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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
309 of 571
NXP Semiconductors
UM10316
Chapter 21: LPC29xx CAN 0/1
If an incoming message is detected the acceptance filter first tries to find the ID in the
FullCAN section, then continues by searching the following sections. In the event of an
identifier match during the acceptance filter process, the received FullCAN message
object data is moved from the receive buffer of the appropriate CAN controller into the
FullCAN message-object section.
shows the detailed layout structure of one
FullCAN message stored in the FullCAN message-object section of the look-up table. The
base address of a specific message-object data can be calculated by the contents of the
CAEOTA and the index i of the ID in the section (see
). Message object data
address = (12
×
i).
Since the FullCAN message-object section of the look-up table can be accessed both by
the acceptance filter internal-state machine and by the CPU, there is a method for
ensuring that no CPU reads from a FullCAN message-object occurring while the internal
state-machine is writing to that object. The acceptance filter uses a three-state semaphore
encoded with the two semaphore bits SEM[1:0] for each message object. This
mechanism provides the CPU with information about the current state of acceptance filter
internal-state machine activity in the FullCAN message-object section.
15 to 13 SCC
Odd index: CAN controller number
12
MDB
Odd index: message disable bit. Logic 0 is message enabled and
logic 1 is message disabled
11
-
Not used
10 to 0
ID[28:18]
Odd index: 11-bit CAN 2.0 B identifier
Table 261. FullCAN message-object layout
Bit
Symbol
Description
Msg_O 0
31
FF
CAN frame format
30
RTR
Remote frame request
29 to 26 -
Not used
25 to 24 SEM[1:0]
Semaphore bits
23 to 23 -
Not used
22 to 16 RXDLC[6:0]
Data-length code
15 to 11 -
Not used
10 to 0
ID[28:18]
Identifier bits 28 to 18
Msg_O 4
31 to 24 RXDATA4[7:0]
Receive data 4
23 to 16 RXDATA3[7:0]
Receive data 3
15 to 8
RXDATA2[7:0]
Receive data 2
7 to 0
RXDATA1[7:0]
Receive data 1
Msg_O 8
31 to 24 RXDATA8[7:0]
Receive data 8
23 to 16 RXDATA7[7:0]
Receive data 7
15 to 8
RXDATA6[7:0]
Receive data 6
7 to 0
RXDATA5[7:0]
Receive data 5
Table 260. Standard frame-format FullCAN identifier section
…continued
Bit
Symbol
Description