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FlexCAN Module
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor
25-3
The CAN protocol was primarily, but not only, designed to be used as a vehicle serial data bus, meeting
the specific requirements of this field: real-time processing, reliable operation in the EMI environment of
a vehicle, cost-effectiveness, and required bandwidth. A general working knowledge of the CAN protocol
revision 2.0 is assumed in this document. For details, refer to the CAN protocol revision 2.0 specification.
25.3.1
The CAN System
A typical CAN system is shown in
Figure 25-3. Typical CAN System
Each CAN station is connected physically to the CAN bus through a transceiver. The transceiver provides
the transmit drive, waveshaping, and receive/compare functions required for communicating on the CAN
bus. It can also provide protection against damage to the FlexCAN caused by a defective CAN bus or
defective stations.
25.3.2
Modes of Operation
25.3.2.1
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.
25.3.2.2
Freeze Mode
Freeze mode is entered by setting:
•
CANMCR
n
[FRZ], and
•
CANMCR
n
[HALT], or by asserting the BKPT signal.
CAN Bus
FlexCAN
CANRX
Transceiver
CAN Station 1
CAN Station 2
CANTX
ColdFire Processor
CAN Station n
Содержание MCF5253
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