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Philips Semiconductors
Preliminary User Manual
ARM-based Microcontroller
LPC2119/2129/2292/2294
If Extended (29-bit) Identifiers are used in the application, at least one of the other two tables in Acceptance Filter RAM must not
be empty, one for individual Extended Identifiers and one for ranges of Extended Identifiers. The table of individual Extended
Identifiers must be arranged in ascending numerical order.
31
29
28
0
Identifier
Controller #
Figure 37: Entry in either Extended Identifier Table
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 the Receive Frame Status register 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 the Receive Frame Status register
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.
CAN Controllers and Acceptance Filter
206
May 03, 2004
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