NXP Semiconductors LPC24XX UM10237 - Manual (Page 506)

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User manual Rev. 04 — 26 August 2009 506 of 792
NXP Semiconductors
UM10237
Chapter 18: LPC24XX CAN controllers CAN1/2
16. Configuration and search algorithm
The CAN Identifier Look-up Table Memory can contain explicit identifiers and groups of
CAN identifiers for Standard and Extended CAN Frame Formats. They are organized as a
sorted list or table with an increasing order of the Source CAN Channel (SCC) together
with CAN Identifier in each section.
SCC value equals CAN_controller - 1, i.e., SCC = 0 matches CAN1 and SCC = 1
matches CAN2.
Every CAN identifier is linked to an ID Index number. In case of a CAN Identifier match,
the matching ID Index is stored in the Identifier Index of the Frame Status Register
(CANRFS) of the according CAN Controller.
16.1 Acceptance filter search algorithm
The identifier screening process of the acceptance filter starts in the following order:
1. FullCAN (Standard Frame Format) Identifier Section
2. Explicit Standard Frame Format Identifier Section
3. Group of Standard Frame Format Identifier Section
4. Explicit Extended Frame Format Identifier Section
5. Group of Extended Frame Format Identifier Section
Note: Only activated sections will take part in the screening process.
In cases where equal message identifiers of same frame format are defined in more than
one section, the first match will end the screening process for this identifier.
For example, if the same Source CAN Channel in conjunction with the identifier is defined
in the FullCAN, the Explicit Standard Frame Format and the Group of Standard Frame
Format Identifier Sections, the screening will already be finished with the match in the
FullCAN section.
In the example of Figure 18–81 , Identifiers with their Source CAN Channel have been
defined in the FullCAN, Explicit and Group of Standard Frame Format Identifier Sections.
This example corresponds to a LPC2290 compatible part that would have 6 CAN
controllers.