Khaled A. Al-Utaibi
alutaibi@uoh.edu.sa
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Computers are Every Where
What is Computer Engineering?
Design Levels
Computer Engineering Fields
What is a Microcomputer ?
Course Objectives
The Stored Program Concept
The Stored Program Processing Cycle
Three-Bus System Architecture
The 80x86 Family
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Microcomputer systems are becoming an
essential part of any product or equipment in all
fields including
−House Appliances
−Office Equipment
−Telecommunications
−Transportation
−Traffic Control
−Medical Equipment
−Industrial Control
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Work
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A microcomputer is an electronic device with a
microprocessor as its central processing unit
(CPU), a memory, and input/output (I/O)
facilities.
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When a microcomputer is equipped with a
keyboard and screen for input and output and is
running an operating system (DOS, Windows,
Linux, etc) it is called a personal computer.
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To introduce the fundamental hardware and
software concepts needed for the design of
microcomputers system.
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To introduce the fundamental hardware and
software concepts needed for the design of
microcomputers system.
− Functions of various processor pins
− Memory/IO Read and Write bus cycles
− Main types of memory technology
− Memory internal organization
− Design memory interfaces.
− Computer serial and parallel interfaces
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To introduce the fundamental hardware and
software concepts needed for the design of
microcomputers system.
− How interrupts are used to implement I/O control and
data transfers
− Design interrupt service routines and I/O drivers using
assembly language.
− Data access from magnetic and optical disk drives
using DMA
− Types of bus interfaces in a computer system
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Most of today’s computer systems are based on
a design principle proposed by Dr. John Von
Neumann (1946).
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The basic stored program computer (Von
Neumann Architecture) consists of three major
parts: (1) CPU, (2) Memory, (3) I/O Devices.
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The basic stored program cycle consists of three
major steps: (1) Fetch, (2) Decode, (3) Execute.
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Clock Generator:
− Controls the basic timing of the computer
− It generates a square wave signal
− This signal is used to synchronize all activities within
the computer
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Registers:
− Two types (general purpose, special purpose)
− General purpose registers are used to store temporary
information
− Special purpose registers are used for specific tasks
(e.g. the accumulator)
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Fetching, Decoding and Executing an
Instruction:
− The basic processing cycle begins with a memory fetch
or read cycle
− The Instruction Pointer (IP) holds the address of next
instruction to be fetched.
− This address is output on the system address bus.
− The memory address decoder examines the binary
value of the address on the system address bus and
selects the proper memory location.
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Fetching, Decoding and Executing an
Instruction:
−The CPU activate the memory read control through
the system control bus.
−This causes the selected data byte (i.e. instruction) in
the memory to be placed onto the data bus.
−The instruction is then placed in the Instruction
Register (IR).
−Once in the CPU, the instruction is decoded and
executed.
− When executing the instruction is completed, the
cycle is repeated.
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The Instruction Set:
− The job of the Instruction Decoder (ID) is to recognize
and activate appropriate controls in the CPU needed to
execute the instruction.
− The list of all instructions recognized by the ID is called
the instruction set .
− Microprocessors are classified based on the
specification of the instruction sets into two categories:
 (1) Complex Instruction Set Computers (CISC) and
 (2) Reduced Instruction Set Computers (RISC)
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Modern CPUs:
− Most microprocessors today are designed to allow the
fetch and execute cycles to overlap.
− This is done by dividing the CPU into two units:
 (1) a Bus Interface Unit (BIU) and
 (2) an Execution Unit (EU).
− The job of the BIU is to fetch instructions from
memory and store them in a special instruction queue.
− The EU then fetches instructions from this queue (not
from memory).
− Some processors have a pipelined execution unit that
allows the decoding and execution of instructions to
overlap.
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A bus is a collection of electronic signal lines all
dedicated to a particular task.
The architecture considered in the previous slides
consists of three types of buses: address, data,
and control buses.
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The Data Bus:
−The data bus consists of internal and external data
buses.
−The internal data bus connects the internal
components of the CPU (e.g. Registers, ALU, etc.) to the
data I/O pins of the CPU.
− The external data bus connects the data I/O pins of the
CPU to the memory and I/O devices (e.g. printer,
monitor, etc).
−The width of the internal data bus in bits is usually used
to classify a microprocessor (e.g. 8-bit, 16-bit, 32-bi
microprocessors)
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The Data Bus:
−The width of the internal data bus is usually the same as
the external data bust – but not always.
− The 80386 processor has 32-bit internal and 32-bit
external data buses.
− The 80386SX processor has 32-bit internal data bus, but
16-bit external data bus.
− The Pentium processor has 32-bit internal data bus and
64-bit external data bus.
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Memory Banks:
−How a 64-bit (or 32-bit or 16-bit) processor can access
an 8-bit-wide memory?
−The memory is divided into banks.
− The 8086 processor (16-bit) requires 2 banks (16/8=2).
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Memory Banks:
−How a 64-bit (or 32-bit or 16-bit) processor can access
an 8-bit-wide memory?
−The memory is divided into banks.
− The 80486 processor (32-bit) requires 4 banks (32/8=4).
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The address Bus:
−It is used to identify the memory location or I/O device
(also called I/O port) to be accessed by the CPU
−The width of this bus in the 80x86 family varies from
one processor to the other for example:
 The 8086/8088 processors have 20-bit address bus.
 The 80286 processor has 24-bit address bus.
 The 80386/80486/Pentium processors have 32-bit address
bus.
 The Pentium Pro processor has 36-bit address bus.
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Example 1:
How many different memory addresses can an 8086
output? Repeat for 80286 and 80386 processors.
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Example 1:
How many different memory addresses can an 8086
output? Repeat for 80286 and 80386 processors.
−8086 processor has 20 address lines
−Addressable memory locations = 220 = 1M
−80286 processor has 24 address lines
−Addressable memory locations = 224 = 24x220 = 16M
−80386 processor has 32 address lines
−Addressable memory locations = 232 = 22x230 = 4G
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The Control Bus:
−How can we tell if the address on the address bus is a
memory address or an I/O port ?
− How can we tell if the memory or I/O access is a read or
write operation ?
− These questions are answered by the control bus.
− Each time the processor outputs an address, it also
activates one of 4 control signals
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(1) Memory Read
(2) Memory Write
(3) I/O Read
(4) I/O Write
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The 8086 Microprocessor (1978):
−20-bit address bus.
−16-bit internal data bus.
−16-bit external data bus.
−Separate bus interface unit (BIU) and execution unit
(EU).
−16-bit registers (with the ability to access the high or
low 8 bits separately).
−Built in hardware multiply and divide instructions.
−Support for an external floating-point math
coprocessor.
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The 8088 Microprocessor (1979):
−20-bit address bus.
−16-bit internal data bus.
−8-bit external data bus.
−Separate bus interface unit (BIU) and execution unit
(EU).
−16-bit registers (with the ability to access the high or
low 8 bits separately).
−Built in hardware multiply and divide instructions.
−Support for an external floating-point math
coprocessor.
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The 80186 & 80188 Microprocessors (1982):
−A personal computer (PC) based on the 8086/8088
microprocessors requires several additional chips such
as: a clock generator, a programmable timer, a
programmable interrupt controller, a direct memory
access controller and a circuitry to select the I/O
devices.
−To simplify the design, Intel introduced the 80186 &
80188 microprocessors.
−The 80186/80188 integrates on a single chip an
8086/8088 microprocessor and all the chips mentioned
above.
−The 80186 & 80188 are often referred to as highintegration processors
−Used as a microcontroller
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The 80286 Microprocessor (1982):
−24-bit address bus.
−16-bit internal data bus.
−16-bit external data bus.
−Designed to be software compatible with 8086 &
80186 microprocessors.
−Provides two programming modes:
 Real Mode
 Protected Mode
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The 80286 Microprocessor (Real Mode):
−The processor function exactly like the 8086 processor.
−That is, any 8086 program can be run on a Real Mode
80286 processor without any change.
−The 80286 processor uses only its 20 least significant
address lines.
−So, the memory space is limited to 1 MB.
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The 80286 Microprocessor (Protected Mode):
−In this mode, the processor supports a multiprogram
environment.
−It gives each program a predetermined amount of
memory.
−This uses the full memory space which is 16MB.
−This mode is called Protected Mode because several
programs can be loaded into
memory at once (each in its
own segment), but are protected
from each other.
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The 80386 Microprocessor (1984):
−32-bit address bus.
−32-bit internal data bus.
−32-bit external data bus.
−32-bit registers.
−Provides three modes:
 Real Mode (identical to that of 80286)
 Protected Mode (manages 4 GB of
memory in a way similar to that of the
80286).
 Virtual Mode (similar to Real Mode,
except that multiple 8086 processors can
run simultaneously
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The 80386 Microprocessor (1989):
−32-bit address bus.
−32-bit internal and external data bus.
−32-bit registers.
−On-chip cache (stores the most recently used
instructions and data )
−Integrated Floating-Point Unit (FPU)
−Real & Protected Modes as in 80386
−Pipelined design
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The Pentium Microprocessor (1993):
−32-bit address bus.
−32-bit internal
−64-bit external data bus.
−32-bit registers.
−Two instructions pipelines
−On-chip cache
−Integrated FPU