LM3S5C36 Datasheet, PDF (754/1068 Pages) Texas Instruments – Stellaris® LM3S5C36 Microcontroller

Controller Area Network (CAN) Module
16.3.4
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
The following steps illustrate how to configure a transmit message object.
1. In the CAN IFn Command Mask (CANIFnCMASK) register:
■ Set the WRNRD bit to specify a write to the CANIFnCMASK register; specify whether to
transfer the IDMASK, DIR, and MXTD of the message object into the CAN IFn registers using
the MASK bit
■ Specify whether to transfer the ID, DIR, XTD, and MSGVAL of the message object into the
interface registers using the ARB bit
■ Specify whether to transfer the control bits into the interface registers using the CONTROL
bit
■ Specify whether to clear the INTPND bit in the CANIFnMCTL register using the CLRINTPND
bit
■ Specify whether to clear the NEWDAT bit in the CANNWDAn register using the NEWDAT bit
■ Specify which bits to transfer using the DATAA and DATAB bits
2. In the CANIFnMSK1 register, use the MSK[15:0] bits to specify which of the bits in the 29-bit
or 11-bit message identifier are used for acceptance filtering. Note that MSK[15:0] in this
register are used for bits [15:0] of the 29-bit message identifier and are not used for an 11-bit
identifier. A value of 0x00 enables all messages to pass through the acceptance filtering. Also
note that in order for these bits to be used for acceptance filtering, they must be enabled by
setting the UMASK bit in the CANIFnMCTL register.
3. In the CANIFnMSK2 register, use the MSK[12:0] bits to specify which of the bits in the 29-bit
or 11-bit message identifier are used for acceptance filtering. Note that MSK[12:0] are used
for bits [28:16] of the 29-bit message identifier; whereas MSK[12:2] are used for bits [10:0] of
the 11-bit message identifier. Use the MXTD and MDIR bits to specify whether to use XTD and
DIR for acceptance filtering. A value of 0x00 enables all messages to pass through the
acceptance filtering. Also note that in order for these bits to be used for acceptance filtering,
they must be enabled by setting the UMASK bit in the CANIFnMCTL register.
4. For a 29-bit identifier, configure ID[15:0] in the CANIFnARB1 register for bits [15:0] of the
message identifier and ID[12:0] in the CANIFnARB2 register for bits [28:16] of the message
identifier. Set the XTD bit to indicate an extended identifier; set the DIR bit to indicate transmit;
and set the MSGVAL bit to indicate that the message object is valid.
5. For an 11-bit identifier, disregard the CANIFnARB1 register and configure ID[12:2] in the
CANIFnARB2 register for bits [10:0] of the message identifier. Clear the XTD bit to indicate a
standard identifier; set the DIR bit to indicate transmit; and set the MSGVAL bit to indicate that
the message object is valid.
6. In the CANIFnMCTL register:
754
January 23, 2012
Texas Instruments-Production Data