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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:
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
0
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
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
0
Serial boot control—showing the use of the flash-based password (factory default 0x55AA)
Summary of Contents for PXN2020
Page 1: ...PXN20 Microcontroller Reference Manual Devices Supported PXN2020 PXN2120 PXN20RM Rev 1 06 2011...
Page 42: ...PXN20 Microcontroller Reference Manual Rev 1 lxiv Freescale Semiconductor...
Page 64: ...Introduction PXN20 Microcontroller Reference Manual Rev 1 1 22 Freescale Semiconductor...
Page 112: ...Signal Description PXN20 Microcontroller Reference Manual Rev 1 3 44 Freescale Semiconductor...
Page 118: ...Resets PXN20 Microcontroller Reference Manual Rev 1 4 6 Freescale Semiconductor...
Page 372: ...e200z6 Core Z6 PXN20 Microcontroller Reference Manual Rev 1 13 8 Freescale Semiconductor...
Page 412: ...e200z0 Core Z0 PXN20 Microcontroller Reference Manual Rev 1 14 14 Freescale Semiconductor...
Page 821: ...Media Local Bus MLB PXN20 Microcontroller Reference Manual Rev 1 Freescale Semiconductor 27 49...
Page 822: ...Media Local Bus MLB PXN20 Microcontroller Reference Manual Rev 1 27 50 Freescale Semiconductor...
Page 1376: ...Memory Map PXN20 Microcontroller Reference Manual Rev 1 A 118 Freescale Semiconductor...