Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement - Manual (Page 145)

High-Speed Microcontroller User’s
Guide: Network Microcontroller
Supplement
145
CAN 0 Message Center y Arbitration Register 3 (C0MyAR3)
ID28–ID0
Bits 2–1
(C0MyAR3 only)
WTOE
Bit 0 (C0MxAR3 only)
CAN 0 message center y arbitration registers 0–3. These bits form the arbitration value/identification
number for message center y. When the message center is configured in a transmit mode, these regis-
ters are the source of the 29-bit ID message field (when EX/ST = 1) or the 11-bit ID message field (when
EX/ST = 0). When EX/ST = 1, the 29 message ID bits correspond to ID28–ID0 as shown above. When
EX/ST = 0, the message ID bits 10–0 correspond to ID28–18 in C0MyAR0 and C0MyAR1.
When configured in a receive mode, these registers serve as the arbitration value for message center y,
against which incoming messages are compared to ascertain if they are valid for that message center.
When EX/ST = 1, all 29 bits of the arbitration are used, but when EX/ST = 0, only the most significant 11
bits are used.
Note that when a message is successfully loaded, the entire message is loaded to the message center.
So, if message ID masking was enabled (MEME = 1), it is possible to overwrite the arbitration register
bits that were defined as “don’t care” for incoming message acceptance.
Reserved. Bits 2 and 1 of the C0MyAR3 register are not used in arbitration. These bits can be modified
by the application software.
Write-over enable. This bit controls the ability of a new message to overwrite an existing message in
the corresponding message center in receive mode. The DTUP and EXTRQ bits for the message cen-
ter in question must also be considered to determine the effect of this bit as follows. The WTOE bit
should only be programmed when the SWINT bit is set.
WTOE DTUP EXTRQ RESULT WHEN NEW MESSAGE DETECTED
0 0 0
There is currently no unread message or pending external frame
request in the message center, so the matching message is written
to the appropriate message center (1–15).
0 1 x
The message center (1–15) has an unread message or pending
external frame request. The incoming matching message is ignored
and the message center remains unchanged. The CAN module
proceeds to the next lower-priority message center to evaluate the
incoming message ID and arbitration bits and related masking
operations. (No overwrite.)
0 x 1
The message center (1–15) has an unread message or pending
external frame request. The incoming matching message is ignored
and the message center remains unchanged. The CAN module
proceeds to the next lower-priority message center to evaluate the
incoming message ID and arbitration bits and related masking
operations. (No overwrite.)
1 0 x
There is currently no unread message or pending external request
in the message center, so the matching message is written to
appropriate message center (1–15).
1 1 x
The new matching message is stored, overwriting the previously
stored message. The ROW bit is set to indicate the overwrite
operation.
MOVX Address 1 7 6 5 4 3 2 1 0
Xxxxy5h ID4 ID3 ID2 ID1 ID0 0 0 WTOE
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