CP3BT23_14 Datasheet, PDF (129/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
www.ti.com
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
Error Frame
As shown in Figure 18-7, the Error Frame consists of the error flag and the error delimiter bit fields. The
error flag field is built up from the various error flags of the different nodes. Therefore, its length may vary
from a minimum of six bits up to a maximum of twelve bits depending on when a module has detected the
error. Whenever a bit error, stuff error, form error, or acknowledgment error is detected by a node, the
node starts transmission of an error flag at the next bit. If a CRC error is detected, transmission of the
error flag starts an error flag for a previous error condition has already been started.
If a device is in the error active state, it can send a “dominant” error flag, while a error passive device is
only allowed to transmit “recessive” error flags. This is done to prevent the CAN bus from getting stuck
due to a local defect. For the various CAN device states, please refer to Error Types on Figure 18-7.
ERROR FRAME
DATA FRAME OR
REMOVE FRAME
6
ERROR
FLAG
<6
ECHO
ERROR FLAG
8
ERROR
DELIMITER
INTER-FRAME OR
OVERLOAD FRAME
Note:
d = dominant
r = recessive
ddddddd
dd r r r r r r r rd
An error frame can start anywhere within a frame
Figure 18-7. Error Frame
DS024
Overload Frame
As shown in Figure 18-8, an overload frame consists of the overload flag and the overload delimiter bit
fields. The bit fields have the same length as the error frame field: six bits for the overload flag and eight
bits for the delimiter. The overload frame can only be sent after the end of frame (EOF) field and in this
way destroys the fixed form of the intermission field. As a result, all other nodes also detect an overload
condition and start the transmission of an overload flag. After an overload flag has been transmitted, the
overload frame is closed by the overload delimiter.
Note: The CAN module never initiates an overload frame due to its inability to process an incoming
message. However, it is able to recognize and respond to overload frames initiated by other devices.
OVERLOAD FRAME
END OF FRAME OR
ERROR DELIMITER OR
OVERLOAD DELIMITER
6
OVERLOAD
FLAG
8
OVERLOAD
DELIMITER
INTER-FRAME SPACE
OR ERROR FRAME
Note:
d = dominant
r = recessive
ddddddd r r r r r r r r
An overload frame can only start at the end of a frame
Figure 18-8. Overload Frame
DS025
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