Intel 87C196CB Manual De Usuario
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7-7
CAN SERIAL COMMUNICATIONS CONTROLLER
7.3.3
Message Frames
A message object is contained within a message frame that adds control and error-detection bits
to the content of the message object. The frame for an extended message differs slightly from that
for a standard message, but they contain similar information. A data frame contains a message
object with data to be transmitted; a remote frame is a request for another node to transmit a data
frame, so it contains no data.
to the content of the message object. The frame for an extended message differs slightly from that
for a standard message, but they contain similar information. A data frame contains a message
object with data to be transmitted; a remote frame is a request for another node to transmit a data
frame, so it contains no data.
Figure 7-3 illustrates standard and extended message frames. Table 7-6 and Table 7-7 describe
their contents and summarize the minimum message lengths. Actual message lengths may differ
because the CAN controller adds bits during transmission (see “Error Detection and Management
Logic” on page 7-9). After each message frame, an intermission field consisting of three recessive
(1) bits separates messages. This intermission may be followed by a bus idle time.
their contents and summarize the minimum message lengths. Actual message lengths may differ
because the CAN controller adds bits during transmission (see “Error Detection and Management
Logic” on page 7-9). After each message frame, an intermission field consisting of three recessive
(1) bits separates messages. This intermission may be followed by a bus idle time.
Figure 7-3. CAN Message Frames
Table 7-5. Effect of Masking on Message Identifiers
Transmit message object ID
1 1 0 0 0 0 0 0 0 0 0
Mask (0 = don’t care; 1 = must match)
0 0 0 0 0 0 0 0 0 1 1
Received remote message object ID
0 0 1 1 1 1 1 1 1 0 0
Resulting message object ID
0 0 1 1 1 1 1 1 1 0 0
18-bit
Identifier
11 bit
Identifier
S
O
F
S
R
R
R
R
I
D
E
E
R
T
R
r
1
r
0
0–8 Bytes
15-bit
CRC
CRC
DLC
11-bit
Identifier
S
O
F
R
T
R
I
D
E
E
r
0
0–8 Bytes
15-bit
CRC
CRC
DLC
End of
Frame
Frame
Ack
F.
CRC
Field
Data Field
Control
Field
Arbitration
Field
End of
Frame
Frame
Ack
F.
CRC
Field
Data Field
Control
Field
Arbitration
Field
A2599-01
Standard Frame
Extended Frame