HW components and microcontroller Essay
A microcontroller ( besides microcontroller unit, MCU or AµC ) is a little computing machine on a individual incorporate circuit consisting of a comparatively simple CPU combined with support maps such as a crystal oscillator, timers, watchdog timer, consecutive and linear I/O etc. Program memory in the signifier of NOR flash or OTP ROM is besides frequently included on bit, every bit good as a typically little sum of RAM.
Microcontrollers are designed for little or dedicated applications.Microcontrollers are used in automatically controlled merchandises and devices, such as car engine control systems, distant controls, office machines, contraptions, power tools, and playthings. [ 3 ]A microcontroller is so similar to the microprocessor inside a Personal computer.
Both microprocessor and microcontroller contain a Central Processing Unit, or CPU. The CPU executes instructions that perform the basic logic, math, and informations traveling map of a computing machine. To do a complete computing machine, a microprocessor requires memory for hive awaying informations and plans, and I/O interfaces for linking external device like a keyboard and shows. In contrast, a microcontroller is a single-chip computing machine because it contains memory and I/O devices in add-on to CPU.
[ 4 ]By cut downing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally command even more devices and procedures. Assorted signal microcontrollers are common, incorporating parallel constituents needed to command non-digital electronic systems. [ 3 ]
1.1.1 PIC Microcontroller
PIC is a household of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1640 originally developed by General Instrument ‘s Microelectronics Division. The name PIC ab initio referred to “ Programmable Interface Controller ” . [ 3 ] or “ Programmable Integrated Circuit ” .Movies are popular with both industrial developers and hobbyists likewise due to their low cost, broad handiness, big user base, extended aggregation of application notes, handiness of low cost or free development tools, and consecutive scheduling ( and re-programming with brassy memory ) capableness.
[ 5 ]
PIC is used in this system because:
1. Movies are really various and can be used in practical undertakings such as burglar dismaies, remote controls, redstem storksbills and merely about anything that anyone can believe approximately could utilize a individual bit ego contained computing machines.2. The PIC linguistic communication provides an easy manner to compose procedural box-and pointer diagrams to be included in paperss, and it is sufficiently flexible to be rather utile for province charts, flow charts, simple circuit schematics and other sorts of illustration affecting insistent utilizations of simple geometric signifiers.
1.1.2 Types of the PIC ‘s Pins:
The pins of the PIC ‘for all PIC ‘s ‘ are divided into pins that must be connected and pins that is optional.
188.8.131.52 pins that must be connected
– M-CLR: the above line means this pin works utilizing 0 ‘active low ‘ .
– It means reset for the computing machine, it is active low and it ‘s pin no.1.- Reset for the computing machine means, reset for the plan counter ‘return to the beggary of the executed codification ‘ .- Logic 0 agencies reset for the PIC, this province was used when the PIC coatings put to deathing the plan.- Logic 1 agencies, the PIC is active, this province was used while holding infinite cringle.- Most of the clip it is connected to the Vcc ‘logic 1 ‘ to allow the PIC plants.
– Oscillation: a periodic fluctuation between two things based on alterations in energy [ 1 ] .
– An oscillator is a mechanical or electronic device that works on the rules of oscillation [ 1 ] .- Computers, redstem storksbills, tickers, wirelesss, and metal sensors are among the many devices that use oscillators [ 1 ] .- The frequence at which an oscillator plant is normally determined by a quartz crystal [ 1 ] .
– When a direct current is applied to such a crystal, it vibrates at a frequence that depends on its thickness, and on the mode in which it is cut from the original mineral stone [ 1 ] .- Some oscillators employ combinations of inductances, resistances, and/or capacitances to find the frequence. However, the best stableness ( stability of frequence ) is obtained in oscillators that use quartz crystals [ 1 ] .- Some oscillators are inside the microcontroller and these are called internal oscillator.- Normally specified in MHz ( MHz ) , and is an of import factor in finding the rate at which a computing machine can execute instructions.
– The power supply is normally a power supply unit, which converts the AC electromotive force into DC electromotive force degree, which is needed to run the device.- The chief map of the power supply is to supply the system with fixed electromotive force needed to maintain the ratio of AC rippling of little degrees, in add-on to good stableness and organisation.- Typical electromotive force for about all PICs is ( 5 electromotive force ) so there is restriction on the electromotive force of PIC that will be illustrated in the tabular array below:Table ( 3.1 ) : ” restriction on electromotive force of PIC ”
|Voltage value( V )||Consequence of that electromotive force value|
|5.5 to 6||The PIC might be burned ‘it will damage ‘|
|5||The PIC is working “ logic 1 ”|
|4.5||The PIC still working|
|The PIC will work but it may non put to death all of the codification instructions|
|Less than 2.5||The PIC will non work “ logic 0 ”|
– The figure of power supply pins varies in conformity with the type of the PIC being used ( e.g. PIC 18F452 has 4-pins ” 2VSS and 2VDD, VSS indicates to Ground, and VDD to 5 V.
184.108.40.206 Pins That Is Optional
– It ‘s called 8-bit accountant.- These pins are divided into groups that are called ports.- Number of ports varies from one PIC MCU to another harmonizing to its type.- Each port has a constellation registry inside the PIC and it is called TRISE registry.- TRISE registry is a data way registry that controls the way of informations ( input or end product ) of each pin of that port.
For illustration holding TRISA cleared ( 0 which is the default ) will configure all pins of PORTA as end product.- TRISE registry ever consists of 8-bits even if the port itself does n’t hold 8-pins “ e.g. 6-pins as in port a ” .- ‘0 ‘ indicates that the pin is end product and ‘1 ‘ indicates that the pin is input.- An illustration of the TRISE registry of port B is shown in the figure below:To hive away values in the TRISE registry it must be written in the hex signifier so either ( $ ) or ( 0X ) will be used before the value that will be stored.In the system PIC 16F876A and PIC18F452 were used.
1.1.3 PIC 16F876A
A· PIC 16F87XA16F87XA1 2 3 4
1. It is called the household figure ( F.
N ) .
It specifies the size of informations coach.The 16-bits are divided as follows:14-bits are for informations transmittal ‘size of informations ‘ , and 2-bits are for references hence the PIC is divided into four subdivisions as in the figure below:a.
Is the reference of memory subdivision ( no.1 )It ‘s produced by the two spots that are taken from the 16-bits as followers:The Probability of 2-bits is: 00,01,10,11.B. These are called bit select and they are connected to the reference decipherer which is connected to the reference coach.
They work as the enable line “ depending on the reference comes to the decipherer that will trip the specified subdivision ‘e.g. If the input of the decipherer is 00 so the end product will be 1000 as illustrated below:So subdivision no.1 ‘with reference 00 ‘ will be activated.This is a really utile manner of fetching and hive awaying informations in the PIC because it ‘s a speedy and a simple 1 that saves clip ‘i.e.
no long hold ‘ .
2. F: means brassy memory, which can be written on it and erased the informations it contained for 100,000 times without any occurring harm.
Accessing this sort of memory is really speedy so, that saves clip.There are two types of this memory with differences between them as illustrated in the tabular array below:Table ( 3.2 ) : ” differences between F and C “
|symbol||name||No. of accessing clip||Monetary value||use|
|F||Flash||100,000||More expensive than C||For development|
|C||Commercial||Merely one time||____||For commercial|
The C memory could be used if there is no demand to modify its stored informations so the accommodation will do a harm and loss of informations.
87X: it indicates the sequence of the PIC in its household.
4. A: agencies enhanced in the velocity or in the memory,
For the 1s that do n’t hold the A in its name the velocity of their crystal oscillator is 4 MHz but for the 1s that have it is ( 4-20 ) MHz It affects the figure of executed instructions because by increasing the frequence the figure of executed instructions will increase.PIC16F876A has 28-pins, as illustrated in the figure ( 3.5 ) :A· 8 Pins for port B, C and D.A· 6 pins for port A.
A· 3 pins for power supply: 2 pins for VSS ( land ) , and 1 pins for VDD ( 5 V ) .A· 2 pins for the oscillator, OSC1 and OSC2.A· 1 pin for M-CLR.Note that some of the pins of each PORT are multiplexed to make different maps when needed
4 PIC 18F452
1 2 31. To bespeak the no. of informations spots in the informations coach which is equal to 18-bits so it ‘s called PIC18XXXX due to its informations spots.
2. It means brassy memory “ as illustrated in the old PIC ” .3. It indicates the sequence of the PIC in its household.
PIC 18F452 was used:
– As a microcontroller due high public presentation, low cost, low electromotive force and power, little footmark and ease-of-use.
– Because it supports, Flash plan memory, Hardware timers, AD transition, Consecutive communications ‘because of the presence of the constitutional USART ‘ , and Lots of digital input and end product pins.
PIC18F452 has 40-pins, as illustrated in the figure ( 3.6 ) :
A· 8 Pins for port B, C and D.A· 6 pins for port A.A· 3 pins for port E.
A· 4 pins for power supply: 2 pins for Vss ( land ) , and 2 pins for VDD ( 5 V ) .A· 2 pins for the oscillator, OSC1 and OSC2.A· 1 pin for M-CLR.
1.1.5 Microcontroller and PIC Features:
220.127.116.11 Microcontroller Features
– 100,000 erase/write rhythm Enhanced Flash plan memory typical.- 1,000,000 erase/write rhythm Data EEPROM memory typical.- Data EEPROM Retention & gt ; 40 old ages.
– Self-reprogrammable under package control.- In-Circuit Consecutive Programminga„? ( ICSPa„? ) via two pins.- Single-supply 5V In-Circuit Serial Programming.- Programmable codification protection.
– Power salvaging Sleep manner.- Selectable oscillator options.- In-Circuit Debug ( ICD ) via two pins.
18.104.22.168 PIC16F876A High-Performance RISC CPU:
– Merely 35 single-word instructions to larn ‘only when utilizing assembly for programming ‘ .
– All single-cycle instructions except for plan subdivisions, which are two-cycle.- Operating velocity: DC – 20 MHz clock input DC – 200 ns direction rhythm.- Up to 8K tens 14 words of Flash Program Memory, Up to 368 tens 8 bytes of Data Memory ( RAM ) , Up to 256 tens 8 bytes of EEPROM Data Memory.
5.3 PIC18F852 High-Performance RISC CPU:
– Degree centigrade compiler optimized architecture/instruction set, Source codification compatible with the PIC16 and PIC17 direction sets.- Up to 32K of brassy plan memory, up to 256 bytes of EEPROM Data Memory.- Up to 10 MIPs operation, DC – 40 MHz clock input.- Addressable USART faculty ‘there is no banking here ‘ .
1.5.4 Extra Features
Those characteristics result because of the PIC engineering “ CMOS Technology ” :- Low-power, high-velocity Flash/EEPROM engineering.- Fully inactive design.- Wide operating electromotive force scope ( 2.0V to 5.
5V ) .- Commercial and Industrial temperature ranges.- Low-power ingestion.A· Inside a PIC there is an internal timer.
A capacitance is a inactive electronic constituent dwelling of a brace of music directors separated by a insulator. When a electromotive force possible difference exists between the music directors, an electric field is present in the insulator. This field shops energy and produces a mechanical force between the home bases.
Capacitors are widely used in electronic circuits to barricade the flow of direct current while leting jumping current to go through, to filtrate out intervention, to smooth the end product of power supplies, and for many other intents. They are used in resonating circuits in wireless frequence equipment to choose peculiar frequences from a signal with many frequences. [ ]
There are two types of capacitance:
a- Ceramic capacitance: is a capacitance constructed of jumping beds of metal and ceramic, with the ceramic stuff playing as the insulator.In this system a Ceramic capacitance was employed in three places for:
1. Noise unsusceptibility.
A ceramic capacitance frequently has high frequence to avoid the system from being affected by external microwave ; therefore it acts as a low base on balls filter that filters out intervention.
to avoid the repeat of reset operation.b- Chemical capacitance:It consists of a semi-liquid electrolyte solution in the signifier of a jelly ‘electrode ‘and really thin bed of oxide ‘dielectric ‘ .Besides called Electrolytic Capacitors by and large used when really big electrical capacity values are required,
This system employs the Chemical capacitance in two places for:
1. Smoothing: to assist cut down the rippling electromotive force.2. Voltage stabilisation: to utilize the capacitance as a electromotive force beginning to the full circuit to forestall the loss of PIC electromotive force that wo n’t allow it to work decently.
A resistance is a two-terminal electronic constituent that produces a electromotive force across its terminuss that is relative to the electric current through it in conformity with Ohm ‘s jurisprudence: [ ]V = IR
In this undertaking there are two types of resistance:
1. Pull-up resistance:
– It ‘s connected with the electromotive force beginning ‘VCC ‘ .- It ‘ used to protect the PIC input pins from being in the float province ‘when the input pin does n’t hold a value ‘ .
2. Pull-down resistance:
– It ‘s connected with the land ‘0 V ‘ .- It ‘ used to protect the PIC input pins from being in the float province ‘when the input pin does n’t hold a value ‘ .
In electronics a rectifying tube is a two-terminal electronic constituent that conducts electric current in merely one way. The term normally refers to a semiconducting material rectifying tube, the most common type today, which is a crystal of semiconducting material connected to two electrical terminuss, a P-N junction.The most common map of a rectifying tube is to let an electric current in one way ( called the forward way ) while barricading current in the opposite way ( the contrary way ) . This unidirectional behaviour is called rectification, and is used to change over jumping current to direct current.Diodes are used to modulate electromotive force ( Zener rectifying tubes ) , and bring forth light ( light breathing rectifying tubes ) .
1.5 LED ( Light Emitting Diode )
One of the most utile types of rectifying tubes is a LED. The LED green goodss light when it is forward-biased. The most common LEDs have a typical ruddy colour, although they may be amber, green, or blue.The LED is a semiconducting material device that emits incoherent visible radiation when forward-biased. The colour of the light depends on the chemical composing of the semiconducting stuff.The right mutual opposition of LED can normally be determined by detecting that the longest terminus is the anode.
If the terminuss have been altered, so it is hazardous to seek to find mutual opposition by detecting the LED ‘s internal. So a more reliable hint to the LED ‘s mutual opposition is the level check on the LED ‘s base, which indicates the cathode. [ ]
1.6 Voltage Regulator
A Voltage Regulator ( besides called a “ regulator ” ) an electrical regulator designed to automatically keep a changeless electromotive force degree. [ 9 ] Voltage Regulator has merely three legs and appears to be a relatively simple device but it is really a really complex integrated circuit.
A regulator converts changing input electromotive force and produces a changeless “ regulated ” end product electromotive force. Voltage regulators are available in a assortment of end products, typically – 5 Vs, 9 Vs and 12 Vs. The last two figures in the name indicate the end product electromotive force. [ 10 ]The most common portion Numberss start with the Numberss 78 or 79 and finish with two figures bespeaking the end product electromotive force. The figure 78 represents positive electromotive force and 79 negative one. The 78XX series of electromotive force regulators are designed for positive input.
And the 79XX series is designed for negative input. [ 11 ]The “ LM78XX ” series of electromotive force regulators are designed for positive input. For applications necessitating negative input the “ LM79XX ” series is used. See table ( 3.
3 ) .Table ( 3.3 ) : ” Example of Voltage Regulator ”
|LM7805||+ 5 Vs|
|LM7809||+ 9 Vs|
|LM7812||+ 12 Vs|
|LM7905||– 5 Vs|
|LM7909||– 9 Vs|
|LM7912||– 12 Vs|
Voltage regulators are really robust. They can defy over-current draw due to short circuits and besides over-heating.
In both instances the regulator will close down earlier harm occurs. The lone manner to destruct a regulator is to use rearward electromotive force to its input. Reverse mutual opposition destroys the regulator about immediately.
To avoid this possibility you should ever utilize diode protection of the power supply. This is particularly of import when utilizing nine volt battery supplies as it is common for people to ‘test ‘ the battery by linking it one manner and so the other. Even this short ‘test ‘ would destruct the regulator if a protection rectifying tube were non used.
Input electromotive force:
As a general regulation the input electromotive force should be limited to 2 to 3 Vs above the end product electromotive force. The LM78XX series can manage up to 30 Vs input, but the power difference between the input voltage/current ratio and end product voltage/current ratio appears as heat. If the input electromotive force is unnecessarily high the regulator will acquire really hot. Unless sufficient heat-sinking is provided so the regulator will close down.
[ 12 ]
1.7 Real Time Clock ( RTC )
A real-time clock ( RTC ) is a clock that keeps path of the current clip even when the device is turned off. RTCs are present in about any electronic device which needs to maintain accurate clip like computing machines and embedded system.RTCs frequently have an alternate beginning of power, so they can go on to maintain clip while the primary beginning of power is off or unavailable, This alternate beginning of power is usually a Li battery in older systems, but some newer systems use a ace capacitance, because they are rechargeable and can be soldered.Most RTCs use a crystal oscillator, in many instances the oscillator ‘s frequence is 32.
768 kilohertz. [ ]RTC has I2C protocol ( IC to IC communicating ) that is used when 2-IC communication with each other.I2C protocol based on directing informations serially in the presence of a consecutive clock.RTC ( DS1307 ) which has 8 pins was used in the system as illustrated in the figure below:Note that SCL pin is n’t responsible of clip bring forthing inside the RTC.
1.8 Liquid Crystal Display ( LCD )
8.1 Definition and Mechanism of LCD
A liquid crystal show ( LCD ) is a thin, level panel used for electronically exposing information such as text, symbols, Numberss, images and traveling images. Its utilizations include proctors for computing machines and telecastings se figure ( 3.13 ) that shows a 16A-2 LCD.It is an electronically-modulated optical device made up of any figure of pels filled with liquid crystals and arrayed in forepart of a light beginning ( backlight ) or reflector to bring forth images in colour or monochrome.LCD shows utilize two sheets of polarising stuff with a liquid crystal between them. An electric current passed through the liquid causes the crystals to aline so that visible radiation can non go through through them.
Each crystal, hence, is like a shutter, either leting visible radiation to go through through or barricading the light [ 1 ] as you can see in figure ( 3.14 ) .It can be configured to drive a dot-matrix liquid show under the control of a 4 or 8-bits microprocessor [ 2 ] ‘ this system uses 4-bit manner to cut down the figure of PIC used pins that connect LCD to the PIC ‘ .
Among its major characteristics are its lightweight building, its portability, and its ability to be produced in much larger screen sizes than are practical building of cathode beam tubing ( CRT ) show engineering. Besides its low electrical power ingestion enables it to be used in battery-powered electronic equipment.Since all the maps such as show RAM, character generator and liquid crystal driver, required for driving a dot-matrix liquid crystal show are internally provided on one bit, a minimal system can be interfaced with this controller driver [ 2 ]
2 LCD 16*2
This system includes LCD 16*2:16 indicate to the figure of columns and 2 indicate to figure of rows. That means it can expose 32 characters as maximal figure of characters.LCD will have information from the PIC in ASCII signifier so the LCD ‘s microcontroller will manage that.LCD 16*2 has 14 pins as shown in the figure below:Volt: it ‘s connected to the land ( 0 V ) .VDD: it ‘s connected to the power supply ( 5 Vs ) .
VEE: it ‘s for contrast, It ‘s connected to a 330I© resistance in order to hold high clarity.Roentgen: it stands for registry select that identifies that the coming information is either information for presenting or bid for acting, so if the RS value is 0 that means its bid otherwise it ‘s informations.RW: the R is for reading information from the LCD ‘sending information to the PIC ‘ , and W is for composing informations on the LCD ‘ having information from the PIC ‘ .
In this undertaking the lone demand of the LCD is to compose on it, so it will be ever connected to the land ‘ because W is active low ‘ .Tocopherol: it means enable and its used to do the full LCD either to work or non ‘it ‘s controlled by the PIC ‘ .D0 – D7: for informations that will be displayed on the LCD, but This system uses merely 4-pins of the informations 8-pins and they are: D7, D6, D5 and D4, The staying pins will be connected to the land.A· Some of the LCDs have other pins that are used for backlight and marked by the ( + a?’ ) symbols, But this system did n’t utilize them.
1.9.1 Definition of computer keyboard
A computer keyboard is a set of buttons arranged in a block which normally bears figures and other symbols but non a complete set of alphabetical letters.
If it largely contains Numberss so it can besides be called a numeral computer keyboard [ 2 ] .Computer keyboards are found on many alphameric keyboards and on other devices such as reckoners and telephones which require mostly numeral input [ 3 ] , computer keyboard is the most widely used input devices of a microcontroller [ 2 ] see figure ( 3.16 ) .At the lowest degree, keyboards are organized in a matrix of rows and columns. The CPU accesses both rows and column through ports ; hence, with a port of microcontroller, a 4X3 matrix of keys can be connected. When a key pressed, a row and column make a connexion ; otherwise, there is no connexion between row and column [ 1 ] .
9.2 Scanning and Identifying the Key Pressed [ 1 ]
A Figure ( 3.17 ) shows a 4X3 matrix connected to a port of the PIC ( e.g.
PortD ) . The rows ( R1 through R4 ) are connected to end product pins of the port and the columns ( C1 through C3 ) are connected to input pins of it. Note that, merely 7 pins of the port were used.To observe a pressed key, foremost, the microcontroller initiates the value of pin 0 through 7 of PortD to zero, so it sends 1000 to R1 R2 R3 R4 and it reads the columns. If the informations read from the columns is C1 C2 C3 =000, no key has been pressed and the procedure continues to following measure, If the informations read from the columns is C1 C2 C3 =100, this means that a key in the R1 row and C1 column has been pressed. That is ‘1 ‘ and if the informations read from the columns is C1 C2 C3 =010, this means that a key in the R1 row and C2 column has been pressed. That is ‘2 ‘ .
All of these operations will happen in a subprogram ( for e.g. it ‘s called ‘Check Column ‘ ) before go forthing this subprogram, microcontroller will put a variable ( for e.g. it ‘s called ‘Key Pressed ‘ ) to bespeak that there is a key pressed.Table ( 3.4 ) represents the significance of each combination of informations received at C1 C2 C3.
Table ( 3.4 ) : ” Key pressed ”A· Notice that the value of the rows is input value and the value of columns is end product value.Two keys can non be pressed at the same clip ; there is clip different between imperativenesss a key with another key. The variable ‘e.g. Key Pressed ‘ indicates that there is a key pressed in this clip. Before go forthing the full subprogram, if ‘Key Pressed ‘ has been set, the microcontroller Set the variable ‘KeyAlreadyPressed ‘ . This variable will non be cleared until this subprogram detect that there is no key pressed.
So, if imperativenesss more than two key, merely the first key will be read.To see if any key is pressed, the columns are scanned over and over in an infinite cringle until one of them has a 1 on it.It ‘s inefficient if the computer keyboard being scanned without any intervals of clip. This interval can be generated by timer.See the figure below that illustrates the internal design of the 4A-3 computer keyboard.
Both the rows and the columns are connected to PIC microcontroller.Pull-down resistances of 10KI© were used in the computer keyboard as shown in the figure above for:Case 1: when the key is n’t pressed the resistance will forestall the affiliated pin from come ining the drifting province.Case 2: when the key is pressed the resistance will protect the PIC from being burnt by high current value, therefore the current value wo n’t transcend 20mA ‘the allowable sum of current for PIC ‘ .In this undertaking keypad used to give the police officer the ability to modify the allowed clip continuance for parking and to direct the stored informations to his laptop by come ining a specific word ‘password ‘ .
1 Pc consecutive port
Consecutive ports are a type of computing machine interface that complies with the RS-232 criterion. They are 9-pin connections that relay information, entrance or outgoing, one byte at a clip. Each byte is broken up into a series of eight spots, therefore the term consecutive port.
So the protocol that used in personal computer series is RS-232.A· RS-232Recommended Standard – 232 is a telecommunications criterion for binary consecutive communications between devices. RS-232 utilizations positive and negative electromotive forces, for illustration, RS-232 uses a electromotive force below minus five Vs to stand for a logic one and a electromotive force above five Vs to stand for a logic nothing. [ ]
1.10.2 Consecutive Communications Interface in PIC ( USART )
USART stands for Universal Synchronous Asynchronous Receiver Transmitter, it can have and convey, and utilize Full semidetached house asynchronous operation, that means ( both transmittal and response can happen at the same clip ) , the most common usage of the USART in asynchronous manner is to pass on to a Personal computer consecutive port utilizing the RS-232 protocol.
The USART end products and inputs logic degree signals on the TX and RX pins of the PIC.The signals on the USART pins of the microcontroller usage logic degrees. This means that for a five V supply, the signals will be near to five Vs when they are high and close to land when they are low. When pass oning with other logic devices, these signals can be used straight.
USART has the undermentioned belongingss:
1. 8 spot informations.2.
1 stop spot.3. No para cheque.
To interface PIC with the Personal computer a MAX232 is needed. This IC will be connected on one side to the Sub-D9 of the Personal computer and on the other side to the PIC ( USART ) .It ‘s required to interface to RS-232 electromotive force degrees. The PIC should non be straight connected to RS-232 signals,The information is non inverted even though RS-232 utilizations negative electromotive forces to stand for a logic 1.
By and large, when utilizing the USART for RS-232 communications, the signals must be inverted and degree shifted.In this system a MAX-232 MAXIM that has 16 pins was used, see figure ( 3.20 ) .As illustrated in the figure above:- 4-capacitors were used to bring forth a 12-volt end product for personal computer consecutive port that is connected with it.- There are 8-pins for consecutive connexion ; 4-pins for consecutive one and the others for consecutive two because of that we can link another devices that need consecutive interfacing.- Each consecutive consists of 2-TX for transmittal and 2-RX for having between the affiliated devices but in our undertaking there will be merely one TX ( for directing informations from the PIC ) and one RX ( for having informations by the Personal computer ) .
1.11 And gate:
AND gate is a digital logic gate that implements logical concurrence, A HIGH end product ( 1 ) consequences merely if both the inputs to the AND gate are HIGH ( 1 ) . If neither or merely one input to the AND gate is HIGH, a LOW end product consequences.The input of the AND gate will be taken from the RFID reader.The AND gate was used to acknowledge the input that is coming from the RFID readers.