FD controller area network (FDCAN) RM0440
1960/2126 RM0440 Rev 4
Depending on the configuration of the filter element (SFEC/EFEC) a match triggers one of
the following actions:
• Store received frame in FIFO 0 or FIFO 1
• Reject received frame
• Set High Priority Message interrupt flag IR[HPM]
• Set High Priority Message interrupt flag IR[HPM] and store received frame in FIFO 0 or
FIFO 1.
Acceptance filtering is started after the complete identifier has been received. After
acceptance filtering has completed, and if a matching Rx FIFO has been found, the
Message Handler starts writing the received message data in 32-bit portions to the matching
Rx FIFO. If the CAN protocol controller has detected an error condition (e.g. CRC error), this
message is discarded with the following impact:
• Rx FIFO
Put index of matching Rx FIFO is not updated, but related Rx FIFO element (partly)
overwritten with received data. For error type see PSR.LEC and PSR.DLEC. In case
the matching Rx FIFO is operated in overwrite mode, the boundary conditions
described in Rx FIFO Overwrite Mode have to be considered.
Note: When an accepted message is written to one of the two Rx FIFOs, the unmodified received
identifier is stored independently from the used filter(s). The result of the acceptance filter
process is strongly depending on the sequence of configured filter elements.
Range filter
The filter matches for all received frames with Message IDs in the range defined by
SF1ID/SF2ID and EF1ID/EF2ID.
There are two possibilities when range filtering is used together with extended frames:
• EFT = 00: The Message ID of received frames is AND-ed with the Extended ID AND
Mask (XIDAM) before the range filter is applied
• EFT = 11: The Extended ID AND Mask (XIDAM) is not used for range filtering
Filter for dedicated IDs
A filter element can be configured to filter for one or two specific Message IDs. To filter for
one specific Message ID, the filter element has to be configured with SF1ID = SF2ID and
EF1ID = EF2ID.
Classic bit mask filter
Classic bit mask filtering is intended to filter groups of Message IDs by masking single bits of
a received Message ID. With classic bit mask filtering SF1ID/EF1ID is used as Message ID
filter, while SF2ID/EF2ID is used as filter mask.
A 0 bit at the filter mask masks out the corresponding bit position of the configured ID filter,
e.g. the value of the received Message ID at that bit position is not relevant for acceptance
filtering. Only those bits of the received Message ID where the corresponding mask bits are
one are relevant for acceptance filtering.
In case all mask bits are one, a match occurs only when the received Message ID and the
Message ID filter are identical. If all mask bits are 0, all Message IDs match.
To Next Page
Loading...
Need help?
General
