Analog Devices ADSP-BF506F Hardware Reference Manual page 720

Interface Overview
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 (
Each CAN node then begins transmitting its message starting with the
message ID. While transmitting, the CAN controller samples the
pin to verify that the logic level being driven is the value it just placed on
the pin. This is where the names for the logic levels apply. If a trans-
CANTX
mitting node places a recessive '1' on
the pin, it knows that another node has placed a dominant bit on
CANRX
the bus, which means another node has higher priority. So, if the value
sensed on
CANRX
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
structure.
ARBITRATION PHASE
1 11
SOF IDENTIFIER RTR
SOF - START OF FRAME (SINGLE BIT = 0)
RTR - REMOTE TRANSMISSION REQUEST (REMOTE FRAME = 1)
IDE - IDENTIFIER EXTENSION (EXTENDED ID FRAME = 1)
r0 - RESERVED FOR FUTURE EXPANSION
- DATA LENGTH CONTROL (NUMBER OF DATA BYTES IN FRAME)
DLC
- CYCLIC REDUNDANCY CHECK (ERROR BITS IN FRAME)
CRC
- ACKNOWLEDGE (RECEIVER DRIVES ONE DOMINANT BIT TO ACK)
ACK
- END OF FRAME (SERIES OF 7 RECESSIVE BITS = b#1111111)
EOF
- INTERFRAME SPACE (3 RECESSIVE BITS = b#111 )
IFS
Figure 17-5. Standard CAN Frame
Figure 17-5 is a basic 11-bit identifier frame. After the
is the bit, which indicates whether the frame contains data (data
RTR
frame) or is a request for data associated with the message identifier in the
frame being sent (remote frame).
17-8
) signals the beginning of a new frame.
SOF
is the value driven on
Figure 17-5 for more details regarding CAN frame
1 1 1 4 0 ... 64
IDE r0 DLC 0...8 BYTES
ADSP-BF50x Blackfin Processor Hardware Reference
and detects a dominant '0' on
CANTX
, transmission continues, oth-
CANTX
16 2 7 3
CRC ACK EOF IFS
SOF
CANRX
and identifier