant
forces a hard synchronization, initiating the CAN controller receive mode.
Arbitration Field: (Standard and Extended Format)
The Arbitration Field contains the identifier of the message and a dominant Remote Request (RTR) bit.
The identifier is composed of one field in the standard 11-bit format or two fields in the extended 29-bit
format. Two additional bits, the Substitution Remote Request (SRR) bit and the Identifier Extension
(IDE) bit, separate the two fields in the Extended Format.
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