ST SPC560P34 - Table 450. Examples of Legal and Illegal Passwords

Boot Assist Module (BAM) RM0046
832/936 Doc ID 16912 Rev 5
This means that even if censorship was inadvertently enabled by writing to the censorship
control registers, there is an opportunity to get back into the microcontroller using the default
private password of 0xFEED_FACE_CAFE_BEEF.
When configuring the private password, each half word (16-bit) must contain at least one "1"
and one "0". Some examples of legal and illegal passwords are shown in Table 450:
In uncensored devices it is possible to download code via LINFlex or FlexCAN (Serial Boot
Mode) into internal SRAM even if the 64-bit private password stored in the flash and
provided during the boot sequence is a password that does not conform to the password
rules.
Nonvolatile System Censorship Control registers (NVSCI0 and NVSCI1)
These registers are used together to define the censorship configuration. After factory test
these registers are programmed as shown below which disables censorship:
● NVSCI0 = 0x55AA_55AA
● NVSCI1 = 0x55AA_55AA
Each 32-bit register is split into an upper and lower 16-bit field. The upper 16 bits (the SC
field) are used to control serial boot mode censorship. The lower 16 bits (the CW field) are
used to control flash memory boot censorship.
Caution:
If the contents of the shadow flash memory are erased and the NVSCI0,1 registers are not
re-programmed to a valid value, the microcontroller will be permanently censored with no
way for you to regain access. A microcontroller in this state cannot be debugged or re-
flashed.
Censorship configuration
The steps to configuring censorship are:
1. Define a valid 64-bit password that conforms to the password rules.
2. Using the table and flow charts below, decide what level of censorship you require and
configure the NVSCI0,1 values.
3. Re-program the shadow flash memory and NVPWD0,1 and NVSCI0,1 registers with
your new values. A POR is required before these will take effect.
Caution:
If
(NVSCI0 and NVSCI1 do not match)
or
(Either NVSCI0 or NVSCI1 is not set to 0x55AA)
then the microcontroller will be permanently censored with no way to get back in.
Table 450. Examples of legal and illegal passwords
Legal (valid) passwords Illegal (invalid) passwords
0x0001_0001_0001_0001
0xFFFE_FFFE_FFFE_FFFE
0x1XXX_X2XX_XX4X_XXX8
0x0000_XXXX_XXXX_XXXX
0xFFFF_XXXX_XXXX_XXXX