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MPC563XM Reference Manual, Rev. 1
1302
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
more than one MB with the same ID, received messages will be queued into the MBs. The CPU can
examine the Time Stamp field of the MBs to determine the order in which the messages arrived.
The matching algorithm described above can be changed to be the same one used in previous versions of
the FlexCAN module. When the BCC bit in MCR is negated, the matching algorithm stops at the first MB
with a matching ID that it founds, whether this MB is free or not. As a result, the message queueing feature
does not work if the BCC bit is negated.
Matching to a range of IDs is possible by using ID Acceptance Masks. FlexCAN supports individual
masking per MB. Please refer to
Section 28.4.4.13, “Rx Individual Mask Registers
During the matching algorithm, if a mask bit is asserted, then the corresponding
ID bit is compared. If the mask bit is negated, the corresponding ID bit is “don’t care”. Please note that the
Individual Mask Registers are implemented in RAM, so they are not initialized out of reset. Also, they can
only be programmed if the BCC bit is asserted and while the module is in Freeze Mode.
FlexCAN also supports an alternate masking scheme with only three mask registers (RGXMASK,
RX14MASK and RX15MASK) for backwards compatibility. This alternate masking scheme is enabled
when the BCC bit in the MCR Register is negated.
NOTE
The individual Rx Mask per Message Buffer feature may not be available in
low cost MCUs. Please consult the specific MCU documentation to find out
if this feature is supported. If not supported, the RXGMASK, RX14MASK
and RX15MASK registers are available, regardless of the value of the BCC
bit.
28.5.6
Data Coherence
In order to maintain data coherency and FlexCAN proper operation, the CPU must obey the rules described
in
Section 28.5.2, “Transmit Process
Section 28.5.4, “Receive Process
an MB structure within FlexCAN other than those specified may cause FlexCAN to behave in an
unpredictable way.
28.5.6.1
Transmission Abort Mechanism
The abort mechanism provides a safe way to request the abortion of a pending transmission. A feedback
mechanism is provided to inform the CPU if the transmission was aborted or if the frame could not be
aborted and was transmitted instead. In order to maintain backwards compatibility, the abort mechanism
must be explicitly enabled by asserting the AEN bit in the MCR.
In order to abort a transmission, the CPU must write a specific abort code (1001) to the Code field of the
Control and Status word. When the abort mechanism is enabled, the active MBs configured as trasmission
must be aborted first and then they may be updated. If the abort code is written to an MB that is currently
being transmitted, or to an MB that was already loaded into the SMB for transmission, the write operation
is blocked and the MB is not deactivated, but the abort request is captured and kept pending until one of
the following conditions are satisfied:
•
The module loses the bus arbitration