53.5.1.1 Software Initialization

Software initialization is started by setting bit MCAN_CCCR.INIT, either by software or by a hardware reset, when an uncorrected bit error was detected in the Message RAM, or by going Bus_Off. While MCAN_CCCR.INIT is set, message transfer from and to the CAN bus is stopped and the status of the CAN bus output CANTX is recessive (HIGH). The counters of the Error Management Logic EML are unchanged. Setting MCAN_CCCR.INIT does not change any configuration register. Resetting MCAN_CCCR.INIT finishes the software initialization. Afterwards the 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 (≡ Bus_Idle) before it can take part in bus activities and start the message transfer.

Access to the MCAN configuration registers is only enabled when both bits MCAN_CCCR.INIT and MCAN_CCCR.CCE are set (protected write).

MCAN_CCCR.CCE can only be configured when MCAN_CCCR.INIT = ‘1’. MCAN_CCCR.CCE is automatically cleared when MCAN_CCCR.INIT = ‘0’.

The following registers are cleared when MCAN_CCCR.CCE = ‘1’:

  • High Priority Message Status (MCAN_HPMS)
  • Receive FIFO 0 Status (MCAN_RXF0S)
  • Receive FIFO 1 Status (MCAN_RXF1S)
  • Transmit FIFO/Queue Status (MCAN_TXFQS)
  • Transmit Buffer Request Pending (MCAN_TXBRP)
  • Transmit Buffer Transmission Occurred (MCAN_TXBTO)
  • Transmit Buffer Cancellation Finished (MCAN_TXBCF)
  • Transmit Event FIFO Status (MCAN_TXEFS)

The Timeout Counter value MCAN_TOCV.TOC is loaded with the value configured by MCAN_TOCC.TOP when MCAN_CCCR.CCE = ‘1’.

In addition, the state machines of the Tx Handler and Rx Handler are held in idle state while MCAN_CCCR.CCE = ‘1’.

The following registers are only writeable while MCAN_CCCR.CCE = ‘0’

  • Transmit Buffer Add Request (MCAN_TXBAR)
  • Transmit Buffer Cancellation Request (MCAN_TXBCR)

MCAN_CCCR.TEST and MCAN_CCCR.MON can only be set when MCAN_CCCR.INIT = ‘1’ and MCAN_CCCR.CCE = ‘1’. Both bits may be cleared at any time. MCAN_CCCR.DAR can only be configured when MCAN_CCCR.INIT = ‘1’ and MCAN_CCCR.CCE = ‘1’.