MPC5566 Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 22-29
The following bullets apply only if:
reception queue is disabled,
no other matching buffers in the reception queue or for the last available queue element when all other MBs
are not free to receive (the last queue element is overwritten in this manner for a single MB in non-queue
mode). If the reception queue is enabled, the state machine searches for the next matching message buffer.
• If while an MB is locked and an RX frame with a matching ID is received, the RX frame cannot
be stored in the MB and remains in the SMB. The CANx_ESR does not indicate the RX frame
remained in the SMB.
• If while a MB is locked when two or more RX frames with matching ID are received, the last RX
frame remains in the SMB, while all preceding RX frames are lost. The CANx_ESR does not
indicate that the preceding frames are discarded.
• If a locked MB is released and a matching frame exists in the SMB, the frame is transferred to the
matching MB.
22.4.5 CAN Protocol Related Features
22.4.5.1 Remote Frames
A remote frame is a special kind of frame. The user can program a MB to be a request remote frame by
writing the MB as transmit with the RTR bit set to 1. After the remote request frame is transmitted
successfully, the MB becomes a receive message buffer, with the same ID as before.
When a remote request frame is received by FlexCAN, its ID is compared to the IDs of the transmit
message buffers with the CODE field ‘1010’. If there is a matching ID, then the MB frame is transmitted.
If the matching MB has the RTR bit set, then FlexCAN2 transmits a remote frame as a response.
A 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 must match.
In the case that a remote request frame was received and matched a MB, this message buffer immediately
enters the internal arbitration process, but is considered as normal TX MB, with no higher priority. The
data length of this frame is independent of the DLC field in the remote frame that initiated its transmission.
22.4.5.2 Overload Frames
FlexCAN2 transmits overload frames if the dominant bit satisfies any of the following conditions:
• First or second bit of intermission
• Seventh (last) bit of the end-of-frame field in RX frames
• Eighth bit (last) of error frame delimiter or overload frame delimiter
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