PXS20RM Datasheet, PDF (637/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

FlexCAN Module
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.
24.4.7.1 Precautions When Using Global Mask and Individual Mask Registers
Mask filtering alignment is affected based on the setting of the FEN and BCC of MCR. The following
table shows recommended actions depending on FEN and BCC settings.
Table 24-8. Recommended FEN and BCC settings
Case
Case1
Case 2
Case 3
Case 4
MCR[FEN]
RxFIFO
FEN=0
FEN=1
FEN=1
Don’t Care
MCR[BCC]
RxIndividual
Mask
BCC=0
BCC=0
BCC=0
BCC=1
Notes
RXGMASK, RX14MASK and RX15MASK can safely be
used.This allows backwards compatibility to older devices (e.g.
devices without the individual masks feature). In this case,
individual masks are not used.
1st alternative:
Don't use RXGMASK, RX14MASK and RX15MASK in this case,
leave the masks in their reset state.
2nd alternative:
Do not configure any MB as Rx (i.e. let all MBs as either Tx or
inactive). In this case, the masks RXGMASK, RX14MASK and
RX15MASK can be used to affect ID Tables without affecting the
filtering process for Rx MBs
If MCR[BCC] = 1, then the RXIMRs are enabled an thus the
masks RXGMASK, RX14MASK and RX15MASK are not
used.Particularly, when MCR[FEN] = 0, RxFifo is disabled;
RXGMASK, RX14MASK and RX15MASK don't affect filtering.
Individual masks used.
24.4.8 CAN Protocol Related Features
24.4.8.1 Remote Frames
Remote frame is a special kind of frame. The user can program an 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 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.
Freescale Semiconductor
PXS20 Microcontroller Reference Manual, Rev. 1
24-37