Message RAM
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SPNU563A–March 2018
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Controller Area Network (DCAN) Module
27.5 Message RAM
The DCAN Message RAM contains message objects and ECC bits for the message objects.
27.5.1 Structure of Message Objects
Figure 27-4 shows the structure of a message object.
The grayed fields are those parts of the message object that are represented in dedicated registers. For
example, the transmit request flags of all message objects are represented in centralized transmit request
registers.
Figure 27-4. Structure of a Message Object
Message Object
UMask Msk[28:0] MXtd MDir EoB unused NewDat MsgLst RxIE TxIE IntPnd RmtEn TxRqst
MsgVal ID[28:0] Xtd Dir DLC[3:0] Data 0 Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7
Table 27-2. Message Object Field Descriptions
Name Value Description
MsgVal Message valid
0 The message object is ignored by the Message Handler.
1 The message object is to be used by the Message Handler.
Note: The CPU should reset the MsgVal bit of all unused Messages Objects during the initialization
before it resets bit Init in the CAN Control Register. MsgVal must also be reset if the messages object
is no longer used in operation. For reconfiguration of message objects during normal operation see
Section 27.7.6 and Section 27.7.7.
UMask Use Acceptance Mask
0 Mask bits (Msk[28:0], MXtd and MDir) are ignored and not used for acceptance filtering.
1 Mask bits are used for acceptance filtering.
Note: If the UMask bit is set to 1, the message object's mask bits have to be programmed during
initialization of the message object before MsgVal is set to 1.
ID[28:0] Message Identifier
ID[28:0] 29-bit ("extended") identifier bits
ID[28:18] 11-bit ("standard") identifier bits
Msk[28:0] Identifier Mask
0 The corresponding bit in the message identifier is not used for acceptance filtering (don't care).
1 The corresponding bit in the message identifier is used for acceptance filtering.
Xtd Extended Identifier
0 The 11-bit ("standard") identifier will be used for this message object.
1 The 29-bit ("extended") identifier will be used for this message object.
MXtd Mask Extended Identifier
0 The extended identifier bit (IDE) has no effect on the acceptance filtering.
1 The extended identifier bit (IDE) is used for acceptance filtering.
Note: When 11-bit ("standard") identifiers are used for a message object, the identifiers of received
data frames are written into bits ID[28:18]. For acceptance filtering, only these bits together with mask
bits Msk[28:18] are considered.
Dir Message Direction
0 Direction = receive: On TxRqst, a remote frame with the identifier of this message object is
transmitted. On reception of a data frame with matching identifier, the message is stored in this
message object.
1 Direction = transmit: On TxRqst, a data frame is transmitted. On reception of a remote frame with
matching identifier, the TxRqst bit of this message object is set (if RmtEn = 1).
MDir Mask Message Direction
0 The message direction bit (Dir) has no effect on the acceptance filtering.
1 The message direction bit (Dir) is used for acceptance filtering.
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