Microprocessor Notes 1

8/20/2019 Microprocessor Notes 1

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A Microprocessor-based systemThe block diagram of a microprocessor-based system:

>>In order for the microprocessor to function as a programmable

device, it must work in a complete system comprising of three

components : microprocessor, memory and input/output. This

system is called microprocessor‐ based system or microcomputer

system. These three components will work together or interact

with each other to perform a given task.

System Buses

>>The three components of the microcomputer system is

connected by three busses, also known as system bus.

>>These busses is used to transfer information (data) internally

and externally to the microprocessor.

Address Bus

>>It carries the address of a unique memory or input/output

(I/O) device

>>The address bus is ʹunidirectional ́, over which the

microprocessor sends an address code to the memory or

input/output. The size (width) of the address bus is specified by

the number of bits it can handle.


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>>The more bits there are in the address bus, the more memory

locations a microprocessor can access. A 16 bit address bus is

capable of addressing 65,536 (64K) addresses.

Data Bus

>> The data bus carries data stored in memory (or an I/O device)

to the CPU or from the CPU to the memory (or I/O device)

>> The data bus is ʹbi‐directional ́, on which data or instruction

codes are transferred into the microprocessor or on which the

result of an operation or computation is sent out from the

microprocessor to the memory or input/ output.

>>Depending on the particular microprocessor, the data bus can

handle 8 bit or 16 bit data.

Control Bus

>>a collection of control signals that coordinate and synchronize

the whole system

>>The control bus is used by the microprocessor to send out or

receive timing and control signals in order to coordinate and

regulate its operation and to communicate with other devices, i.e.

memory or input/output.


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CPU

>> Microprocessor is also called Central Processing Unit (CPU)

since it is the functional centre of the computer system and it is

used to process data.

>> Microprocessor: A multipurpose , programmable logic device (IC) that reads

binary instructions from a storage device called memory , accepts

binary data as input and processes data according to those

instructions, and provide results as output.

(A multipurpose device: it can be used to perform various

sophisticated computing tasks or functions, as well as simple

tasks.

A programmable device: it can be instructed to perform given

tasks within its capability.)

>> Microprocessor is designed to understand and execute many

binary instructions.


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Memory

>>The memory in a computer system stores the data and instructions of

the programs.

>>Memory is the term used to the various storage devices in

which are used to store the programs and data for the

microprocessor.

>>These storage devices are made of semiconductor devices, and

also known as Primary Storage Devices.

Input/Output >>The input/output unit allows the microprocessor to

communicate with the outside world, either to receive or to send

data.

>>Most of the time, the input/output unit will also act as an

interface for the microprocessor, that is to convert the data into a

suitable format for the microprocessor.

>>Data can

be

in

the

form

of

parallel

(8

bit)

or

serial

format

(single

line).

>>Input devices are devices that input data or send data to the

computer. Input devices are such as keyboard, punched card

readers, sensors, switches, etc.


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>>Output devices are devices that output data or perform various

operations under the control of the CPU. Output devices are

LEDs, 7‐segment display unit, speaker, CRT, printer, digital

speedometer, fuel

injectors,

etc.

Inside The Microprocessor>>Internally, the microprocessor is made up of 3 main units.

The Arithmetic/Logic Unit (ALU)

The Control Unit.

Register Array>> Microprocessor:

A multipurpose , programmable logic device (IC) that reads

binary instructions from a storage device called memory , accepts

binary data as input and processes data according to those

instructions, and

provide

results

as

output.

(A multipurpose device: it can be used to perform various

sophisticated computing tasks or functions, as well as simple

tasks.


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A programmable device: it can be instructed to perform given

tasks within its capability.)

>> Microprocessor is designed to understand and execute many

binary instructions.

>> Microprocessor is also called Central Processing Unit (CPU)

since it is the functional centre of the computer system and it is

used to process data.

Block diagram of a typical CPU

Register Section >>An array of registers for holding data while it is being

manipulated.


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>>The register section/array consists completely of circuitry used

to temporarily store data or program codes until they are sent to

the ALU or to the control section or to memory.

>>The number

of

registers

are

different

for

any

particular

CPU,and the more >>register a CPU have will result in easier

programming tasks.

Arithmetic and Logic Unit (ALU)

>>This section, under the control of control section carries out the

actual processing of data , normally describe as data

manipulation. This consists largely of arithmetic operations

(ADDition, SUBtraction, INCrementing, DECrementing etc) and logical operations (ANDing, ORing, XORing, NOTing etc).

>>The ALU carries out these operations in the following manner :‐

>>stores data fetched from memory or I/O in the registers

>>fetches this data as needed from the registers and/or from

relevant accumulators

>>send this data either to its arithmetic circuitry or logical

circuitry, where necessary, where the necessary arithmetic or logical operations are carried out

>>send results of its arithmetic or logical operation to

relevant accumulator, to the memory, or to the I/O

interfaces.

Control Unit

>>The control section/unit is the part of the microcomputer that

controls its basic operations. It is made up of the control signal generating circuitry (clock) and the command (instruction)

decoder.

>>The control section fetches pre‐programmed instructions from

memory (op‐code fetch cycle) as needed and temporarily stores


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them in the command register (also known as Instruction

Register IR).

>>These instructions are then decoded by the operation decoder

(decode cycle) ,

which

sends

control

signals

to

the

relevant

parts of the microcomputer system (via the system busses) to

cause them to carry out the required operation (execute cycle)

>>The timing with which these control signals are generated is

determined by the clock. The number of T‐states tells the

time taken for the CPU to execute that particular instruction.

CPU structure

The main functions are>>data transfer

>>arithmetic and logic operations

>>decision making (instructional flow control)

>>The register array consists of at least one accumulator, program counter

and stack pointer.

>>The control unit controls all the operations in a CPU and basically it

puts the CPU in one of the fetch and execution phases.

>>The major

types

of

operations

controlled

by

the

control

signals:

>> sending of data from one part of the microcomputer to

another (read or write cycle)

>>inputting and outputting of data to/from the

microcomputer (I/O read or write cycle)

>>Arithmetic and Logic calculations.

>>Halting of computer instructions.

>>Jumping to

another

instruction

during

running

(execution)

of a program.


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Operation of the CPU

Fetch cycle (phase):

The CPU puts the address of the instruction to be executed on

the address bus. The address information comes from the program

counter (PC) maintained by the control unit.

The control bus holds the information for reading the memory

location and the data bus holds the instruction from the memory which is

stored into the instruction register (IR)

PC is updated to point to the next instruction.

Execute cycle (phase):

Instruction in the IR is decoded

The required data transfer and the required logical and

arithmetic operation are performed

The result is written back either to one of the registers or

memory or I/O device

Common operations performed in ALU :

addition, subtraction,logical AND, OR, XOR, NOT

increment, decrement, shift, clear, etc.


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Microcomputer

CPU on a single IC microprocessor (µP).

The terms CPU, µP and MPU (microprocessor unit) are

synonymous

CPU is the combination of the ALU and control unit of anycomputer.

When the CPU is a single IC; it is called a µP and is also referred

to as the MPU.

When the MPU is connected to memory and I/O, the arrangement

becomes a MICROCOMPUTER.

Many different MPUs are produced by many different IC vendors (e.g.,

Intel, Motorola, Texas Instruments, Zilog, National Semiconductors,

etc.).

Major differences are inword size,

the number and types of instructions that can be performed,

the types of external control signals available,

the amount of memory that can be addressed.

Organization of a microprocessor-based system

Let’s expand the picture a bit.

Microcontroller


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A microcontroller unit (MCU) contains an MPU, memory, and

I/O circuitry on a single chip.

Such a chip can perform control operations without the need for

any external circuitry.

e.g. Motorola MC68HC11 (also a microprocessor in the expandedmultiplexed mode) e.g.

Intel 8051

Microprocessors vs microcontrollers

Microprocessor

>>Microprocessors: high performance, general purpose “brains” for PCs

and workstations

>>Instruction decode and control, arithmetic/logic operations, registers,

timing, external control>>Includes memory management unit, lots of cache

>>Performance is the most important feature (cost is important, but

secondary)

>>Used mainly in desktop machines

Microcontroller

>>Microcontrollers: devices with high levels of integration for

embedded control

>>Microprocessor functions plus on-chip memory and peripheralfunctions (e.g. ports, timers)

>>Integrated RAM and ROM, no cache

>>Includes lots of peripherals

>>Used mainly in “embedded” applications and often involves real-time

control

>>Important features include: low cost, low power consumption, number

of integrated peripherals, interrupt response time, amount of RAM and

ROM


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The block diagram of a microcontroller

Memory >>The memory in a computer system stores the data and instructions of

the programs.

>>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.

Main memory typesThe semiconductor memory is of 2 types that is Read Only

Memory (ROM) and Read Write Memory (RWM). RWM is

popularly known as Random Access Memory (RAM) :‐

ROM (read-only memory)

>>programmed permanently at the factory, cannot be altered

EPROM (erasable programmable ROM)

>>nonvolatile, written electrically but erased optically

EEPROM (electrically ROM)

>>nonvolatile, both written and erased electrically RAM (random-access memory)

( RWM read and write memory

ROM (read-only memory)


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>>The registers inside the microprocessor –Read OnlyMemory (ROM)

>>used to store information that does not change. –It is used to store programs and data that need not to be altered,

i.e. permanent storage. Programs and data stored in ROMs can

only be read by the CPU.

>>Special equipment is used to write programs and data into the

ROMs and is called EPROM Programmer.

>>The monitor program is normally stored in the ROM.

>>Monitor program is actually the ‘resource manager’ of the

microcomputer system, similar to DOS or Windows in a personal

computer.

>>An example of a EPROM chip is the 2764 (8K X 8).

Random Access Memory (RAM)

(also known as Read/Write Memory(RWM)).>>used to store information supplied by the user. such as

programs and data.It is used to store user programs and data, and can be altered at

any time, i.e. temporary storage.

>>The information stored in RAM or RWM can be easily read and

altered by the CPU.

>>The contents (data or programs) stored is lost if power supply

to this chip is turned off. An example of a RWM chip is the CMOS

6116 (2K

X

8).


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Memory Map and AddressesThe memory map is a picture representation of the

address range and shows where the different memorychips are located within the address range.

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


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results either in memory or produces it on an

output device.

The three cycle instruction executionmodel

Fetch, Decode and Execute Cycles >>To use the right names for the cycles:–The

microprocessor fetches each instruction,– decodesit,–

Then executes it.>>To execute a program, the microprocessor

“reads” each instruction from memory, “interprets”

it, then “executes” it.

>>This sequence is continued until all instructions

are performed.

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Microprocessor Notes 1