MC912DG128ACPVE Datasheet, PDF (329/478 Pages) Freescale Semiconductor, Inc – Upward compatible with M68HC11 instruction set

Freescale Semiconductor, Inc.
MSCAN Controller
Message Storage
status of the foreground receive buffer. When the buffer contains a
correctly received message with matching identifier this flag is set.
After the msCAN12 successfully received a message into the
background buffer and if the message passes the filter, it copies the
content of RxBG into RxFG⁽¹⁾, sets the RXF flag, and emits a receive
interrupt to the CPU⁽²⁾. A new message (which may follow immediately
after the IFS field of the CAN frame) will be received into RxBG. The
over-writing of the background buffer is independent of the identifier filter
function.
The user’s receive handler has to read the received message from
RxFG and to reset the RXF flag in order to acknowledge the interrupt
and to release the foreground buffer.
An overrun condition occurs when both the foreground and the
background receive message buffers are filled with correctly received
messages with accepted identifiers and a further correctly received
message with accepted identifier is received from the bus. The latter
message will be discarded and an error interrupt with overrun indication
will occur if enabled. As long as both buffers remain filled, the msCAN12
is able to transmit messages but it will discard all incoming messages.
NOTE:
The msCAN12 will receive its own messages into the background
receive buffer RxBG but will not overwrite RxFG and will not emit a
receive interrupt nor will it acknowledge (ACK) its own messages on the
CAN bus. The exception to this rule is that when in loop-back mode
msCAN12 will treat its own messages exactly like all other incoming
messages.
1. Only if the RXF flag is not set.
2. The receive interrupt will occur only if not masked. A polling scheme can be applied on RXF
also.
MC68HC912DT128A — Rev 4.0
MOTOROLA
MSCAN Controller
For More Information On This Product,
Go to: www.freescale.com
Technical Data
329