LM3S5D56 Datasheet, PDF (759/1146 Pages) Texas Instruments – Stellaris® LM3S5D56 Microcontroller

Stellaris^® LM3S5D56 Microcontroller
16.3.5
16.3.6
■ Optionally set the UMASK bit to enable the mask (MSK, MXTD, and MDIR specified in the
CANIFnMSK1 and CANIFnMSK2 registers) for acceptance filtering
■ Optionally set the TXIE bit to enable the INTPND bit to be set after a successful transmission
■ Optionally set the RMTEN bit to enable the TXRQST bit to be set on the reception of a matching
remote frame allowing automatic transmission
■ Set the EOB bit for a single message object
■ Configure the DLC[3:0] field to specify the size of the data frame. Take care during this
configuration not to set the NEWDAT, MSGLST, INTPND or TXRQST bits.
7. Load the data to be transmitted into the CAN IFn Data (CANIFnDA1, CANIFnDA2, CANIFnDB1,
CANIFnDB2) registers. Byte 0 of the CAN data frame is stored in DATA[7:0] in the CANIFnDA1
register.
8. Program the number of the message object to be transmitted in the MNUM field in the CAN IFn
Command Request (CANIFnCRQ) register.
9. When everything is properly configured, set the TXRQST bit in the CANIFnMCTL register. Once
this bit is set, the message object is available to be transmitted, depending on priority and bus
availability. Note that setting the RMTEN bit in the CANIFnMCTL register can also start message
transmission if a matching remote frame has been received.
Updating a Transmit Message Object
The CPU may update the data bytes of a Transmit Message Object any time via the CAN Interface
Registers and neither the MSGVAL bit in the CANIFnARB2 register nor the TXRQST bits in the
CANIFnMCTL register have to be cleared before the update.
Even if only some of the data bytes are to be updated, all four bytes of the corresponding
CANIFnDAn/CANIFnDBn register have to be valid before the content of that register is transferred
to the message object. Either the CPU must write all four bytes into the CANIFnDAn/CANIFnDBn
register or the message object is transferred to the CANIFnDAn/CANIFnDBn register before the
CPU writes the new data bytes.
In order to only update the data in a message object, the WRNRD, DATAA and DATAB bits in the
CANIFnMSKn register are set, followed by writing the updated data into CANIFnDA1, CANIFnDA2,
CANIFnDB1, and CANIFnDB2 registers, and then the number of the message object is written to
the MNUM field in the CAN IFn Command Request (CANIFnCRQ) register. To begin transmission
of the new data as soon as possible, set the TXRQST bit in the CANIFnMSKn register.
To prevent the clearing of the TXRQST bit in the CANIFnMCTL register at the end of a transmission
that may already be in progress while the data is updated, the NEWDAT and TXRQST bits have to be
set at the same time in the CANIFnMCTL register. When these bits are set at the same time, NEWDAT
is cleared as soon as the new transmission has started.
Accepting Received Message Objects
When the arbitration and control field (the ID and XTD bits in the CANIFnARB2 and the RMTEN and
DLC[3:0] bits of the CANIFnMCTL register) of an incoming message is completely shifted into
the CAN controller, the message handling capability of the controller starts scanning the message
RAM for a matching valid message object. To scan the message RAM for a matching message
object, the controller uses the acceptance filtering programmed through the mask bits in the
CANIFnMSKn register and enabled using the UMASK bit in the CANIFnMCTL register. Each valid
January 23, 2012
759
Texas Instruments-Production Data