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 CPUs internal IR
• The PC is increment to prepare for the next fetch
  from memory

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• 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 computers 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