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Chapter 34 CAN Controller
2.Register Description
2.5 Message Object in the Message Memory
There are 32 Message Objects (up to 128 depending on the implementation) 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, these accesses are handled via the IFx Interface Registers.
Figure 2-4 gives an overview of the two structures of a Message Object.
Figure 2-4 Structure of a Message Object in the Message Memory
(Note) The CPU must reset the MsgVal bit of all unused Message Objects during the initialization before it
resets bit Init in the CAN Control Register. This bit must also be reset before the identifier ID28-0,
the control bits Xtd, Dir, or the Data Length Code DLC3-0 are modified, or if the Message Object is
no longer required.
(Note) If the UMask bit is set to one, the Message Object’s mask bits have to be programmed during
initialization of the Message Object before MsgVal is set to one.
Message Object
UMask Msk28-0 MXtd MDir EoB NewDat MsgLst RxIE TxIE IntPnd RmtEn TxRqst
MsgVal ID28-0 Xtd Dir DLC3-0 Data0 Data1 Data2 Data3 Data4 Data5 Data6 Data7
MsgVal Message Valid
0 The Message Object is ignored by the Message Handler.
1 The Message Object is configured and should be considered by the Message Handler.
UMask Use Acceptance Mask
0 Mask ignored.
1 Use Mask (Msk28-0, MXtd, and MDir) for acceptance filtering.
ID28-0 Message Identifier
ID28 -
ID0
29-bit Identifier (“Extended Frame”).
ID28 -
ID18
11-bit Identifier (“Standard Frame”).
Msk28-0 Identifier Mask
0 The corresponding bit in the identifier of the message object cannot inhibit the match in the
acceptance filtering.
1 The corresponding identifier bit is used for acceptance filtering.
Xtd Extended Identifier
0 The 11-bit (“standard”) Identifier will be used for this Message Object.
