Serial Comm+Adc

8/8/2019 Serial Comm+Adc

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Serial

communication


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Contents

Types of communication.

UART in 8051.

Max circuitry.

Baud rate in 8051.

Registers regarding serial communication.

Programming steps.


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Serial Communication

1.Parallel

2.Serial

Type of Communication


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Parallel transmission


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Serial transmission


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Synchronous transmission


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Asynchronous transmission


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An UART, universal asynchronous receiver /transmitteris responsible forperforming the main

taskin serial communications with computers.

The device changesincoming parallelinformation toserial data which can be sent on a communication

line. A second UART can be used to receive the

information.

To communicate with pc orother devices we needsome standardslike RS232.

A driver(MAX232) is used to convert TTL level to

RS232 voltage level.

UART in 8051


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Value of capacitors is 10uF

Max circuitry

Controller

section

RS232

section


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BaudRates in the 8051

The 8051 transfers and receives data serially at many

different baud rates by using UART.

UARTdivides the machine cycle frequency by 32 and

sends it to Timer 1 to set the baud rate.

Signal change for each roll over of timer 1

XTAL

oscillator 12

32

By UART

Machine cycle

frequency28800 Hz

To timer 1

To set the

Baud rate

921.6 kHz

11.0592 MHz

Timer 1


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BaudRates in the 8051

Timer 1, mode 2 (8-bit, auto-reload)

Define TH1 to set the baud rate.

XTAL = 11.0592 MHz The system frequency = 11.0592 MHz / 12 = 921.6

kHz

Timer 1 has 921.6 kHz/ 32 = 28,800 Hz as source.

TH1=FDH means that UARTsends a bit every 3

timer source.

Baud rate = 28,800/3= 9,600 Hz


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SCONRegister

Serial control register: SCON

SM0, SM1 Serial port mode specifier

REN (Receive enable) set/cleared by softwareto enable/disable reception.

TI Transmit interrupt flag.

RI Receive interrupt flag.

SM2 = TB8= TB8=0 (not widely used)

SM0 SM1 SM2 REN TB8 RB8 TI RI

* SCON is bit-addressable.


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SM0, SM1

SM1 and SM0 determine the framing of data.

SCON.6 (SM1) and SCON.7 (SM0)

Only mode 1 is compatible with

COM port of PC.SM1SM0 Mode Operating Mode BaudRate

0 0 0 Shift register Fosc./12

0 1 1 8-bit UART Variable by timer1

1 0 2 9-bit UART Fosc./64 or Fosc./32

1 1 3 9-bit UART Variable


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REN (Receive Enable)

SCON.4

Set/cleared by software to enable/disable reception.

REN=1

If we want the 8051 to both transfer and

receive data, REN must be set to 1.

REN=0

The receiver is disabled.

The 8051 can not receive data.


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TI (Transmit Interrupt Flag)

SCON.1

When the 8051 finishes the transfer of the 8-

bit ch

aracter, it raises th

eT

I flag. TI is raised byhardware at the beginning of

the stop bit in mode 1.

Must be cleared by software.


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RI (Receive Interrupt)

SCON.0

Receive interrupt flag. Set byhardware

halfway t

hroug

hth

e stop bit time in mode 1.Must be cleared by software.

When the 8051 receives data serially via RxD,

it gets rid of the start and stop bits and place

the byte in the SBUF register.

Then 8051 rises RI to indicate that a byte.

RI is raised at the beginning of the stop bit.


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Transfer Data with the TI flag

The following sequence is the steps that the 8051

goes through in transmitting a character via TxD:

1. The byte character to be transmitted is written into the

SBUF register.2. It transfers the start bit.

3. The 8-bit characteris transferred one bit at a time.

4. The stop bitis transferred.

SBUF

TxD

bit by bit

8-bit char

UARTTI


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1.Load SCON register.

2.Laod TMOD register(select timer mode 2).

3. Load baud rate in TH.4. Start the timer.

5. Place character in SBUF.

6. Monitor TI flag.

7. Clear TI flag.

Steps to transmit data

from uc to pc


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1.Load SCON register.

2.Laod TMOD register(select timer mode 2).

3. Load baud rate in TH.4. Start the timer.

5. Monitor RI flag.

7. Read SBUF.

8. Clear RI.

Steps to Receive data

from pc to uc


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#include

void main()

{

int i;

char arr[]="Advance Technology;

TMOD=0x20;

SCON=0x50;

TH1=0xFD;

TR1=1;

while(1)

{

for(i=0;i


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Analog to digital

converter (ADC)


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Contents

About ADC(0809).

Pin description of 0809 ADC.

Interfacing with 8051.

Programming steps.


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An analog-to-digital converter is a device which

converts continuous signals to discrete digital

numbers. The reverse operation is performed by

a digital-to-analog converter (DAC).

Typically, an ADC is an electronic device that

converts an input analog voltage (or current) toa digital number proportional to the magnitude

of the voltage or current.

Analog to DigitalConverter


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ADC 0809

8 analog

Channelmultiplexing.


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Interfacing ofADC with 8051


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1.Set initial values of SOC,EOC and OE.

2.Set ADD A, ADD B,ADD C.

3.Low to high pulse on ALE.

4.Low to high pulse on SOC with clock.

5.Monitor EOC bit.

6.Read data.7.Repeat the steps.

Steps to interface 0809 ADC

with 8051 uc


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#include

sbit ALE=P1^3;sbit SOC=P0^0;

sbit OE=P0^2;

sbit EOC=P0^1;

sbit SET0=P1^0;sbit SET1=P1^1;

sbit SET2=P1^2;

sbit CLOCK=P0^3;

void clock(void);

void delay(int x);

void main(void)

{

while(1)

{


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SET0=1;

SET1=1; //for the select line

SET2=1;

ALE=1;SOC=1;

clock();

ALE=0;

SOC=0;clock();

while(!EOC);

OE=1;

P3=P2;

}

}

void clock(void)

{int a,b;

for(b=0;b

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