ST72521R9-Auto STMicroelectronics, ST72521R9-Auto Datasheet - Page 197

• Manufacturer Part Number: ST72521R9-Auto
• Description: 8-bit MCU for automotive
• Manufacturer: STMicroelectronics

Specifications of ST72521R9-Auto

• Hdflash Endurance: 100 cycles, data retention 20 years
• Clock Sources: crystal/ceramic resonator oscillators, internal RC oscillator and bypass for external clock
• 4 Power Saving Modes: Halt, Active Halt, Wait and Slow

ST72521xx-Auto
17.5.3
Unexpected message transmission
Symptom
The previous message received by pCAN, even if this message did not pass the receive
filter, will be retransmitted by pCAN with a correct identifier and DLC but with corrupted data.
The data bytes will be a copy of the identifier bytes IDHR and IDLR in the following repetitive
pattern:
DATA_0 = IDHR
DATA_1 = IDLR
DATA_2 = IDHR
DATA_3 = IDLR
etc.
DATA_7 = IDLR
If no message has been received before the problem occurs then identifier byte values are
random but the data bytes are in the same repetitive pattern.
Details
The buffers of the pCAN cell are configurable as receive or transmit buffers. By default, all
buffers are configured in reception. To use a buffer to transmit a CAN message the
application has to reserve this buffer for transmission by setting the LOCK bit in the BCSR
register. So the buffer is then locked for any further reception and reserved for transmission.
Once a transmission has been requested by a write access to data byte 7 of the buffer the
application might need to abort this transmission request. To do so, the application can reset
the LOCK bit in the BCSR register.
If the message is pending (RDY bit set) but not currently being transmitted, then clearing the
LOCK bit will abort it immediately.
If the message is pending (RDY bit set) and currently being transmitted then the message
will not be interrupted but the CAN core will wait until the end of this transmission attempt.
Then software must clear the LOCK bit again to abort the transmission.
An unexpected transmission can occur:
IF the application resets the LOCK bit
WHILE the CAN core is preparing the transmission
pending in another buffer
THEN the LOCK bit is reset but the transmission is not stopped. Instead the content of the
page 0 buffer will be transmitted.
Impact on the application
pCAN will echo some messages sent by other nodes. Identifier and DLC will be correct but
data are corrupted as described previously.
a. The preparation lasts two bit times just before SOF; this is the critical window during which the LOCK bit must
not be reset by the application.
Doc ID 17660 Rev 1
(a)
AND there is no other transmission
Controller area network (CAN)
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