Interface Overview
9-8
ADSP-BF537 Blackfin Processor Hardware Reference
Each CAN node then begins transmitting its message starting with the
message ID. While transmitting, the CAN controller samples the
CANRX
pin to verify that the logic level being driven is the value it just placed on
the
CANTX
pin. This is where the names for the logic levels apply. If a trans-
mitting node places a recessive ‘1’ on
CANTX
and detects a dominant ‘0’ on
the
CANRX
pin, it knows that another node has placed a dominant bit on
the bus, which means another node has higher priority. So, if the value
sensed on
CANRX
is the value driven on
CANTX
, transmission continues, oth-
erwise the CAN controller senses that it has lost arbitration and
configuration determines what the next course of action is once arbitra-
tion is lost. See
for more details regarding CAN frame
structure.
is a basic 11-bit identifier frame. After the
SOF
and identifier is
the
RTR
bit, which indicates whether the frame contains data (data frame)
or is a request for data associated with the message identifier in the frame
being sent (remote frame).
L
Due to the inherent nature of the CAN protocol, a dominant bit in
the
RTR
field wins arbitration against a remote frame request
(
RTR
=
1
) for the same message ID, thereby defining a remote request
to be lower priority than a data frame.
Figure 9-5. Standard CAN Frame
SOF
IDENTIFIER RTR
1
11
1
ARBITRATION PHASE
CRC
IDE
ACK
0...8 BYTES
r0
DLC
1
4
1
0 ... 64
16
2
7
3
EOF
IFS
SOF
RTR
CRC
IDE
ACK
r0
DLC
EOF
IFS
- START OF FRAME (SINGLE BIT = 0)
- REMOTE TRANSMISSION REQUEST (REMOTE FRAME = 1)
- IDENTIFIER EXTENSION (EXTENDED ID FRAME = 1)
- RESERVED FOR FUTURE EXPANSION
- DATA LENGTH CONTROL (NUMBER OF DATA BYTES IN FRAME)
- CYCLIC REDUNDANCY CHECK (ERROR BITS IN FRAME)
- ACKNOWLEDGE (RECEIVER DRIVES ONE DOMINANT BIT TO ACK)
- END OF FRAME (SERIES OF 7 RECESSIVE BITS = b#1111111)
- INTERFRAME SPACE (3 RECESSIVE BITS = b#111 )
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...