FlexCAN ModuleMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 25-3The CAN protocol was primarily, but not only, designed to be used as a vehicle serial data bus, meetingthe specific requirements of this field: real-time processing, reliable operation in the EMI environment ofa vehicle, cost-effectiveness, and required bandwidth. A general working knowledge of the CAN protocolrevision 2.0 is assumed in this document. For details, refer to the CAN protocol revision 2.0 specification.25.3.1 The CAN SystemA typical CAN system is shown in Figure 25-3.Figure 25-3. Typical CAN SystemEach CAN station is connected physically to the CAN bus through a transceiver. The transceiver providesthe transmit drive, waveshaping, and receive/compare functions required for communicating on the CANbus. It can also provide protection against damage to the FlexCAN caused by a defective CAN bus ordefective stations.25.3.2 Modes of Operation25.3.2.1 Normal ModeIn normal mode, the module operates receiving and/or transmitting message frames, errors are handlednormally, and all the CAN protocol functions are enabled. User and supervisor modes differ in the accessto some restricted control registers.25.3.2.2 Freeze ModeFreeze mode is entered by setting:• CANMCRn[FRZ], and• CANMCRn[HALT], or by asserting the BKPT signal.CAN BusFlexCANCANRXTransceiverCAN Station 1 CAN Station 2CANTXColdFire ProcessorCAN Station n
