Boot Assist Module (BAM)
PXN20 Microcontroller Reference Manual, Rev. 1
9-4 Freescale Semiconductor
The censorship control word (CCW) is a 32-bit word of data stored in the shadow row of internal flash
memory. This memory location is read and interpreted by hardware as part of the boot process. It is used
with the BOOTCFG bit to enable/disable the internal flash memory and the Nexus interface. The memory
address of the censorship control word is 0x00FF_FDE0. The censorship control word is programmed to
be 0x55AA_55AA. This results in a device that is not censored and uses a flash-based password for
serial-boot mode.
Figure 9-1. Censorship Control Word (CCW)
The BAM code uses the state of the DISNEX bit to determine if the serial password downloaded in
serial-boot mode is compared to a fixed public value (0xFEED_FACE_CAFE_BEEF) or is compared to a
flash value stored in the shadow row of internal flash at address 0x00FF_FDD8.
Serial—Flash Password 1 Don't care 0x55AA Enabled Disabled Flash
Serial—Public Password Any other value Disabled Enabled Public
Table 9-2. Boot Modes (continued)
Boot Mode Name BOOTCFG
Censorship
Control
0x00FF_FDE0
Serial Boot
Control
0x00FF_FDE2
Internal
Flash
State
Nexus State
Serial
Password
Censorship control word at 0x00FF_FDE0:
0123456789101112131415
0101010110101010
Censorship control—showing an uncensored part (factory default 0x55AA)
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0101010110101010
Serial boot control—showing the use of the flash-based password (factory default 0x55AA)
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