CP3BT23_14 Datasheet, PDF (126/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
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Control Field
The Control field consists of six bits. For standard frames it starts with the ID Extension bit (IDE) and a
reserved bit (RB0). For extended frames, the control field starts with two reserved bits (RB1, RB0). These
bits are followed by the 4bit Data Length Code (DLC).
The CAN receiver accepts all possible combinations of the reserved bits (RB1, RB0). The transmitter must
be configured to send only zeros.
Data Length Code (DLC)
The DLC field indicates the number of bytes in the data field. It consists of four bits. The data field can be
of length zero. The admissible number of data bytes for a data frame ranges from 0 to 8.
Data Field
The Data field consists of the data to be transferred within a data frame. It can contain 0 to 8 bytes. A
remote frame has no data field.
Cyclic Redundancy Check (CRC)
The CRC field consists of the CRC sequence followed by the CRC delimiter. The CRC sequence is
derived by the transmitter from the modulo 2 division of the preceding bit fields, starting with the SOF up
to the end of the data field, excluding stuff-bits, by the generator polynomial:
x15 + x14 + x10 + x8 + x7 +x4 + x3 + 1
(15)
The remainder of this division is the CRC sequence transmitted over the bus. On the receiver side, the
module divides all bit fields up to the CRC delimiter excluding stuff bits, and checks if the result is zero.
This will then be interpreted as a valid CRC. After the CRC sequence a single “recessive” bit is
transmitted as the CRC delimiter.
ACK Field
The ACK field is two bits long and contains the ACK slot and the ACK delimiter. The ACK slot is filled with
a “recessive” bit by the transmitter. This bit is overwritten with a “dominant” bit by every receiver that has
received a correct CRC sequence. The second bit of the ACK field is a “recessive” bit called the
acknowledge delimiter.
The End of Frame field closes a data and a remote frame. It consists of seven “recessive” bits.
126 CAN Module
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