Security in expanded mode

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Security in expanded mode

NXP Employee
NXP Employee

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Posted: Mon Jul 11, 2005  3:17 pm


Am I missing something?


I want to secure and operate out of the internal Flash in the S(X)12 but use the extenal bus for data RAM. I know enough not to put any code, even vectors, in the external RAM. But from everything I've read, I have to turn security off if I want to operate out of internal Flash in NX mode.



Posted: Mon Jul 11, 2005  5:10 pm


I think you have the correct understanding. As far as I know it is NOT possible to have all the following 3 turned on simultaneously on the S12X:

- Normal Expanded Mode.

- Internal Flash turned on and code execute out of it.

- Flash security turned on.


You can however have any 2 of the above 3 turned on simultaneously.


By the way: This is also the case on the HCS12 parts, or at least most of the latest mask sets that really have security working.


Hope this helps,



Posted: Tue Jul 12, 2005  6:59 pm


It just doesn't seem safe that they allow such a large security risk by allowing to enable the external bus while secure. We often don't imagine what the intruder might do with the system even by manipulating seemingly harmless data on the external bus.


I would trust Freescale to know what they're doing, since all I can say is, "I don't see why..."

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