The 8051 Microcontroller

1. The 8051 Microcontroller Chapter 1 INTRODUCTION TO MICROCONTROLLERS

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

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

4. 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

5. 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

6. 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

7. 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

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