When the security bit is enabled, the Embedded Trace Macrocell (ETM) is disabled and access to the Flash through the SWD interface or through the Fast Flash Programming interface is forbidden. This ensures the confidentiality of the code programmed in the Flash.
The security bit is GPNVM0.
Disabling the security bit can only be achieved by asserting the ERASE signal at ‘1’, and after a full Flash erase is performed. When the security bit is deactivated, all accesses to the Flash are permitted.