Benefits of Microcomputer:

  • Low cost (computer  cost + installation + maintenance) 
  • Small size, low weight & low power
  • No need for air conditioning
  • Design & packaging of PC is simple
  • User can handle installation 

Microprocessor(μP) as a CPU

  • μP - CPU on single IC
  • Building Computer is simplified. 
  • To handle variety of peripheral device - more powerful PC 
  • Special purpose ICs like interrupt controller, DMA controller, interval timer, etc are included as support chips to μP . 
  • Recently, special chip-set provides the functions of all support chips.

Bus Concept

During execution of a program in a computer, information flows from one unit to other.

Types of Information

  • Instruction
  • Memory Address
  • Data
  • Register Address
  • Control Signals
  • Input/Output command
  • Input / Output device address

To the central units (CPU, Memory & DMA Controller)  other peripheral subsystems (i/o controllers) are interfaced. 

Types of Information between CPU & Memory:

1. Memory Address

i. During instruction fetch, contents of Program Counter are sent to MAR in memory

ii. During operand fetch, contents of register in CPU are sent to MAR.

2. Memory Data

 i. During instruction fetch, contents of MDR are sent to IR in CPU.

ii. During operand fetch, contents of MDR are sent to register in CPU. Communication between the units incorporating the bus concepts are divided into Data, Address and Control.

Multiple paths – high cost of hardware

3. Types

Data            Address             Control

Data – Instruction & data

Address – Memory address/ Peripheral address

Control – control signals like mem read/write, I/O read/write, interrupt, reset.

When used?

Data

Control 

Address

Bus Arbitration

CPU (Bus master) decides who should control the bus when more than one unit wants bus at same time.

Only CPU & DMA controller controls the bus

Any unit can make bus request & waits for CPU to sanction it.

BUS Concept

Bidirectional Bus

Categories of signals on the bus

  1. O/P signals from microprocessor
  2. I/P signals to microprocessor
  3. Signals both o/p from & i/p to microprocessor

Operand Store

  • μP puts mem address from internal register on to address bus
  • μP puts data from one of internal registers onto data bus
  • μP issues Memory write signal on control bus
  • Memory takes contents on data bus & stores in given location

Data Bus

  • Bidirection (from μP to memory & from memory to μP) – internal mechanism
  • I/p & O/P to CPU & Memory 

Address bus

  • Uni directional (from μP to memory)
  • CPU never receives info from address bus
  • Only in built-in cache – bidirectional to support cache invalidation.
  • Data cant be sent

Control bus 

  • Collection of control signals generated by & sent to μP
  • 11 Control signals 

To remember:

  1. i/p or o/p from or to μP
  2. Task it does
  3. DMA involved or not?

Control Bus Signals

  1. Memory Read
  2. Memory Write
  3. I/O Read
  4. I/O write
  5. Interrupt
  6. Interrupt Acknowledge
  7.  Hold Request
  8.  Hold Acknowledgement
  9. Reset
  10. Clock
  11. Ready

Demultiplexing Bus

Multipurpose micro processor

Objectives

  • Reduction of hardware circuits
  • Exploitation of μP for better utilization
  • Design flexibility, Open to modifications

Extra Functions:

  1. Self Test
  • POST – Power-On Self-Test – execute as soon as PC is powered on
  • Verifies hardware fault
  • On error – PC halts with error message/code/abnormal symptom
  • POST routines are stored in ROM
  1.  Bootstrap Program
  • IPL – Initial Program Load 
  • by firmware on ROM
  • POST Program Pass control to bootstrap
  1.  Initialization of Programmable LSI
  • Parameters to LSI
  • mode of operation desired 
  • command to be executed 

Interface to Operating System & IOCS

BIOS – Basic Input Output Control System DOS – Disk Operating System

Advanced System Concepts Location

Operand Store

  1. μP puts mem address from internal register on to address bus
  2. μP puts data from one of internal registers onto data bus
  3. μP issues Memory write signal on control bus
  4. Memory takes contents on data bus & stores in given location

Data Bus

  1. Bidirection (from μP to memory & from memory to μP) – internal mechanism
  2. I/p & O/P to CPU & Memory 

Memory Protection Mechanism