Abstract: An exemplary byte-oriented microcontroller includes a program memory, a program memory bus, and a core circuit. The program memory bus has a bus width wider than one instruction byte, and the core circuit is coupled to the program memory through the program memory bus for executing at least one instruction by processing a plurality of instruction bytes fetched from the program memory. The core circuit includes a fetch unit, for fetching the instruction bytes through the program memory bus and re-ordering the fetched instruction bytes to form a complete instruction.