Information

Soft reset is synchronous and has to follow an internal request/acknowledge procedure

across clock domains. Therefore, it may take some time to fully propagate its effects. The

SOFT_RST bit remains asserted while soft reset is pending, so software can poll this bit

to know when the reset has completed. Also, soft reset can not be applied while clocks

are shut down in any of the low power modes. The low power mode should be exited and

the clocks resumed before applying soft reset.

The clock source (CLK_SRC bit) should be selected while the module is in Disable

Mode. After the clock source is selected and the module is enabled (MDIS bit negated),

FlexCAN automatically goes to Freeze Mode. In Freeze Mode, FlexCAN is un-

synchronized to the CAN bus, the HALT and FRZ bits in MCR Register are set, the

internal state machines are disabled and the FRZ_ACK and NOT_RDY bits in the MCR

transmission or reception of CAN frames. Note that the Message Buffers and the Rx

Individual Mask Registers are not affected by reset, so they are not automatically

initialized.

For any configuration change/initialization it is required that FlexCAN is put into Freeze

Mode (see Freeze Mode). The following is a generic initialization sequence applicable to

the FlexCAN module:

• Initialize the Module Configuration Register

• Enable the individual filtering per MB and reception queue features by setting

the IRMQ bit

• Enable the warning interrupts by setting the WRN_EN bit

• If required, disable frame self reception by setting the SRX_DIS bit

• Enable the Rx FIFO by setting the RFEN bit

• Enable the abort mechanism by setting the AEN bit

• Enable the local priority feature by setting the LPRIO_EN bit

• Initialize the Control Register

• Determine the bit timing parameters: PROPSEG, PSEG1, PSEG2, RJW

• Determine the bit rate by programming the PRESDIV field

• Determine the internal arbitration mode (LBUF bit)

• Initialize the Message Buffers

• The Control and Status word of all Message Buffers must be initialized

Chapter 42 CAN (FlexCAN)

K10 Sub-Family Reference Manual, Rev. 6, Nov 2011

Freescale Semiconductor, Inc. 1159