UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
1074 of 1269
NXP Semiconductors
UM10503
Chapter 42: LPC43xx C_CAN
There are 32 Message Objects in the Message RAM. To avoid conflicts between CPU
access to the Message RAM and CAN message reception and transmission, the CPU
cannot directly access the Message Objects. The message objects are accessed through
the IFx Interface Registers.
42.6.2.1 Message objects
A message object contains the information from the various bits in the message interface
registers.
below shows a schematic representation of the structure of the
message object. The bits of a message object and the respective interface register where
this bit is set or cleared are shown. For bit functions see the corresponding interface
register.
42.6.2.2 CAN message interface command request registers
A message transfer is started as soon as the CPU has written the message number to the
Command Request Register. With this write operation the BUSY bit is automatically set to
‘1’ and the signal CAN_WAIT_B is pulled LOW) to notify the CPU that a transfer is in
progress. After a wait time of 3 to 6 CAN_CLK periods, the transfer between the Interface
Register and the Message RAM has completed. The BUSY bit is set back to zero and the
signal CAN_WAIT_B is set back).
Table 940. Message interface registers
IF1 register names
IF1 register set
IF2 register names
IF2 register set
IF1_CMDREQ
IF1 command request
IF2_CMDREQ
IF2 command request
IF1_CMDMASK
IF1 command mask
IF2_CMDMASK
IF2 command mask
IF1_MASK1
IF1 mask 1
IF2_MSK1
IF2 mask 1
IF1_MASK2
IF1 mask 2
IF2_MSK2
IF2 mask 2
IF1_ARB1
IF1 arbitration 1
IF2_ARB1
IF2 arbitration 1
IF1_ARB2
IF1 arbitration 2
IF2_ARB2
IF2 arbitration 2
IF1_MCTRL
IF1 message control
IF2_MCTRL
IF2 message control
IF1_DA1
IF1 data A1
IF2_DA1
IF2 data A1
IF1_DA2
IF1 data A2
IF2_DA2
IF2 data A2
CIF1_DB1
IF1 data B1
IF2_DB1
IF2 data B1
IF1_DB2
IF1 data B2
IF2_DB2
IF2 data B2
Table 941. Structure of a message object in the message RAM
UMASK
MSK[28:0]
MXTD
MDIR
EOB
NEWDAT
MSGLST
RXIE
TXIE
INTPND
IF1/2_MCTRL
IF1/2_MSK1/2
IF1/2_MCTRL
RMTEN
TXRQST
MSGVAL
ID[28:0]
XTD
DIR
DLC3
DLC2
DLC1
DLC0
IF1/2_MCTRL
IF1/2_ARB1/2
IF1/2_MCTRL
DATA0
DATA1
DATA2
DATA3
DATA4
DATA5
DATA6
DATA7
IF1/2_DA1
IF1/2_DA2
IF1/2_DB1
IF1/2_DB2