DS80C390_00 Datasheet, PDF (129/155 Pages) Dallas Semiconductor – High-Speed Microcontroller User’s Guide Supplement

DS80C390 High-Speed Microcontroller User’s Guide Supplement
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 will be written to 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 will be ignored and the message center
remains unchanged. The CAN module will proceed 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 will be ignored and the message center
remains unchanged. The CAN module will proceed 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 frame request in the message center, so the
matching message will be written to appropriate
message center (1-15)
1
1
x The new matching message will be stored, overwriting
the previously stored message. The ROW bit will be set
to indicate the overwrite operation.
Special notes for message center 15
The ROW bit in message center 15 is associated with an overwrite of the shadow
buffer for message center 15. The EXTRQ and DTUP bits are also shadow
buffered to allow the buffered message and the message center 15 value to take on
different relationships. The EXTRQ and DTUP values read by software are the
current message center 15 values, rather than those of the shadow buffer as is the
case with the ROW bit. The shadow buffer is automatically loaded into message
center 15 when both the DTUP bit and EXTRQ bit are cleared. If either DTUP=1
or EXTRQ=1 when clearing the other, any message in the shadow buffer will not
be transferred to the message 15 registers, and any incoming messages for
message 15 will be stored in the shadow buffer if WTOE = 1, or will be lost if
WTOE = 0.
Special notes concerning remote frames
For remote frames, which can be received by transmit message centers (1-14) in
case of a matching identifier, WTOE and EXTRQ are evaluated. If ((WTOE = 1)
OR (WTOE = 0 and EXTRQ = 1)), the respective transmit message center (1-14)
arbitration bits can be overwritten.
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