NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
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Revision V1.30
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Message Object in the Message Memory
There are 32 Message Objects in the Message RAM. To avoid conflicts between application software
access to the Message RAM and CAN message reception and transmission, the CPU cannot directly
access the Message Objects, these accesses are handled through the IFn Interface Registers. The
following table provides an overview of the structures of a Message Object.
Message Object
UMask
Msk
[28:0]
MXtd
MDir
EoB
NewDat
MsgLst
RxIE
TxIE
IntPnd
RmtEn
TxRqst
MsgVal
ID
[28:0]
Xtd
Dir
DLC
[3:0]
Data0
Data1
Data2
Data3
Data4
Data5
Data6
Data7
Table 5.24-8 Structure of a Message Object in the Message Memory
The Arbitration Registers ID28-0, Xtd, and Dir are used to define the identifier and type of outgoing
messages and are used (together with the mask registers Msk28-0, MXtd, and MDir) for acceptance
filtering of incoming messages. A received message is stored in the valid Message Object with
matching identifier and Direction = receive (Data Frame) or Direction = transmit (Remote Frame).
Extended frames can be stored only in Message Objects with Xtd = one, standard frames in Message
Objects with Xtd = zero. If a received message (Data Frame or Remote Frame) matches with more
than one valid Message Object, it is stored into that with the lowest message number.
Message Handler Registers
All Message Handler registers are read only. Their contents (TxRqst, NewDat, IntPnd, and MsgVal
bits of each Message Object and the Interrupt Identifier) are status information provided by the
Message Handler FSM.