The subject Microcontroller Based System Design explains the architecture, programming concepts, memory, I/O interfacing of PIC microcontrollers, ARM processor, M68HC11 microcontroller and also the variants on chip peripherals and interfacings.A Microprocessor and microcontroller (MCU) is a system-on-chip that you can find in all kinds of embedded systems. MCUs integrate a processor core, memory, and several programmable peripherals such as input/output ports, timers, analogue-to-digital converters, digital-to-analogue converters, parallel and serial communications, and more onto a single chip. This higher integration allows an engineer to reduce the size, cost and power consumption (for battery powered, efficient applications). This makes the microcontrollers are found in a wide range of applications, such as process control and communication systems. The objective of studying Microcontroller based system design is to develop this understanding.