LM3S8962 Datasheet, PDF (441/684 Pages) List of Unclassifed Manufacturers – Microcontroller

Stellaris® LM3S8962 Microcontroller
A data frame contains data for transmission, whereas a remote frame contains no data and is used
to request the transmission of a specific message object. The CAN data/remote frame is constructed
as shown in Figure 16-2 on page 441.
Figure 16-2. CAN Data/Remote Frame
Start
Of Frame
Remote
Transmission
Request
Bus
Idle
S
O
F
Message Delimiter
R
T
R
Control
Field
Data Field
Number ₁
Of Bits
11 or 29
16
0 . . . 64
Delimiter
Bits
CRC
A
Sequence ^C
K
EOP IFS ^Bus
Idle
15 1 1 1
7
3
Arbitration Field
CRC Sequence
CRC
Field
End of
Frame
Field
Interframe
Field
Bit Stuffing
CAN Data Frame
Acknowledgement
Field
16.2.1
The protocol controller transfers and receives the serial data from the CAN bus and passes the data
on to the message handler. The message handler then loads this information into the appropriate
message object based on the current filtering and identifiers in the message object memory. The
message handler is also responsible for generating interrupts based on events on the CAN bus.
The message object memory is a set of 32 identical memory blocks that hold the current configuration,
status, and actual data for each message object. These are accessed via either of the CAN message
object register interfaces.
The message memory is not directly accessible in the Stellaris^® memory map, so the Stellaris^® CAN
controller provides an interface to communicate with the message memory via two CAN interface
register sets for communicating with the message objects. As there is no direct access to the
message object memory, these two interfaces must be used to read or write to each message object.
The two message object interfaces allow parallel access to the CAN controller message objects
when multiple objects may have new information that must be processed. In general, one interface
is used for transmit data and one for receive data.
Initialization
Software initialization is started by setting the INIT bit in the CAN Control (CANCTL) register (with
software or by a hardware reset) or by going bus-off, which occurs when the transmitter's error
counter exceeds a count of 255. While INIT is set, all message transfers to and from the CAN bus
are stopped and the CANnTX signal is held High. Entering the initialization state does not change
the configuration of the CAN controller, the message objects, or the error counters. However, some
configuration registers are only accessible while in the initialization state.
To initialize the CAN controller, set the CAN Bit Timing (CANBIT) register and configure each
message object. If a message object is not needed, label it as not valid by clearing the MSGVAL bit
June 22, 2010
441
Texas Instruments-Production Data