ST ST10F276E - Page 439

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UM0404 CAN modules
Bit Function
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.
Note: The CPU must reset the MsgVal bit of all unused Messages Objects during
the initialization before it resets bit Init in the CAN Control Register. This bit must
also be reset before the identifier ID(28:0), the control bits Xtd, Dir, or the Data
Length Code DLC(3:0) are modified, or if the Messages Object is no longer
required.
UMask
Use Acceptance Mask
’0’: Mask ignored.
’1’: Use Mask (Msk28-0, MXtd, and MDir) for acceptance filtering.
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.
ID(28:0)
Message Identifier
ID(28:18): 11-bit Identifier (Standard Frame).
ID(28:0): 29-bit Identifier (Extended Frame).
Msk(28:0)
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 standard Identifier (11 bit) will be used for this Message Object.
’1’: The extended Identifier (29 bit) 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 ID28 to ID18. For
acceptance filtering, only these bits together with mask bits Msk28 to Msk18 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, that message is stored in this Message Object.
’1’: Direction = Transmit: on TxRqst, the respective Message Object is transmitted
as a Data Frame. On reception of a Remote Frame with matching identifier, the
TxRqst bit of this Message Object is set (if RmtEn = one).