PXR40RM Datasheet, PDF (814/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

FlexCAN Module
• Low power modes
24.1.3 Modes of Operation
The FlexCAN module has these functional modes: Normal Mode (User and Supervisor), Freeze Mode,
Listen-Only Mode and Loop-Back Mode. There are also these low power modes: Disable Mode and Stop
Mode.
• Normal Mode (User or Supervisor):
In Normal Mode, the module operates receiving and/or transmitting message frames, errors are
handled normally and all the CAN Protocol functions are enabled. User and Supervisor Modes
differ in the access to some restricted control registers.
• Freeze Mode:
It is enabled when the FRZ bit in the FLEXCAN_x_MCR Register is asserted. If enabled, Freeze
Mode is entered when the HALT bit in FLEXCAN_x_MCR is set or when Debug Mode is
requested at MCU level. In this mode, no transmission or reception of frames is done and
synchronicity to the CAN bus is lost. See Section 24.4.9.1, Freeze Mode, for more information.
• Listen-Only Mode:
The module enters this mode when the LOM bit in the Control Register is asserted. In this mode,
transmission is disabled, all error counters are frozen and the module operates in a CAN Error
Passive mode [Ref. 1]. Only messages acknowledged by another CAN station will be received. If
FlexCAN detects a message that has not been acknowledged, it will flag a BIT0 error (without
changing the REC), as if it was trying to acknowledge the message.
• Loop-Back Mode:
The module enters this mode when the LPB bit in the Control Register is asserted. In this mode,
FlexCAN performs an internal loop back that can be used for self test operation. The bit stream
output of the transmitter is internally fed back to the receiver input. The Rx CAN input pin is
ignored and the Tx CAN output goes to the recessive state (logic ‘1’). FlexCAN behaves as it
normally does when transmitting and treats its own transmitted message as a message received
from a remote node. In this mode, FlexCAN ignores the bit sent during the ACK slot in the CAN
frame acknowledge field to ensure proper reception of its own message. Both transmit and receive
interrupts are generated.
• Module Disable Mode:
This low power mode is entered when the MDIS bit in the FLEXCAN_x_MCR Register is asserted
by the CPU. When the FlexCAN module is disabled, the module sends a request to disable the
clocks to the CAN Protocol Interface and Message Buffer Management sub-modules. Exit from
this mode is done by negating the MDIS bit in the FLEXCAN_x_MCR Register. See
Section 24.4.9.2, Module Disable Mode, for more information.
• Stop Mode:
This low power mode is entered when Stop Mode is requested at MCU level. When in Stop Mode,
the module puts itself in an inactive state and then informs the CPU that the clocks can be shut
down globally. Exit from this mode happens when the Stop Mode request is removed.
24-4
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor