NXP Semiconductors LPC24XX UM10237 User Manual
Page 508
UM10237_4
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 04 — 26 August 2009
508 of 792
NXP Semiconductors
UM10237
Chapter 18: LPC24XX CAN controllers CAN1/2
receive interrupt whenever a CAN message is accepted and received. Software has to
move the received message out of the receive buffer from the according CAN controller
into the user RAM.
To cover dashboard like applications where the controller typically receives data from
several CAN channels for further processing, the CAN Gateway block was extended by a
so-called FullCAN receive function. This additional feature uses an internal message
handler to move received FullCAN messages from the receive buffer of the according
CAN controller into the FullCAN message object data space of Look-up Table RAM.
When fullCAN mode is enabled, the Acceptance Filter itself takes care of receiving and
storing messages for selected Standard ID values on selected CAN buses, in the style of
“FullCAN” controllers.
In order to set this bit and use this mode, two other conditions must be met with respect to
the contents of Acceptance Filter RAM and the pointers into it:
•
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 (see
Figure 18–78 “Entry in FullCAN and individual standard identifier tables” on
). 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