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43.2.3 Modes of operation
The FlexCAN module has these functional modes:
• Normal mode (User or Supervisor):
In Normal mode, the module operates receiving and/or transmitting message frames,
errors are handled normally, and all CAN Protocol functions are enabled. User and
Supervisor Modes differ in the access to some restricted control registers.
• Freeze mode:
Freeze mode is enabled when the FRZ bit in MCR is asserted. If enabled, Freeze
mode is entered when MCR[HALT] is set or when Debug mode is requested at MCU
level and MCR[FRZ_ACK ] is asserted by the FlexCAN. In this mode, no
transmission or reception of frames is done and synchronicity to the CAN bus is lost.
See
for more information.
• Loop-Back mode:
The module enters this mode when the LPB field in the Control 1 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.
• Listen-Only mode:
The module enters this mode when the LOM field in the Control 1 Register is
asserted. In this mode, transmission is disabled, all error counters are frozen, and the
module operates in a CAN Error Passive mode. 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.
For low-power operation, the FlexCAN module has:
• Module Disable mode:
Introduction
KV4x Reference Manual, Rev. 2, 02/2015
1080
Preliminary
Freescale Semiconductor, Inc.
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