LM3S5632 Luminary Micro, Inc, LM3S5632 Datasheet - Page 494

• Manufacturer Part Number: LM3S5632
• Description: Lm3s5632 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Controller Area Network (CAN) Module
17.4.9
17.4.10
Table 17-2. Receive Message Object Bit Settings
494
Register
Value
Bit
CANIFnARB2
MsgVal
Receive/Transmit Priority
The receive/transmit priority for the message objects is controlled by the message number. Message
object 1 has the highest priority, while message object 32 has the lowest priority. If more than one
transmission request is pending, the message objects are transmitted in order based on the message
object with the lowest message number. This should not be confused with the message identifier
as that priority is enforced by the CAN bus. This means that if message object 1 and message object
2 both have valid messages that need to be transmitted, message object 1 will always be transmitted
first regardless of the message identifier in the message object itself.
Configuring a Receive Message Object
Table 17-2 on page 494 specifies the bit settings for a transmit message object.
The Xtd and ID bit fields in the CANIFnARBn registers are set by an application. They define the
identifier and type of accepted received messages. If an 11-bit Identifier (Standard Frame) is used,
it is programmed to bits [12:2] of CANIFnARB2, and the remaining identifier bits are ignored by the
CAN controller. When a data frame with an 11-bit Identifier is received, only bits 12:2 of CANIFnARB2
are valid and the rest are set to 0.
If the RxIE bit is set, the IntPnd bit is set when a received data frame is accepted and stored in
the message object.
When the message handler stores a data frame in the message object, it stores the received Data
Length Code and eight data bytes. If the Data Length Code is less than 8, the remaining bytes of
the message object are overwritten by nonspecified values.
The CAN mask registers can be used to allow groups of data frames to be received by a message
object. The CAN mask registers, CANIFnMSKn, configure which groups of frames are received by
a message object. The UMask bit in the CANIFnMCTL register enables the Msk bits in the
CANIFnMSKn register to filter which frames are received. The MXtd bit should be set if only 29-bit
extended identifiers should be received by this message object.
Configuration
Dir = 1 (direction = transmit)
RmtEn = 1
UMask = 1 or 0
Dir = 1 (direction = transmit)
RmtEn = 0
UMask = 0
Dir = 1 (direction = transmit)
RmtEn = 0
UMask = 1
1
appl
Arb
CANIFnCMSK
Data
appl
Mask
appl
CANIFnMCTL
Description
At the reception of a matching remote frame, the TxRqst bit of this message object is set.
The rest of the message object remains unchanged, and the controller will transfer the data
in the message object.
At the reception of a matching remote frame, the TxRqst bit of this message object remains
unchanged; the remote frame is ignored. This remote frame is disabled and will not
automatically respond or indicate that the remote frame ever happened.
At the reception of a matching remote frame, the TxRqst bit of this message object is reset.
The arbitration and control field (ID + Xtd + RmtEn + DLC) from the shift register is stored
into the message object in the message RAM and the NewDat bit of this message object is
set. The data field of the message object remains unchanged; the remote frame is treated
similar to a received data frame. This is useful for a remote data request from another CAN
device for which the Stellaris
must fill the data and answer the frame manually.
EoB
1
CANIFnARB2
Preliminary
Dir
0
®
NewDat
controller does not have readily available data. The software
0
MsgLst
0
RxIE
appl
CANIFnMCTL
TxIE
0
IntPnd
0
RmtEn
0
June 02, 2008
TxRqst
0