LM3S8G62 Datasheet, PDF (765/1096 Pages) Texas Instruments – Stellaris® LM3S8G62 Microcontroller

OBSOLETE: TI has discontinued production of this device.
Stellaris^® LM3S8G62 Microcontroller
Table 16-3. Message Object Configurations
Configuration in CANIFnMCTL
Description
■ DIR = 1 (direction = transmit); programmed in the At the reception of a matching remote frame, the TXRQST bit of this
CANIFnARB2 register
message object is set. The rest of the message object remains
unchanged, and the controller automatically transfers the data in
■ RMTEN = 1 (set the TXRQST bit of the
the message object as soon as possible.
CANIFnMCTL register at reception of the frame
to enable transmission)
■ UMASK = 1 or 0
■ DIR = 1 (direction = transmit); programmed in the At the reception of a matching remote frame, the TXRQST bit of this
CANIFnARB2 register
message object remains unchanged, and the remote frame is
ignored. This remote frame is disabled, the data is not transferred
■ RMTEN = 0 (do not change the TXRQST bit of the _{and nothing indicates that the remote frame ever happened.}
CANIFnMCTL register at reception of the frame)
■ UMASK = 0 (ignore mask in the CANIFnMSKn
register)
■ DIR = 1 (direction = transmit); programmed in the At the reception of a matching remote frame, the TXRQST bit of this
CANIFnARB2 register
message object is cleared. The arbitration and control field (ID +
XTD + RMTEN + DLC) from the shift register is stored into the message
■ RMTEN = 0 (do not change the TXRQST bit of the _{object in the message RAM, and the NEWDAT bit of this message}
CANIFnMCTL register at reception of the frame) _{object is set. The data field of the message object remains}
unchanged; the remote frame is treated similar to a received data
■ UMASK = 1 (use mask (MSK, MXTD, and MDIR in _{frame. This mode is useful for a remote data request from another}
the CANIFnMSKn register) for acceptance filtering) _{CAN device for which the Stellaris controller does not have readily}
available data. The software must fill the data and answer the frame
manually.
16.3.9
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 prioritization is separate from that of the message
identifier which is enforced by the CAN bus. As a result, if message object 1 and message object
2 both have valid messages to be transmitted, message object 1 is always transmitted first regardless
of the message identifier in the message object itself.
16.3.10 Configuring a Receive Message Object
The following steps illustrate how to configure a receive message object.
1. Program the CAN IFn Command Mask (CANIFnCMASK) register as described in the
“Configuring a Transmit Message Object” on page 762 section, except that the WRNRD bit is set
to specify a write to the message RAM.
2. Program the CANIFnMSK1and CANIFnMSK2 registers as described in the “Configuring a
Transmit Message Object” on page 762 section to configure which bits are used for acceptance
filtering. 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
July 24, 2012
765
Texas Instruments-Production Data