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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
1244 of 1441
NXP Semiconductors
UM10503
Chapter 45: LPC43xx/LPC43Sxx C_CAN
45.6.2 Message interface registers
There are two sets of interface registers which are used to control the CPU access to the
Message RAM. The interface registers avoid conflicts between CPU access to the
Message RAM and CAN message reception and transmission by buffering the data to be
transferred. A complete Message Object (see
) or parts of the Message
Object may be transferred between the Message RAM and the IFx Message Buffer
registers in one single transfer.
The function of the two interface register sets is identical (except for test mode Basic).
One set of registers may be used for data transfer to the Message RAM while the other
set of registers may be used for the data transfer from the Message RAM, allowing both
processes to be interrupted by each other.
Each set of interface registers consists of message buffer registers controlled by their own
command registers. The command mask register specifies the direction of the data
transfer and which parts of a message object will be transferred. The command request
register is used to select a message object in the message RAM as target or source for
the transfer and to start the action specified in the command mask register.
Fig 164. Block diagram of a message object transfer
IF1 MASK1, 2
IF1 ARBITRATION 1/2
IF1 MESSAGE CTRL
IF1 DATA A1/2
IF1 DATA B1/2
IF2 MASK1, 2
IF2 ARBITRATION 1/2
IF2 MESSAGE CTRL
IF2 DATA A1/2
IF2 DATA B1/2
MESSAGE RAM
MESSAGE OBJECT 1
MESSAGE OBJECT 2
.
.
.
MESSAGE OBJECT 32
transfer a
message object
read transfer
write transfer
APB
bus
MESSAGE BUFFER
REGISTERS
IF1 COMMAND REQUEST
IF1 COMMAND MASK
IF2 COMMAND REQUEST
IF2 COMMAND MASK
INTERFACE
COMMAND REGISTERS
MESSAGE HANDLER
TRANSMISSION REQUEST 1/2
NEW DATA 1/2
INTERRUPT PENDING1/2
MESSAGE VALID1/2
CAN
bus
receive
transfer a
CAN frame
transmit
CAN CORE/
SHIFT REGISTERS