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Functional description
43.5.8.1 Remote frames
Remote frame is a special kind of frame. The user can program a mailbox to be a Remote
Request Frame by configuring the mailbox as Transmit with the RTR bit set to '1'. After
the remote request frame is transmitted successfully, the mailbox becomes a Receive
Message Buffer, with the same ID as before.
When a remote request frame is received by FlexCAN, it can be treated in three ways,
depending on Remote Request Storing (CTRL2[RRS]) and Rx FIFO Enable
(MCR[RFEN]) bits:
• If RRS is negated the frame's ID is compared to the IDs of the Transmit Message
Buffers with the CODE field 0b1010. If there is a matching ID, then this mailbox
frame will be transmitted. Note that if the matching mailbox has the RTR bit set, then
FlexCAN will transmit a remote frame as a response. The received remote request
frame is not stored in a receive buffer. It is only used to trigger a transmission of a
frame in response. The mask registers are not used in remote frame matching, and all
ID bits (except RTR) of the incoming received frame should match. In the case that a
remote request frame is received and matches a mailbox, this message buffer
immediately enters the internal arbitration process, but is considered as a normal Tx
mailbox, with no higher priority. The data length of this frame is independent of the
DLC field in the remote frame that initiated its transmission.
• If RRS is asserted the frame's ID is compared to the IDs of the receive mailboxes
with the CODE field 0b0100, 0b0010 or 0b0110. If there is a matching ID, then this
mailbox will store the remote frame in the same fashion of a data frame. No
automatic remote response frame will be generated. The mask registers are used in
the matching process.
• If RFEN is asserted FlexCAN will not generate an automatic response for remote
request frames that match the FIFO filtering criteria. If the remote frame matches one
of the target IDs, it will be stored in the FIFO and presented to the CPU. Note that for
filtering formats A and B, it is possible to select whether remote frames are accepted
or not. For format C, remote frames are always accepted (if they match the ID).
Remote Request Frames are considered as normal frames, and generate a FIFO
overflow when a successful reception occurs and the FIFO is already full.
43.5.8.2 Overload frames
FlexCAN does transmit overload frames due to detection of following conditions on
CAN bus:
1150
KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
Freescale Semiconductor, Inc.
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