Maxim Integrated High-Speed Microcontroller Users Guide: Network Microcontroller Supplement User 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

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).

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.)

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.)

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).

The new matching message is stored, overwriting the previously

stored message. The ROW bit is set to indicate the overwrite

operation.

MOVX Address

Xxxxy5h

ID4

ID3

ID2

ID1

ID0

WTOE

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