To Get MOre Information About Microcontroller

Microcontroller

How does the microcontroller operate?

Even though there is a large number of different types of microcontrollers and even more programs created for their use only, all of them have many things in common. Thus, if you learn to handle one of them you will be able to handle them all. A typical scenario on the basis of which it all functions is as follows:

1. Power supply is turned off and everything is still…the program is loaded into the microcontroller, nothing indicates what is about to come…
2. Power supply is turned on and everything starts to happen at high speed! The control logic unit keeps everything under control. It disables all other circuits except quartz crystal to operate. While the preparations are in progress, the first milliseconds go by.
3. Power supply voltage reaches its maximum and oscillator frequency becomes stable. SFRs are being filled with bits reflecting the state of all circuits within the microcontroller. All pins are configured as inputs. The overall electronis starts operation in rhythm with pulse sequence. From now on the time is measured in micro and nanoseconds.
4. Program Counter is set to zero. Instruction from that address is sent to instruction decoder which recognizes it, after which it is executed with immediate effect.
5. The value of the Program Counter is incremented by 1 and the whole process is repeated...several million times per second.

What are microontrollers and what are they used for?

Like all good things, this powerful component is basically very simple. It is made by mixing tested and high- quality "ingredients" (components) as per following receipt:

1. The simplest computer processor is used as the "brain" of the future system.
2. Depending on the taste of the manufacturer, a bit of memory, a few A/D converters, timers, input/output lines etc. are added
3. All that is placed in some of the standard packages.
4. A simple software able to control it all and which everyone can easily learn about has been developed.

On the basis of these rules, numerous types of controllers were designed and they quickly became man's invisible companion. Their incredible simplicity and flexibility conquered us a long time ago and if you try to invent something about them, you should know that you are probably late, someone before you has either done it or at least has tried to do it.

The following things have had a crucial influence on development and success of the microcontrollers:

• Powerful and carefully chosen electronics embedded in the microntrollers can independetly or via input/output devices (switches, push buttons, sensors, LCD displays, relays etc.), control various processes and devices such as industrial automation, electric current, temperature, engine performance etc.
• Very low prices enable them to be embedded in such devices in which, until recent time it was not worthwhile to embed anything. Thanks to that, the world is overwhelmed today with cheap automatic devices and various “smart” appliances.
• Prior knowledge is hardly needed for programming. It is sufficient to have a PC (software in use is not demanding at all and is easy to learn) and a simple device (called the programmer) used for “loading” ready-to-use programs into the microcontroller.

So, if you are infected with a virus called electronics, there is nothing left for you to do but to learn how to use and control its power.

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Advantages and Disadvantages

Advantages of Microcontrollers

a)      Microcontrollers act as a microcomputer without any digital parts.

b)     As the higher integration inside microcontroller reduce cost and size of the system.

c)      Usage of microcontroller is simple, easy for troubleshoot and system maintaining.

d)     Most of the pins are programmable by the user for performing different functions.

e)      Easily interface additional RAM, ROM,I/O ports.

f)       Low time required for performing operations.

Disadvantages of Microcontrollers

a)      Microcontrollers have got more complex architecture than that of microprocessors.

b)     Only perform limited number of executions simultaneously.

c)      Mostly used in micro-equipments.

d)     Cannot interface high power devices directly.

Microcontroller Structure

CPU

CPU is the brain of a microcontroller .CPU is responsible for fetching the instruction, decodes it, then finally executed. CPU connects every part of a microcontroller into a single system. The primary function of CPU is fetching and decoding instructions. Instruction fetched from program memory must be decoded by the CPU.

Memory

The function of memory in a microcontroller is same as microprocessor. It is used to store data and program. A microcontroller usually has a certain amount of RAM and ROM (EEPROM, EPROM, etc) or flash memories for storing program source codes.

Parallel input/output ports

Parallel input/output ports are mainly used to drive/interface various devices such as LCD’S, LED’S, printers, memories, etc to a microcontroller.

Serial ports

Serial ports provide various serial interfaces between microcontroller and other peripherals like parallel ports.

Timers/counters

This is the one of the useful function of a microcontroller. A microcontroller may have more than one timer and counters. The timers and counters provide all timing and counting functions inside the microcontroller. The major operations of this section are perform clock functions, modulations, pulse generations, frequency measuring, making oscillations, etc. This also can be used for counting external pulses.

Analog to Digital Converter (ADC)

ADC converters are used for converting the analog signal to digital form. The input signal in this converter should be in analog form (e.g. sensor output) and the output from this unit is in digital form. The digital output can be use for various digital applications (e.g. measurement devices).

Digital to Analog Converter (DAC)

DAC perform reversal operation of ADC conversion.DAC convert the digital signal into analog format. It usually used for controlling analog devices like DC motors, various drives, etc.

Interrupt control

The interrupt control used for providing interrupt (delay) for a working program .The interrupt may be external (activated by using interrupt pin) or internal (by using interrupt instruction during programming).

Special functioning block

Some microcontrollers used only for some special applications (e.g. space systems and robotics) these controllers containing additional ports to perform such special operations. This considered as special functioning block.

Basic of Microcontroller

1) A microcontroller basically contains one or more following components:

• Central processing unit(CPU)
• Random Access Memory)(RAM)
• Read Only Memory(ROM)
• Input/output ports
• Timers and Counters
• Interrupt Controls
• Analog to digital converters
• Digital  analog converters
• Serial interfacing ports
• Oscillatory circuits

2) A microcontroller internally consists of all features required for a computing system and functions as a computer without adding any external digital parts in it.

3) Most of the pins in the microcontroller chip can be made programmable by the user.

4) A microcontroller has many bit handling instructions that can be easily understood by the programmer.

5) A microcontroller is capable of handling Boolean functions.

6) Higher speed and performance.

7) On-chip ROM structure in a microcontroller provides better firmware security.

8 ) Easy to design with low cost and small size.

Applications

Microcontrollers are widely used in modern electronics equipments. Some basic applications of microcontroller is given below.

• Used in biomedical instruments.
• Widely used in communication systems.
• Used as peripheral controller in PC.
• Used in robotics.
• Used in automobile fields

Different Microprocessor and Microcontroller

Microprocessor is an IC which has only the CPU inside them i.e. only the processing powers such as Intel’s Pentium 1,2,3,4, core 2 duo, i3, i5 etc. These microprocessors don’t have RAM, ROM, and other peripheral on the chip. A system designer has to add them externally to make them functional. Application of microprocessor includes Desktop PC’s, Laptops, notepads etc.

But this is not the case with Microcontrollers. Microcontroller has a CPU, in addition with a fixed amount of RAM, ROM and other peripherals all embedded on a single chip.

 At times it is also termed as a mini computer or a computer on a single chip. Today different manufacturers produce microcontrollers with a wide range of features available in different versions. Some manufacturers are ATMEL, Microchip, TI, Freescale, Philips, Motorola etc. 

Microcontrollers are designed to perform specific tasks. Specific means applications where the relationship of input and output is defined. Depending on the input, some processing needs to be done and output is delivered. For example, keyboards, mouse, washing machine, digicam, pendrive, remote, microwave, cars, bikes, telephone, mobiles, watches, etc. Since the applications are very specific, they need small resources like RAM, ROM, I/O ports etc and hence can be embedded on a single chip. This in turn reduces the size and the cost.

Microprocessor find applications where tasks are unspecific like developing software, games, websites, photo editing, creating documents etc. In such cases the relationship between input and output is not defined. They need high amount of resources like RAM, ROM, I/O ports etc. 

The clock speed of the Microprocessor is quite high as compared to the microcontroller. Whereas the microcontrollers operate from a few MHz to 30 to 50 MHz, today’s microprocessor operate above 1GHz as they perform complex tasks .

Comparing microcontroller and microprocessor  in terms of cost is not justified. Undoubtedly a microcontroller is far cheaper than a microprocessor. However microcontroller cannot be used in place of microprocessor and using a microprocessor is not advised in place of a microcontroller as it makes the application quite costly. Microprocessor cannot be used stand alone. They need other peripherals like RAM, ROM, buffer, I/O ports etc and hence a system designed around a microprocessor is quite costly.

Comparison between Microprocessor and Microcontroller

Microcontroller

Introduction

Microcontrollers are hidden inside a surprising number of products these days. If your microwave oven has an LED or LCD screen and a keypad, it contains a microcontroller. All modern automobiles contain at least one microcontroller, and can have as many as six or seven: The engine is controlled by a microcontroller, as are the anti-lock brakes, the cruise control and so on.

Any device that has a remote control almost certainly contains a microcontroller : TVs, VCRs and high-end stereo systems all fall into this category. Nice SLR and digital cameras, cell phones, camcorders, answering machines, laser printers, telephones (the ones with caller ID, 20-number memory, etc.), pagers, and feature-laden refrigerators, dishwashers, washers and dryers (the ones with displays and keypads).

A microcontroller is a computer. All computers whether we are talking about a personal desktop computer or a large mainframe computer or a microcontroller  have a several things in common :

• All computers have a CPU (central processing unit) that executes programs. If you are sitting at a desktop computer right now reading this article, the CPU in that machine is executing a program that implements the Web browser that is displaying this page.
•  The CPU loads the program from somewhere. On your desktop machine, the browser program is loaded from the hard disk.
•  The computer has some RAM (random-access memory) where it can store "variables."
• And the computer has some input and output devices so it can talk to people. On your desktop machine, the keyboard and mouse are input devices and the monitor and printer are output devices. A hard disk is an I/O device. It handles both input and output .

Application of Microprocessor

Example 1: LEDs

Example : Use the 8085 to turn on LEDs. The 8085 should be connected to eight LEDs at address 01H and the program should turn on LEDs 6,7 and 8

Solution : The 8-bit data lines are connected to the LEDs through an output latch addressed at 01H.

BUS system

Data Bus

• As name tells that it is used to transfer data within Microprocessor and Memory/Input or Output devices. It is bidirectional as Microprocessor requires to send or receive data.
• The data bus also works as address bus when multiplexed with lower order address bus. Data bus is 8 Bits long.
•  The word length of a processor depends on data bus, that why Intel 8085 is called 8 bit Microprocessor because it have an 8 bit data bus.

Address Bus

• It is a group of wires or lines that are used to transfer the addresses of Memory or I/O devices. It is without direction .
• In Intel 8085 microprocessor, Address bus was of 16 bits. This means that Microprocessor 8085 can transfer maximum 16 bit address which means it can address 65,536 different memory locations. 

Control Bus

Microprocessor uses control bus to process data, that is what to do with the selected memory location.

Some control signals are Read, Write and Operation code fetch. Various operations are performed by microprocessor with the help of control bus. This is a dedicated bus, because all timing signals are generated according to control signal.

Microprocessor Organization

ALU(Arithmetic Logic Unit)

• The part of a computer that performs all arithmetic computations, such as addition and multiplication, and all comparison operations. The ALU is one component of the CPU (central processing unit).
• To perform simple addition, subtraction, multiplication, division, and logic operation

Control Unit

• Control unit is circuitry that directs operations within the computer's processor by directing the input and output of a computer system.
•  A control unit works by gathering input through a series of commands it receives from instructions in a running programs and then outputs those commands into control signals that the computer and other hardware attached to the computer carry out.
• Example below :

Register

• A processor register is a local storage space on a processor that holds data that is being processed by CPU.
• Processor has a local storage area known as a register that performs most of the operations that the processor cannot perform directly.Any kind of data must first be identified by the register before it can be manipulated by the processor.

Accumulator

Accumulator is a AL register in which intermediate arithmetic and logic results are stored.Without a register like an accumulator, it would be necessary to write the result of each calculation (addition, multiplication, shift, etc.) to main memory, perhaps only to be read right back again for use in the next operation. 

                                    

Condition Code Register

• Contains flags set by the processor during the execution of instructions.Consists of individual bits are set or clear depending on the result of an operation. These bits can remember processing states between instruction.
• Different instruction affect the condition register in different way. Depend on processor type , a data , transfer instruction may not affect any flag , while an addition may affect several flag  

Program Counter

• The Program Counter (PC) is a register structure that contains the address pointer value of the current instruction. Each cycle, the value at the pointer is read into the instruction decoder and the program counter is updated to point to the next instruction
• Programmers do not have direct control over the program counter like they do with other registers. The program counter indicates where the CPU is in its current instruction sequence.

Stack Pointer

• The stack pointer is used to make sub-routines possible. By always pointing to the last used memory location, a push command can be used to add onto the stack and a pull to retrieve the last operation.
• Therefore, before executing a set of instructions, the current address can be pushed to the stack and at the end of the execution of the set of instructions, the address can be pulled from the stack making it possible to return to the previous location.
• The stack pointer must be initialized before it can be used.

Evolution Of Microprocessor

1.1         DATA SIZE : NIBBLE, BYTE, WORD, LONG WORD.

     The capacity of a microprocessor is normally referred to how many bits of data can be handled at one time, or what is the memory size (the amount of data cells of memory, determined by the amount of address lines/bits) accessible by the system.  Thus it is important to have a great understanding about data size.

     Data size is a mean of measure to determine how much data can be stored in a single cell of memory.  Imagine you are looking at the post boxes at a post office.  Each box can store a certain amount of letter (assumed all letters have equal size).  The size of each post box the greater numbers of letter can be stored.  Similarly in memory storage, a memory storage can be distributed into many single cell with equal data size.  In digital form, the smallest size of a single cell is called 1 bit.

     If a single cell can store 4 bit of data, the cell size is called Nibble. Subsequently 8 bits is called Byte, 16 bits is Word and 32 is Long Word.

     A single cell sized 1 bit can store either logic 0 or logic 1.  In other word, two different situations can be stored or represented.  Thus the range of data is 0-1.

Data size : n = 1

Data capacity : 2ⁿ = 2¹ = 2

Range : 0  - 1 

A single cell sized 4 bit (Nibble) can store 16 possible situations.

Data size : n = 4

Data capacity : 2ⁿ = 2⁴ = 16

Range : 0  - 15 

    Figure above shows the different data sizes in a graphic manner.  Please note that the data size is determined by the number of bit (n), and is label from 0 to n-1.  For the data type Byte, Word and Long Word allocate the MSB as the sign bit, to determine that value of remaining bits is positive or negative.

     For the data which has more bits, it is easier to divide it into dual-half portions i.e. upper (MSB section) and lower portions (LSB section).

ü  1 Byte consists of two nibbles, upper nibble and lower nibble.

ü  1 Word consists of two bytes, upper byte and lower byte.

ü  1 Long Word consists of two word, upper word and lower word.

Basic Computer System

A computer has the following units:

·         Input Unit

·         Output Unit

·         Memory Unit

·         Central Processing Unit

Block Diagram

1. Input: This is the process of entering data and programs in to the computer system. You should know that computer is an electronic machine like any other machine which takes as inputs raw data and performs some processing giving out processed data. Therefore, the input unit takes data from us to the computer in an organized manner for processing.

2. Storage: The process of saving data and instructions permanently is known as storage. Data has to be fed into the system before the actual processing starts. It is because the processing speed of Central Processing Unit (CPU) is so fast that the data has to be provided to CPU with the same speed. Therefore the data is first stored in the storage unit for faster access and processing. This storage unit or the primary storage of the computer system is designed to do the above functionality. It provides space for storing data and instructions.

The storage unit performs the following major functions:

• All data and instructions are stored here before and after processing.

• Intermediate results of processing are also stored here.

3. Processing: The task of performing operations like arithmetic and logical operations is called processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit and makes all sorts of calculations based on the instructions given and the type of data provided. It is then sent back to the storage unit.

4. Output: This is the process of producing results from the data for getting useful information. Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form. Again the output is also stored inside the computer for further processing.

5. Control: The manner how instructions are executed and the above operations are performed. Controlling of all operations like input, processing and output are performed by control unit. It takes care of step by step processing of all operations inside the computer.

FUNCTIONAL UNITS

In order to carry out the operations mentioned in the previous section the computer allocates the task between its various functional units. The computer system is divided into three separate units for its operation. They are

1) arithmetic logical unit

2) control unit.

3) central processing unit.

Arithmetic Logical Unit (ALU)  Logical Unit

Logical Unit : After you enter data through the input device it is stored in the primary storage unit. The actual processing of the data and instruction are performed by Arithmetic Logical Unit. The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to ALU from storage unit when required. After processing the output is returned back to storage unit for further processing or getting stored.

Control Unit (CU)

The next component of computer is the Control Unit, which acts like the supervisor seeing that things are done in proper fashion. Control Unit is responsible  for  coordinating various operations using time signal. The control unit determines the sequence in which computer programs and instructions are executed. Things like processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them. It also acts as a switch board operator when several users access the computer simultaneously. Thereby it coordinates the activities of computer’s peripheral equipment as they perform the input and output.

Central Processing Unit (CPU)

The ALU and the CU of a computer system are jointly known as the central processing unit. You may call CPU as the brain of any computer system. It is just like brain that takes all major decisions, makes all sorts of calculations and directs different parts of the computer functions by activating and controlling the operations.

 MICROCOMPUTER SYSTEM

We already learned that in a basic computer system, a Central Processing Unit (CPU) consists of both ALU and Control Units.  In a microcomputer the CPU is usually implemented on a single chip, which is the microprocessor.  Some system may need several additional chips to be connected to a microprocessor chip to make the CPU.  It is common to refer to the microprocessor as the MPU (microprocessor unit), since it is the CPU of the microcomputer.

·         Since microcomputer system is actually a basic computer system, the main elements of the internal constructions and function are similar.  However, the following outlines some important features in mode specific manner of a microcomputer system as a comparison to the basic computer system.

a)  CPU (Central Processing Unit)

·         A silicon chip that works as ‘heart’ of the computer.

·         Receive instructions from memory to implement a task.

b)    Memory Unit.

·         Store data and programs.

·         Divided into two (2) main categories:

1)    Primary Memory:

ROM (Read Only Memory)

·         Data can only be read but cannot be written into it.

·         The stored data will not disappear when the power supply is disconnected.

2.   Secondary Memory:

·         RAM can only keep data in temporary basis, thus we need a permanent storage,        which is also called secondary storage.

·         The example of secondary storage are floppy disc and hard disk.  Another type is CDROM (Compact-disc ROM), which can store up to 600 million characters and it is suitable for storing huge size of information.

C)    Input/Output (I/O) Unit

·         I/O unit contains the interface circuits needed to allow the peripheral to proper communicate with the rest of the computer.

·         In some cases these interface circuits are LSI chips designed by the MPU manufacturer to interface the MPU to a variety of I/O devices.  In other cases the interface circuits may be as simple as buffer register.

·         I/O unit allows user (external environment) to communicate with the computer system via interface unit that connected to the peripheral devices.  The peripheral devices such as keyboard, printer, sensor that measuring vehicle speed etc.

·         The port size of I/O unit is equivalent to the data bus size of the microprocessor.

Introduction

A microprocessor  incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC) or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output. It is an example of sequential digital logic, as it has internal memory. Microprocessors operate on numbers and symbols represented in the binary numeral system.

History of Microprocessor