LM3S5652 Luminary Micro, Inc, LM3S5652 Datasheet - Page 495

• Manufacturer Part Number: LM3S5652
• Description: Lm3s5652 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

17.4.3
17.4.4
Table 17-1. Transmit Message Object Bit Settings
June 02, 2008
Register
Value
Bit
CANIFnARB2
MsgVal
sufficient), the whole message object has to be configured before the transmission of this message
is requested.
The transmission of any number of message objects may be requested at the same time; they are
transmitted according to their internal priority, which is based on the message identifier for the
message object. Messages may be updated or set to not valid any time, even when their requested
transmission is still pending. The old data is discarded when a message is updated before its pending
transmission has started. Depending on the configuration of the message object, the transmission
of a message may be requested autonomously by the reception of a remote frame with a matching
identifier.
There are two sets of CAN Interface Registers (CANIF1x and CANIF2x), which are used to access
the Message Objects in the Message RAM. The CAN controller coordinates transfers to and from
the Message RAM to and from the registers. The function of the two sets are independent and
identical and can be used to queue transactions.
Transmitting Message Objects
If the internal transmit shift register of the CAN module is ready for loading, and if there is no data
transfer between the CAN Interface Registers and message RAM, the valid message object with
the highest priority that has a pending transmission request is loaded into the transmit shift register
by the message handler and the transmission is started. The message object's NewDat bit is reset
and can be viewed in the CANNWDAn register. After a successful transmission, and if no new data
was written to the message object since the start of the transmission, the TxRqst bit in the
CANIFnCMSK register is reset. If the TxIE bit in the CANIFnMCTL register is set, the IntPnd bit
in the CANIFnMCTL register is set after a successful transmission. If the CAN module has lost the
arbitration or if an error occurred during the transmission, the message is re-transmitted as soon
as the CAN bus is free again. If, meanwhile, the transmission of a message with higher priority has
been requested, the messages are transmitted in the order of their priority.
Configuring a Transmit Message Object
Table 17-1 on page 495 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 the outgoing message. If an 11-bit Identifier (Standard Frame) is used, it is
programmed to bits [12:2] of CANIFnARB2, and the remaining identifier bits are not used by the
CAN controller.
If the TxIE bit is set, the IntPnd bit is set after a successful transmission of the message object.
When the RmtEn bit is set, a matching received remote frame causes the TxRqst bit to be set and
the message object automatically transfers the message object's data or generates an interrupt
indicating a remote frame was requested. This can be strictly a single message identifier or it can
be a range of values specified in the message object. The CAN mask registers, CANIFnMSKn,
configure which groups of frames are identified as remote frame requests. The UMask bit in the
CANIFnMCTL register enables the Msk bits in the CANIFnMSKn register to filter which frames are
identified as a remote frame request. The MXtd bit should be set if only 29-bit extended identifiers
should trigger a remote frame request.
1
appl
Arb
CANIFnCMSK
Data
appl
Mask
appl
CANIFnMCTL
EoB
1
CANIFnARB2
Preliminary
Dir
1
NewDat
0
MsgLst
0
RxIE
CANIFnMCTL
0
TxIE
appl
LM3S5652 Microcontroller
IntPnd
0
RmtEn
appl
TxRqst
0
495