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45.4.10.2 Module Disable mode

This low power mode is normally used to temporarily disable a complete FlexCAN

block, with no power consumption. It is requested by the CPU through the assertion of

the MDIS bit in the MCR Register and the acknowledgement is obtained through the

assertion by the FlexCAN of the LPM_ACK bit in the same register. The CPU must only

consider the FlexCAN in Disable mode when both request and acknowledgement

conditions are satisfied.

If the module is disabled during Freeze mode, it requests to disable the clocks to the PE

and CHI sub-modules, sets the LPM_ACK bit and negates the FRZ_ACK bit. If the

module is disabled during transmission or reception, FlexCAN does the following:

• Waits to be in either Idle or Bus Off state, or else waits for the third bit of

Intermission and then checks it to be recessive

• Waits for all internal activities like arbitration, matching, move-in and move-out to

finish. A pending move-in is not taken into account.

• Ignores its Rx input pin and drives its Tx pin as recessive

• Shuts down the clocks to the PE and CHI sub-modules

• Sets the NOTRDY and LPMACK bits in MCR

The Bus Interface Unit continues to operate, enabling the CPU to access memory mapped

registers, except the Rx Mailboxes Global Mask Registers, the Rx Buffer 14 Mask

FIFO Information Register, the Message Buffers, the Rx Individual Mask Registers, and

the reserved words within RAM may not be accessed when the module is in Disable

Mode. Exiting from this mode is done by negating the MDIS bit by the CPU, which

causes the FlexCAN to request to resume the clocks and negate the LPM_ACK bit after

the CAN protocol engine recognizes the negation of disable mode requested by the CPU.

45.4.10.3 Stop mode

This is a system low-power mode in which all MCU clocks can be stopped for maximum

power savings. The Stop mode is globally requested by the CPU and the

acknowledgement is obtained through the assertion by the FlexCAN of a Stop

Acknowledgement signal. The CPU must only consider the FlexCAN in Stop mode when

both request and acknowledgement conditions are satisfied.

Chapter 45 CAN (FlexCAN)

K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012

Freescale Semiconductor, Inc.

Preliminary

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