Download Chapter 1 Introduction

Chapter 1
Introduction
Introduction to microprocessors … Chapter 1
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Introduction
•
In this course we will discus the microprocessor.
•
We will discuss it from two perspectives.
– First, as a unit within a microcomputer system.
– Second, as a stand-alone system for controlling
other systems.
•
From the microprocessor’s perspective it doesn’t
change any thing. The difference comes from our
interaction with it.
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What is a Microprocessor?
•
The word comes from the combination micro and
processor.
– Processor means a device that processes
whatever. In this context processor means a
device that processes numbers, specifically binary
numbers, 0’s and 1’s.
• To process means to manipulate. It is a general term
that describes all manipulation. Again in this context, it
means to perform certain operations on the numbers that
depend on the microprocessor’s design.
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What about micro?
•
Micro is a new addition.
– In the late 1960’s, processors were built using
discrete elements.
• These devices performed the required operation, but
were too large and too slow.
– In the early 1970’s the microchip was invented. All
of the components that made up the processor
were now placed on a single piece of silicon. The
size became several thousand times smaller and
the speed became several hundred times faster.
The “MicroProcessor” was born.
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Definition of the Microprocessor
The microprocessor is a programmable
device that takes in numbers, performs on
them arithmetic or logical operations
according to the program stored in
memory and then produces other
numbers as a result.
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Definition (Contd.)
•
Lets expand each of the underlined words:
– Programmable device: The microprocessor can
perform different sets of operations on the data it
receives depending on the sequence of instructions
supplied in the given program.
By changing the program, the microprocessor
manipulates the data in different ways.
– Instructions: Each microprocessor is designed to
execute a specific group of operations. This group of
operations is called an instruction set. This instruction
set defines what the microprocessor can and cannot
do.
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Definition (Contd.)
– Takes in: The data that the microprocessor
manipulates must come from somewhere.
• It comes from what is called “input devices”.
• These are devices that bring data into the system from
the outside world.
• These represent devices such as a keyboard, a mouse,
switches, and the like.
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Definition (Contd.)
– Numbers: The microprocessor has a very narrow view on
life. It only understands binary numbers.
A binary digit is called a bit (which comes from binary digit).
The microprocessor recognizes and processes a group of
bits together. This group of bits is called a “word”.
The number of bits in a Microprocessor’s word, is a measure
of its “abilities”.
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Definition (Contd.)
– Words, Bytes, etc.
• The earliest microprocessor (the Intel 8088 and Motorola’s
6800) recognized 8-bit words.
– They processed information 8-bits at a time. That’s why they are
called “8-bit processors”. They can handle large numbers, but in
order to process these numbers, they broke them into 8-bit pieces
and processed each group of 8-bits separately.
• Later microprocessors (8086 and 68000) were designed with
16-bit words.
– A group of 8-bits were referred to as a “half-word” or “byte”.
– A group of 4 bits is called a “nibble”.
– Also, 32 bit groups were given the name “long word”.
• Today, all processors manipulate at least 32 bits at a time and
there exists microprocessors that can process 64, 80, 128 bits
or more at a time.
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Definition (Contd.)
– Arithmetic and Logic Operations:
• Every microprocessor has arithmetic operations such as
add and subtract as part of its instruction set.
– Most microprocessors will have operations such as
multiply and divide.
– Some of the newer ones will have complex operations
such as square root.
• In addition, microprocessors have logic operations as
well. Such as AND, OR, XOR, shift left, shift right, etc.
• Again, the number and types of operations define the
microprocessor’s instruction set and depends on the
specific microprocessor.
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Definition (Contd.)
– Program: A program is a sequence of instructions
that bring data into the microprocessor, processes
it and sends it out.
• There are many programming languages (C, C++,
FORTRAN, and JAVA…) However, these programming
languages can be grouped into three main levels (these
days a fourth level is developing).
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Definition (Contd.)
– Programming Languages
• Machine language
– Machine language is the lowest level programming
language. It is a language intended to be understood by
the microprocessor (the machine) only.
In this language, every instruction is described by binary
patterns.
e.g. 11001101 may mean 1 + 2
This is the form in which instructions are stored in memory.
This is the only form that the microprocessor understands.
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Definition (Contd.)
– Programming Languages
• Assembly language
– This language is more understandable by humans. In this
language, the binary patterns are assigned mnemonics
(short abbreviated names).
e.g. “Add 1,2” is assigned to the machine language pattern
11001101 mentioned above to refer to the operation 1+2.
There is usually one assembly language instruction for
each machine language instruction.
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Definition (Contd.)
– Programming Languages
• High level languages
– These are languages like C, PASCAL and FORTRON.
These are more natural for humans to use than assembly
or machine languages. They are also more compact (i.e. it
takes less statements to write the program).
One high level instruction translates into many assembly or
machine language instructions.
e.g. x = y + z may translate into:
MOV
1000, R1
MOV
1004, R2
ADD
R1, R2
MOV
R1, 1008
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Definition (Contd.)
– Programming Languages
• The new level being developed: is ultra high level
languages which would contain things like C++, and
JAVA.
– Here a single instruction may translate into hundreds of
assembly or machine language instructions.
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Definition (Contd.)
– Stored in memory :
• First, what is memory?
– Memory is the location where information is kept while not
in current use.
– Memory is a collection of storage devices. Usually, each
storage device holds one bit. Also, in most kinds of
memory, these storage devices are grouped into groups of
8. These 8 storage locations can only be accessed
together. So, one can only read or write in terms of bytes to
and form memory.
– Memory is usually measured by the number of bytes it can
hold. It is measured in Kilos, Megas and lately Gigas. A
Kilo in computer language is 210 =1024. So, a KB
(KiloByte) is 1024 bytes. Mega is 1024 Kilos and Giga is
1024 Mega.
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Definition (Contd.)
– Stored in memory:
• When a program is entered into a computer, it is stored in
memory. Then as the microprocessor starts to execute
the instructions, it brings the instructions from memory
one at a time.
• Memory is also used to hold the data.
– The microprocessor reads (brings in) the data from
memory when it needs it and writes (stores) the results into
memory when it is done.
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Definition (Contd.)
– Produces: For the user to see the result of the
execution of the program, the results must be
presented in a human readable form.
• The results must be presented on an output device.
• This can be the monitor, a paper from the printer, a
simple LED or many other forms.
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A Microprocessor-based system
From the above description, we can draw the
following block diagram to represent a
microprocessor-based system:
Output
Input
Memory
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Inside The Microprocessor
•
Internally, the microprocessor is made up of 3
main units.
– The Arithmetic/Logic Unit (ALU)
– The Control Unit.
– An array of registers for holding data while it is
being manipulated.
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Organization of a microprocessor-based system
•
Let’s expand the picture a bit.
I/O
Input / Output
ALU
Register
Array
Control
System Bus
Memory
ROM RAM
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Organization of the Microprocessor
– The microprocessor can be divided into three
main pieces:
• Arithmetic/Logic Unit
– Performs all computing and logic operations such as
addition and subtraction as well as AND, OR and XOR.
• Register Array
– A collection of registers within the microprocessor itself.
These are used primarily for data storage during program
execution. The number and the size of these registers
differ from one microprocessor to the other.
• Control Unit
– As the name implies, the control Unit controls what is
happening in the microprocessor. It provides the necessary
control and timing signals to all operations in the
microprocessor as well as its contact to the outside world.
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How do the units interact
Assume that the user has given the following instruction:
ADD R1, R2, R3
(Which translates to: add Register 1 to Register 2 and place the result in Register 3.)
•
•
•
•
•
•
The control unit receives the bit pattern for this instruction
(0100011011) from memory.
It decodes the bit pattern and determines that this is an Add operation
(0100).
It also determines that the inputs to the addition come from Register R1
(01) and Register R2 (10).
It finally determines that the results go into register R3 (11).
It issues a control signal connecting one input of the adder (in the ALU)
to register R1 (in the Register Array) and the other input to register R2.
Then after an appropriate amount of time, it issues a control signal to
register R3 to store the output of the adder.
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How do the units interact
EN
EN
R1
EN
R2
S0
S1
R3
EN
R4
S0
4 X 1 MUX
4 X 1 MUX
S1
Adder
The control unit is in complete control of the system at all times. It
controls the behavior using select and enable inputs to the different
elements of the system.
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Memory
•
Memory stores information such as instructions and data
in binary format (0 and 1). It provides this information to
the microprocessor whenever it is needed.
•
Usually, there is a memory “sub-system” in a
microprocessor-based system. This sub-system includes:
– The registers inside the microprocessor
– Read Only Memory (ROM)
• used to store information that does not change.
– Random Access Memory (RAM) (also known as Read/Write
Memory).
• used to store information supplied by the user. Such as
programs and data.
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Memory
•
To execute a program:
– the user enters its instructions in binary format into the
memory.
– The microprocessor then reads these instructions and
whatever data is needed from memory, executes the
instructions and places the results either in memory or
produces it on an output device.
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Input/Output ( I/O )
•
Input and output devices are the system’s means
of communicating with the outside world. These
devices are collectively known as peripherals.
– Input devices transfer binary information from the
outside world to the microprocessor.
• Examples of input devices are: keyboard, mouse, bar
code reader, scanner and the like.
– Output devices transfer binary information from
the microprocessor to the outside world.
• Theses include things like an LED, a monitor, a printer
and the like.
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System Bus
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A communication path between the
microprocessor and peripherals.
– It is simply a group of wires carrying the voltages
and currents representing the different bit values.
•
The microprocessor communicates with only one
peripheral at a time.
•
Controlling the bus is done by the Control Unit.
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The three cycle instruction execution model
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To execute a program, the microprocessor
“reads” each instruction from memory,
“interprets” it, then “executes” it.
•
To use the right names for the cycles:
– The microprocessor fetches each instruction,
– decodes it,
– Then executes it.
•
This sequence is continued until all instructions
are performed.
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Machine Language
•
The number of bits that form the “word” of a
microprocessor is fixed for that particular processor.
– These bits define a maximum number of combinations.
• For example an 8-bit microprocessor can have at most 28 = 256
different combinations.
•
However, in most microprocessors, not all of these
combinations are used.
– Certain patterns are chosen and assigned specific
meanings.
– Each of these patterns forms an instruction for the
microprocessor.
– The complete set of patterns makes up the
microprocessor’s machine language.
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The 8085 Machine Language
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The 8085 (from Intel) is an 8-bit microprocessor.
– The 8085 uses a total of 246 bit patterns to form
its instruction set.
– These 246 patterns represent only 74 instructions.
• The reason for the difference is that some (actually most)
instructions have multiple different formats.
– Because it is very difficult to enter the bit patterns
correctly, they are usually entered in hexadecimal
instead of binary.
• For example, the combination 0011 1100 which
translates into “increment the number in the register
called the accumulator”, is usually entered as 3C.
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Assembly Language
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Entering the instructions using hexadecimal is quite
easier than entering the binary combinations.
– However, it still is difficult to understand what a
program written in hexadecimal does.
– So, each company defines a symbolic code for the
instructions.
– These codes are called “mnemonics”.
– The mnemonic for each instruction is usually a group
of letters that suggest the operation performed.
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Assembly Language
•
Using the same example from before,
– 00111100 translates to 3C in hexadecimal
– Its mnemonic is: “INR A”.
– INR stands for “increment register” and A is short for
accumulator.
•
Another example is: 1000 0000,
– Which translates to 80 in hexadecimal.
– Its mnemonic is “ADD B”.
– “Add register B to the accumulator and keep the result
in the accumulator”.
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Assembly Language
•
It is important to remember that a machine
language and its associated assembly language
are completely machine dependent.
– In other words, they are not transferable from one
microprocessor to a different one.
•
For example, Motorolla has an 8-bit
microprocessor called the 6800.
– The 8085 machine language is very different from
that of the 6800. So is the assembly language.
– A program written for the 8085 cannot be
executed on the 6800 and vice versa.
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“Assembling” The Program
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How does assembly language get translated into
machine language?
– There are two ways:
– 1st there is “hand assembly”.
• The programmer translates each assembly language
instruction into its equivalent hexadecimal code (machine
language). Then the hexadecimal code is entered into
memory.
– The other possibility is a program called an
“assembler”, which does the translation
automatically.
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High Level Languages
•
•
We said earlier that assembly and machine language are
completely dependent on the microprocessor. They can
not be easily moved from one to the other.
To allow programs to be developed for multiple machines
high level languages were developed.
– These languages describe the operation of the program in
general terms.
– These programs are translated into microprocessor specific
assembly language using a compiler or interpreter program.
• These programs take as an input high level statements such as
“ I = j + k; ” and translate them to machine language compatible
with the microprocessor being used.
High level language
Source code
Compiler
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Assembler
Machine language
Object code
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Compiler vs. Interpreter
•
What is the difference between Compiler and Interpreter?
– A compiler translates the entire program at once and produces the
object code.
– An interpreter “ compiles “ the source code one line at-a-time. The
object code for each line is produced, executed, and forgotten.
Each time the program is to be executed, it has to be re-interpreted.
• Interpreters are very inefficient. Compilers produce object code that is
quite a bit smaller and faster to execute.
•
Compilers are still inefficient when complete control is
needed and when memory is very critical.
• In such a situation, it is better to do the job yourself.
– Writing a program in assembly language may not be easy. But,
you can control exactly how things are being done and which
instruction is being used to perform each operation.
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The Hardware/Software Interaction
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The hardware of a computer system is the collection of
chips that make up its different pieces, including the
microprocessor.
– The hardware consists of five main systems:
-
The microprocessor
Memory (RAM & ROM)
Storage (Disk, CD)
Input Devices (keyboard, mouse)
Output Devices (monitor, printer).
Microprocessor
Input
Memory
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Output
Storage
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The Hardware/Software interaction
•
Software refers to any program that executes on
the hardware.
– It contains very low level programs that control the
behavior of the hardware all the way to
complicated applications like 3D graphics, video
editing, and circuit simulation and design.
•
The interaction between the two systems
(hardware and software) is managed by a group
of programs known collectively as Operating
system.
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The Operating System
•
The operating system is a layer between the application
programs and the hardware.
– Pieces of the operating system control the operation of the
disks, the monitor, the keyboard, the mouse, the printer, the
sound card, and even memory.
• When a program wants to use one of these items, it sends a
request to the operating system and the operating system in
turn will perform the operation.
•
When the computer is first turned on, the operating
system starts to execute. It stays running as long as the
computer is operating.
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The Operating System
•
The interaction of the user with the computer is through
the operating system.
– When the user invokes a program, the operating system
starts the process and makes the program start executing.
The program is executed on top of the operating system.
Application
Operating
Application Programs
Operating System
Hardware
Hardware
System
Programs
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Operating Systems
•
Examples of operating systems are:
–
–
–
–
–
•
MS-DOS
MS Windows
Macintosh OS
OS/2
UNIX
Most operating systems are hardware specific:
– For example, windows only runs on
microprocessors made by Intel or those that
behave the same way (i.e. “compatible”).
•
Other operating systems (like UNIX) are
designed to work on any platform (hardware).
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