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Received Frame
Message Object
Acceptance Mask of
Message Object
ID
match
ID
match
Figure 20-14 Received Message Identifier Acceptance Check
20.3.8.2 Transmit Acceptance Filtering
A message is requested for transmission by setting a transmit request in the message
object that holds the message. If more than one message object have a valid transmit
request for the same CAN node, one of these message objects is chosen for
transmission, because only a single message object can be transmitted at one time on
a CAN bus.
A message object is qualified for transmission on a CAN node if the following four
conditions are met (see also
1. The message object is allocated to the message object list of the CAN node.
2. Bit MOSTATn.MSGVAL is set.
3. Bit MOSTATn.TXRQ is set.
4. Bit MOSTATn.TXEN0 and MOSTATn.TXEN1 are set.
A priority scheme determines which one of all qualifying message objects is transmitted
first. It is assumed that message object a (MOa) and message object b (MOb) are two
message objects qualified for transmission. MOb is a list successor of MOa. For both
message objects, CAN messages CANa and CANb are defined (identifier, IDE, and RTR
are taken from the message-specific bit fields and bits MOARn.ID, MOARn.IDE and
MOCTRn.DIR).
If both message objects belong to the same priority class (identical PRI bit field in register
MOARn), MOa has a higher transmit priority than MOb if one of the following conditions
is fulfilled.
•
PRI = 10
and CAN message MOa has higher or equal priority than CAN message
B
MOb with respect to CAN arbitration rules (see
•
PRI = 01
or PRI = 11
B
User's Manual
MultiCAN, V2.24
Identifier of
Identifier of
= 0: ID of the received frame fits to message object
> 0: ID of the received frame does not fit to message object
Figure
20-15).
(priority by list order).
B
Controller Area Network Controller (MultiCAN)
0 = Bit match
1 = No match
Bitwise
XOR
Bitwise
AND
Table 20-14
20-36
TC1728
ID
match
MCA06271
on
Page
20-110).
V1.0, 2011-12
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