CAN Controllers and Acceptance Filter 211 May 03, 2004
Philips Semiconductors Preliminary User Manual
LPC2119/2129/2292/2294ARM-based Microcontroller
1. The Standard Frame Individual Start Address Register (SFF_sa) must be greater than or equal to the number of IDs for
which automatic receive storage is to be done, times two. SFF_sa must be rounded up to a multiple of 4 if necessary.
2. The EndOfTable register must be less than or equal to 0x800 minus 6 times the SFF_sa value, to allow 12 bytes of
message storage for each ID for which automatic receive storage will be done.
When these conditions are met and eFCAN is set:
• The area between the start of Acceptance Filter RAM and the SFF_sa address, is used for a table of individual Standard IDs
and CAN Controller/bus identification, sorted in ascending order and in the same format as in the Individual Standard ID table
(see Figure 35 on page 205). Entries can be marked as “disabled” as in the other Standard tables. If there are an odd number
of “FullCAN” ID’s, at least one entry in this table must be so marked.
• The first (SFF_sa)/2 IDindex values are assigned to these automatically-stored ID’s. That is, IDindex values stored in the Rx
Frame Status Register, for IDs not handled in this way, are increased by (SFF_sa)/2 compared to the values they would have
when eFCAN is 0.
• When a Standard ID is received, the Acceptance Filter searches this table before the Standard Individual and Group tables.
• When a message is received for a controller and ID in this table, the Acceptance filter reads the received message out of the
CAN controller and stores it in Acceptance Filter RAM, starting at (EndOfTable) + its IDindex*12.
• The format of such messages is shown in Table 155.
The FF, RTR, and DLC fields are as described in Table 133, “CAN Rx Frame Status Register (CANRFS - 0xE00x x020),” on
page 199. Hardware sets the SEM field to 01 when it begins to update a message, and to 11 when it finishes doing so. Software
should clear SEM to 00 as part of accessing a message. Software must access the three words in a message in a particular
way to ensure that they are all from the same received message. Figure below shows how software should use the SEM field
to ensure this.
Table 155: Format of Automatically Stored Rx Message
Address
31 24 23 16 15 10 8 7 0
0
F
F
R
T
R
0000 SEM 0000 DLC 00000 ID
+4 Rx Data 4 Rx Data 3 Rx Data 2 Rx Data 1
+8 Rx Data 8 Rx Data 7 Rx Data 6 Rx Data 5
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