DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
346 of 571
NXP Semiconductors
UM10316
Chapter 21: LPC29xx CAN 0/1
•
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.
•
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. 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
11.1 FullCAN message layout
The FF, RTR, and DLC fields are as described in
Since the FullCAN message object section of the Look-up table RAM can be accessed
both by the Acceptance Filter and the CPU, there is a method for insuring that no CPU
reads from FullCAN message object occurs while the Acceptance Filter hardware is
writing to that object.
For this purpose the Acceptance Filter uses a 3-state semaphore, encoded with the two
semaphore bits SEM1 and SEM0 (see
Table 21–298 “Format of automatically stored Rx
) for each message object. This mechanism provides the CPU with information
about the current state of the Acceptance Filter activity in the FullCAN message object
section.
The semaphore operates in the following manner:
Table 298. Format of automatically stored Rx messages
Address
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
0
F
F
R
T
R
0000
SEM
[1:0]
0000
DLC
00000
ID.28 ... ID.18
+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