CHAPTER 1. OVERVIEW

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1.1 INTRODUCTION

Data acquisition is the process of gathering signals from the measurement sources and

digitizing those signals for storage and analysis. The data of the real world are translated into signals

that can be manipulated by the computer. A Data acquisition system comprises of signal source, signal

connection, signal conditioning and signal measurement. Signal source is a transducer to measure

physical phenomena. Signal conditioning is the process of amplification, filtering and isolation.

1.2 AIM OF THE PROJECT:

This Project deals with development of multi-channel analog data though a PC. It uses an

ADC acd0808 to convert from analog to digital. A microcontroller to control the ADC and send data

to mobile through at the baud rate of 9600. And a MAX 232 chip to convert the RS232 signal. The

ADC0808 and ADC0809 each consists of an analog signal multiplexer, an 8-bit successive-

approximation converter, and related control and output circuitry. The analog multiplexer selects 1 of

8 single-ended input channels as determined by the address decoder.

1.3 METHODOLOGY:

Here microcontroller generates three bit data and applies it to the ADC. Using these bits as

selection bits it selects a channel among the available eight channels.This ADC consists a 8 to 1

multiplexer. so analog signal generated by the sensors will be converted into digital form.This digital

signal is given to the PC via MAX232.

Since serial communication is used for communication with PC the logical levels to be

changed. This is done by MAX232.The result will be displayed on a display system.

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1.4 IMPORTANCE AND APPLICATIONS:

The existing project can be used for limited purpose, which it can be further improved to its

next generation for a large number of appliances.

1.Automatic control of out door lighting system using light dependant resistor as a sensing element.

2.Door locking system using digital gadget locking.

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CHAPTER 2. DESCRIPTION OF COMPONENTS

2.1 POWER SUPPLY CIRCUIT:

There are many types of power supply. Most are designed to convert high voltage AC

mains electricity to a suitable low voltage supply for electronics circuits and other devices. A power

supply can by broken down into a series of blocks, each of which performs a particular function. They

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are Transformer, Rectifier, Smoothing component and Regulator. The power supply circuit generating

5V and 12V DC voltages is shown in figure.

FIGURE 1.1: CIRCUIT DIAGRAM OF A REGULATED POWER SUPPLY

The components of the power supply circuit are described below along with output

graph.

Transformer:

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A transformer steps down high voltage AC mains to low voltage AC. Here we are using a

center-tap transformer of 18v-0-18v, 1A. The transformer output is given to the rectifier circuit. The

transformer component with its output voltage is shown in figure 1.3.

FIGURE 1.2: TRANSFORMER OUTPUT VOLTAGE

Rectifier:

A rectifier converts AC to DC, but the DC output is varying. There are several types of

rectifiers; here we use a bridge rectifier.

The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both

half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure 1.4. The circuit

has four diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite

ends of the bridge. The load resistance is connected between the other two ends of the bridge.

For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas

diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load

resistance RL and hence the load current flows through RL. For the negative half cycle of the input ac

voltage, diodes D2 and D4 conduct whereas D1 and D3 remain OFF. The conducting diodes D2 and

D4 will be in series with the load resistance RL and hence the current flows through RL in the same

direction as in the previous half cycle. Thus a bi-directional wave is converted into unidirectional.

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FIGURE 1.3: RECTIFIER DIAGRAM

The output waveform of the rectifier is shown in figure.

The varying DC output is suitable for lamps, heaters and standard motors. It is not suitable for

electronic circuits unless they include a smoothing capacitor.

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Regulator:

Regulator eliminates ripple by setting DC output to a fixed voltage. Voltage regulators ICs are

available with fixed (typically 5, 12 and 15V) or variable output voltages. Negative voltage regulators

are also available. We have used 2 regulators in the power supply circuitry namely 7805 and 7812 for

5v and 12v dc voltage. At the output of the regulator, a 0.1µf capacitor is used in order to avoid any

high frequency voltage spikes at the output.

2.2 AT89C52 MICRO-CONTROLLER

FEATURES:

Compatible with MCS-51TM Products

8 Kbytes of In-System Reprogram able Flash Memory- Endurance: 1,00Write/Erase Cycles

Fully Static Operation: 0 Hz to 24 MHz

Three-Level Program Memory Lock

256 x 8-Bit Internal RAM

32 Programmable I/O Lines

Three 16-Bit Timer/Counters

Eight Interrupt Sources

Programmable Serial Channel

Low Power Idle and Power Down Modes

DESCRIPTION:

The AT89C52 is a low-power, high-performance CMOS 8-bit microcomputer with 4

Kbytes of Flash Programmable and Erasable Read Only Memory (PEROM). The device is

manufactured using Atmel’s high-density non-volatile memory technology and is compatible with the

industry standard MCS-51Ô instruction set and pin out. The on-chip Flash allows the program

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memory to be reprogrammed in-system or by a conventional non-volatile memory programmer. By

combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C52 is a powerful

microcomputer, which provides a highly flexible and cost effective solution to many embedded

control applications.

2.2.1 ARCHITECTURE OF AT89C52:

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2.2.2 PIN CONFIGURATION:

Pin Description:

Fig.2.1Pin Diagram Of 8052

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VCC:

Supply voltage.

GND:

Ground.

Port 0:

Port 0 is an 8-bit open-drain bi-directional I/O port.

As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can

be used as high impedance inputs. Port 0 may also be configured to be the multiplexed low order

address/data bus during accesses to external program and data memory. In this mode P0 has internal

pull-ups. Port 0 also receives the code bytes during Flash programming, and outputs the code bytes

during program verification. External pull-ups are required during program verification.

Port 1:

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups.

The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they are

pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally

being pulled low will source current (IIL) because of the internal pull-ups. Port 1 also receives the

low-order address bytes during Flash programming and verification.

Port 2:




being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order

address byte during fetches from external program memory and during accesses to external data

memory that uses 16-bit addresses (MOVX @ DPTR). In this application, it uses strong internal pull-

ups when emitting 1s. During accesses to external data memory that uses 8-bit addresses (MOVX @

RI); Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order

address bits and some control signals during Flash programming and verification.

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Port 3:




being pulled low will source current (IIL) because of the pull-ups.

Port 3 also serves the functions of various special features of the AT89C51 as listed below:

Table 2.1. Pin Functions Of Port 3

Port 3 also receives some control signals for Flash programming and verification.

RST:

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

ALE/PROG:

Address Latch Enable output pulse for latching the low byte of the address during accesses to external

memory. This pin is also the program pulse input (PROG) during Flash programming.

In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used

for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each

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Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt 1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6WR (external data memory Write

strobe)

P3.7RD (external data memory read

strobe)

access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR

location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise,

the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in

external execution mode.

:

Program Store Enable is the read strobe to external program memory. When the AT89C51 is

executing code from external program memory, is activated twice each machine cycle, except

that two activations are skipped during each access to external data memory.

/VPP:

External Access Enable must be strapped to GND in order to enable the device to fetch code from

external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is

programmed, will be internally latched on reset. should be strapped to VCC for internal

program executions. This pin also receives the 12-volt programming enable voltage (VPP) during

Flash programming, for parts that require 12-volt VPP.

XTAL1:

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2:

Output from the inverting oscillator amplifier

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2.2.3 MEMORY ORGANIZATION:

The 89c52 micro controller has separate address for program memory and data

memory. The logical separation of program and data memory allows the data memory to

be accessed by 8-bit address, which can be quickly stored and manipulated by an 8-bit

CPU. Nevertheless, 16-bit data memory address can also be generated through the DPTR

register. Program memory (ROM, EPROM) can only be read, not written to. There can

be up to 64k bytes if program memory the lowest 4k bytes of program are on chip. In the

ROM less versions, all program memory is external. The read strobe for external program

is the PSEN (program store enable). Data memory (RAM) occupies a separate address

space from program memory the lowest 128 bytes of data memory are on chip. Up to 64

bytes of external RAM can be addressed in the external data memory space. In the ROM

less version, the lowest 128bytes of data memory are on chip. The CPU generates read

and write signals, RD and WR, as needed during external data memory access. External

program memory may be combined if desired by applying the RD and PSEN signals to

the inputs of an AND gate and using the output of the gate as the read strobe to the

external program/data memory.

The 128 byte of RAM are divided into 3 segments

a). Register banks 0 – 3 (00 – 1FH)

b). Bit addressable area (20H – 2FH)

c). Scratch pad area (30H – 7FH)

If the SP is initialized to this area enough bytes should be left aside

to prevent SP data destruction.

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Register Banks:

The 8051 use 8 "R" registers, which are used in many of its instructions. These "R" registers are numbered from 0 through 7 (R0, R1, R2, R3, R4, R5, R6, and R7). These registers are generally used to assist in manipulating values and moving data from one memory location to another.

For example: To add the value of R4 to the Accumulator, we would execute the following instruction.

ADD A, R4

Thus if the Accumulator (A) contained the value 6 and R4 contained the value 3, the Accumulator would contain the value 9 after this instruction was executed. However, as the memory map shows, the "R" Register R4 is really part of Internal RAM. Specifically, R4 is address 04h. This can be seeing in the bright green section of the memory map. Thus the above instruction accomplishes the same thing as the following operation: ADD A, 04h

This instruction adds the value found in Internal RAM address 04h to the value of the Accumulator, leaving the result in the Accumulator. Since R4 is really Internal RAM 04h, the above instruction effectively accomplished the same thing.

2.2.5 SPECIAL FUNCTION REGISTERS:

A and B REGISTERS:

They are used during math and logically operations. The register A is also used for all data transfers between the micro controller and memory. The B register is

used during multiplication and divided operations. For other instructions it can be treated as another scratch pad register.

PSW: It contains math flags; user flags F0 and register select bits RS1 and RS0 to determine the working register bank.

Fig.2.2 Program Status Word

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STACK AND STACK POINTER:

Stack is used to hold and retrieve data quickly. The 8 – bit SP is incremented

before data is stored during PUSH and CALL executions. While the stack may reside any

where in on-chip RAM, the SP is initialized to 07H after the stack to begin at

manipulated as a 16 – bit register or as two independent 8 – bit registers.

PC:

It addresses the memory locations that program instructions are to be fetched. It is

the only register that does not have any internal address.

FLAGS:

They are 1 – bit register provided to store the results of certain program

instructions. Other instructions can test the conditions of the flags and make the decisions

accordingly. To conveniently address, they are grouped inside the PSW and PCON.

The micro controller has 4 main flags: carry(c), auxiliary carry (AC), over

flow (OV), parity (P) and 3 general-purpose flags: F0, GF0 and GF1.

PORTS:

All ports are bi-directional; each consists of a latch, an output driver and an input buffer.

P0, P1, P2 and P3 are the SFR latches ports 0, 1, 2 and 3 respectively. The main functions

of each port are mentioned below.

Port0: input/output bus port, address output port and data input/output port.

Port1: Quasi-bi-directional input/output port.

Port2: Quasi-bi-directional input/output port and address output port.

Port3: Quasi-bi-directional input/output port and control input/output pin.

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SBUF:

The microcontroller has serial transmission circuit that uses SBUF register to hold

data. It is actually two separate registers, a transmit buffer and a receive buffer register.

When data is moved to SBUF, it goes to transmit buffer, where it is held for serial

transmission and when it is moved from SBUF, it comes from the receive buffer.

TIMER REGISTER:

Register pairs (TH0, TL1), (TH1, TL1) are the 16-bit counter registers for

timer/counters 0 and 1.

CONTROL REGISTERS:

SFR’s, IP, TMOD, SCON, and PCON contain control and status bits for the

interrupt system, Timers/counters and the serial port.

2.2.6 OSCILLATOR AND CLOCK CIRCUIT:

This circuit generates the clock pulses by which all internal operations are

synchronized. For the microcontroller to yield standard baud rates, the crystal frequency

is chosen as 11.059MHz.

RESET:

The reset switch is the RST pin of the microcontroller, which is the input to a

Schmitt trigger. It is accomplished by holding the RST pin HIGH for at least two

machine cycles while the oscillator frequency is running the CPU responds by generating

an internal reset

Oscillator Characteristics

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.

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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.

Figure2.3: Oscillator Connections

2.3 ADDRESSING MODES:

An "addressing mode" refers to how you are addressing a given memory location. In summary, the addressing modes are as follows, with an example of each:

Immediate Addressing MOV A, #20hDirect Addressing MOV A, 30hIndirect Addressing MOV A, @R0External Direct MOVX A, @DPTRCode Indirect MOVC A, @A+DPTR

Table.2.2 Addressing Modes2.4 TIMERS:

The 8051 come equipped with two timers, both of which may be controlled, set, read, and configured individually.

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The 8051 timers have three general functions:

1. Keeping time and/or calculating the amount of time between events.2. Counting the events themselves.

3. Generating baud rates for the serial port.

The three timer uses are distinct so we will talk about each of them separately. The first two uses will be discussed in this chapter while the use of timers for baud rate generation will be discussed in the chapter relating to serial ports.

TIMER SFRs:

As mentioned before, the 8051 have two timers, one timer is TIMER0 and the other is TIMER1. The two timers share two SFRs (TMOD and TCON), which control the timers, and each timer also has two SFRs dedicated solely to itself (TH0/TL0 and TH1/TL1).

We’ve given SFRs names to make it easier to refer to them, but in reality an SFR has a numeric address. It is often useful to know the numeric address that corresponds to an SFR name.

The SFRs relating to timers are:

SFR Name Description SFR Address

TH0 Timer 0 High Byte 8Ch

TL0 Timer 0 Low Byte 8Ah

TH1 Timer 1 High Byte 8Dh

TL1 Timer 1 Low Byte 8Bh

TCON Timer Control 88h

TMOD Timer Mode 89h

Table2.3 SFR Descriptions

When you enter the name of an SFR into an assembler, it internally converts it to a number. For example, the command:

MOV TH0, #25h;

Moves the value 25h into the TH0 SFR. However, since TH0 is the same as SFR

address 8Ch this command is equivalent to:

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MOV 8Ch, #25h;

Now, back to the timers. First, lets talk about Timer 0.

Timer 0 has two SFRs: TH0 and TL0.

You may just think of this as the high and low byte of the timer. That is to say, when Timer 0 has a value of 0, both TH0 and TL0 will contain 0. When Timer 0 has the value 1000, TH0 will hold the high byte of the value (3 decimal) and TL0 will contain the low byte of the value (232 decimal). Reviewing low/high byte notation, recall that you must multiply the high byte by 256 and add the low byte to calculate the final value. That is to say:

TH0*256+TL0=1000

3 * 256 + 232 = 1000

Timer 1 works the exact same way, but its SFRs are TH1 and TL1.

TMOD SFR:

The TMOD SFR is used to control the mode of operation of both timers. Each bit of the SFR gives the specific information concerning how to run a timer. The high four bits (bits 4 through 7) relate to Timer 1. Whereas the lower four bits (bits 0 through 3) perform the exact function, for timer 0.

The individual bits of TMOD have the following functions:

TMOD (89h) SFR

Bit Name Explanation of Function Timer

7 GATE1When this bit is set the timer will only run when INT1 (P3.3) is high. When this bit is clear the timer will run regardless of the state of INT1.

1

6 C/T1When this bit is set the timer will count events on T1 (P3.5). When this bit is clear the timer will be incremented every machine cycle.

1

5 T1M1 Timer mode bit (see below) 1


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3 GATE0When this bit is set the timer will only run when INT0 (P3.2) is high. When this bit is clear the timer will run regardless of the state of INT0.

0

2 C/T0When this bit is set the timer will count events on T0 (P3.4). When this bit is clear the timer will be incremented every machine cycle.

0



As you can see in the above chart, four bits (two for each timer) are used to specify a mode of operation. The modes of operation are:

TxM1 TxM0 Timer Mode Description of Mode

0 0 0 13-bit Timer.

0 1 1 16-bit Timer

1 0 2 8-bit auto-reload

1 1 3 Split timer mode

Table2.4 Timer modes13-bit Time Mode (mode 0):

Timer mode "0" is a 13-bit timer. When the timer is in 13-bit mode, TLx will count from 0 to 31. When TLx is incremented from 31, it will "reset" to 0 and increment THx. Thus, effectively, only 13 bits of the two-timer bytes are being used: bits 0-4 of TLx and bits 0-7 of THx. This also means, the timer can only contain 8192 values. If you set a 13-bit timer to 0, it will overflow back to zero 8192 machine cycles later.

16-bit Time Mode (mode 1):

Timer mode "1" is a 16-bit timer. This is a very commonly used mode. It functions just like 13-bit mode except that all 16 bits are used.

TLx is incremented from 0 to 255. When TLx is incremented from 255, it resets to 0 and causes THx to be incremented by 1. Since this is a full 16-bit timer, the timer may contain up to 65536 distinct values. If you set a 16-bit timer to 0, it will overflow back to 0 after 65,536 machine cycles.

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8-bit Time Mode (mode 2):

Timer mode "2" is an 8-bit auto-reload mode. What is that, you may ask? Simple. When a timer is in mode 2, THx holds the "reload value" and TLx is the timer itself. Thus, TLx starts counting up. When TLx reaches 255 and is subsequently incremented, instead of resetting to 0 (as in the case of modes 0 and 1), it will be reset to the value stored in THx.

Split Timer Mode (mode 3):

Timer mode "3" is a split-timer mode. When Timer 0 is placed in mode 3, it essentially becomes two separate 8-bit timers. That is to say, Timer 0 is TL0 and Timer 1 is TH0. Both timers count from 0 to 255 and overflow back to 0.

TCON SFR:

Finally, there’s one more SFR that controls the two timers and provides valuable information about them.

The TCON SFR has the following structure:

TCON (88h) SFR

Bit NameBit Address

Explanation of Function Timer

7 TF1 8FhTimer 1 Overflow. The micro controller sets this bit when Timer 1 overflows.

1

6 TR1 8EhTimer 1 Run. When this bit is set Timer 1 is turned on. When this bit is clear Timer 1 is off.

1

5 TF0 8DhTimer 0 Overflow. The micro controller sets this bit when Timer 0 overflows.

0

4 TR0 8ChTimer 0 Run. When this bit is set Timer 0 is turned on. When this bit is clear Timer 0 is off.

0

As you may notice, we’ve only defined 4 of the 8 bits. That’s because the other 4 bits of the SFR don’t have anything to do with timers, they have to do with Interrupts and they will be discussed in the chapter that addresses interrupts.

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A new piece of information in this chart is the column "bit address." This is because this SFR is "bit-addressable." What does this mean? It means if you want to set the bit TF1.which is the highest bit of TCON--you could execute the command:

MOV TCON, #80h

Or, since the SFR is bit-addressable, you could just execute the command:

SETB TF1.

This has the benefit of setting the high bit of TCON without changing the value of

any of the other bits of the SFR. Usually when you start or stop a timer you don’t

want to modify the other values in TCON, so you take advantage of the fact that the

SFR is bit-addressable.

Initializing a Timer:

Now that we’ve discussed the timer-related SFRs we are ready to write code that will initialize the timer and start it running.

As you’ll recall, we first must decide what mode we want the timer to be in. In this case, we want a 16-bit timer that runs continuously.

We must first initialize the TMOD SFR. Since we are working with timer 0 we will be using the lowest 4 bits of TMOD. The first two bits, GATE0 and C/T0 are both 0 since we want the timer to be independent of the external pins. 16-bit mode is timer mode 1 so we must clear T0M1 and set T0M0. Effectively, the only bit we want to turn on is bit 0 of TMOD. Thus to initialize the timer, we execute the instruction:

MOV TMOD, #01h.

Timer 0 is now in 16-bit timer mode. However, the timer is not running. To start the timer running we must set the TR0 bit we can do that by executing the instruction:

SETB TR0.

Upon executing these two instructions timer 0 will immediately begin counting, being incremented once every machine cycle (every 12 crystal pulses).

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2.5 INTERRUPTS:

The micro controller provides 6 interrupt sources, 2 external interrupts, 2 timer

interrupts and a serial port interrupt and a reset. The external interrupts (INT0 & INT1)

can each be either level activated or transition activated depending on bits IT0 and IT1 in

register TCON. The flags that actually generate these interrupts are IE0 & IE1 bits in

TCON.

TF0 and TF1 generate the timer 0 & 1 interrupts, which are set by a roll over in

their respective timer/counter registers. When a timer interrupt is generated the on-chip

hardware clears the flag that generated it when the service routine is vectored to.

The serial port interrupt is generated by logical OR of R1 & T1. Neither of these

flags is cleared by hardware when service routine is vectored to. In fact, the service

routine itself determines whether R1 & T1 generated the interrupt, and the bit is cleared

in the software.

Upon reset, all interrupts are disabled, meaning that none will be responded to

by the micro controller if they are activated. The interrupts must be enabled by software

in order for the micro controller to respond to them.

.

2.5.1 SERIAL INTERRUPTS:

Serial Interrupts are slightly different than the rest of the interrupts. This is due to

the fact that there is two interrupt flags: RI and TI. If either flag is set, a serial interrupt is

triggered. As you will recall from the section on the serial port, the RI bit is set when a

byte is received by the serial port and the TI bit is set when a byte has been sent.

This means that when your serial interrupt is executed, it may have been triggered

because the RI flag was set or because the TI flag was set or because both flags were set.

Thus, your routine must check the status of these flags to determine what action is

appropriate. Also, since the 8051 does not automatically clear the RI and TI flags you

must clear these bits in your interrupt handler.

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CHAPTER 3. SERIAL COMMUNICATION

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http://www.8052.com/tutser.phtml

One of the 8051s many powerful features is its integrated UART, otherwise

known as a serial port. The fact that the 8051 have an integrated serial port means that

you may very easily read and write values to the serial port.

However, we do not have to do this. Instead, we simply need to configure the

serial ports operation mode and baud rate. Once configured, all we have to do is write to

an SFR to write a value to the serial port or read the same SFR to read a value from the

serial port. The 8051 will automatically let us know when it has finished sending the

character we wrote and will also let us know whenever it has received a byte so that we

can process it.

3.1 SETTING THE SERIAL PORT MODE:

Bit Name Bit Address Explanation of Function

7 SM0 9Fh Serial port mode bit 0

6 SM1 9Eh Serial port mode bit 1.

5 SM2 9Dh Multiprocessor Communications Enable (explained later)

4 REN 9Ch Receiver Enable. This bit must be set in order to receive characters.

3 TB8 9Bh Transmit bit 8. The 9th bit to transmit in mode 2 and 3.

2 RB8 9Ah Receive bit 8. The 9th bit received in mode 2 and 3.

1 TI 99h Transmit Flag. Set when a byte has been completely transmitted.

0 RI 98h Receive Flag. Set when a byte has been completely received.

The first things we must do when using the 8051s integrated serial port is,

obviously, configure it. This lets us tell the 8051 how many data bits we want, the baud

rate we will be using, and how the baud rate will be determined. First, let’s present the

"Serial Control" (SCON) SFR and define what each bit of the SFR represents:

Additionally, it is necessary to define the function of SM0 and SM1 by an additional

table:

SM0 SM1 Serial Mode Explanation Baud Rate

0 0 0 8-bit Shift Register Oscillator / 12

0 1 1 8-bit UART Set by Timer 1 (*)

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1 0 2 9-bit UART Oscillator / 64 (*)

1 1 3 9-bit UART Set by Timer 1 (*)

Table.3.1 Serial Mode Setting

(*) Note: The baud rate indicated in this table is doubled if PCON.7 (SMOD) is set.

The SCON SFR allows us to configure the Serial Port. The first four bits (bits 4 through 7) are configuration bits.

Bits SM0 and SM1 let us set the serial mode to a value between 0 and 3. The four modes are defined in the chart im immediately above. As you can see, selecting the Serial Mode selects the mode of operation (8-bit/9-bit, UART or Shift Register) and also determines how the baud rate will be calculated. In modes 0 and 2 the baud rate is fixed based on the oscillator’s frequency. In modes 1 and 3 the baud rate is variable based on how often Timer 1 overflows.

The next bit, SM2, is a flag for "Multiprocessor communication." Generally, whenever a byte has been received the 8051 will set the "RI" (Receive Interrupt) flag. This lets the program know that a byte has been received and that it needs to be processed. However, when SM2 is set the "RI" flag will only be triggered if the 9th bit received was a "1". That is to say, if SM2 is set and a byte is received whose 9th bit is clear, the RI flag will never be set. This can be useful in certain advanced serial applications. For now it is safe to say that you will almost always want to clear this bit so that the flag is set upon reception of any character.

The next bit, REN, is "Receiver Enable." This bit is very straightforward: If you want to receive data via the serial port, set this bit. You will almost always want to set this bit.

The last four bits (bits 0 through 3) are operational bits. They are used when actually sending and receiving data, they are not used to configure the serial port.

The TB8 bit is used in modes 2 and 3. In modes 2 and 3, a total of nine data bits are transmitted. The first 8 data bits are the 8 bits of the main value, and the ninth bit is taken from TB8. If TB8 is set and a value is written to the serial port, the data bits will be written to the serial line followed by a "set" ninth bit. If TB8 is clear the ninth bit will be "clear."

The RB8 also operates in modes 2 and 3 and functions essentially the same way as TB8, but on the reception side. When a byte is received in modes 2 or 3, a total of nine bits are received. In this case, the first eight bits received are the data of the serial byte received and the value of the ninth bit received will be placed in RB8.

27

TI (Transmit Interrupt) is bit 1 of the SCON register. This is an extremely important flag bit in the SCON register. When the 8051 finish the transfer of the 8-bit character, it raises the TI flag to indicate that it is ready to transfer another byte. The TI bit is raised at the beginning of the stop bit.

Finally, the RI bit means "Receive Interrupt." It functions similarly to the "TI" bit, but it indicates that a byte has been received. That is to say, whenever the 8051 have received a complete byte it will trigger the RI bit to let the program know that it needs to read the value quickly, before another byte is read.

3.2 SETTING THE SERIAL PORT BAUD RATE:

Once the Serial Port Mode has been configured, as explained above, the program must configure the serial ports baud rate. This only applies to Serial Port modes 1 and 3. The Baud Rate is determined based on the oscillator’s frequency when in mode 0 and 2. In mode 0, the baud rate is always the oscillator frequency divided by 12. This means if you’re crystal is 11.059 MHz; mode 0 baud rate will always be 921,583 baud. In mode 2 the baud rate is always the oscillator frequency divided by 64, so a 11.059Mhz crystal speed will yield a baud rate of 172,797.

In modes 1 and 3, the baud rate is determined by how frequently timer 1 overflows. The more frequently timer 1 overflows, the higher the baud rate. There are many ways one can cause timer 1 to overflow at a rate that determines a baud rate, but the most common method is to put timer 1 in 8-bit auto-reload mode (timer mode 2) and set a reload value (TH1) that causes Timer 1 to overflow at a frequency appropriate to generate a baud rate.

To determine the value that must be placed in TH1 to generate a given baud rate, we may use the following equation (assuming PCON.7 is clear).

TH1 = 256 - ((Crystal / 384) / Baud)

If PCON.7 is set then the baud rate is effectively doubled, thus the equation becomes:

TH1 = 256 - ((Crystal / 192) / Baud)

3.3 MAX-232:

28

Since the RS-232 is not compatible with today’s microprocessors and micro

controllers, we need a line driver to convert the RS_232’s signals to TTL voltage levels

that will be acceptable to 89C52’s TxD and RxD pins.

One example of such a converter is MAX-232 from maxim corp. the MAX232

converts RS232 voltage levels to TTL voltage levels and vice versa.

. FIGURE 3.1: PIN DESCRIPTION

29

3.4 INTERFACING OF MAX-232 WITH AT89C52:

FIG: 3.2. Interfacing RS232 with8052

3.5 ABSOLUTE MAXIMUM RATINGS:

Input supply voltage range, Vcc: -0.3 to 6V

Positive output supply voltage range: VS + Vcc: -3 to 15V

Negative output supply voltage range: VS -0.3V to -15V

Input voltage range, VI: Driver: -3VtoVcc+0.3V

Receiver: 30V

Output voltage range, Vo: T1out, T2out VS -0.3V to VS+ +0.3V

R1out,R2out: -0.3V to Vcc +0.3V

Short-circuit duration, T1out,T2out: unlimited

Package thermal impedance, D package: 113 C/W

Storage temperature range, Tstg: -65 to 150 c.

30

CHAPTER 4. ANALOG TO DIGITAL CONVERTERS

31

Digital circuitry can be connected to sensor devices if they are inherently digitalized

by themselves. Switches, relays, and encoders are easily interfaced with gate circuits due

to the on/off nature of their signals. However, when analog devices are involved,

interfacing is needed to translate analog signals into digital quantities. When data

acquisition hardware receives an analogue signal from sensor it converts it to a voltage. It

then digitizes it with an analogue-to-digital converter, ready for transfer to a computer.

Characteristic parameters for A-D converters are: resolution, sample and hold

acquisition time, linearity, throughput etc. some of the specifications are defined below:

Resolution: Resolution defines the smallest change in the input voltage that can be

detected and encoded by the ADC. Resolution of the A-D converter is the number of

steps the input range is divided into. The resolution is usually expressed by the number of

bits in its output code (n) and the number of steps is 2 to the power n.

Sample and Hold Acquisition Time: A sample and hold circuit freezes the analogue

input voltage at the moment the sample is required. This voltage is held constant whilst

the A-D converter digitizes it. The acquisition time is the time between releasing the hold

state and the output of the sample circuit settling to the new input voltage value.

Throughput: Throughput is the maximum rate at which the A-D converter can output

data values. In general it will be the inverse of the sum of conversion time and acquisition

time. Conversion time is the time taken by an ADC to produce the valid digital output

corresponding to the analog input. Throughput can be increased by using a pipelined A-D

converter, so a second conversion can start while the first is still in progress.

Accuracy: Absolute accuracy or error of an ADC at a given output code is defined as the

difference between the corresponding theoretical analog value and the actual input

voltage required to produce that code.

There are many types of ADC’s such as Flash, Dual slope integrating, Successive

approximation, Delta-sigma etc.

32

4.1 HARDWARE DESIGN

4.1.1 DATA ACQUISITION SYSTEM

ADC0808 is the data acquisition component with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals. The ADC0808 offers high speed, high accuracy, minimal temperature dependence and minimal power consumption. The pin diagram of ADC0808 is shown in figure 4.1

FIGURE 4.1: PIN DIAGRAM OF ADC0808

ADC0808 contains an 8-channel single-ended analog signal multiplexer.

A particular input channel is selected by using the address decoder. The input states for

the address lines are used to select the required channel. The address is latched into the

decoder on the low-to-high transition.

33

The main component of this single chip data acquisition system is its 8-bit analog-to-

digital converter. This converter is designed to give fast, accurate, and repeatable

conversions over a wide range of temperatures. The converter is partitioned into three

major sections: the 256R ladder network, the successive approximation register, and the

comparator.

Successive approximation register counts by trying all values of bits, starting with

most significant bit and finishing at the least significant bit. Throughout the count

process, the register monitors the comparator's output to see if the binary count is less

than or greater than the analog signal input, adjusting the bit values accordingly. The A/D

converter's successive approximation register (SAR) is reset on the positive edge of the

start conversion (SC) pulse. The conversion is begun on the falling edge of the start

conversion pulse. A conversion in process will be interrupted by receipt of a new start

conversion pulse. Continuous conversion may be accomplished by tying the end of-

conversion (EOC) output to the SC input. End-of-conversion will go low between 0 and 8

clock pulses after the rising edge of start conversion. The block diagram of ADC0808 is

shown in figure.

The successive approximation register (SAR) performs 8 iterations to approximate the

input voltage. For any SAR type converter, n iterations are required for an n-bit

converter. To supply clock to the ADC0808 we are using 555 timers in Astable mode.

4.1.2 555 TIMER:

"555" integrated circuit is used for time-delay and oscillator functions. In

the time-delay or monostable mode of operation, the timed interval is controlled by a

single external resistor and capacitor network. In the astable mode of operation, the

frequency and duty cycle may be independently controlled with two external resistors and

a single external capacitor. The internal circuit diagram of 555 timer IC is shown in

figure 4.4.

34

FIG 4.2 : 555 TIMER

The threshold and trigger levels are normally two-thirds and one-third,

respectively, of VCC. These levels can be altered by use of the control voltage terminal.

When the trigger input falls below the trigger level, the flip-flop is set and the output goes

high. If the trigger input is above the trigger level and the threshold input is above the

threshold level, the flip-flop is reset and the output is low. RESET can override all other

inputs and can be used to initiate a new timing cycle. When RESET goes low, the flip-

flop is reset and the output goes low. Whenever the output is low, a low-impedance path

is provided between DISCH and ground.

Operation of Astable circuit:

The circuit diagram of a 555 timer configured in Astable mode is shown in

figure 4.5.With the output high (+Vcc) the capacitor C1 is charged by current flowing

through R1 and R2. The threshold and trigger inputs monitor the capacitor voltage and

when it reaches 2/3Vs (threshold voltage) the output becomes low and the discharge pin is

connected to 0V.

35

FIGURE 4.3: ASTABLE CIRCUIT

The capacitor now discharges with current flowing through R2 into the

discharge pin. When the voltage falls to 1/3Vs (trigger voltage) the output becomes high

again and the discharge pin is disconnected, allowing the capacitor to start charging again

.This cycle repeats continuously unless the reset input is connected to 0V, thus producing

a square wave with a time period of 0.7 (R1+2R2) C1. The square wave generated by

the Astable circuit of 555 timer is given to the 10th pin of ADC0808 to drive the clock.

36

CHAPTER 5. SENSORS

37

Sensors are the devices which are used to sense different parameters .The sensed

signal is converted into our required type with the help of transducers. Potentiometers can

be used to detect variations in voltage and resistance. With proper arrangement they can

also detect variations in angular displacement. It converts variations in all parameters in

terms of voltage. We have to use proper calibrations to convert these voltage variations

back into physical phenomenon. Variations in temperature can be detected and measured

using various types of temperature sensors such as RTDS, thermocouples, ultrasonic and

thermistors. In this project, we are using LM35 sensor which is a thermistor. For

measuring humidity, we are using SYH-2 and potentiometers.

5.1 TEMPERATURE SENSOR

The LM35 series are precision integrated-circuit temperature sensors, whose output

voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus

has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not

required to subtract a large constant voltage from its output to obtain convenient

Centigrade scaling. The LM35 does not require any external calibration or trimming to

provide typical accuracies of ±¼°C at room temperature and ±¾°C over a full -55 to

+150°C temperature range. Low cost is assured by trimming and calibration at the wafer

level. The LM35's low output impedance, linear output, and precise inherent calibration

make interfacing to readout or control circuitry especially easy. It can be used with single

power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply,

it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over

a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C

range (-10° with improved accuracy). The LM35 series is available packaged in hermetic

TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available

in the plastic TO-92 transistor package. The LM35D is also available in an 8-lead surface

mount small outline package and a plastic TO-220 package.

38

5.1.1 FEATURES:

Calibrated directly in ° Celsius (Centigrade)

Linear + 10.0 mV/°C scale factor

0.5°C accuracy guarantee able (at +25°C)

Rated for full -55° to +150°C range

Suitable for remote applications

Low cost due to wafer-level trimming

Operates from 4 to 30 volts

Less than 60 µA current drain

Low self-heating, 0.08°C in still air

Non-linearity only ±¼°C typical

Low impedance output, 0.1 Ohm for 1 mA load

Why to Use LM35s to Measure Temperature?

You can measure temperature more accurately than a using a thermistor. The sensor

circuitry is sealed and not subject to oxidation, etc.

The LM35 generates a higher output voltage than thermocouples and may not require

that the output voltage be amplified.

What Does An LM35 Look Like?

39

What Does an LM35 Do? How does it work?

It has an output voltage that is proportional to the Celsius temperature.

The scale factor is .01V/oC

The LM35 does not require any external calibration or trimming and

maintains an accuracy of +/-0.4 oC at room temperature and +/- 0.8 oC over a range of 0 oC to +100 oC.

Another important characteristic of the LM35DZ is that it draws only 60

micro amps from its supply and possesses a low self-heating capability. The sensor self-

heating causes less than 0.1 oC temperature rise in still air.

The LM35 comes in many different packages, including the following.

TO-92 plastic transistor-like package,

T0-46 metal can transistor-like package

8-lead surface mount SO-8 small outline package

What Can You Expect When You Use An LM35?

You will need to use a voltmeter to sense Vout.

The output voltage is converted to temperature by a simple

conversion factor.

The sensor has a sensitivity of 10mV / oC.

Use a conversion factor that is the reciprocal that is 100V / oC.

The general equation used to convert output voltage to temperature is:

Temperature ( oC) = Vout * (100 oC/V)

So if Vout is 1V , then, Temperature = 100 oC

The output voltage varies linearly with temperature.

How Do You Use An LM35? (Electrical Connections)

40

Here is a commonly used circuit. For connections refer to the picture above.

In this circuit, parameter values commonly used are:

Vc = 4 to 30v

5v or 12 v are typical values used.

Ra = Vc /10-6

Actually, it can range from 80 KW to 600 KW , but most just use

8 KW

Fig.5.1 LM35

5.2 HUMIDITY SENSOR:

Resistive humidity sensors designed for measuring relative humidity.

Characterized by great sensitivity and linearity, miniature and light housing and

narrow hysteresis and wide operating range.

The SYH-2T4W sensors are temperature compensated - fitted with built-in

thermistor Rt. Suitable for air humidifiers and dryers, ventilation and air conditioning

systems, air cleaners, incubators,humidity meters, greenhouses, vehicles, etc.

41

SPECIFICATIONS:

Items: syh-2,syh-2s

Rated voltage: AC 1Vrms

Rated power: AC 0.22mW

Operating temp.: 0-60 c

Operating humidity: 20-95%Rh

Standard characteristics: at 25 c,60%RH

Storage temperature: -30 to 85 c

Storage humidity: within 95%Rh

Humidity accuracy: 5%RH(at 25 c,60%RH)

Humidity response time: <60 sec(40 to 80%RH)

Hysterisis: +/-2%RH

42

CHAPTER 6. BLOCK DIAGRAM, CODING AND CONCLUSION

43

6. block diagram of the project:

Fig.5.2 Block Diagram

44

PC MAX-232 MC89C52

ADC0808

CLK

sensors555 TIMER

FIG.5.3.OVERVIEW OF DATA ACQUISITION SYSTEM USING 89C52

45

7. CODING

#include<reg52.h>#include<math.h>

sbit ale=P1^4;sbit oe=P1^5; sbit sc=P1^6;sbit eoc=P1^7;

sbit add_a=P1^0;sbit add_b=P1^1;sbit add_c=P1^2;

sfr port2=0xa0;unsigned int c02,c01,c03,c1,c2,c3,c4,t,dispdata,cnl;

int display (float);

void serialintr(void) interrupt 4 { //SERIAL INTERRUPT ROUTINE //TO TRANSMIT THE

// OUTPUT TO THE unsigned int x; //HYPER TERMINAL

if(RI==1){

x=SBUF; RI=0; if(x=='0') { cnl=0; }

if(x=='1') { cnl=1; }

46

if(x=='2') { cnl=2; }

if(x=='3') { cnl=3; } if(x=='4') { cnl=4; } if(x=='5') { cnl=5; } if(x=='6') { cnl=6; } if(x=='7') { cnl=7; }

if(x=='t') {

IE=0X00;

SBUF='\n';while(TI==0);TI=0;

c1=c1+48;SBUF=c1;while(TI==0);TI=0;


47

c3=c3+48; SBUF=c3;while(TI==0);TI=0;

SBUF='.';while(TI==0);TI=0;


SBUF=' ';while(TI==0);TI=0;

SBUF='c';while(TI==0);TI=0;

SBUF='\n';while(TI==0); TI=0;

} if(x=='x') {

IE=0X00;



SBUF=' '; while(TI==0);TI=0;

48

t=t+48;SBUF=t;while(TI==0);TI=0;




c3=c3+48; SBUF=c3;while(TI==0);TI=0;



SBUF='V';while(TI==0);TI=0;

} if(x=='h'){

IE=0X00;


49



c3=c3+48; SBUF=c3;




SBUF='H';while(TI==0);TI=0;


} } }

void main(void){ unsigned int u,v,z,s,f;

50

float y,d; y=19.53;

port2=0xFF;

TMOD=0X20; TH1=0XFD; SCON=0X50; TR1=1; IE=0X90; //ENABLE SERIAL INTERRUPT

eoc=1;ale=0;oe=0;sc=0;

while(1) {

if(cnl==0){ add_a=0; add_b=0; add_c=0; } if(cnl==1) { add_a=1; add_b=0; add_c=0; } if(cnl==2) { add_a=0; add_b=1; add_c=0; } if(cnl==3) { add_a=1; add_b=1; add_c=0; } if(cnl==4)

51

{ add_a=0; add_b=0; add_c=1; } if(cnl==5) { add_a=1; add_b=0; add_c=1; } if(cnl==6) { add_a=0; add_b=1; add_c=1; } if(cnl==7) { add_a=1; add_b=1; add_c=1; }

for(f=0;f<3000;f++);

ale=1;

for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);

sc=1;

for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);

ale=0;sc=0;

52

for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);oe=1

for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);for(f=0;f<3000;f++);

s=port2;// ADC DIGITAL O/P 0N PORT1 STORED IN Sz=0xA; //HEX TO DEC CONVERSION v=port2/z;u=port2%z;v=v*10;d=u+v;d=d*y;

display(d);

oe=0;

IE=0X90; //ENABLE SERIAL INTERRUPT

}

}

53

int display ( float result) {

unsigned int dispdata; result=result/1000; //MILLI VOLTS TO VOLTS dispdata=result*1000; //ROUTINE TO SEPARATE EACH DIGIT OF THE VOLTAGE VALUE c4=dispdata%10;

c01=dispdata/1000;c1=c01%10;

c02=dispdata/100;c2=c02%10;

c03=dispdata/10;c3=c03%10;

t=dispdata/10000;

return(0);

}

CONCLUSION:

54

As this world is readily growing up for ‘Era of automation and global

Communication’ this concept of controlling devices remotely regardless of load at which

the devices operate and the functions they perform, will surely fuel the Scope of

technology. This concept can definitely serve as a platform for new Innovations and help

us get better with time.

The existing project can be used for limited purpose, which it can be further

improved to its next generation for a large number of appliances.

As now the kit is interfaced with only few devices with other port pins being left

open for further expansion of the system. This could result in including the other house

hold appliances such as tube light, electric heaters; tape audio deck, etc, thus providing a

complete tool for house hold purpose.

This kit may be modified in the hardware as well as the software in a little manner to

obtain regulation of certain devices.

a) Automatic control of out door lighting system using light dependant resistor as a

sensing element.

b) Door locking system using digital gadget locking.

c) We can measure pressure, humidity and velocity.

Thus all the above parameters are chosen to control with the help of micro

controller, as nowadays the embedded controllers are playing a vital in the industries and

in western countries such as United States and other places lot of demand exist for

controllers. There by this project work serves as a guidance to enter into those fields,

which gives much encouragement and helps in growing and climbing the ladder.

BIBILOGRAPHY

55

TEXT BOOKS:

The 8051 Micro controller and embedded systems by Mazidi.

The 8051 Micro controller Architecture, programming &

Applications by Kenneth J.Ayala.

56

APPENDIX

ASCII CODES:

57

Documents

Contents