A processing system connected to an apparatus includes a non-volatile memory (NVM) for storing firmware needed by the processing system; and an NVM control interface capable of writing and reading data stored in the NVM; wherein the NVM control interface reads a previous piece of data being already written into the NVM prior to a current piece of data and transmits the previous piece of data to the apparatus for comparison with original data that was previously written into the NVM, and the NVM control interface writes the current piece of data into the NVM.