MPC563XM Reference Manual, Rev. 1
618
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
Each byte of data received is stored in the device memory, starting at the address specified in the
previous protocol step, and incrementing through memory until the number of bytes of data
received and stored in memory matches the number specified in the previous protocol step.
BAM program buffers incoming data, collecting up to eight bytes. The buffered data is written to
the RAM with 64 bit writes to prevent ECC errors, which may happen if the device RAM is
protected by 64 bit ECC code.
Once the buffered data is written to the RAM the BAM program refreshes the SWT watchdog
NOTE
Only system RAM supports 64-bit writes; therefore, attempting to
download data to other RAM apart from system RAM will cause errors.
If the start address of the downloaded data is not on an 8-byte boundary, the
BAM will write 0x0 to the memory locations from the proceeding 8-byte
boundary to the start address (maximum 4 bytes). The BAM also writes 0x0
to all memory locations from the last byte of data downloaded to the
following 8 byte boundary (maximum 7 bytes) and additional 8 zero bytes
to prevent possible ECC errors may be caused by the CPU prefetching.
4. Switch to the loaded code.
The BAM program waits for the last echo message transmission to complete, then the active
communication controller is disabled. Its pins revert to GPIO inputs.
To provide compatibility with older devices, the BAM writes the e200z335 core time base registers
(TBU and TBL) with 0x0 and enables the e200z335 core watchdog to cause a reset after a time-out
period of 2.5 x 2
27
system clock cycles and disables SWT watchdog. See
for examples
of time out periods.
The BAM code passes control to the loaded code at start address, which was received in step 2 of
the protocol.
NOTE
The loaded code must periodically refresh the core watchdog timer or
change the timeout period to a value that will not cause resets during normal
operation.
21.5.5.5
Baud Rate Detection Procedure
To improve baud rate detection accuracy the baud rate detection routine is copied to the beginning of the
system RAM from the BAM ROM. Then the CPU branches to the RAM.
The device configures the CNRX_A and RXD_A pins as general purpose inputs and starts to poll them
until one of them goes low.
If the CNRX_A pin transitions first, the BAM program starts CAN baud rate detection routine, ignoring
RXD_A. After detecting the CAN baud rate, the BAM program transitions to the CAN download protocol
routine described above.
Содержание MPC5632M
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