CP3BT23_14 Datasheet, PDF (132/324 Pages) Texas Instruments – CP3BT23 Reprogrammable Connectivity Processor with Bluetooth and Dual CAN Interfaces

CP3BT23
SNOSCX3A – JULY 2013 – REVISED JANUARY 2014
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18.2.5 Error Counters
There are multiple mechanisms in the CAN protocol to detect errors and inhibit erroneous modules from
disabling all bus activities. Each CAN module includes two error counters to perform error management.
The receive error counter (REC) and the transmit error counter (TEC) are 8bits wide, located in the 16-bit
wide CANEC register. The counters are modified by the CAN module according to the rules listed in
Table 18-2, which provides an overview of the CAN error conditions and the behavior of the CAN module;
for a detailed description of the error management and fault confinement rules, refer to the CAN
Specification 2.0B.
If the MSB (bit 7) of the REC is set, the node is error passive and the REC will not increment any further.
The Error counters can be read by application software as described under CAN Error Counter Register
(CANEC).
Table 18-2. Error Counter Handling
Condition
Receive Error Counter Conditions
A receiver detects a bit error during sending an active error flag.
A receiver detects a “dominant“ bit as the first bit after sending an error flag
After detecting the 14th consecutive “dominant“ bit following an active error flag or overload flag,
or after detecting the 8th consecutive “dominant“ bit following a passive error flag. After each
sequence of additional 8 consecutive “dominant” bits.
Any other error condition (stuff, frame, CRC, ACK)
A valid reception or transmission
Transmit Error Counter Conditions
A transmitter detects a bit error while sending an active error flag
After detecting the 14th consecutive “dominant“ bit following an active error flag or overload flag
or after detecting the 8th consecutive “dominant“ bit following a passive error flag. After each
sequence of additional 8 consecutive ‘dominant’ bits.
Any other error condition (stuff, frame, CRC, ACK)
A valid reception or transmission
Action
Increment by 8
Increment by 8
Increment by 8
Increment by 1
Decrement by 1 unless counter is
already 0
Increment by 8
Increment by 8
Increment by 8
Decrement by 1 unless counter is
already 0
Special error handling for the TEC counter is performed in the following situations:
• A stuff error occurs during arbitration, when a transmitted “recessive” stuff bit is received as a
“dominant” bit. This does not lead to an increment of the TEC.
• An ACK-error occurs in an error passive device and no “dominant” bits are detected while sending the
passive error flag. This does not lead to an increment of the TEC.
• If only one device is on the bus and this device transmits a message, it will get no acknowledgment.
This will be detected as an error and the message will be repeated. When the device goes “error
passive” and detects an acknowledge error, the TEC counter is not incremented. Therefore the device
will not go from ”error passive” to the “bus off” state due to such a condition.
132 CAN Module
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