mc68hc912bc32 Freescale Semiconductor, Inc, mc68hc912bc32 Datasheet - Page 247

• Manufacturer Part Number: mc68hc912bc32
• Description: M68hc12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

When a high priority message is scheduled by the application software, it may become necessary to abort
a lower priority message being set up in one of the three transmit buffers. Because messages that are
already under transmission cannot be aborted, the user has to request the abort by setting the
corresponding abort request flag (ABTRQ) in the transmission control register (CTCR). The msCAN12
grants the request, if possible, by setting the corresponding abort request acknowledge (ABTAK) and the
TXE flag to release the buffer and by generating a transmit interrupt. The transmit interrupt handler
software can tell from the setting of the ABTAK flag whether the message was aborted (ABTAK = 1)
or sent in the meantime (ABTAK = 0).
16.4 Identifier Acceptance Filter
The identifier acceptance registers (CIDAR0–CIADAR7) define the acceptable patterns of the standard
or extended identifier (ID10–ID0 or ID28–ID0). Any of these bits can be marked don’t care in the identifier
mask registers (CIDMR0–CIDMR7).
A filter hit is indicated to the application software by:
These identifier hit flags (IDHIT2–IDHIT0) clearly identify the filter section that caused the acceptance.
They simplify the application software’s task to identify the cause of the receiver interrupt. When more
than one hit occurs (two or more filters match), the lower hit has priority.
A flexible, programmable generic identifier acceptance filter has been introduced to reduce the CPU
interrupt loading. The filter is programmable to operate in four different modes:
Freescale Semiconductor
1. Two identifier acceptance filters, each to be applied to the full 29 bits of the identifier and to three
•
•
A set RXF (receive buffer full flag)
See
Three bits in the identifier acceptance control register
See
bits of the CAN frame: RTR, IDE, and SRR. This mode implements two filters for a full length CAN
2.0B compliant extended identifier.
(CIDAR0–CIDAR3, CIDMR0–CIDMR3) produces a filter 0 hit. Similarly, the second filter bank
(CIDAR4–CUIDAR7, CIDMR4–CIDMR7) produces a filter 1 hit.
16.12.5 msCAN12 Receiver Flag
16.12.9 msCAN12 Identifier Acceptance Control
ID28
ID10
AC7
AC7
CIDMRO
Figure 16-3. 32-Bit Maskable Identifier Acceptance Filter
CIDARO
IDR0
IDR0
ID21 ID20
AC0 AC7
AC0 AC7
ID3 ID2
M68HC12B Family Data Sheet, Rev. 9.1
CIDMR1
CIDAR1
IDR1
IDR1
ID accepted (Filter 0 hit)
Figure 16-3
IDE
Register) and
ID15 ID14
AC0 AC7
AC0 AC7
shows how the first 32-bit filter bank
CIDMR2
CIDAR2
IDR2
Register).
AC0
AC0
ID7
ID6
AC7
AC7
CIDMR3
CIDAR3
IDR3
Identifier Acceptance Filter
RTR
AC0
AC0
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