| A microcontroller (also MCU or µC) is a computer-on-a-chip. It is a type of microprocessor emphasizing high integration, low power consumption, self-sufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor (the kind used in a PC). In addition to the usual arithmetic and logic elements of a general purpose microprocessor, the microcontroller typically integrates additional elements such as read-write memory for data storage, read-only memory, such as flash for code storage, EEPROM for permanent data storage, peripheral devices, and input/output interfaces. At clock speeds of as little as a few MHz or even lower, microcontrollers often operate at very low speed compared to modern day microprocessors, but this is adequate for typical applications. They consume relatively little power (milliwatts), and will generally have the ability to sleep while waiting for an interesting peripheral event such as a button press to wake them up again to do something. Power consumption while sleeping may be just nanowatts, making them ideal for low power and long lasting battery applications.
Microcontrollers are frequently used in automatically controlled products and devices, such as automobile engine control systems, remote controls, office machines, appliances, power tools, and toys. By reducing the size, cost, and power consumption compared to a design using a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to electronically control many more processes.
The majority of computer systems in use today are embedded in other machinery, such as telephones, clocks, appliances, and vehicles. An embedded system may have minimal requirements for memory and program length. Input and output devices may be discrete switches, relays, or solenoids. An embedded controller may lack any human-readable interface devices at all. For example, embedded systems usually don't have keyboards, screens, disks, printers, or other recognizable I/O devices of a personal computer. Microcontrollers may control electric motors, relays or voltages, and may read switches, variable resistors or other electronic devices.
Embedded microprocessors, although similar to normal microprocessors, require little to no human interaction. This eliminates the need for a human "supervisor." The embedded microprocessor relies on the stored programs and data being sent to and from the microprocessor to control its behavior.
Embedded microprocessors interact with their environments through an interrupt system. Interrupts are electronic signals sent from external devices that let the processor know that they are done retrieving some data, or converting a signal, or whenever they need to use the processor. The processor then enters its interrupt handler (which is usually just another program) and decodes the source of the interrupt to take the correct action.
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