Modes Of Operation - NXP Semiconductors freescale KV4 Series Reference Manual

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Introduction

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.

• 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:

for more information.

KV4x Reference Manual, Rev. 2, 02/2015

Freescale Semiconductor, Inc.