mc68hc08qa24 Freescale Semiconductor, Inc, mc68hc08qa24 Datasheet - Page 347

• Manufacturer Part Number: mc68hc08qa24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

MC68HC08QA24
Freescale Semiconductor
The MSCAN08 then will schedule the message for transmission and will
signal the successful transmission of the buffer by setting the TXE flag.
A transmit interrupt will be emitted
to drive the application software to re-load the buffer.
In case more than one buffer is scheduled for transmission when the
CAN bus becomes available for arbitration, the MSCAN08 uses the local
priority setting of the three buffers for priorisation. For this purpose,
every transmit buffer has an 8-bit local priority field (PRIO). The
application software sets this field when the message is set up. The local
priority reflects the priority of this particular message relative to the set
of messages being emitted from this node. The lowest binary value of
the PRIO field is defined as the highest priority.
The internal scheduling process takes place whenever the MSCAN08
arbitrates for the bus. This is also the case after the occurrence of a
transmission error.
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 MSCAN08 will then grant the
request, if possible, by setting the corresponding abort request
acknowledge (ABTAK) and the TXE flag to release the buffer and by
emitting a transmit interrupt. The transmit interrupt handler software can
tell from the setting of the ABTAK flag whether the message was actually
aborted (ABTAK = 1) or sent (ABTAK = 0).
1. The transmit interrupt will occur only if not masked. A polling scheme can be applied on
TXE also.
CAN Controller
(1)
when TXE is set and can be used
CAN Controller
Technical Data
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