11.3.1 Initialization

To use the CAN controller, the peripheral clock must be enabled using the RCGCCAN register (see Section 4.2.96). In addition, the clock to the appropriate GPIO module must be enabled using the RCGCGPIO register (see Section 4.2.87). To find out which GPIO port to enable, see the device-specific data sheet. Set the GPIO AFSEL bits for the appropriate pins (see Section 17.5.10). Configure the PMCn fields in the GPIOPCTL register to assign the CAN signals to the appropriate pins. See Section 17.5.22 and the device-specific data sheet.

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 error counter of the transmitter 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 in the CAN IFn Arbitration 2 (CANIFnARB2) register. Otherwise, the whole message object must be initialized, as the fields of the message object may not have valid information, causing unexpected results. Both the INIT and CCE bits in the CANCTL register must be set in order to access the CANBIT register and the CAN Baud Rate Prescaler Extension (CANBRPE) register to configure the bit timing. To leave the initialization state, the INIT bit must be cleared. Afterwards, the internal Bit Stream Processor (BSP) synchronizes itself to the data transfer on the CAN bus by waiting for the occurrence of a sequence of 11 consecutive recessive bits (indicating a bus idle condition) before it takes part in bus activities and starts message transfers. Message object initialization does not require the CAN to be in the initialization state and can be done on the fly. However, message objects should all be configured to particular identifiers or set to not valid before message transfer starts. To change the configuration of a message object during normal operation, clear the MSGVAL bit in the CANIFnARB2 register to indicate that the message object is not valid during the change. When the configuration is completed, set the MSGVAL bit again to indicate that the message object is once again valid.