8051 tutorial

Introduction to microcontrollers

A micro-controller can be compared to a small stand alone computer, it is a very powerful device, which is capable of executing a series of pre-programmed tasks and interacting with other hardware devices. Being packed in a tiny integrated circuit (IC) whose size and weight is usually negligible, it is becoming the perfect controller for robots or any machines requiring some kind of intelligent automation. A single microcontroller can be sufficient to control a small mobile robot, an automatic washer machine or a security system. Any microcontroller contains a memory to store the program to be executed, and a number of input/output lines that can be used to interact with other devices, like reading the state of a sensor or controlling a motor.

8051-8052 Instruction Set

Instruction Set and Timing

In order to understand--and better make use of--the 8051, it is necessary to understand some underlying information concerning timing.

Basic Registers

If you've worked with any other assembly languages you will be familiar with the concept of an Accumulator register.

Special Function Registers

The 8051 is a flexible microcontroller with a relatively large number of modes of operations. Your program may inspect and/or change the operating mode of the 8051 by manipulating the values of the 8051's Special Function Registers (SFRs).

Types of Memory

The 8051 has three very general types of memory. To effectively program the 8051 it is necessary to have a basic understanding of these memory types.

Program Flow

When an 8051 is first initialized, it resets the PC to 0000h. The 8051 then begins to execute instructions sequentially in memory unless a program instruction causes the PC to be otherwise altered. There are various instructions that can modify the value of the PC; specifically, conditional branching instructions, direct jumps and calls, and "returns" from subroutines. Additionally, interrupts, when enabled, can cause the program flow to deviate from its otherwise sequential scheme.


The 8051 comes equipped with two timers, both of which may be controlled, set, read, and configured individually. The 8051 timers have three general functions: 1) Keeping time and/or calculating the amount of time between events, 2) Counting the events themselves, or 3) Generating baud rates for the serial port.

8051 Tutorial: Addressing Modes

Serial Communication

One of the 8051s many powerful features is its integrated UART, otherwise known as a serial port. The fact that the 8051 has an integrated serial port means that you may very easily read and write values to the serial port. If it were not for the integrated serial port, writing a byte to a serial line would be a rather tedious process requring turning on and off one of the I/O lines in rapid succession to properly "clock out" each individual bit, including start bits, stop bits, and parity bits.

8052 Tutorial