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access that sets MSGVAL) to prevent the storage of a frame that belongs to the old
context of the message object. Therefore, a message object re-configuration should
consist of the following steps:
1. Clear MSGVAL bit
2. Re-configure the message object while MSGVAL = 0
3. Clear RTSEL bit and set MSGVAL again
RXEN
Bit MOSTATn.RXEN enables a message object for frame reception. A message object
can receive CAN messages from the CAN bus only if RXEN = 1. The MultiCAN module
evaluates RXEN only during receive acceptance filtering. After receive acceptance
filtering, RXEN is ignored and has no further influence on the actual storage of a received
message in a message object.
Bit RXEN enables the "soft phase out" of a message object: after clearing RXEN, a
currently received CAN message for which the message object has won acceptance
filtering is still stored in the message object but for subsequent messages the message
object no longer wins receive acceptance filtering.
RXUPD, NEWDAT and MSGLST
An ongoing frame storage process is indicated by the RXUPD (Receive Updating) flag
in the MOSTATn register. RXUPD is set with the start and cleared with the end of a
message object update, which consists of frame storage as well as flag updates.
After storing the received frame (identifier, IDE bit, DLC; including the Data Field for Data
Frames), the NEWDAT (New Data) bit of the message object is set. If NEWDAT was
already set before it becomes set again, bit MSGLST (Message Lost) is set to indicate
a data loss condition.
The RXUPD and NEWDAT flags can help to read consistent frame data from the
message object during an ongoing CAN operation. The following steps are
recommended to be executed:
1. Clear NEWDAT bit.
2. Read message content (identifier, data etc.) from the message object.
3. Check that both, NEWDAT and RXUPD, are cleared. If this is not the case, go back
to step 1.
4. When step 3 was successful, the message object contents are consistent and has
not been updated by the MultiCAN module while reading.
Bits RXUPD, NEWDAT and MSGLST have the same behavior for the reception of Data
as well as Remote Frames.
User's Manual
MultiCAN, V2.24
Controller Area Network Controller (MultiCAN)
20-43
TC1728
V1.0, 2011-12
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