Datasheet

39.6.5.1 Acceptance Filtering
The CAN offers the possibility to configure two sets of acceptance filters, one for standard identifiers and
one for extended identifiers. These filters can be assigned to an Rx Buffer or to Rx FIFO 0,1. For
acceptance filtering each list of filters is executed from element #0 until the first matching element.
Acceptance filtering stops at the first matching element. The following filter elements are not evaluated for
this message.
The main features are:
• Each filter element can be configured as
– range filter (from - to)
– filter for one or two dedicated IDs
– classic bit mask filter
• Each filter element is configurable for acceptance or rejection filtering
• Each filter element can be enabled / disabled individually
• Filters are checked sequentially, execution stops with the first matching filter element
Related configuration registers are:
• Global Filter Configuration GFC
• Standard ID Filter Configuration SIDFC
• Extended ID Filter Configuration XIDFC
• Extended ID AND Mask XIDAM
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
• Store received frame in Rx Buffer
• Store received frame in Rx Buffer and generate pulse at filter event pin
• 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 Buffer or Rx FIFO has been found, the Message Handler starts
writing the received message data in portions of 32 bit to the matching Rx Buffer or Rx FIFO. If the CAN
protocol controller has detected an error condition (e.g. CRC error), this message is discarded with the
following impact on the affected Rx Buffer or Rx FIFO:
Rx Buffer
New Data flag of matching Rx Buffer is not set, but Rx Buffer (partly) overwritten with received data. For
error type see PSR.LEC respectively PSR.FLEC.
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 respectively PSR.FLEC. 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, or into an Rx Buffer, the
unmodified received identifier is stored independent of the filter(s) used. The result of the acceptance
filter process is strongly depending on the sequence of configured filter elements.
SAM D5x/E5x Family Data Sheet
CAN - Control Area Network
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1214