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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.
Altera recommends always setting
MDir
to 1. Ignoring the message direction bit is an advanced
technique that must be handled with great care.
Important:
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.
on page 25-6
on page 25-6
on page 25-6
on page 25-7
on page 25-7
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).
CAN Controller Introduction
Altera Corporation
cv_54025
Extended Identifier Mask (
MXtd
)
25-6
2013.12.30