SPRUHM9H October 2014 – May 2024 TMS320F28075 , TMS320F28075-Q1 , TMS320F28076
The initialization mode is entered either by software (by setting the Init bit in the CAN_CTL register), by hardware reset, or by going bus-off. While the Init bit is set, the message transfer from and to the CAN bus is stopped, and the status of the CAN_TX output is recessive (high). The CAN error counters are not updated. Setting the Init bit does not change any other configuration register.
To initialize the CAN controller, the CPU has to configure the CAN bit timing and those message objects that are used for CAN communication. Message objects that are not needed, can be deactivated with the MsgVal bits cleared.
The access to the Bit Timing Register for the configuration of the bit timing is enabled when both Init and CCE bits in the CAN Control register are set.
Clearing the Init bit finishes the software initialization. Afterwards, the bit stream processor (BSP) synchronizes to the data transfer on the CAN bus by waiting for the occurrence of a sequence of 11 consecutive recessive bits (= Bus Idle) before the BSP can take part in bus activities and start the message transfer. For more details, see Section 21.11.
The initialization of the message objects is independent of the Init bit; however, all message objects must be configured with particular identifiers or set to "not-valid" before the message transfer is started.
It is possible to change the configuration of message objects during normal operation by the CPU. After setup and subsequent transfer of message object from interface registers to message RAM, the acceptance filtering is applied to it when the modified message object number is same or smaller than the previously found message object. This makes sure of data consistency even when changing message objects; for example, while there is a pending CAN frame reception.