Interface Overview
17-8
ADSP-BF50x Blackfin Processor Hardware Reference
pin is always high. If two CAN nodes transmit at the same time, dominant
bits overwrite recessive bits.
The CAN protocol defines that all nodes trying to send a message on the
CAN bus attempt to send a frame once the CAN bus becomes available.
The start of frame indicator (
SOF
) signals the beginning of a new frame.
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
Figure 17-5
for more details regarding CAN frame
structure.
Figure 17-5
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).
Figure 17-5. 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 )
Содержание EZ-KIT Lite ADSP-BF506F
Страница 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 132: ...Unique Information for the ADSP BF50x Processor 4 22 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 342: ...Unique Information for the ADSP BF50x Processor 7 106 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 484: ...Unique Information for the ADSP BF50x Processor 10 60 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 493: ...ADSP BF50x Blackfin Processor Hardware Reference 11 9 Core Timer Unique Information for the ADSP BF50x Processor None ...
Страница 494: ...Unique Information for the ADSP BF50x Processor 11 10 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 506: ...Unique Information for the ADSP BF50x Processor 12 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 544: ...Unique Information for the ADSP BF50x Processor 13 38 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 712: ...Unique Information for the ADSP BF50x Processor 16 62 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 972: ...Unique Information for the ADSP BF50x Processor 20 38 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Страница 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...