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Verify Backdoor Key causes Reset

Question asked by Shawn Lammers on Apr 12, 2017
Latest reply on Apr 18, 2017 by Radek Sestak

We have a project using a 9S12XEQ512 micro where we need to secure the micro but allow access through the backdoor key feature.

 

Add added the ability to our application program accept a key over a serial port and then use the flash commands to perform the key verification process and this worked fine.

 

I then moved the exact same code to our bootloader and now when I execute the process by writing to the FSTAT register the micro resets. The strange thing is this only happens when running in single chip mode. When I run it through the debugger the code executes as expected. The verify key command fails as its not supported in special single chip mode, but at least the micro does not reset.

 

In single chip mode, if I just comment out the line to complete the sequence

// FSTAT = 0x80;

then the micro does not reset so I am quite sure this is causing the problem.

 

Does anyone know why the mico would reset just be executing a flash command sequence?

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