CP3BT23_14 Datasheet, PDF (125/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
www.ti.com
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
18.2.1 CAN Frame Types
Communication via the CAN bus is basically established by means of four different frame types:
• Data Frame
• Remote Frame
• Error Frame
• Overload Frame
Data and remote frames can be used in both standard and extended frame format. If no message is being
transmitted, i.e., the bus is idle, the bus is kept at the “recessive” level.
Remote and data frames are non-return to zero (NRZ) coded with bit-stuffing in every bit field, which holds
computable information for the interface, i.e., start of frame, arbitration field, control field, data field (if
present), and CRC field.
Error and overload frames are also NRZ coded, but without bit-stuffing.
After five consecutive bits of the same value (including inserted stuff bits), a stuff bit of the inverted value
is inserted into the bit stream by the transmitter and deleted by the receiver. The following shows the
stuffed and destuffed bit stream for consecutive ones and zeros.
Original or unstuffed bit stream
Stuffed bit stream (stuff bits in bold)
Table 18-1.
10000011111 . . .
1000001111101 . . .
01111100000 . . .
0111110000010 . . .
18.2.2 CAN Frame Fields
Data and remote frames consist of the following bit fields:
• Start of Frame (SOF)
• Arbitration Field
• Control Field
• Data Field
• CRC Field
• ACK Field
• EOF Field
Start of Frame (SOF)
The Start of Frame (SOF) indicates the beginning of data and remote frames. It consists of a single
“dominant” bit. A node is only allowed to start transmission when the bus is idle. All nodes have to
synchronize to the leading edge (first edge after the bus was idle) caused by the SOF of the node which
starts transmission first.
Arbitration Field
The Arbitration field consists of the identifier field and the RTR (Remote Transmission Request) bit. For
extended frames there is also a SRR (Substitute Remote Request) and a IDE (ID Extension) bit inserted
between ID18 and ID17 of the identifier field. The value of the RTR bit is “dominant” in a data frame and
“recessive” in a remote frame.
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