Introduction

A microcontroller is a complete small computer built onto a single integrated circuit (IC). It combines a comparatively simple CPU with the support circuits a system usually needs — a crystal oscillator, a watchdog timer, timers/counters, and both serial and analog input/output — so that one chip can run a whole application on its own.

The microcontroller grew directly out of the microprocessor. Once computer architecture and IC fabrication had matured, engineers could place a general-purpose CPU on a single chip: the first was Intel's 4-bit 4004, released in 1971 and often called a "computer on a chip". Through the late 1970s many semiconductor companies were making microprocessors, and personal computers reached millions of users. Built with the same miniature fabrication techniques but additionally programmed for a fixed job, the microcontroller became a simpler, lower-cost, physically tiny chip aimed at small dedicated applications.

Because it is optimised for control rather than raw computing power, a microcontroller can run at very low clock frequencies — some as low as 32 kHz — and draw only microwatts to milliwatts of power; in sleep mode its consumption can fall to nanowatts, which makes long-life battery products practical.

Its prime job is to control a machine using a fixed program stored in ROM. Microcontrollers are found inside DVD players, clock radios, video games, telephones, washing machines and dryers, microwave ovens, televisions, automobiles, photocopiers, power tools and toys — anywhere an automatically controlled product needs a small, dependable brain.

In this chapter of Karnataka 2nd PUC Electronics we study the popular 8051 microcontroller and the PIC family — their architecture, addressing modes, instruction set and assembly-language programming — all of which are frequently tested in the II PUC board exam.