Introduction
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 21-3
bus. It can also provide protection against damage to the FlexCAN caused by a defective CAN bus or
defective stations.

21.1.3 Features

Following are the main features of the FlexCAN module:
Full implementation of the CAN protocol specification version 2.0B
Standard data and remote frames (up to 109 bits long)
Extended data and remote frames (up to 127 bits long)
0–8 bytes data length
Programmable bit rate up to 1 Mbps
Content-related addressing
Up to 16 flexible message buffers of 0–8 bytes data length, each configurable as Rx or Tx, all
supporting standard and extended messages
Listen-only mode capability
Three programmable mask registers: global (for MBs 0–13), special for MB14, and special for
MB15
Programmable transmission priority scheme: lowest ID or lowest buffer number
Time Stamp based on 16-bit free-running timer
Global network time, synchronized by a specific message
Programmable I/O modes
Maskable interrupts
Independent of the transmission medium (an external transceiver is assumed)
Open network architecture
Multimaster bus
High immunity to EMI
Short latency time due to an arbitration scheme for high-priority messages

21.1.4 Modes of Operation

21.1.4.1 Normal Mode

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.

21.1.4.2 Freeze Mode

Freeze mode is entered by:
Setting CANMCR[FRZ], and
Setting CANMCR[HALT], or by asserting the BKPT line.
Once entry into freeze mode is requested, the FlexCAN waits until an intermission or idle condition exists
on the CAN bus, or until the FlexCAN enters the error passive or bus off state. Once one of these
conditions exists, the FlexCAN waits for the completion of all internal activity like arbitration, matching,
move-in, and move-out. When this happens, the following events occur:
The FlexCAN stops transmitting/receiving frames.