Information

0 = Extended frames are rejected and standard frames can be accepted
RXIDA — Rx Frame Identifier (Format A)
Specifies an ID to be used as acceptance criteria for the FIFO. In the standard frame
format, only the 11 most significant bits (29 to 19 ) are used for frame identification. In
the extended frame format, all bits are used.
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.
45.4 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 45-70). Similarly, a Tx MB with a 0b1000 or 0b1001 code is also inactive
(refer to Table 45-71).
Functional description
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
1148
Preliminary
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