What is Microcontroller?

A microcontroller (also microcontroller unit, MCU or µC) is a small computer on a single integrated circuit consisting of a relatively simple CPU combined with support functions such as a crystal oscillator, timers, watchdog timer, serial and analog I/O etc. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for small or dedicated applications. Thus, in contrast to the microprocessors used in personal computers and other high-performance or general purpose applications, simplicity is emphasized. Some microcontrollers may operate at clock rate frequencies as low as 4 kHz, as this is adequate for many typical applications, enabling low power consumption (milliwatts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption.

Microcontrollers are 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 and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems.

As of 2008 there are several dozen microcontroller architectures and vendors including:
- 68HC11
- 8051
- ARM processors (from many vendors) using ARM7 or Cortex-M3 cores are generally microcontrollers
- STMicroelectronics STM8S (8-bit), and STM32 (32-bit)
- Atmel AVR (8-bit), AVR32 (32-bit), and AT91SAM
- Freescale ColdFire (32-bit) and S08 (8-bit)
- Hitachi H8, Hitachi SuperH
- Hyperstone E1/E2 (32-bit, First full integration of RISC and DSP on one processor core
- MIPS (32-bit PIC32)
- NEC V850
- PIC (8-bit PIC16, PIC18, 16-bit dsPIC33 / PIC24)
- PowerPC ISE
- PSoC (Programmable System-on-Chip)
- Rabbit 2000
- Texas Instruments MSP430 (16-bit), C2000 (32-bit), and Stellaris (32-bit)
- Toshiba TLCS-870
- Zilog eZ8, eZ80

and many others, some of which are used in very narrow range of applications or are more like applications processors than microcontrollers. The microcontroller market is extremely fragmented, with numerous vendors, technologies, and markets. Note that many vendors sell (or have sold) multiple architectures.