PXD20RM Datasheet, PDF (184/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

6.5.4.5 Download 64-bit password and password check
The first 64 bits received represent the password. This password is sent to the Password Check procedure
which verifies if it is correct.
The password check data flow is shown in Figure 6-5 where:
• SSCM_STATUS.SEC = 1 means flash secured
• SSCM_STATUS.PUB = 1 means flash with public access.
In case of flash with public access, the received password is compared with the public password
0xFEED_FACE_CAFE_BEEF.
If public access is not allowed but the flash is not secured, the received password is compared with the
value saved on NVPWD0 and NVPWD1 registers.
In both of the previous cases, the comparison is done by the BAM code. The BAM code does not enforce
any compliance checks on the password itself. If comparison fails the BAM forces the MCU into static
mode.
In the case of public access not allowed and flash secured, the password is written into
SSCM.PWCMPH-L registers.
After a fixed time waiting, comparison is done by hardware. Then BAM verifies again SSCM_STATUS’s
SEC flag:
• SEC = 0, flash is now unsecured and BAM continues its task
• SEC = 1, flash is still secured because password was wrong; BAM puts MCU to static mode.
This fixed time depends on the external crystal oscillator frequency (FXOSC). With FXOSC of 12 MHz,
the fixed time is 350 ms.
PXD20 Microcontroller Reference Manual, Rev. 1
6-8
Freescale Semiconductor
Preliminary—Subject to Change Without Notice