MPC5604B/C Microcontroller Reference Manual, Rev. 8
Freescale Semiconductor 425
• Hardware cancellation on Tx message buffers
22.1.3 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 is also a low power mode: Disable 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 MCR 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 22.4.10.1, “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. 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 MCR is asserted. When disabled, the
module shuts down the clocks to the CAN Protocol Interface and Message Buffer Management
submodules. Exit from this mode is done by negating the MDIS bit in the MCR. See
Section 22.4.10.2, “Module Disable Mode for more information.
22.2 External signal description
22.2.1 Overview
The FlexCAN module has two I/O signals connected to the external MCU pins. These signals are
summarized in Table 22-1 and described in more detail in the next subsections.
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