Freescale Semiconductor, Inc.
MSCAN Controller
Identifier Acceptance Filter
cause of the receiver interrupt. When more than one hit occurs (two or
more filters match) the lower hit has priority.
A very flexible programmable generic identifier acceptance filter has
been introduced in order to reduce the CPU interrupt loading. The filter
is programmable to operate in four different modes:
• Two identifier acceptance filters, each to be applied to a) the full
29 bits of the extended identifier and to the following bits of the
CAN frame: RTR, IDE, SRR or b) the 11 bits of the standard
identifier, the RTR and IDE bits of CAN 2.0A/B messages. This
mode implements two filters for a full length CAN 2.0B compliant
extended identifier. Figure 17-3 shows how the first 32-bit filter
bank (CIDAR0–3, CIDMR0–3) produces a filter 0 hit. Similarly, the
second filter bank (CIDAR4–7, CIDMR4–7) produces a filter 1 hit.
• Four identifier acceptance filters, each to be applied to a) the 14
most significant bits of the extended identifier plus the SRR and
IDE bits of CAN 2.0B messages or b) the 11 bits of the standard
identifier, the RTR and IDE bits of CAN 2.0A/B mesages. Figure
17-4 shows how the first 32-bit filter bank (CIDAR0–3, CIDMR0–3)
produces filter 0 and 1 hits. Similarly, the second filter bank
(CIDAR4–7, CIDMR4–7) produces filter 2 and 3 hits.
• Eight identifier acceptance filters, each to be applied to the first 8
bits of the identifier. This mode implements eight independent
filters for the first 8 bits of a CAN 2.0A/B compliant standard
identifier or of a CAN 2.0B compliant extended identifier. Figure
17-5 shows how the first 32-bit filter bank (CIDAR0–3, CIDMR0–3)
produces filter 0 to 3 hits. Similarly, the second filter bank
(CIDAR4–7, CIDMR4–7) produces filter 4 to 7 hits.
• Closed filter. No CAN message will be copied into the foreground
buffer RxFG, and the RXF flag will never be set.
68HC(9)12D60 — Rev 4.0
MOTOROLA
Advance Information
MSCAN Controller
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