5. In the CANIFnMCTL register:
■ 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 RXIE bit to enable the INTPND bit to be set after a successful reception
■ Clear the RMTEN bit to leave the TXRQST bit unchanged
■ Set the EOB bit for a single message object
■ Set 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.
6. Program the number of the message object to be received in the MNUM field in the CAN IFn
Command Request (CANIFnCRQ) register. Reception of the message object begins as soon
as a matching frame is available on the CAN bus.
When the message handler stores a data frame in the message object, it stores the received Data
Length Code and eight data bytes in the CANIFnDA1, CANIFnDA2, CANIFnDB1, and CANIFnDB2
register. Byte 0 of the CAN data frame is stored in DATA[7:0] in the CANIFnDA1 register. If the
Data Length Code is less than 8, the remaining bytes of the message object are overwritten by
unspecified 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 MXTDbit in the CANIFnMSK2 register
should be set if only 29-bit extended identifiers are expected by this message object.
14.2.11 Handling of Received Message Objects
The CPU may read a received message any time via the CAN Interface registers because the data
consistency is guaranteed by the message handler state machine.
Typically, the CPU first writes 0x007F to the CANIFnCMSK register and then writes the number of
the message object to the CANIFnCRQ register. That combination transfers the whole received
message from the message RAM into the Message Buffer registers (CANIFnMSKn, CANIFnARBn,
and CANIFnMCTL). Additionally, the NEWDAT and INTPND bits are cleared in the message RAM,
acknowledging that the message has been read and clearing the pending interrupt generated by
this message object.
If the message object uses masks for acceptance filtering, the CANIFnARBn registers show the
full, unmasked ID for the received message.
The NEWDAT bit in the CANIFnMCTL register shows whether a new message has been received
since the last time this message object was read. The MSGLST bit in the CANIFnMCTL register
shows whether more than one message has been received since the last time this message object
was read. MSGLST is not automatically cleared, and should be cleared by software after reading its
status.
Using a remote frame, the CPU may request new data from another CAN node on the CAN bus.
Setting the TXRQSTbit of a receive object causes the transmission of a remote frame with the receive
object's identifier. This remote frame triggers the other CAN node to start the transmission of the
matching data frame. If the matching data frame is received before the remote frame could be
June 22, 2010372
Texas Instruments-Production Data
Controller Area Network (CAN) Module
