MAC7200 datasheet(586/976 Pages) FREESCALE

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The Generic FlexCAN2 Module

MAC7200 Microcontroller Family Reference Manual, Rev. 2

508

Freescale Semiconductor

28.2.4

Modes of Operation

The FlexCAN module has four functional modes: Normal Mode (User and Supervisor), Freeze Mode,

Listen-Only Mode and Loop-Back Mode. There are also three low power modes: Disable Mode, Doze

Mode and Stop Mode.

28.2.4.1

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.

28.2.4.2

Freeze Mode:

It is enabled when the FRZ bit in the MCR Register is asserted. If enabled, Freeze Mode is entered when

the HALT bit in 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 28.2.7.8.1, “Freeze

Mode,” for more information.

28.2.4.3

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. 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.

28.2.4.4

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.

28.2.4.5

Module Disable Mode:

This low power mode is entered when the MDIS bit in the MCR Register is asserted. When disabled, the

module shuts down 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 MCR Register. See

Section 28.2.7.8.2, “Module Disable Mode,” for more information.

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