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FlexCAN Module
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1437
Error, Tx Warning and Rx Warning interrupt mask bits are located in the Control Register, and the
Wake-Up interrupt mask bit is located in the MCR.
32.5.11 Bus interface
The CPU access to FlexCAN registers are subject to the following rules:
•
Read and write access to supervisor registers in User Mode results in access error.
•
Read and write access to unimplemented or reserved address space also results in access error. Any
access to unimplemented message buffer or Rx Individual Mask Register locations results in
access error. Any access to the Rx Individual Mask Register space when MCR[MBFEN] is negated
results in access error.
•
If MCR[MAXMB] is programmed with a value smaller than the available number of message
buffers, then the unused memory space can be used as general purpose RAM space. Note that the
Rx Individual Mask Registers can only be accessed in Freeze Mode, and this is still true for unused
space within this memory. Note also that reserved words within RAM cannot be used. As an
example, suppose FlexCAN is configured with 64 message buffers and MCR[MAXMB] is
programmed with zero. The maximum number of message buffers in this case becomes one. The
message buffer memory starts at 0x0060, but the space from 0x0060 to 0x007F is reserved (for
SMB usage), and the space from 0x0080 to 0x008F is used by the one message buffer. This leaves
us with the available space from 0x0090 to 0x047F. The available memory in the Mask Registers
space would be from 0x0884 to 0x097F.
NOTE
Unused message buffer space must not be used as general purpose RAM
while FlexCAN is transmitting and receiving CAN frames.
32.6
Initialization/Application information
This section provide instructions for initializing the FlexCAN module.
32.6.1
FlexCAN initialization sequence
The FlexCAN module may be reset in three ways:
•
MCU level hard reset, which resets all memory mapped registers asynchronously
•
MCU level soft reset, which resets some of the memory mapped registers synchronously (refer to
to see what registers are affected by soft reset)
•
SOFTRST bit in MCR, which has the same effect as the MCU level soft reset
Soft reset is synchronous and has to follow an internal request/acknowledge procedure across clock
domains. Therefore, it may take some time to fully propagate its effects. The SOFTRST bit remains
asserted while soft reset is pending, so software can poll this bit to know when the reset has completed.
Also, soft reset can not be applied while clocks are shut down in any of the low power modes. The low
power mode should be exited and the clocks resumed before applying soft reset.
Содержание MPC5644A
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