A method of integrated circuit includes: providing a non-volatile memory circuit for securely and permanently recording and protecting key data content having Y bits; providing a programmable memory circuit for storing user configuration data content having X bits greater than Y bits; converting the user configuration data content having X bits into user configuration key content having Y bits; comparing the user configuration key content having Y bits with the key data content having Y bits; selecting fallback configuration data content having X bits as output data when the user configuration key content does not match the key data content; selecting the user configuration data content having X bits as the output data when the user configuration key content matches the key data content; and receiving the output data of the decision circuit and performing at least one corresponding capability operation according to the output data.