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The host processor must set the
MsgVal
bit of all unused message objects to 0 before it resets the initialization
bit (
Init
) of the CAN control register (
CCTRL
) to initialize the CAN controller.
MsgVal
must also be set
to 0 when the message object is no longer in use.
The
MsgVal
field is directly readable from the message valid registers (
MOVALA
,
MOVALB
,
MOVALC
,
MOVALD
, and
MOVALX
). However, to write to the
MsgVal
field for a specific message object, the host
processor must write to the message interface registers.
New Data (
NewDat
)
• 0= No new data has been written into the data portion of this message object by the message handler
since last time this flag was cleared by the host processor.
• 1= The message handler or the host processor has written new data to the data portion of this message
object.
The
NewDat
field is directly readable from the new data registers (
MONDA
,
MONDB
,
MONDC
,
MONDD
, and
MONDX
). However, to write to the
NewDat
field for a specific message object, the host processor must write
to the message interface registers.
Message Lost (
MsgLst
)
• 0= No message lost since last time this bit is was last reset by the host processor
• 1= The message handler stored a new message into this object when the
NewDat
bit was still set, indicating
the host processor has lost a message.
MsgLst
is valid only in message objects with the message direction bit (
Dir
) set to receive.
Interrupt Pending (
IntPnd
)
• 0= This message object is not the source of an interrupt.
• 1= This message object is the source of an interrupt. The interrupt identifier field in the CAN interrupt
register (
CIR
) points to this message object if there is no other interrupt source with higher priority.
The
IntPnd
field is directly readable from the interrupt pending registers (
MOIPA
,
MOIPB
,
MOIPC
,
MOIPD
,
and
MOIPX
). However, to write to the
IntPnd
field for a specific message object, the host processor must
write to the message interface registers.
Transmit Interrupt Enable (
TxIE
)
• 0=
TxIE
is disabled.
IntPnd
is left unchanged after the successful transmission of a frame.
• 1=
TxIE
is enabled.
IntPnd
is set after a successful transmission of a frame.
Receive Interrupt Enable (
RxIE
)
• 0=
RxIE
is disabled.
IntPnd
is left unchanged after a successful reception of a frame.
• 1=
RxIE
is enabled.
IntPnd
is set after a successful reception of a frame.
Remote Enable (
RmtEn
)
• 0=
RmtEn
is disabled. At the reception of a remote frame,
TxRqst
is left unchanged.
• 1=
RmtEn
is enabled. At the reception of a remote frame,
TxRqst
is set.
Transmit Request (
TxRqst
)
• 0= This message object is not waiting for transmission.
• 1= The transmission of this message object is requested and is not complete.
CAN Controller Introduction
Altera Corporation
cv_54025
New Data (
NewDat
)
25-4
2013.12.30