Owner's manual

MAXQ7665/MAXQ7666 User’s Guide
4-18
CAN 0 Message Center y Arbitration Register 3 (C0MyAR3)
CAN 0 Message Center y Arbitration Registers 0 to 3 (C0MyAR0 to C0MyAR3). These bits form the arbitration value/identification
number for the message center y. When the message center is configured in a transmit mode, these registers 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 cor-
respond to ID28–ID0 as shown above. When EX/ST = 0, the message ID bits 10–0 correspond to ID28–ID18 in C0MyAR0 and
C0MyAR1.
When configured in a receive mode, these registers serve as the arbitration value for message center y, against which incoming mes-
sages 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 cares for incoming message
acceptance.
Bits 2, 1 (C0MyAR3 Only): Reserved. These bits are not used in arbitration. These bits can be modified by the application software.
A read of these bits will always return 0.
Bit 0 (C0MyAR3 Only): Writeover Enable (WTOE). 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 center in question must also be con-
sidered to determine the effect of this bit as shown below. The WTOE bit can only be programmed when the SWINT bit is set.
Bit #
76543210
Name ID4 ID3 ID2 ID1 ID0 — — WTOE
Reset X X X X X X X X
Access rw rw rw rw rw rw rw rw
Dual Port
Address
(8y+2)h(L)
WTOE DTUP EXTRQ RESULT WHEN NEW MESSAGE IS DETECTED
000
There is currently no unread message or pending external frame request in the message center, so the matching
message is written to appropriate message center (1–15).
01x
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.)
0x1
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.)
10x
There is currently no unread message or pending external frame request in the message center, so the matching
message is written to appropriate message center (1–15).
11x
The new matching message is stored, overwriting the previously stored message. The ROW bit is set to indicate
the overwrite operation.
X = Don’t care
r = read, w = write (via C0DP/C0DB)
Maxim Integrated