Microcode is stored in a program memory and intended to be executed by a central processing unit of a processing unit. The processing unit may include a memory controller associated with each program memory and a hardware peripheral. The method includes, in response to a request to update the microcode, a transmission, to each hardware peripheral, of a global authorization request signal obtained from an elementary authorization request signal generated by each corresponding memory controller, a transmission of a global authorization signal obtained from an elementary authorization signal generated by each hardware peripheral in response to the global authorization request signal and after satisfying a predetermined elementary condition, and an updating of each microcode by the corresponding memory controller only after the global authorization signal is received.