Microcontrollers are specialized microprocessors. Three of the most popular processor architectures include the Harvard architecture where data memory and program memory are accessed separately, the von Neumann architecture where data memory and program memory are accessed from the same bus, and the modified Harvard architecture which is a combination of the previously mentioned two. The central processing unit (composed of the arithmetic logic unit, registers and control unit) functions as the brain or core of the processor. The central processing unit processes machine code stored in memory to control all of its functions. The machine code is compiled or assembled from the processor’s instruction set which defines all of the operations of the microcontroller. To complement their functionality, microcontrollers include a suite of peripherals such as input/output pins, timers, a real-time clock, and communications controllers.