Nxp Semiconductors UM10237 用户手册

UM10237_2

© NXP B.V. 2008. All rights reserved.

The table of ranges of Extended Identifiers must contain an even number of entries, of the 
same form as in the individual Extended Identifier table. Like the Individual Extended 
table, the Extended Range must be arranged in ascending numerical order. The first and 
second (3rd and 4th …) entries in the table are implicitly paired as an inclusive range of 
Extended addresses, such that any received address that falls in the inclusive range is 
received (accepted). Software must maintain the table to consist of such word pairs.

There is no facility to receive messages to Extended identifiers using the fullCAN method.

Five address registers point to the boundaries between the tables in Acceptance Filter 
RAM: fullCAN Standard addresses, Standard Individual addresses, Standard address 
ranges, Extended Individual addresses, and Extended address ranges. These tables 
must be consecutive in memory. The start of each of the latter four tables is implicitly the 
end of the preceding table. The end of the Extended range table is given in an End of 
Tables register. If the start address of a table equals the start of the next table or the End 
Of Tables register, that table is empty.

When the Receive side of a CAN controller has received a complete Identifier, it signals 
the Acceptance Filter of this fact. The Acceptance Filter responds to this signal, and reads 
the Controller number, the size of the Identifier, and the Identifier itself from the Controller. 
It then proceeds to search its RAM to determine whether the message should be received 
or ignored.

If fullCAN mode is enabled and the CAN controller signals that the current message 
contains a Standard identifier, the Acceptance Filter first searches the table of identifiers 
for which reception is to be done in fullCAN mode. Otherwise, or if the AF doesn’t find a 
match in the fullCAN table, it searches its individual Identifier table for the size of Identifier 
signalled by the CAN controller. If it finds an equal match, the AF signals the CAN 
controller to retain the message, and provides it with an ID Index value to store in its 
Receive Frame Status register.

If the Acceptance Filter does not find a match in the appropriate individual Identifier table, 
it then searches the Identifier Range table for the size of Identifier signalled by the CAN 
controller. If the AF finds a match to a range in the table, it similarly signals the CAN 
controller to retain the message, and provides it with an ID Index value to store in its 
Receive Frame Status register. If the Acceptance Filter does not find a match in either the 
individual or Range table for the size of Identifier received, it signals the CAN controller to 
discard/ignore the received message.

The AccBP and AccOff bits of the acceptance filter mode register are used for putting the 
acceptance filter into the Bypass and Off mode. The eFCAN bit of the mode register can 
be used to activate a FullCAN mode enhancement for received 11-bit CAN ID messages.