NXP Semiconductors KE1xF Series, Reference Manual, Page: 1433 / 1483

RXIDB_0, RXIDB_1 — Rx Frame Identifier (Format B)
Specifies an ID to be used as acceptance criteria for the FIFO. In the standard frame
format, the 11 most significant bits (a full standard ID) (29 to 19 and 13 to 3) are used for
frame identification. In the extended frame format, all 14 bits of the field are compared to
the 14 most significant bits of the received ID.
RXIDC_0, RXIDC_1, RXIDC_2, RXIDC_3 — Rx Frame Identifier (Format C)
Specifies an ID to be used as acceptance criteria for the FIFO. In both standard and
extended frame formats, all 8 bits of the field are compared to the 8 most significant bits
of the received ID.
IDHIT — Identifier Acceptance Filter Hit Indicator
This 9-bit field indicates which Identifier Acceptance Filter was hit by the received
message that is in the output of the Rx FIFO. See
Rx FIFO for more information.
50.5 Functional description
The FlexCAN module is a CAN protocol engine with a very flexible mailbox system for
transmitting and receiving CAN frames. The mailbox system is composed by a set of
Message Buffers (MB) that store configuration and control data, time stamp, message ID
and data (see
Message buffer structure ). The memory corresponding to the first 38 MBs
can be configured to support a FIFO reception scheme with a powerful ID filtering
mechanism, capable of checking incoming frames against a table of IDs (up to 128
extended IDs or 256 standard IDs or 512 8-bit ID slices), with individual mask register
for up to 32 ID Filter Table elements.
Simultaneous reception through FIFO and mailbox is supported. For mailbox reception, a
matching algorithm makes it possible to store received frames only into MBs that have
the same ID programmed on its ID field. A masking scheme makes it possible to match
the ID programmed on the MB with a range of IDs on received CAN frames. For
transmission, an arbitration algorithm decides the prioritization of MBs to be transmitted
based on the message ID (optionally augmented by 3 local priority bits) or the MB
ordering.
Before proceeding with the functional description, an important concept must be
explained. A Message Buffer is said to be "active" at a given time if it can participate in
both the Matching and Arbitration processes. An Rx MB with a 0b0000 code is inactive
(refer to
Table 50-5 ). Similarly, a Tx MB with a 0b1000 or 0b1001 code is also inactive
(refer to Table 50-6 ).
Chapter 50 CAN (FlexCAN)
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
NXP Semiconductors 1433