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The IFLAG[BUF7I] (Rx FIFO Overflow) is asserted when an incoming message was lost
because the Rx FIFO is full. Note that the flag will not be asserted when the Rx FIFO is
full and the message was captured by a Mailbox. The flag remains asserted until the CPU
clears it.
Clearing one of those three flags does not affect the state of the other two.
An interrupt is generated if an IFLAG bit is asserted and the corresponding mask bit is
asserted too.
A powerful filtering scheme is provided to accept only frames intended for the target
application, reducing the interrupt servicing work load. The filtering criteria is specified
by programming a table of up to 128 32-bit registers, according to CTRL2[RFFN]
setting, that can be configured to one of the following formats (see also Rx FIFO
structure):
• Format A: 128 IDAFs (extended or standard IDs including IDE and RTR)
• Format B: 256 IDAFs (standard IDs or extended 14-bit ID slices including IDE and
RTR)
• Format C: 512 IDAFs (standard or extended 8-bit ID slices)
Note
A chosen format is applied to all entries of the filter table. It is
not possible to mix formats within the table.
Every frame available in the FIFO has a corresponding IDHIT (Identifier Acceptance
Filter Hit Indicator) that can be read by accessing the RXFIR register. The
RXFIR[IDHIT] field refers to the message at the output of the FIFO and is valid while
the IFLAG[BUF5I] flag is asserted. The RXFIR register must be read only before
clearing the flag, which guarantees that the information refers to the correct frame within
the FIFO.
Up to 32 elements of the filter table are individually affected by the Individual Mask
Registers (RXIMRx), according to the setting of CTRL2[RFFN], allowing very powerful
filtering criteria to be defined. If the IRMQ bit is negated, then the FIFO filter table is
affected by RXFGMASK.
45.4.8 CAN protocol related features
This section describes the CAN protocol related features.
Functional description
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
1166
Preliminary
Freescale Semiconductor, Inc.
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