Users Guide: Network Microcontroller Supplement User Manual

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 ar
e 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 contr
ols the ability of a new message to overwrite an existing message in
the corresponding message center in r
eceive 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 WH E N N EW MESSAG E DET ECTED
0 0 0
There is c urrently n o u nread mess age or pending ext er nal frame
request in t he mess ag e ce nt er, so the matc h i ng m e ssage is wr it te n
to th e appropriate message cent er (1– 1 5).
0 1 x
The m essag e c ent er (1–15) has a n unread m e s sag e or pend ing
ex t erna l fr am e reque st. T h e in c o ming mat c h i ng message i s ig n ored
and the m essag e c e nt er remai ns un c ha nged. Th e C AN modu l e
proceeds to t he n ext l ow er-prior ity m ess age c e nt er to e v al u a te t he
in c o mi ng m ess age ID and arbitrati o n b its a nd re lat ed masking
operatio ns. (No o v erwrite .)
0 x 1
The m essag e c ent er (1–15) has a n unread m e s sag e or pend ing
ex t erna l fr am e reque st. T h e in c o ming mat c h i ng message i s ig n ored
and the m essag e c e nt er remai ns un c ha nged. Th e C AN modu l e
proceeds to t he n ext l ow er-prior ity m ess age c e nt er to e v al u a te t he
in c o mi ng m ess age ID and arbitrati o n b its a nd re lat ed masking
operatio ns. (No o v erwrite .)
1 0 x
There is c urrently n o u nread mess age or pending ext er nal reque s t
in the m essag e c e nt er , so the m atch ing mess ag e i s wr itte n t o
appropriate m essag e ce nt er (1– 15).
1 1 x
The n ew matc h i ng me ssage is st or ed, o verwr it ing t h e pre v i o usly
st ored mess ag e. T he ROW bit is s e t to indi c a te the overwrite
operatio n.
MOVX Address
1
7 6543210
Xxxxy5h ID4 ID3 ID2 ID1 ID0 0 0 WTOE
Maxim Integrated