Boot Assist Module (BAM)
MPC5606S Microcontroller Reference Manual, Rev. 7
174 Freescale Semiconductor
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, comparison is done by the BAM application. If password validation fails,
the BAM pushes the MCU into static mode.
In case of public access not allowed and flash secured, the password is written into the
SSCM.PWCMPH-L registers.
After a fixed waiting time, a comparison is done by hardware. Then the BAM again verifies
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 into static mode
This fixed time depends on the external crystal oscillator frequency (FXOSC). With FXOSC of 12 MHz,
the fixed time is 350 ms.
Figure 6-5. Password check flow
6.5.4.6 Download start address, VLE bit and code size
The next 8 bytes received by the MCU contain a 32-bit start address, the VLE mode bit, and a 31-bit code
length, as shown in
Figure 6-6.
The VLE bit (Variable Length Instruction) is used to indicate for which instruction set the code has been
compiled. This device family supports only VLE = 1. This bit is used for backward compatibility.
Write received password to
SSCM.PWCMPH-L
verify if Flash is
unsecured
SSCM.
STATUS.
PUB
SSCM.
STATUS.
SEC
comparison with
password saved on
NVPWD0-1
=1
=0
=1
=0
Wait
comparison with
0xFEEDFACE
CAFEBEEF
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