MPC5777C PASS "Unmatchable" passwords

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MPC5777C PASS "Unmatchable" passwords

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krywes
Contributor I

Hi all..

We're in the process of activating the PASS module on MPC5777C. While experimenting with this on a set of CPUs we discovered that it appears that there are passwords that the PASS Module will not match against. In our first attempt we set the PASS0 password in UTEST to 0x00..00, PASS1 to 0x11..11 etc, and found that when device was advanced to "OEM Production" life cycle we could unlock PASS1 to PASS3, but PASS0 with the all-zeros password never matched (i.e. was not unlocked even when correct password was given). Our assumption on this was that 0x00..00 maybe is the value returned from UTEST NWM to PASS in case of for example a read protection, ECC error or similar, so this value is intentionally never accepted as a correct value. Also it appears as if 0xFF..FF is not accepted either, maybe since this represents a non-programmed password?

Searching in documentation such as Ref Manual for MPC5777C, or AN12092, gave no hint if this is actually the case or not.

Are there any "unmatchable" passwords in the PASS module? And can these in such case be used to intentionally disable a PASS group from ever being matched, much in the same manner as the "Test Mode Disable Override Passcode" have a set of unmatchable passwords?

Best Regards
/Jimmy W

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davidtosenovjan
NXP TechSupport
NXP TechSupport

PASS passwords must contain at least one '1' bit and one '0' bit. Or another way of saying it is that they cannot consist of all 1's or all 0's. This is what makes the default erased-flash contents of the password location invalid to use as a PASS password.

This info has already been reported to the documentation team, and it should be included in the next release of RM.

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davidtosenovjan
NXP TechSupport
NXP TechSupport

PASS passwords must contain at least one '1' bit and one '0' bit. Or another way of saying it is that they cannot consist of all 1's or all 0's. This is what makes the default erased-flash contents of the password location invalid to use as a PASS password.

This info has already been reported to the documentation team, and it should be included in the next release of RM.

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krywes
Contributor I

Thanks for the reply. 

One quick followup: I assume that the same is true for the JTAG-password?

Best Regards
/Jimmy W

 

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