The
TxRqst
field is directly readable from the transmission request registers (
MOTRA
,
MOTRB
,
MOTRC
,
MOTRD
, and
MOTRX
). However, to write to the
TxRqst
field for a specific message object, the host processor
must write to the message interface registers.
End of Block (
EoB
)
• 0= Message object belongs to a FIFO buffer block and is not the last message object of that FIFO buffer
block.
• 1= Single message object or last message object of a FIFO buffer block.
This bit is used to concatenate two or more message objects (up to 128) to build a FIFO buffer. For single
message objects (not belonging to a FIFO buffer), this bit must always be set to 1.
Message Object Mask Bits
The message object mask bits, together with the arbitration bits, are used for acceptance filtering of incoming
messages.
on page 25-5
on page 25-5
on page 25-6
on page 25-6
Use Acceptance Mask (
UMask
)
• 0= Ignore mask.
Msk[28:0]
,
MXtd
, and
Mdir
have no effect on acceptance filtering. For an incoming
message to be accepted, all the following conditions must be met:
• The received message is a data frame with message direction set to 0 (receive) or is a remote frame
with message direction set to 1 (transmit).
• The received message identifier matches the message identifier (
ID[28:0]
) of the message object.
• The received identifier extension bit matches the identifier extension bit (
Xtd
) of the message object.
• 1= Use mask (
Msk[28:0]
,
MXtd
, and
MDir
) for acceptance filtering if the respective mask bits are set
up for acceptance filtering. For an incoming message to be accepted, all the following conditions must
be met:
• The received message is a data frame with message direction set to 0 (receive) or is a remote frame
with message direction set to 1 (transmit) with the
MDir
mask bit enabled.
• The received message identifier matches the message identifier (
ID[28:0]
) of the message object
with the
Msk[28:0]
mask bits enabled
• The received identifier extension bit matches the identifier extension bit (
Xtd
) of the message object,
with the
MXtd
mask bit enabled.
If the
UMask
bit is set to 1, the message object's mask bits have to be programmed during the
initialization of the message object before
MsgVal
is set to 1.
Note:
Identifier Mask (
Msk[28:0]
)
The identifier mask filters the corresponding bits in
ID[28:0]
.
• 0= The corresponding identifier bit has no effect on the acceptance filter.
• 1= The corresponding identifier bit is used for acceptance filtering.
Altera Corporation
CAN Controller Introduction
25-5
End of Block (
EoB
)
cv_54025
2013.12.30