The controller is composed of a program counter, an instruction register, an instruction decoder, a timing generator, and an operation controller. Its main functions are: fetching an instruction from memory and pointing out the location of the next instruction in memory. Decode and test the instructions, and generate corresponding operation control signals in order to execute the specified actions. Directs and controls the direction of data flow between the CPU, memory, and input and output devices.The most common network protocols and communication software stacks are 16-bit or 32-bit. Communication peripherals are available for some 8-bit devices, but 16-bit and 32-bit MCUs tend to be more efficient choices. Nonetheless, 8-bit MCUs are commonly used in a variety of control, sensing, and interface applications.