FlexCAN
MPC5606S Microcontroller Reference Manual, Rev. 7
Freescale Semiconductor 705
FIFO by reading one or more frames. A warning interrupt is also generated when four frames are
accumulated in the FIFO.
A powerful filtering scheme is provided to accept only frames intended for the target application, thus
reducing the interrupt servicing work load. The filtering criteria is specified by programming a table of
eight 32-bit registers that can be configured to one of the following formats (see also Section 18.3.3, Rx
FIFO Structure):
• Format A: 8 extended or standard IDs (including IDE and RTR)
• Format B: 16 standard IDs or 16 extended 14-bit ID slices (including IDE and RTR)
• Format C: 32 standard or extended 8-bit ID slices
NOTE
A chosen format is applied to all eight registers of the filter table. It is not
possible to mix formats within the table.
The eight elements of the filter table are individually affected by the first eight Individual Mask Registers
(RXIMR0–RXIMR7), allowing very powerful filtering criteria to be defined. The rest of the RXIMR,
starting from RXIM8, continue to affect the regular MBs, starting from MB8. If the BCC bit is negated (or
if the RXIMR are not available for the particular MCU), then the FIFO filter table is affected by the legacy
mask registers as follows: element 6 is affected by RX14MASK, element 7 is affected by RX15MASK
and the other elements (0 to 5) are affected by RXGMASK.
18.4.8 CAN protocol related features
18.4.8.1 Remote frames
A remote frame is a special kind of frame. The user can program an MB to be a Request Remote frame
type 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 this MB frame will be
transmitted. Note that if the matching MB has the RTR bit set, then FlexCAN will transmit 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 should match.
In the case that a Remote Request frame was received and matched an MB, this message buffer
immediately enters the internal arbitration process, but is considered as a 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.
If the Rx FIFO is enabled (bit FEN set in MCR), 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
To Next Page
Loading...
