UM10562 Datasheet, PDF (577/942 Pages) NXP Semiconductors – LPC408x/407x User manual

NXP Semiconductors
UM10562
Chapter 20: LPC408x/407x CAN controller
already in the FullCAN or in the Explicit Identifier section if enabled. The rest of the
defined identifiers of this group (0x5B to 0x5F) will find a match in this Group Identifier
Section.
This way the user can switch dynamically between different filter modes for same
identifiers.
20.16 FullCAN mode
The FullCAN mode is based on capabilities provided by the CAN Gateway module. This
block uses the Acceptance Filter to provide filtering for both CAN channels.
The concept of the CAN Gateway block is mainly based on a BasicCAN functionality. This
concept fits perfectly in systems where a gateway is used to transfer messages or
message data between different CAN channels. A BasicCAN device is generating a
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 84 “Entry in FullCAN and individual standard identifier tables” on
page 569). 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.
UM10562
User manual
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 13 September 2012
© NXP B.V. 2012. All rights reserved.
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