MPC5604B/C Microcontroller Reference Manual, Rev. 8
66 Freescale Semiconductor
Figure 5-3. Flash memory boot mode sequence
5.1.1.2 Alternate boot sectors
Some applications require an alternate boot sector so that the main boot code can be erased and
reprogrammed in the field. When an alternate boot is needed, you can create two bootable sectors:
• The valid boot sector located at the lowest address is the main boot sector.
• The valid boot sector located at the next available address is the alternate boot sector.
This scheme ensures that there is always one active boot sector even if the main boot sector is erased.
5.1.2 Serial boot mode
Serial boot provides a mechanism to download and then execute code into the microcontroller SRAM.
Code may be downloaded using either FlexCAN or LINFlex (RS232). After the SSCM has detected that
serial boot mode has been requested, execution is transferred to the BAM which handles all of the serial
boot mode tasks. See Section 5.2, Boot Assist Module (BAM), for more details.
5.1.3 Censorship
Censorship can be enabled to protect the contents of the flash memory from being read or modified. In
order to achieve this, the censorship mechanism controls access to the:
• JTAG / Nexus debug interface
• Serial boot mode (which could otherwise be used to download and execute code to query or modify
the flash memory)
SSCM searches flash
boot sectors for valid
Valid
BOOT_ID found?
SSCM reads reset
vector address
Yes No
BOOT_ID (0x5A)
SSCM transfers
execution to e200z0h core
which runs BAM code
BAM code executes
wait instruction
System in static mode
e200z0h core starts
executing code at
vector address
(requires reset to recover)
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