Data scrambling method that controls code density

A data scrambling method performed by a memory controller coupled to a non-volatile memory device to control a code density, the method comprising:

• receiving, by the memory controller, a plain code which is a code to be stored in the non-volatile memory device and a storage address at which the plain code is recorded;
• determining, by the memory controller, an appearance frequency rank corresponding to the plain code, using an encoding table (ET) including appearance frequency rank information respectively corresponding to plain codes;
• calculating, by the memory controller, an adjustment rank corresponding to the plain code, using the appearance frequency rank and a random number that is generated based on the address of storage address;
• determining, by the memory controller, a cipher code corresponding to the appearance frequency rank of the plain code, using the adjustment rank and an encoding cipher coder (ECC) table including adjustment rank information determined by an objective function for cipher codes to make an average cell state of the non-volatile memory device about equal to a target state to control the code density;
• and
• storing, by the memory controller, the cipher code in the storage address.