Altera Cyclone V Device Handbook page 1005

25-6
Extended Identifier Mask (
Extended Identifier Mask (MXtd)
• 0= The extended frame identifier bit (Xtd) has no effect on the acceptance filtering
• 1= The extended frame identifier bit (Xtd) is used for acceptance filtering
When 11-bit (standard) identifiers are used for a message object, the identifiers of received data frames are
written to bits ID28 to ID18. For acceptance filtering, only these bits, together with mask bits Msk28 to
Msk18, are used.
Mask Message Direction (MDir)
• 0= The message direction bit (Dir) has no effect on the acceptance filtering.
• 1= The message direction bit (Dir) is used for acceptance filtering.
Important: Altera recommends always setting MDir to 1. Ignoring the message direction bit is an advanced
technique that must be handled with great care.
CAN Message Bits
The arbitration fields ID28-0, Xtd, and Dir are used to define the identifier and type of outgoing messages
and are used (together with the mask fields Msk28-0, MXtd, and MDir) for acceptance filtering of incoming
messages. A received message is stored to the valid message object with matching identifier when the direction
is set to receive a data frame or transmit a remote frame. Extended frames can be stored only in message
objects with Xtd is set to 1, standard frames in message objects with Xtd is set to 0. If a received message
(data frame or remote frame) matches more than one valid message object, it is stored to the object with the
lowest message number.
Message Identifier (ID[28:0])
Extended Frame Identifier (Xtd)
Message Direction (Dir)
Data Length Code (DLC[3:0])
Data Bytes 0-7 (Data 0[7:0] - Data 7[7:0])
Message Identifier (ID[28:0])
• ID28-ID0: 29-bit identifier (extended frame)
• ID28-ID18: 11-bit identifier (standard frame)
Extended Frame Identifier (Xtd)
• 0= The 11-bit (standard) identifier is used for this message object.
• 1= The 29-bit (extended) identifier is used for this message object.
Message Direction (Dir)
• 0= receive direction. When TxRqst is set to 1, 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= transmit direction. When TxRqst is set to 1, 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 to 1 (if RmtEn = 1).
Altera Corporation
MXtd )
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on page 25-6
on page 25-6
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2013.12.30
CAN Controller Introduction
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