Microntroller & Its Interfacing(8051)

8/13/2019 Microntroller & Its Interfacing(8051)

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MICROCONTROLLERS

Microcontrollers as the name suggests are small controllers. They are like single chip

computers that are often embedded into other systems to function as

processing/controlling unit. For example the remote control you are using probably has

microcontrollers inside that do decoding and other controlling functions. They are also

used in automobiles, washing machines, microwave ovens, toys ... etc, where automation

is needed.

Embedded system means the processor is embedded into the required application. An

embedded product uses a microprocessor or microcontroller to do one task only. In an

embedded system, there is only one application software that is typically burned into

ROM. Example: printer, keyboard, video game player .

Microprocessor - A single chip that contains the CPU or most of the computer

Microcontroller - A single chip used to control other devices

The microcontroller incorporates all the features that are found in microprocessor. The

microcontroller has built in ROM, RAM, Input Output ports, Serial Port, timers,

interrupts and clock circuit. A microcontroller is an entire computer manufactured on a

single chip. Microcontrollers are usually dedicated devices embedded within an

application. For example, microcontrollers are used as engine controllers in automobiles

and as exposure and focus controllers in cameras. In order to serve these applications,

they have a high concentration of on-chip facilities such as serial ports, parallel input

output ports, timers, counters, interrupt control, analog-to-digital converters, random

access memory, read only memory, etc. The I/O, memory, and on-chip peripherals of amicrocontroller are selected depending on the specifics of the target application. Since

microcontrollers are powerful digital processors, the degree of control and

programmability they provide significantly enhances the effectiveness of the application.


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Microcontroller Vs Microprocessor:-

It is very clear from figure that in microprocessor we have to interface additional circuitry

for providing the function of memory and ports, for example we have to interface

external RAM for data storage, ROM for program storage, programmable peripheral

interface (PPI) 8255 for the Input Output ports, 8253 for timers, USART for serial port.

While in the microcontroller RAM, ROM, I/O ports, timers and serial communication

ports are in built. Because of this it is called as system onchip.

So in micro-controller there is no necessity of additional circuitry which is interfaced in

the microprocessor because memory and input output ports are inbuilt in the

microcontroller. Microcontroller gives the satisfactory performance for small

applications. But for large applications the memory requirement is limited because only

64 KB memory is available for program storage. So for large applications we prefer

microprocessor than microcontroller due to its high processing speed.


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Architecture of 8051:-

It is 8-bit microcontroller, means MC 8051 can Read, Write and Process 8 bit

data. This is mostly used microcontroller in the robotics, home appliances like

mp3 player, washing machines, electronic iron and industries. Mostly used blocks

in the architecture of 8051 are as follows:

a. 128 Byte RAM For Data Storage

MC 8051 has 128 byte Random Access memory for data storage. Random access

memory is non volatile memory. During execution for storing the data the RAM is used.

RAM consists of the register banks, stack for temporary data storage. It also consists of

some special function register (SFR) which are used for some specific purpose like timer,

input output ports etc. Normally microcontroller has 256 byte RAM in which 128 byte is


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used for user space which is normally Register banks and stack. But other 128 byte

RAM which consists of SFRs.

b. 4KB ROM In 8051, 4KB read only memory (ROM) is available for program storage. This is

used for permanent data storage. Or the data which is not changed during the

processing like the program or algorithm for specific applications.

This is volatile memory; the data saved in this memory does not disappear after

power failure.

We can interface up to 64KB ROM memory externally if the application is

large. These sizes are specified different by their companies.

Address Range of PC: Address range of PC means program counter (which

points the next instruction to be executing) can be moved between these

locations or we can save the program from this location to this location.

c. Difference between RAM and ROM

RAM is used for data storage while ROM is used for program storage.

Data of RAM can be changed during processing while data of ROM cant

be changed during processing.

a. We can take an example of calculator. If we want to perform addition of two

numbers then we type the two numbers in calculator, this is saved in the RAM, but

the Algorithms by which the calculation is performed is saved in the ROM. Data

which is given by us to calculator can be changed but the algorithm or program by

which calculation is performed cant be changed.d. Timers & Counters

Timer means which can give the delay of particular time between some events.

For example on or off the lights after every 2 sec. This delay can be provided

through some assembly program but in microcontroller two hardware pins are


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available for delay generation. These hardware pins can be also used for counting

some external events. How much times a number is repeated in the given table is

calculated by the counter.

In MC8051, two timer pins are available T0 and T1, by these timers we cangive the delay of particular time if we use these in timer mode.

We can count external pulses at these pins if we use these pins in counter

mode.

16 bits timers are available. Means we can generate delay between 0000H

to FFFFH.

TMOD, TCON registers are used for controlling timer operation.


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PIN DIAGRAM OF 8051

Power Supply pins

8051 c works with +5V DC source applied to Vcc and 0V to Gnd input pin. It

has an onchip crystal clock generator. As such it must be supported externally byconnecting a crystal across crystal input XTAL1, XTAL2. It has active hign reset input

pin. As such the controller is said to be reset upon application of active hign pulse.


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I/O port pins

A total number of 32 I/O pins are provided as port pins divided into 4 portsport 0, port

1, port 2 and port 3. All ports are both byte and bit addressable. All ports are

programmable. All the ports act as simple input/output ports. All the ports except port 1offer alternate functions. They are as follows.

Port 0 and Port 2: If input pin is grounded then port 0 acts as lower order

8bit address data bus where as port 2 acts as higher order 8 bit address bus.

Port 3: Each and every pin in this port offer some separate functionality

irrespective of level at input pin.

External Access Control pins

(External Access): If is connected to +5V then the

microcontroller fetches code from internal or inbuilt program memory. If it is cnneected

to 0V then the microcontroller fetches code from external program memory.

(Address Latch Enable): It is an active high output pin. It is used

for demultiplexing the address and data by connecting to the G pin of the 74LS373 chip.


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(Program Store Enable)This is an output pin. For opcode fetch operation,

microcontroller asserts output pin as low which can be used for selecting the

external program memory chip. This can also be used as ROM read control signal

1

to the inverting oscillator amplifier and input to the interanal clock operating

circuit.

put from the inverting oscillator amplifier.

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier

which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a

quartz crystal or ceramic resonator may be used. To drive the device from an external

clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in

Figure 2. There are no requirements on the duty cycle of the external clock signal, since

the input to the internal clocking circuitry is through a divide-by-two flip-flop, but

minimum and maximum voltage high and low time specifications must be observed.


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INTERFACING OF 8051

1) LED Interfacing(PORT as o/p):

Port as output: In this topic we study how we send the values on ports and

how we observe that value on ports. The microcontroller always loads the

binary equivalent of value on the ports. For example we send 0x0A. Here 0x

shows the value is in hexadecimal. The binary equivalent of 0x0A is

00001010. So if we send 0x0A the equivalent binary is observed on the port.

The LSB is observed on the LSB pins of port and MSB observed on the MSB

pins of port. Now how we observe the 0 and ones physically. There is

specific voltage level concerned with 0 and 1. These levels are TTL

compatible.

Logic Out put pin

0 Low (0 volt)

1 High(5v10ma according

to data sheet)


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So we can verify the loaded value by checking voltage level using multimeter or by

driving led from this voltage.

Example Program Of LED interfacing With 8051

WAP to interface 8 leds and glow them for some instance and then put it

off.

#include

Void delay();

Void main()

{

P1=0xff;

Delay(500);

P1=0x00;

}

Void delay(int itime)

{

Int i,j;

For(i=0;i


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2) LCD Interfacing

On most displays, the pins are numbered on the LCDs printed circuit board, but if

not, it is quit easy to locate pin1. Since the pin is connected to ground, it often has a

thicker PCB track connected to it, and it is generally connected to the metal work at

some point.

The function of each of the connections is shown in the table below:-

Pins 1 & 2 are the power supply lines, Vss & Vdd. The Vdd pin should be connected to

the positive supply & Vss to the 0V supply or ground.

supplies of 6V & 4.5V both work well, and even 3V is sufficient for some modules.

Consequently, these modules can be effectively and economically powered by

batteries.

Pin 3 is a control pin, Vee, which is used to alter the contrast of the display. Ideally,

these pin should be connected to a variable voltage supply. A preset potentiometer

connected between the power supply lines, with its wiper connected to the contrast pin

is suitable in many cases, but be aware that some modules may require a negative

potential; as low as 7V in some cases. For absolute simplicity, connecting this pin to 0V

will often suffice.

Pin 4 is register select (RS) line.

PIN NO. NAME FUNCTION

1 Vss Ground

2 Vdd +ve supply

3 Vee Contrast

4 RS Register select

5 R/W Read/Write

6 E Enable

7 D0 Data Bit 0

8 D1 Data Bit 1

9 D2 Data Bit 2

10 D3 Data Bit 3

11 D4 Data Bit 4


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12 D5 Data Bit 5

13 D6 Data Bit 6

14 D7 Data Bit 7

Three command control inputs. When this line is low, data bytes transferred to the

display are treated as commands, and data bytes read from the display indicate its

status. By setting the RS line high, character data can be transferred to and from the

module.

Pin 5 is (R/W) line. This line is pulled low in order to write commands or character

data to the module, or pulled high to read character data or status information from

its registers.

Pin 6 is Enable (E) line. This input is used to initiate the actual transfer of commands

or character data between the module and the data lines. When writing to the

display, data is transferred only on the high to low transition of this signal. However,

when reading from the display, data will become available shortly after the low to

high transition and remain available until the signal falls low again.

Pins 7 to 14 are the eight data bus lines (D0 to D7). Data can be transferred to and

from the display, either as a single 8-bit byte or as two 4-bit nibbles. In the latter

case, only the upper four data lines (D4 to D7) are used. This 4-bit mode is

beneficial when using a microcontroller, as fewer I/O lines are required.


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Example Program of LCD interfacing with 8051

WAP to Display ECE ROCKS On LCD

#include

#define lcdport P3

sbit rs=P2^0;


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sbit rw=P2^1;

sbit en=P2^2;

void cmd();

void dat();

void delay(int);

void main()

{

P3=0x00;

P2=0x00;

lcdport=0x38;

cmd();

lcdport=0x0e;

cmd();

lcdport=0x01;

cmd();

lcdport='E';

dat();

lcdport='C';

dat();

lcdport='E';

dat();

lcdport='R';

dat();

lcdport='O';

dat();

lcdport='c';

dat();

lcdport='k';

dat();


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lcdport='s';

dat();

}

void delay(int itime)

{

int i,j;

for(i=0;i


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3) SEVEN SEGMENT DISPLAY

7 segment LED display is very popular and it can display digits from 0 to 9 and quite a

few characters like A, b, C, ., H, E, e, F, n, o,t,u,y, etc. Knowledge about how to

interface a seven segment display to a micro controller is very essential in designing

embedded systems. A seven segment display consists of seven LEDs arranged in the

form of a squarish8slightly inclined to the right and a single LED as the dot character.

Different characters can be displayed by selectively glowing the required LED

segments. Seven segment displays are of two types,common cathode and comm on

anode.In common cathode type , the cathode of all LEDs are tied together to a single

terminal which is usually labeled as com and the anode of all LEDs are left alone as

individual pins labeled as a, b, c, d, e, f, g & h (or dot) . In common anode type, the

anode of all LEDs are tied together as a single terminal and cathodes are left alone as

individual pins. The pin out scheme and picture of a typical 7 segment LED display is

shown in the image below.

Digit drive pattern of a seven segment LED display is simply the different logic

combinations of its terminalsa to h in order to display different digits and characters.

The common digit drive patterns (0 to 9) of a seven segment display are shown in the

table below.


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Digit a b c d e f g

0 1 1 1 1 1 1 0

1 0 1 1 0 0 0 0

2 1 1 0 1 1 0 13 1 1 1 1 0 0 1

4 0 1 1 0 0 1 1

5 1 0 1 1 0 1 1

6 1 0 1 1 1 1 1

7 1 1 1 0 0 0 0

8 1 1 1 1 1 1 1

9 1 1 1 1 0 1 1

Sample Program for counting from 0 to 9 using 7 segment display

#include

void delay(int);

void main()

{

char i,arr[]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0xfd,0x07,0x7f,0x6f};

for(i=0;i


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Microntroller & Its Interfacing(8051)

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