Hi,
if you do not change anything in the flash security byte (can be checked in s19 record) then the device is secured after loading by default.
The BDM always mass erase/unsecures it for debugging before programming. If you only program it (debugger does not prepare device for debugging) with no access to the security byte then it will be secured and not debeggable.
The example of security with temporary unsecuring by special 64bit code received by application can be seen here
https://community.nxp.com/t5/S12-MagniV-Microcontrollers/SW-example-of-Security-feature-with-Backdoo...
The code for temporary unsecure (up to next reset) can be received by some peripheral or it can be launched by some specific event/condition with backdoor key stored in application code as presented in the example.
It is up to you whether you want to use backdoor key. If not use the device can not be unsecured only BDM mass errase command is available.
Best regards,
Ladislav
https://community.nxp.com/t5/S12-MagniV-Microcontrollers/S12Z-unsecure/m-p/1303088
