The 8051 Microcontroller Chapter 1 INTRODUCTION TO MICROCONTROLLERS

The 8051 Microcontroller Chapter 1 INTRODUCTION TO MICROCONTROLLERS

Block diagram of a microcomputer system (CPU, RAM, ROM, A‑BUS, D-BUS, C‑BUS) 2

• CPU: performs all operations on data • Fetching instructions and executing instructions • ALU, IR, PC 3

Fetching an instruction involves several steps : • The contents of the PC are placed on the Address Bus • A READ control signal is activated • The instruction opcode are read from RAM and placed on the Data Bus • The opcode is latched into the CPU’s internal IR • The PC is increment to prepare for the next fetch from memory 4

• Levels of software between the user and the hardware • At the lowest level BIOS (Basic Input/Output System on the IBM PC) • The operating system: collection of programs, provides mechanism to access, manage and effectively utilize the computer’s resources • Application software should provides users to finish their jobs, with little or no knowledge of the operating system 5

• • The difference between the microcontrollers and microprocessors As well as the CPU microcontrollers include RAM, ROM, a serial interface, a parallel interface, timer and interrupt scheduling circuitry - all within the same IC 6

• • Implementation of the NAND operation using an 8051 microcontroller One tradeoff is speed The 8051 assembly language program for this logic operation On an 8051 microcontroller the 3 input NAND function is realized The propagation delay from an input transition to the correct output level is quite long, in comparison to the equivalent TTL circuit The delay is from 3 -17 microsecond for 8051 operation using a 12 MHz crystal The propagation delay is about 10 nanoseconds 7

• The software must perform the operations shown in the flowchart • The logic gate example illustrates that the microcontrollers can implement logic operations 8