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Implementing Backdoor Key sequence on MC9S08PA16

Question asked by Jonas Ketterle on Apr 25, 2014
Latest reply on Apr 29, 2014 by Edward Karpicz

Hi All,


Has anybody used the backdoor key to unlock a secure MCU in the HCS08 family?

I've read all the documentation in the reference manual, but am having trouble getting the unlock sequence right.


I've configured the memory so that KEYEN is enabled and SEC is secured, and to write a custom backdoor key.

const unsigned char NVOPT_F @ 0xff7f = 0xbd;

const unsigned char BackdoorKey[8] @ 0xffb0 = "My BDKey";


Anybody have an example of how they would write the unlock sequence? I tried clearing CCIF and then incrementing through the FCCOB index and writing each key value to the FCCOB register, but there only six locations in the index, and there a total of eight key locations, so I must be misunderstanding something.


Thank you! Your help is appreciated :-)