2.Pc Based Controlling Devices in Industriesabstract

7/29/2019 2.Pc Based Controlling Devices in Industriesabstract

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COMMAND BASED STREET LIGHT CONTROLLINGTHROUGH PC


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INDEX

CONTENTS

1. Abbreviations2. Figures locations

3. Introduction

4. Block Diagram

5. Block Diagram Description

6. Schematic

7. Schematic Description

8. Hardware Components

Power supply

Microcontroller

Max232

relays

pc

9. Circuit Description

10. Software componentsa. About Kielb. Embedded C

11. KEIL procedure description12. Conclusion (or) Synopsis13. Future Aspects


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14. Bibliography

Abbreviations


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Symbo

l

Name

ACC Accumulator

B B register

PSW Program status word

SP Stack pointer

DPTR Data pointer 2 bytes

DPL Low byte

DPH High byte

P0 Port0

P1 Port1

P2 Port2

P3 Port3

IP Interrupt priority control

IE Interrupt enable control

TMOD Timer/counter mode control

TCON Timer/counter control

T2CON Timer/counter 2 control

T2MOD Timer/counter mode2 control

TH0 Timer/counter 0high byte

TL0 Timer/counter 0 low byte

TH1 Timer/counter 1 high byte


TH2 Timer/counter 2 high byte


SCON Serial control

SBUF Serial data buffer

MAX MAXIM (IC manufacturer )

TTL Transistor to Transistor Logic

ATM Automatic Teller Machine

RS 232 Recommended Standard

AC Alternating Current

DC Direct Current

LCD Li uid Cr stal Dis la


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Figure Locations

S.No. Figure Page No.

1

Components of Typical Linear Power

Supply

2 An Electrical Transformer

3 Bridge Rectifier

4 Bridge Rectifier Positive Cycle

5 Bridge Rectifier Negative Cycle

6 Three terminal voltage Regulator

7 Functional Diagram of Microcontroller

8 Pin Diagram of Microcontroller

9 Oscillator connections

10 External clock drive connections

11 A register

12 B register

13 RAM

14 RAM Allocation15 Register Banks

16 PSW

17 DPTR

18 SP

19 PORT 0

20 TL0 and TH0

21 DB9

22 Connecting Microcontroller to PC

23 Types of SIM Structures

24 Smart Card Pin-out


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25 Smart Card Reader

26 LCD

27 MAX 232 Pin-out

28 MAX 232 Operating circuit

29 MAX 232 Logic output

30 Project

31 New Project

32 Select Target device

33 Select device for Target

34 Copy 8051 startup code

35 Source group 1

36 New file

37 Opened new file

38 File Save

39 Add files to the source group

40 Adding files to the source group

41 Compilation

42 After Compilation

43 Build

44 Selecting the Ports to be visualized

45 Start Debugging

INTRODUCTION

EMBEDDED SYSTEMS


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Embedded systems are designed to do some specific task, rather than be a general-

purpose computer for multiple tasks. Some also have real time performance constraints that must

be met, for reason such as safety and usability; others may have low or no performance

requirements, allowing the system hardware to be simplified to reduce costs.

An embedded system is not always a separate block - very often it is physically built-

in to the device it is controlling.

The software written for embedded systems is often called firmware, and is stored in read-only

memory or flash convector chips rather than a disk drive. It often runs with limited computer

hardware resources: small or no keyboard, screen, and little memory.

Now a day's every system is automated in order to face new challenges. In the present

days Automated systems have less manual operations, flexibility, reliability and accurate. Due tothis demand every field prefers automated control systems. Especially in the field of electronics

automated systems are giving good performance. In the present scenario of war situations,

unmanned systems plays very important role to minimize human losses.

Today, there exists no well-defined body of knowledge a student must learn to become

proficient in communications and information systems. This is an emerging field, and builds on

data communications, computer networks, distributed systems, information management, and

applications.

PC control has become an indispensable item of every days life. Starting from routines

like gate openers, window shutters through metering and PC fire alarms to automotive

applications like remote keyless entry and tire pressure monitoring systems. Wireless control

devices have established themselves as a cost-efficient and robust solution for a broad range of

control applications.

In this project we are controlling various devices i.e. various street lights through PC justby typing the commands in communication terminal, in which PC is interfaced with the

microcontroller serially. According to commands given by PC the controller makes the devices

ON or OFF.


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BLOCDIAGRAM:

Block diagram explanation:

This Project mainly consists of Power Supply section, Microcontroller section,

Energy Meter, Smart Card Reader section, LCD display section, Max 232 serial

driver section, Relay section and latch section, GSM modem section, Load sections.

Power supply:

MICRO

CONTROLLE

R

LIGHTING

SYSTEM

PC

MA

X

2

3

2

RELAYS

CIRCUIT

POWER

SUPPLY

DC MOTOR


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In this system we are using 5V power supply for microcontroller of Transmitter section as well

as receiver section. We use rectifiers for converting the A.C. into D.C and a step down

transformer to step down the voltage. The full description of the Power supply section is given in

this documentation in the following sections i.e. hardware components.

Microcontroller (8051):

In this project work the micro-controller is playing a major role. Micro-controllers were

originally used as components in complicated process-control systems. However, because of

their small size and low price, Micro-controllers are now also being used in regulators for

individual control loops. In several areas Micro-controllers are now outperforming their analog

counterparts and are cheaper as well.

Relay Section:This section is nothing but driving circuitry needed to drive the

DEVICES. So this section basically includes a Relay with its protection circuitry. This

section is responsible to drive the Normal devices.

MAX 232 Sections:The microcontroller can communicate with the serial devices

using its single Serial Port. The logic levels at which this serial port operates is TTL

logics. But some of the serial devices operate at RS 232 Logic levels. For example

PC and Smart Card Reader etc. So in order to communicate the Microcontroller witheither Smart Card Reader or PC, a mismatch between the Logic levels occurs. In

order to avoid this mismatch, in other words to match the Logic levels, a Serial

driver is used. And MAX 232 is a Serial Line Driver used to establish communication

between microcontroller and PC (or Smart Card Reader)

SCHEMATIC DIAGRAM:


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SCHEMATIC DESCRIPTION:

Firstly, the required operating voltage for Microcontroller 89C51 is 5V. Hence the 5V

D.C. power supply is needed by the same. This regulated 5V is generated by first stepping down

the 230V to 18V by the step down transformer.

In the both the Power supplies the step downed a.c. voltage is being rectified by the

Bridge Rectifier. The diodes used are 1N4007. The rectified a.c voltage is now filtered using a

C filter. Now the rectified, filtered D.C. voltage is fed to the Voltage Regulator. This voltage

regulator allows us to have a Regulated Voltage. In Power supply given to Microcontroller 5V is

generated using 7805 and in other two power supply 12V is generated using 7812. The rectified;

filtered and regulated voltage is again filtered for ripples using an electrolytic capacitor 100F.


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Now the output from the first section is fed to 40th pin of 89c51 microcontroller to supply

operating voltage and from other power supply to circuitry.

The microcontroller 89C51 with Pull up resistors at Port0 and crystal oscillator of

11.0592 MHz crystal in conjunction with couple of capacitors of is placed at 18th

& 19th

pins of89C51 to make it work (execute) properly.

In this Schematic, P2.0 is connected to relay for device1.P1.0 TO p1.3 are connected to TheLEDS.P3.0, P3.1 are connected to the Max 10,11 pins and 14, 13 pins are connected to the

PC by using DB 9 connector.

20th pin connected to GROUND

40th pin is connected to Vcc

HARDWARE COMPONENTS:

Power supply

Microcontroller

Max232

relays

pc

HARDWARE EXPLANANATION:

MICRO CONTROLLER 89C51

Introduction

A Micro controller consists of a powerful CPU tightly coupled with memory, various I/O

interfaces such as serial port, parallel port timer or counter, interrupt controller, data acquisition

interfaces-Analog to Digital converter, Digital to Analog converter, integrated on to a single

silicon chip.


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If a system is developed with a microprocessor, the designer has to go for external

memory such as RAM, ROM, EPROM and peripherals. But controller is provided all these

facilities on a single chip. Development of a Micro controller reduces PCB size and cost of

design.

One of the major differences between a Microprocessor and a Micro controller is that a

controller often deals with bits not bytes as in the real world application.

Intel has introduced a family of Micro controllers called the MCS-51.

The Major Features:

Compatible with MCS-51 products

4k Bytes of in-system Reprogrammable flash memory

Fully static operation: 0HZ to 24MHZ

Three level programmable clock

128 * 8 bit timer/counters

Six interrupt sources

Programmable serial channel

Low power idle power-down modes

Why AT 89C51

The system requirements and control specifications clearly rule out the use

of 16, 32 or 64 bit micro controllers or microprocessors. Systems using these may

be earlier to implement due to large number of internal features. They are also

faster and more reliable but, 8-bit micro controller satisfactorily serves the above

application. Using an inexpensive 8-bit Microcontroller will doom the 32-bit productfailure in any competitive market place.

Coming to the question of why to use AT89C51 of all the 8-bit microcontroller available

in the market the main answer would be because it has 4 Kb on chip flash memory which is just

sufficient for our application. The on-chip Flash ROM allows the program memory to be


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reprogrammed in system or by conventional non-volatile memory Programmer. Moreover

ATMEL is the leader in flash technology in todays market place and hence using AT 89C51 is

the optimal solution.

AT89C51 MICROCONTROLLER ARCHITECTURE

The 89C51 architecture consists of these specific features:

Eight bit CPU with registers A (the accumulator) and B

Sixteen-bit program counter (PC) and data pointer (DPTR) Eight- bit stack pointer (PSW)

Eight-bit stack pointer (Sp)

Internal ROM or EPROM (8751) of 0(8031) to 4K (89C51)

Internal RAM of 128 bytes:

1. Four register banks, each containing eight registers

2. Sixteen bytes, which maybe addressed at the bit level

3. Eighty bytes of general- purpose data memory

Thirty two input/output pins arranged as four 8-bit ports:p0-p3

Two 16-bit timer/counters: T0 and T1

Full duplex serial data receiver/transmitter: SBUF

Control registers: TCON, TMOD, SCON, PCON, IP, and IE

Two external and three internal interrupts sources.

Oscillator and clock circuits.


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Functional block diagram of micro controller

The 89C51 oscillator and clock:

The heart of the 89C51 circuitry that generates the clock pulses by which all the internal

all internal operations are synchronized. Pins XTAL1 And XTAL2 is provided for connecting a

resonant network to form an oscillator. Typically a quartz crystal and capacitors are employed.

The crystal frequency is the basic internal clock frequency of the microcontroller. The

manufacturers make 89C51 designs that run at specific minimum and maximum frequencies

typically 1 to 16 MHz.


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Fig 3.7.2: - Oscillator and timing circuit

Types of memory:

The 89C51 have three general types of memory. They are on-chip memory,

external Code memory and external Ram. On-Chip memory refers to physically

existing memory on the micro controller itself. External code memory is the code

memory that resides off chip. This is often in the form of an external EPROM.

External RAM is the Ram that resides off chip. This often is in the form of standard

static RAM or flash RAM.


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a) Code memory

Code memory is the memory that holds the actual 89C51 programs that is to

be run. This memory is limited to 64K. Code memory may be found on-chip or off-

chip. It is possible to have 4K of code memory on-chip and 60K off chip memory

simultaneously. If only off-chip memory is available then there can be 64K of off

chip ROM. This is controlled by pin provided as EA

b) Internal RAM

The 89C51 have a bank of 128 of internal RAM. The internal RAM is found on-

chip. So it is the fastest Ram available. And also it is most flexible in terms of

reading and writing. Internal Ram is volatile, so when 89C51 is reset, this memory is

cleared. 128 bytes of internal memory are subdivided. The first 32 bytes are divided

into 4 register banks. Each bank contains 8 registers. Internal RAM also contains

128 bits, which are addressed from 20h to 2Fh. These bits are bit addressed i.e.

each individual bit of a byte can be addressed by the user. They are numbered 00hto 7Fh. The user may make use of these variables with commands such as SETB

and CLR.

FLASH MEMORY:

Flash memory (sometimes called "flash RAM") is a type of constantly-powered non volatile that can be erased and reprogrammed in units of memory

called blocks. It is a variation of electrically erasable programmable read-only

memory (EEPROM) which, unlike flash memory, is erased and rewritten at the byte

level, which is slower than flash memory updating. Flash memory is often used to

hold control code such as the basic input/output system (BIOS) in a personal


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computer. When BIOS needs to be changed (rewritten), the flash memory can be

written to in block (rather than byte) sizes, making it easy to update. On the other

hand, flash memory is not useful as random access memory (RAM) because RAM

needs to be addressable at the byte (not the block) level.

Flash memory gets its name because the microchip is organized so that a

section of memory cells are erased in a single action or "flash." The erasure is

caused by Fowler-Nordheim tunneling in which electrons pierce through a thin

dielectric material to remove an electronic charge from a floating gate associated

with each memory cell. Intel offers a form of flash memory that holds two bits

(rather than one) in each memory cell, thus doubling the capacity of memory

without a corresponding increase in price.

Flash memory is used in digital cellular phones, digital cameras, LAN

switches, PC Cards for notebook computers, digital set-up boxes, embedded

controllers, and other devices.

Memory Type

Features

FLASH Low-cost, high-density, high-speed

architecture; low power; high

reliability

ROM

Read-Only Memory

Mature, high-density, reliable, low

cost; time-consuming mask

required, suitable for high

production with stable code

SRAM

Static Random-Access Memory

Highest speed, high-power, low-

density memory; limited density

drives up cost


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EPROM

Electrically Programmable Read-

Only Memory

High-density memory; must be

exposed to ultraviolet light for

erasure

EEPROMorE2

PROMElectrically Erasable Programmable

Read-Only Memory

Electrically byte-erasable; lowerreliability, higher cost, lowest

density

DRAM

Dynamic Random Access Memory

High-density, low-cost, high-speed,

high-power

Technical Overview of Flash Memory

Flash memory is a nonvolatile memory using NOR technology, which allows the user

to electrically program and erase information. Intel Flash memory uses memory

cells similar to an EPROM, but with a much thinner, precisely grown oxide between

the floating gate and the source (see Figure 2). Flash programming occurs when

electrons are placed on the floating gate. The charge is stored on the floating gate,

with the oxide layer allowing the cell to be electrically erased through the source.

Intel Flash memory is an extremely reliable nonvolatile memory architecture.


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Fig 3.7.3: - Pin diagram of AT89C51

Pin Description:

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 ones 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


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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:

Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers

can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the

internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally 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

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

pull-ups when emitting 1s. During accesses to external data memories that use 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.

Port 3:

Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins

they are pulled high by the internal pull-ups and can be used as inputs. As inputs,

Port 3 pins that are externally being pulled low will source current (IIL) because of

the pull-ups.


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

below:

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

Tab 6.2.1 Port pins and their alternate functions

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 Flashprogramming. In normal operation ALE is emitted at a constant rate of 1/6the oscillator

frequency, and may be used for external timing or clocking purposes. Note, however, that one

ALE pulse is skipped during each 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


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

external execution mode.

PSEN:

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

AT89C51 is executing code from external program memory, PSEN is activated twice each

machine cycle, except that two PSEN activations are skipped during each access to external data

memory.

EA/VPP:

External Access Enable EA 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, EA will be internally latched

on reset.

EA 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:

It is the Output from the inverting oscillator amplifier.


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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 Figs 6.2.3. 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 6.2.4.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.

Fig 6.2.3 Oscillator Connections Fig 6.2.4 External Clock Drive

Configuration

Notes:

1. Under steady state (non-transient) conditions, IOL must be externally

limited as follows:

Maximum IOL per port pin: 10 mA

Maximum IOL per 8-bit port: Port 0: 26 mA

Ports 1, 2, 3: 15 mA

Maximum total IOL for all output pins: 71 mA


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If IOL exceeds the test condition, VOL may exceed the related

specification. Pins are not guaranteed to sink current greater than the

listed test conditions.

2. Minimum VCC for Power-down is 2V.

REGISTERS:

In the CPU, registers are used to store information temporarily. That

information could be a byte of data to be processed, or an address pointing to the

data to be fetched. The vast majority of 8051 registers are 8bit registers. In the

8051 there is only one data type: 8bits. The 8bits of a register are shown in the

diagram from the MSB (most significant bit) D7 to the LSB (least significant bit) D0.

With an 8-bit data type, any data larger than 8bits must be broken into 8-bit chunks

before it is processed. Since there are a large number of registers in the 8051, we

will concentrate on some of the widely used general-purpose registers and cover

special registers in future chapters.

D

7

D

6

D

5

D

4

D

3

D

2

D

1

D

0

The most widely used registers of the 8051 are A (accumulator), B, R0, R1,

R2, R3, R4, R5, R6, R7, DPTR (data pointer), and PC (program counter). All of the

above registers are 8-bits, except DPTR and the program counter. The

accumulator, register A, is used for all arithmetic and logic instructions.


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SFRs (Special Function Registers)

Among the registers R0-R7 is part of the 128 bytes of RAM memory. What about

registers A, B, PSW, and DPTR? Do they also have addresses? The answer is yes. In the 8051,

registers A, B, PSW and DPTR are part of the group of registers commonly referred to as SFR

(special function registers). There are many special function registers and they are widely used.

The SFR can be accessed by the names (which is much easier) or by their addresses. For

example, register A has address E0h, and register B has been ignited the address F0H, as shown

in table.

The following two points should noted about the SFR addresses.

1. The Special function registers have addresses between 80H and FFH. These

addresses are above 80H, since the addresses 00 to 7FH are addresses of RAM

memory inside the 8051.

2. Not all the address space of 80H to FFH is used by the SFR. The unused locations

80H to FFH are reserved and must not be used by the 8051 programmer.

Regarding direct addressing mode, notice the following two points: (a) the address value

is limited to one byte, 00-FFH, which means this addressing mode is limited to accessing RAM

locations and registers located inside the 8051. (b) If you examine the l st file for an assembly

language program, you will see that the SFR registers names are replaced with their addresses as

listed in table.

Symb

ol

Name Addre

ss

ACC Accumulator 0E0H

B B register 0F0H

PSW Program status word 0D0H

SP Stack pointer 81H

DPTR Data pointer 2 bytes

DPL Low byte 82H


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DPH High byte 83H

P0 Port0 80H

P1 Port1 90H

P2 Port2 0A0HP3 Port3 0B0H

IP Interrupt priority control 0B8H

IE Interrupt enable control 0A8H

TMOD Timer/counter mode

control

89H

TCON Timer/counter control 88H

T2CO

N

Timer/counter 2 control 0C8H

T2MO

D

Timer/counter mode2

control

0C9H

TH0 Timer/counter 0high byte 8CH

TL0 Timer/counter 0 low byte 8AH

TH1 Timer/counter 1 high

byte

8DH

TL1 Timer/counter 1 low byte 8BH

TH2 Timer/counter 2 high

byte

0CDH

TL2 Timer/counter 2 low byte 0CCH

RCAP

2H

T/C 2 capture register

high byte

0CBH

RCAP

2L

T/C 2 capture register

low byte

0CAH

SCON Serial control 98H

SBUF Serial data buffer 99H

PCON Power control 87H


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Table: 8051 Special function register Address

A Register (Accumulator)

This is a general-purpose register which serves for storing intermediate results during operating.

A number (an operand) should be added to the accumulator prior to execute an instruction upon

it. Once an arithmetical operation is preformed by the ALU, the result is placed into the

accumulator. If a data should be transferred from one register to another, it must go throughaccumulator. For such universal purpose, this is the most commonly used register that none

microcontroller can be imagined without (more than a half 8051 microcontroller's instructions

used use the accumulator in some way).

B Register

B register is used during multiply and divide operations which can be performed only upon

numbers stored in the A and B registers. All other instructions in the program can use thisregister as a spare accumulator (A).


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During programming, each of registers is called by name so that

their exact address is not so important for the user. During compiling into machine

code (series of hexadecimal numbers recognized as instructions by the

microcontroller), PC will automatically, instead of registers name, write necessary

addresses into the microcontroller.

R Registers (R0-R7)

This is a common name for the total 8 general purpose registers (R0, R1, and R2 ...R7). Even

they are not true SFRs, they deserve to be discussed here because of their purpose. The bank is

active when the R registers it includes are in use. Similar to the accumulator, they are used for

temporary storing variables and intermediate results. Which of the banks will be active depends

on two bits included in the PSW Register. These registers are stored in four banks in the scope ofRAM.

The following example best illustrates the useful purpose of these registers. Suppose that

mathematical operations on numbers previously stored in the R registers should be performed:


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(R1+R2) - (R3+R4). Obviously, a register for temporary storing results of addition is needed.

Everything is quite simple and the program is as follows:

MOV A, R3; Means: move number from R3 into accumulator

ADD A, R4; Means: add number from R4 to accumulator (result remains in accumulator)

MOV R5, A; Means: temporarily moves the result from accumulator into R5

MOV A, R1; Means: move number from R1 into accumulator

ADD A, R2; Means: add number from R2 to accumulator

SUBB A, R5; Means: subtract number from R5 (there are R3+R4)

8051 Register Banks and Stack

RAM memory space allocation in the 8051

There are 128 bytes of RAM in the 8051. The 128 bytes of RAM inside the

8051 are assigned addresses 00 to7FH. These 128 bytes are divided into three

different groups as follows:

1. A total of 32 bytes from locations 00 to 1FH hex are set aside for registerbanks and the stack.

2. A total of 16 bytes from locations 20 to 2FH hex are set aside for bit-

addressable read/write memory.

3. A total of 80 bytes from locations 30H to 7FH are used for read and write

storage, or what is normally called Scratch pad. These 80 locations of

RAM are widely used for the purpose of storing data and parameters nu

8051 programmers.

Register banks in the 8051

A total of 32bytes of RAM are set aside for the register banks and stack.

These 32 bytes are divided into 4 banks of registers in which each bank has

registers, R0-R7. RAM locations 0 to 7 are set aside for bank 0 of R0-R7 where R0 is


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RAM location 0, R1 is RAM location 1, and R2 is location 2, and so on, until memory

location7, which belongs to R7 of bank0. The second bank of registers R0-R7 starts

at RAM location 08 and goes to location 0FH. The third bank of R0-R7 starts at

memory location 10H and goes to location 17H. Finally, RAM locations 18H to 1FH

are set aside for the fourth bank of R0-R7. Fig shows how the 32 bytes are allocated

into 4 banks.

As we can see from fig 1, the bank 1 uses the same RAM space as the

stack. This is a major problem in programming the 8051. we must either not use

register bank1, or allocate another area of RAM for the stack.

Default register bank

If RAM locations 00-1F are set aside for the four register banks, whichregister bank of R0-R7 do we have access to when the 8051 is powered up? The

answer is register bank 0; that is , RAM locations 0, 1,2,3,4,5,6, and 7 are accessed

with the names R0, R1, R2, R3, R4, R5, R6, and R7 when programming the 8051. It

is much easier to refer to these RAM locations with names such as R0, R1 and so on,

than by their memory locations as shown in fig 2.

The register banks are switched by using the D3 & D4 bits of register PSW.


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FIG: RAM Allocation in the 8051


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Fig: 8051 Register Banks and their RAM Addresses

PSW Register (Program Status Word)

This is one of the most important SFRs. The Program Status Word (PSW) contains several status

bits that reflect the current state of the CPU. This register contains: Carry bit, Auxiliary Carry,

two register bank select bits, Overflow flag, parity bit, and user-definable status flag. The ALU

automatically changes some of registers bits, which is usually used in regulation of the program

performing.

P - Parity bit. If a number in accumulator is even then this bit will be automatically set (1),

otherwise it will be cleared (0). It is mainly used during data transmission and receiving via

serial communication.

- Bit 1. This bit is intended for the future versions of the microcontrollers, so it is not supposed to

be here.

OV Overflow occurs when the result of arithmetical operation is greater than 255 (decimal), so

that it can not be stored in one register. In that case, this bit will be set (1). If there is no

overflow, this bit will be cleared (0).

RS0, RS1 - Register bank selects bits. These two bits are used to select one of the four register

banks in RAM. By writing zeroes and ones to these bits, a group of registers R0-R7 is stored in

one of four banks in RAM.

RS1 RS2 Space in RAM

0 0 Bank0 00h-07h

0 1 Bank1 08h-0Fh


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1 0 Bank2 10h-17h

1 1 Bank3 18h-1Fh

F0 - Flag 0. This is a general-purpose bit available to the user.

AC - Auxiliary Carry Flag is used for BCD operations only.

CY - Carry Flag is the (ninth) auxiliary bit used for all arithmetical operations and shift

instructions.

DPTR Register (Data Pointer)

These registers are not true ones because they do not physically exist. They consist of two

separate registers: DPH (Data Pointer High) and (Data Pointer Low). Their 16 bits are used for

external memory addressing. They may be handled as a 16-bit register or as two independent 8-

bit registers. Besides, the DPTR Register is usually used for storing data and intermediate results

which have nothing to do with memory locations.

SP Register (Stack Pointer)


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The stack is a section of RAM used by the CPU to store information temporarily. This

information could be data or an address. The CPU needs this storage area since there are only a

limited number of registers.

How stacks are accessed in the 8051

If the stack is a section of RAM, there must be registers inside the CPU to point to it.

The register used to access the stack is called the SP (Stack point) Register. The stack pointer in

the 8051 is only 8 bits wide; which means that it can take values of 00 to FFH. When the 8051 is

powered up, the SP register contains value 07. This means that RAM location 08 is the first

location used for the stack by the 8051. The storing of a CPU register in the stack is called a

PUSH, and pulling the contents off the stack back into a CPU register is called a POP. In other

words, a register is pushed onto the stack to save it and popped off the stack to retrieve it. The

job of the SP is very critical when push and pop actions are performed.

Pushing onto the stack

In the 8051 the stack pointer (SP) points to the last used location of the stack. As we

push data onto the stack, the stack pointer is incremented by one. Notice that this different frommany microprocessors, notably x86 processors in which the SP is decremented when data is

pushed onto the stack. As each PUSH is executed, the contents of the register are saved on the

stack and SP is incremented by 1. Notice that for every byte of data saved on the stack and then

SP is incremented only once. Notice also that to push the registers onto the stack we must use

their RAM addresses. For example, the instruction PUSH pushes register R1 onto the stack.

Popping from the stack

Popping the contents of the stack back into a given register is the opposite process of

pushing. With every pop, the top byte of the stack is copied to the register specified by the

instruction and the stack pointer is decremented once.

The upper limit of the stack


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As, mentioned earlier, locations 08 to 1FH in the 8051 RAM can be used for the stack.

This is because locations 20-2FH of RAM are reserved for bit-addressable memory and must not

be used by the stack. If in a program we need more than 24 bytes (08 to 1FH=24bytes) of stack,

we can change the SP to point to RAM locations 30-7FH. This is done with the instruction

MOV SP, #XX.

P0, P1, P2, P3 - Input/Output Registers

In case that external memory and serial communication system are not in use then, 4 ports with

in total of 32 input-output lines are available to the user for connection to peripheral

environment. Each bit inside these ports corresponds to the appropriate pin on the

microcontroller. This means that logic state written to these ports appears as a voltage on the pin

(0 or 5 V). Naturally, while reading, the opposite occurs voltage on some input pins is reflected

in the appropriate port bit.

The state of a port bit, besides being reflected in the pin, determines at the same time whether it

will be configured as input or output. If a bit is cleared (0), the pin will be configured as output.

In the same manner, if a bit is set to 1 the pin will be configured as input. After reset, as well as

when turning the microcontroller ON, all bits on these ports are set to one (1). This means that

the appropriate pins will be configured as inputs.

Program counter:

The important register in the 8051 is the PC (Program counter). The program counter

points to the address of the next instruction to be executed. As the CPU fetches the OPCODE

from the program ROM, the program counter is incremented to point to the next instruction. The

program counter in the 8051 is 16bits wide. This means that the 8051 can access program


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addresses 0000 to FFFFH, a total of 64k bytes of code. However, not all members of the 8051

have the entire 64K bytes of on-chip ROM installed, as we will see soon.

Types of instructions

Depending on operation they perform, all instructions are divided in several groups:

Arithmetic Instructions

Branch Instructions

Data Transfer Instructions

Logical Instructions

Logical Instructions with bits

The first part of each instruction, called MNEMONIC refers to the operation an instruction

performs (copying, addition, logical operation etc.). Mnemonics commonly are shortened form

of name of operation being executed. For example:

INC R1; Increment R1 (increment register R1)

LJMP LAB5 ;Long Jump LAB5 (long jump to address specified as LAB5)

JNZ LOOP ;Jump if Not Zero LOOP (if the number in the accumulator is not 0, jump to

address specified as LOOP)

Another part of instruction, called OPERAND is separated from mnemonic at least by one empty

space and defines data being processed by instructions. Some instructions have no operand; some

have one, two or three. If there is more than one operand in instruction, they are separated by

comma. For example:

RET - (return from sub-routine)

JZ TEMP - (if the number in the accumulator is not 0, jump to address specified as

TEMP)

ADD A,R3 - (add R3 and accumulator)

CJNE A,#20,LOOP - (compare accumulator with 20. If they are not equal, jump to

address specified as LOOP)


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Arithmetic instructions

These instructions perform several basic operations (addition, subtraction, division,

multiplication etc.) After execution, the result is stored in the first operand. For example:

ADD A, R1 - The result of addition (A+R1) will be stored in the accumulator.

Arithmetical Instructions

Mnemonic DescriptionByte

Number

Oscillator

Period

ADD A,Rn Add R Register to accumulator 1 1

ADD A,RxAdd directly addressed Rx Register to

accumulator2 2

ADD A,@RiAdd indirectly addressed Register to

accumulator1 1

ADD A,#X Add number X to accumulator 2 2

ADDC A,RnAdd R Register with Carry bit to

accumulator1 1

Branch Instructions

There are two kinds of these instructions:

Unconditional jump instructions: After their execution a jump to a new location from where

the program continues execution is executed.

Conditional jump instructions: If some condition is met - a jump is executed. Otherwise, the

program normally proceeds with the next instruction.


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Branch Instruction


Number

Oscillator

Period

ACALL

adr11

Call subroutine located at address within 2 K

byte Program Memory space2 3

LCALL

adr16

Call subroutine located at any address within

64 K byte Program Memory space3 4

RET Return from subroutine 1 4

RETI Return from interrupt routine 1 4

AJMP adr11Jump to address located within 2 K byte

Program Memory space2 3

LJMP adr16Jump to any address located within 64 K byte

Program Memory space3 4

Data Transfer Instructions

These instructions move the content of one register to another one. The register which content is

moved remains unchanged. If they have the suffix X (MOVX), the data is exchanged with

external memory.

Data Transfer Instruction


Number

Cycle

Number


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MOV A,Rn Move R register to accumulator 1 1

MOV A,RxMove directly addressed Rx register to

accumulator2 2

MOV A,@RiMove indirectly addressed register to

accumulator1 1

MOV A,#X Move number X to accumulator 2 2


These instructions perform logical operations between corresponding bits of two registers. After

execution, the result is stored in the first operand.



Number

Cycle

Number

ANL A,RnLogical AND between accumulator and R

register1 1

ANL A,RxLogical AND between accumulator and

directly addressed register Rx2 2

ANL A,@RiLogical AND between accumulator and

indirectly addressed register1 1

ANL A,#XLogical AND between accumulator and

number X2 2

Logical Operations on Bits

Similar to logical instructions, these instructions perform logical operations. The difference is

that these operations are performed on single bits.


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Logical operations on bits


Number

Cycle

Number

CLR C Clear Carry bit 1 1

CLR bit Clear directly addressed bit 2 2

SETB C Set Carry bit 1 1

SETB bit Set directly addressed bit 2 2

CPL C Complement Carry bit 1 1

CPL bit Complement directly addressed bit 2 2

TIMERSOn-chip timing/counting facility has proved the capabilities of the

microcontroller for implementing the real time application. These includes pulse

counting, frequency measurement, pulse width measurement, baud rate

generation, etc,. Having sufficient number of timer/counters may be a need in a

certain design application. The 8051 has two timers/counters. They can be usedeither as timers to generate a time delay or as counters to count events happening

outside the microcontroller. Let discuss how these timers are used to generate time

delays and we will also discuss how they are been used as event counters.

PROGRAMMING 8051 TIMERS

The 8051 has timers: Timer 0 and Timer1.they can be used either as timers or

as event counters. Let us first discuss about the timers registers and how to

program the timers to generate time delays.


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BASIC RIGISTERS OF THE TIMER

Both Timer 0 and Timer 1 are 16 bits wide. Since the 8051 has an 8-bit

architecture, each 16-bit timer is accessed as two separate registers of low byte

and high byte.

TIMER 0 REGISTERS

The 16-bit register of Timer 0 is accessed as low byte and high byte. the

low byte register is called TL0(Timer 0 low byte)and the high byte register is

referred to as TH0(Timer 0 high byte).These register can be accessed like any other

register, such as A,B,R0,R1,R2,etc.for example, the instruction MOV TL0,

#4Fmoves the value 4FH into TL0,the low byte of Timer 0.These registers can also

be read like any other register.


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TIMER 1 REGISTERS

Timer 1 is also 16-bit register is split into two bytes, referred to as TL1

(Timer 1 low byte) and TH1 (Timer 1 high byte).these registers are accessible n the

same way as the register of Timer 0.

TMOD (timer mode) REGISTER

Both timers TIMER 0 and TIMER 1 use the same register, called TMOD, to set

the various timer operation modes. TMOD is an 8-bit register in which the lower 4

bits are set aside for Timer 0 and the upper 4 bits for Timer 1.in each case; thelower 2 bits are used to set the timer mode and the upper 2 bits to specify the

operation.

MODES:

M1, M0:

M0 and M1 are used to select the timer mode. There are three modes: 0, 1,

2.Mode 0 is a 13-bit timer, mode 1 is a 16-bit timer, and mode 2 is an 8-bit timer.

We will concentrate on modes 1 and 2 since they are the ones used most widely.

We will soon describe the characteristics of these modes, after describing the reset

of the TMOD register.


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GATE Gate control when set. The timer/counter is enabled

only

While the INTx pin is high and the TRx control

pin is.

Set. When cleared, the timer is enabled.

C/T Timer or counter selected cleared for timer

operation

(Input from internal system clock).set for counter

Operation (input TX input pin).

M 1 Mode bit 1

M0 Mode bit 0

M1 M0 MODE Operating Mode

0 0 0 13-bit timer mode

8-bit timer/counter THx with TLx as

5 - Bit pre-scaler.

0 1 1 16-bit timer mode

16-bit timer/counters THx with TLx

are

Cascaded; there is no prescaler

1 0 2 8-bit auto reload

8-bit auto reload timer/counter;THx


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Holds a value that is to be reloaded

into

TLx each time it overflows.

1 1 3 Split timer mode.

C/T (clock/timer)

This bit in the TMOD register is used to decide whether the timer is used as a

delay generator or an event counter. If C/T=0, it is used as a timer for time delay

generation. The clock source for the time delay is the crystal frequency of the 8051.

This section is concerned with this choice. The timers use as an event counter is

discussed in the next section.

Serial Communication:

Computers can transfer data in two ways: parallel and serial. In parallel data

transfers, often 8 or more lines (wire conductors) are used to transfer data to a

device that is only a few feet away. Examples of parallel data transfer are printers

and hard disks; each uses cables with many wire strips. Although in such cases a

lot of data can be transferred in a short amount of time by using many wires in

parallel, the distance cannot be great. To transfer to a device located many meters

away, the serial method is used. In serial communication, the data is sent one bit at

a time, in contrast to parallel communication, in which the data is sent a byte or

more at a time. Serial communication of the 8051 is the topic of this chapter. The

8051 has serial communication capability built into it, there by making possible fast

data transfer using only a few wires.

If data is to be transferred on the telephone line, it must be converted from

0s and 1s to audio tones, which are sinusoidal-shaped signals. A peripheral device


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called a modem, which stands for modulator/demodulator, performs this

conversion.

Serial data communication uses two methods, asynchronous and

synchronous. The synchronous method transfers a block of data at a time, while

the asynchronous method transfers a single byte at a time.

In data transmission if the data can be transmitted and received, it is a

duplex transmission. This is in contrast to simplex transmissions such as with

printers, in which the computer only sends data. Duplex transmissions can be half

or full duplex, depending on whether or not the data transfer can be simultaneous.

If data is transmitted one way at a time, it is referred to as half duplex. If the data

can go both ways at the same time, it is full duplex. Of course, full duplex requires

two wire conductors for the data lines, one for transmission and one for reception,

in order to transfer and receive data simultaneously.

Asynchronous serial communication and data framing

The data coming in at the receiving end of the data line in a serial data

transfer is all 0s and 1s; it is difficult to make sense of the data unless the sender

and receiver agree on a set of rules, a protocol, on how the data is packed, how

many bits constitute a character, and when the data begins and ends.

Start and stop bits

Asynchronous serial data communication is widely used for character-

oriented transmissions, while block-oriented data transfers use the synchronous

method. In the asynchronous method, each character is placed between start and

stop bits. This is called framing. In the data framing for asynchronous

communications, the data, such as ASCII characters, are packed between a start bit

and a stop bit. The start bit is always one bit, but the stop bit can be one or two bits.

The start bit is always a 0 (low) and the stop bit (s) is 1 (high).

Data transfer rate

The rate of data transfer in serial data communication is stated in bps (bits

per second). Another widely used terminology for bps is baud rate. However, the


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baud and bps rates are not necessarily equal. This is due to the fact that baud rate

is the modem terminology and is defined as the number of signal changes per

second. In modems a single change of signal, sometimes transfers several bits of

data. As far as the conductor wire is concerned, the baud rate and bps are the

same, and for this reason we use the bps and baud interchangeably.

The data transfer rate of given computer system depends on

communication ports incorporated into that system. For example, the early

IBMPC/XT could transfer data at the rate of 100 to 9600 bps. In recent years,

however, Pentium based PCS transfer data at rates as high as 56K bps. It must be

noted that in asynchronous serial data communication, the baud rate is generally

limited to 100,000bps.

RS232 Standards

To allow compatibility among data communication equipment made by

various manufacturers, an interfacing standard called RS232 was set by the

Electronics Industries Association (EIA) in 1960. In 1963 it was modified and called

RS232A. RS232B AND RS232C were issued in 1965 and 1969, respectively. Today,

RS232 is the most widely used serial I/O interfacing standard. This standard is used

in PCs and numerous types of equipment. However, since the standard was set

long before the advert of the TTL logic family, its input and output voltage levels arenot TTL compatible. In RS232, a 1 is represented by -3 to -25V, while a 0 bit is +3

to +25V, making -3 to +3 undefined. For this reason, to connect any RS232 to a

microcontroller system we must use voltage converters such as MAX232 to convert

the TTL logic levels to the RS232 voltage levels, and vice versa. MAX232 IC chips

are commonly referred to as line drivers.

RS232 pins

RS232 cable is commonly referred to as the DB-25 connector. In labeling, DB-25Prefers to the plug connector (male) and DB-25S is for the socket connector (female). Since not

all the pins are used in PC cables, IBM introduced the DB-9 Version of the serial I/O standard,

which uses 9 pins only, as shown in table.

DB-9 pin connector


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1 2 3 4 5

6 7 8 9

(Out of computer and exposed end of cable)

Pin Functions:

Pin Description1 Data carrier detect (DCD)2 Received data (RXD)3 Transmitted data (TXD)4 Data terminal ready(DTR)

5 Signal ground (GND)6 Data set ready (DSR)7 Request to send (RTS)8 Clear to send (CTS)9 Ring indicator (RI)

Note: DCD, DSR, RTS and CTS are active low pins.

The method used by RS-232 for communication allows for a simple connection of three lines:

Tx, Rx, and Ground. The three essential signals for 2-way RS-232

Communications are these:

TXD: carries data from DTE to the DCE.

RXD: carries data from DCE to the DTE

SG: signal ground

8051 connection to RS232

The RS232 standard is not TTL compatible; therefore, it requires a line

driver such as the MAX232 chip to convert RS232 voltage levels to TTL levels, and


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vice versa. The interfacing of 8051 with RS232 connectors via the MAX232 chip is

the main topic.

The 8051 has two pins that are used specifically for transferring

and receiving data serially. These two pins are called TXD and RXD and a part of the

port 3 group (P3.0 and P3.1). Pin 11 of the 8051 is assigned to TXD and pin 10 is

designated as RXD. These pins are TTL compatible; therefore, they require a line

driver to make them RS232 compatible. One such line driver is the MAX232 chip.

MAX232 converts from RS232 voltage levels to TTL voltage

levels, and vice versa. One advantage of the MAX232 chip is that it uses a +5V

power source which, is the same as the source voltage for the 8051. In the other

words, with a single +5V power supply we can power both the 8051 and MAX232,

with no need for the power supplies that are common in many older systems. The

MAX232 has two sets of line drivers for transferring and receiving data. The line

drivers used for TXD are called T1 and T2, while the line drivers for RXD are

designated as R1 and R2. In many applications only one of each is used.

Embedded

Controller

RXD

TXD

TXD

RXD2

3

5

GND

MAX 232

CONNECTING C to PC using MAX 232


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INTERRUPTS

A single microcontroller can serve several devices. There are two ways to do that:INTERRUPTS or POLLING.

POLLING:

In polling the microcontroller continuously monitors the status of a given device; when the status

condition is met, it performs the service .After that, it moves on to monitor the next device untileach one is serviced. Although polling can monitor the status of several devices and serve each

of them as certain condition are met.

INTERRUPTS:

In the interrupts method, whenever any device needs its service, the device

notifies the microcontroller by sending it an interrupts signal. Upon receiving an interrupt signal,

the microcontroller interrupts whatever it is doing and serves the device. The program associated

with the interrupts is called the interrupt service routine (ISR).or interrupt handler.

INTERRUPTS Vs POLLING:

The advantage of interrupts is that the microcontroller can serve many devices (not all the

same time, of course); each device can get the attention of the microcontroller based on the

priority assigned to it. The polling method cannot assign priority since it checks all devices in


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round-robin fashion. More importantly, in the interrupt method the microcontroller can also

ignore (mask) a device request for service. This is again not possible with the polling

method. The most important reason that the interrupt method is preferable is that the polling

method wastes much of the microcontrollers time by polling devices that do not need

service. So, in order to avoid tying down the microcontroller, interrupts are used.

INTERRUPT SERVICE ROUTINE

For every interrupt, there must be an interrupt service routine (ISR), or interrupt

handler. When an interrupt is invoked, the microcontroller runs the interrupts

service routine. For every interrupt, there is a fixed location in memory that holds

the address of its ISR. The group of memory location set aside to hold the addresses

of ISR and is called the Interrupt Vector Table. Shown below:

Interrupt Vector Table for the 8051:

S.No. INTERRUPT ROM

LOCATION

(HEX)

PIN FLAG

CLEARING

1. Reset 0000 9 Auto

2. External

hardware

Interrupt 0

0003 P3.2 (12) Auto

3. Timers 0 000B Auto


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interrupt

(TF0)

4. External

hardware

Interrupt

1(INT1)

0013 P3.3 (13) Auto

5. Timers 1

interrupt

(TF1)

001B Auto

6. Serial COM

(RI and TI)

0023 Programmer

clears it

Six Interrupts in the 8051:

In reality, only five interrupts are available to the user in the 8051, but many

manufacturers data sheets state that there are six interrupts since they include

reset .the six interrupts in the 8051 are allocated as above.

1. Reset. When the reset pin is activated, the 8051 jumps to address location

0000.this is the power-up reset.

2. Two interrupts are set aside for the timers: one for Timer 0 and one for Timer

1.Memory location 000BH and 001BH in the interrupt vector table belong to

Timer 0 and Timer 1, respectively.

3. Two interrupts are set aside for hardware external harder interrupts. Pin

number 12(P3.2) and 13(P3.3) in port 3 are for the external hardware

interrupts INT0 and INT1,respectively.These external interrupts are alsoreferred to as EX1 and EX2.Memory location 0003H and 0013H in the

interrupt vector table are assigned to INT0 and INT1, respectively.

4. Serial communication has a single interrupt that belongs to both receive and

transmit. The interrupt vector table location 0023H belongs to this interrupt.


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Notice that a limited number of bytes are set aside for each interrupt. For example,

a total of 8 bytes from location 0003 to 000A is set aside for INT0, external

hardware interrupt 0.similarly,a total of 8 bytes from location 00BH to 0012H is

reserved for TF0, Timer 0 interrupt. If the service routine for a given interrupt is

short enough to fit in the memory space allocated to it, it is placed in the vector

table; otherwise, and an LJMP instruction is placed in the vector table to point to the

address of the ISR. In that rest of the bytes allocated to that interrupt are unused.

From the above table also notice that only three bytes of ROM space are assigned

to the reset pin. they are ROM address location 0,1 and2.address location 3

belongs to external hardware interrupt 0.for this reason, in our program we put the

LJMP as the first instruction and redirect the processor away from the interrupt

vector table, as shown below

Steps in executing an interrupt

Upon activation of an interrupt, the microcontroller goes through the following

steps.

1. It finishes the instruction it is executing and saves the address of the next

instruction (PC) on the stack.

2. It also saves the current status of all the interrupts internally (i.e., not on the

stack).

3. It jumps to a fixed location in memory called the interrupt vector table that

holds the address of the interrupts service routine.

4. The microcontroller gets the address of the ISR from the interrupt vector

table and jumps to it. It starts to execute the interrupt service subroutine

until it reaches the last instruction of the subroutine, which is RETI (return

from interrupt).


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5. Upon executing the RETI instruction, the microcontroller returns to the place

where it was interrupted. First, it gets the program counter (PC) address from

the stack by popping the top two bytes of the stack into the PC. Then it starts

to execute from that address.

Notice from step 5 the critical role of the stack. For this reason, we must be

careful in manipulating the stack contents in the ISR. Specifically, in the ISR, just as

in any CALL subroutine, the number of pushes and pops must be equal.

Enabling and disabling an interrupt:

Upon reset, all interrupt are disabled (masked), meaning that none will be

responded to by the microcontroller if they are activated. The interrupt must be

enabled by software in order for the microcontroller to respond to them. There is a

register called IE (interrupt enable) that is responsible for enabling (unmasking) and

disabling (masking) the interrupts.

Notice that IE is a bit-addressable register.

Steps in enabling an interrupt:

To enable an interrupt, we take the following steps:

1. Bit D7 of the IE register (EA) must be set to high to allow the reset to take

effect.If EA=1, interrupts are enabled and will be responded to if their corresponding bit in

IE are high. If EA=0, no interrupt will be responded to, even if the associated bit in

the IE register is high.


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Interrupt Enable Register

D7 D6 D5 D4 D3 D2 D1 D0

EA IE.7 disables all interrupts. If EA=0, no interrupts is acknowledged.

If EA=1, each interrupt source is individually enabled disabled

By setting or clearing its enable bit.

-- IE.6 Not implemented, reserved for future use.*

ET2 IE.5 Enables or disables Timer 2 overflow or capture interrupt (8052

Only)

ES IE.4 Enables or disables the serial port interrupts.

ET1 IE.3 Enables or disables Timers 1 overflow interrupt

EX1 IE.2 Enables or disables external interrupt 1.

ET0 IE.1 Enables or disables Timer 0 overflow interrupt.

EX0 IE.0 Enables or disables external interrupt.

Power supply

EA -- ET2 ES ET1 EX1 ET0


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The power supplies 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.

A d.c power supply which maintains the output voltage constant irrespective of a.c mains

fluctuations or load variations is known as Regulated D.C Power Supply

For example a 5V regulated power supply system as shown below:

Transformer:

A transformer is an electrical device which is used to convert

electrical power from one Electrical circuit to another without change in frequency.

Transformers convert AC electricity from one voltage to another with little loss of power.

Transformers work only with AC and this is one of the reasons why mains electricity is AC.

Step-up transformers increase in output voltage, step-down transformers decrease in output


56/102

voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains

voltage to a safer low voltage. The input coil is called the primary and the output coil is called

the secondary. There is no electrical connection between the two coils; instead they are linked by

an alternating magnetic field created in the soft-iron core of the transformer. The two lines in the

middle of the circuit symbol represent the core. Transformers waste very little power so the

power out is (almost) equal to the power in. Note that as voltage is stepped down current is

stepped up. The ratio of the number of turns on each coil, called the turns ratio, determines the

ratio of the voltages. A step-down transformer has a large number of turns on its primary (input)

coil which is connected to the high voltage mains supply, and a small number of turns on its

secondary (output) coil to give a low output voltage.

An Electrical Transformer

Turns ratio = Vp/ VS = Np/NS

Power Out= Power In

VS X IS=VP X IP

Vp = primary (input) voltage

Np = number of turns on primary coilIp = primary (input) current


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RECTIFIER:

A circuit which is used to convert a.c to dc is known as RECTIFIER. The

process of conversion a.c to d.c is called rectification

TYPES OF RECTIFIERS:

Half wave Rectifier Full wave rectifier

1. Centre tap full wave rectifier.

2. Bridge type full bridge rectifier.

Comparison of rectifier circuits:

Parameter

Type of Rectifier

Half wave Full wave

Bridge

Number of diodes

1

2

4

PIV of diodes

Vm

2Vm Vm

D.C output voltage

Vm/

2Vm/

2Vm/


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Vdc,at

no-load

0.318Vm

0.636Vm 0.636Vm

Ripple factor

1.21

0.482

0.482

Ripple

frequency

f 2f

2f

Rectification

efficiency

0.406

0.812

0.812

Transformer

Utilization

Factor(TUF)

0.287 0.693 0.812

RMS voltage Vrms Vm/2 Vm/2 Vm/2

Full-wave Rectifier:

From the above comparision we came to know that full wave bridge rectifier as

more advantages than the other two rectifiers. So, in our project we are using full

wave bridge rectifier circuit.

Bridge Rectifier: A bridge rectifier makes use of four diodes in a bridge arrangement to achieve

full-wave rectification. This is a widely used configuration, both with individual diodes

wired as shown and with single component bridges where the diode bridge is wired

internally.

A bridge rectifier makes use of four diodes in a bridge arrangement as shown

in fig(a) to achieve full-wave rectification. This is a widely used configuration, both

with individual diodes wired as shown and with single component bridges where the

diode bridge is wired internally.


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Fig(A)

Operation:

During positive half cycle of secondary, the diodes D2 and D3 are in forward biased

while D1 and D4 are in reverse biased as shown in the fig(b). The current flow

direction is shown in the fig (b) with dotted arrows.

Fig(B)


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During negative half cycle of secondary voltage, the diodes D1 and D4 are in

forward biased while D2 and D3 are in reverse biased as shown in the fig(c). The

current flow direction is shown in the fig (c) with dotted arrows.

Fig(C)

Filter:

A Filter is a device which removes the a.c component of rectifier

output

but allows the d.c component to reach the load

Capacitor Filter:

We have seen that the ripple content in the rectified output of half waverectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48%

such high percentages of ripples is not acceptable for most of the applications.

Ripples can be removed by one of the following methods of filtering.


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(a) A capacitor, in parallel to the load, provides an easier by pass for the ripples

voltage though it due to low impedance. At ripple frequency and leave the d.c.to

appears the load.

(b) An inductor, in series with the load, prevents the passage of the ripple current

(due to high impedance at ripple frequency) while allowing the d.c (due to low

resistance to d.c)

(c) various combinations of capacitor and inductor, such as L-section filter

section filter, multiple section filter etc. which make use of both the properties

mentioned in (a) and (b) above. Two cases of capacitor filter, one applied on half

wave rectifier and another with full wave rectifier.

Filtering is performed by a large value electrolytic capacitor connected across the DC

supply to act as a reservoir, supplying current to the output when the varying DC voltage from

the rectifier is falling. The capacitor charges quickly near the peak of the varying DC, and then

discharges as it supplies current to the output. Filtering significantly increases the average DC

voltage to almost the peak value (1.4 RMS value).

To calculate the value of capacitor(C),

C = *3*f*r*Rl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000F Hence large value of capacitor is placed to

reduce ripples and to improve the DC component.

Regulator:


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Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable

output voltages. The maximum current they can pass also rates them. Negative

voltage regulators are available, mainly for use in dual supplies. Most regulators

include some automatic protection from excessive current ('overload protection')

and overheating ('thermal protection'). Many of the fixed voltage regulator ICs have

3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown

on the right. The LM7805 is simple to use. You simply connect the positive lead of

your unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin,

connect the negative lead to the Common pin and then when you turn on the

power, you get a 5 volt supply from the output pin.

Fig 6.1.6 A Three Terminal Voltage Regulator

78XX:

The Bay Linear LM78XX is integrated linear positive regulator with three

terminals. The LM78XX offer several fixed output voltages making them useful in

wide range of applications. When used as a zener diode/resistor combination

replacement, the LM78XX usually results in an effective output impedance

improvement of two orders of magnitude, lower quiescent current. The LM78XX is

available in the TO-252, TO-220 & TO-263packages,

Features:

Output Current of 1.5A


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Output Voltage Tolerance of 5%

Internal thermal overload protection

Internal Short-Circuit Limited

No External Component

Output Voltage 5.0V, 6V, 8V, 9V, 10V,12V, 15V, 18V, 24V

Offer in plastic TO-252, TO-220 & TO-263

Direct Replacement for LM78XX

MAX-232:The MAX232 from Maxim was the first IC which in one package contains the necessary drivers(two) and receivers (also two), to adapt the RS-232 signal voltage levels to TTL logic. It becamepopular, because it just needs one voltage (+5V) and generates the necessary RS-232 voltagelevels (approx. -10V and +10V) internally. This greatly simplified the design of circuitry.Circuitry designers no longer need to design and build a power supply with three voltages (e.g.-12V, +5V, and +12V), but could just provide one +5V power supply, e.g. with the help of asimple 78x05 voltage converter.

The MAX232 has a successor, the MAX232A. The ICs are almost identical, however, the

MAX232A is much more often used (and easier to get) than the original MAX232, and theMAX232A only needs external capacitors 1/10th the capacity of what the original MAX232needs.

It should be noted that the MAX 232(A) is just a driver/receiver. It does not generate thenecessary RS-232 sequence of marks and spaces with the right timing, it does not decode the RS-232 signal, it does not provide a serial/parallel conversion. All it does is to convert signalvoltage levels. Generating serial data with the right timing and decoding serial data has to bedone by additional circuitry, e.g. by a 16550 UART or one of these small micro controllers (e.g.Atmel AVR, Microchip PIC) getting more and more popular.

The MAX232 and MAX232A were once rather expensive ICs, but today they are cheap. It hasalso helped that many companies now produce clones (ie. Sipex). These clones sometimes needdifferent external circuitry, e.g. the capacities of the external capacitors vary. It is recommendedto check the data sheet of the particular manufacturer of an IC instead of relying on Maxim'soriginal data sheet.

The original manufacturer (and now some clone manufacturers, too) offers a large series ofsimilar ICs, with different numbers of receivers and drivers, voltages, built-in or external
http://www.maxim-ic.com/http://en.wikibooks.org/wiki/Serial_Programming:8250_UART_Programminghttp://en.wikibooks.org/wiki/Atmel_AVRhttp://en.wikibooks.org/wiki/Embedded_Systems/PIC_Microcontrollerhttp://www.sipex.com/products/interface.htmhttp://www.maxim-ic.com/http://en.wikibooks.org/wiki/Serial_Programming:8250_UART_Programminghttp://en.wikibooks.org/wiki/Atmel_AVRhttp://en.wikibooks.org/wiki/Embedded_Systems/PIC_Microcontrollerhttp://www.sipex.com/products/interface.htm


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capacitors, etc. E.g. The MAX232 and MAX232A need external capacitors for the internalvoltage pump, while the MAX233 has these capacitors built-in. The MAX233 is also betweenthree and ten times more expensive in electronic shops than the MAX232A because of itsinternal capacitors. It is also more difficult to get the MAX233 than the garden varietyMAX232A.

A Typical Application

The MAX 232(A) has two receivers (converts from RS-232 to TTL voltage levels) and twodrivers (converts from TTL logic to RS-232 voltage levels). This means only two of the RS-232signals can be converted in each direction. The old MC1488/1498 combo provided four driversand receivers.

Typically a pair of a driver/receiver of the MAX232 is used for

TX and RX

And the second one for

CTS and RTS.

There are not enough drivers/receivers in the MAX232 to also connect the DTR, DSR, and DCDsignals. Usually these signals can be omitted when e.g. communicating with a PC's serialinterface. If the DTE really requires these signals either a second MAX232 is needed, or someother IC from the MAX232 family can be used (if it can be found in consumer electronic shopsat all). An alternative for DTR/DSR is also given below.

Maxim's data sheet explains the MAX232 family in great detail, including the pin configurationand how to connect such an IC to external circuitry. This information can be used as-is in owndesign to get a working RS-232 interface. Maxim's data just misses one critical piece ofinformation: How exactly to connect the RS-232 signals to the IC. So here is one possibleexample:

MAX232 to RS232 DB9 Connection as a DCE

MAX232 Pin

Nbr.

MAX232 Pin

Name

Sign

al

Volta

ge

DB9

Pin

7 T2out CTSRS-

2327

8 R2in RTSRS-

2328
http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdfhttp://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf


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9 R2out RTS TTL n/a

10 T2in CTS TTL n/a

11 T1in TX TTL n/a

12 R1out RX TTL n/a

13 R1in TXRS-

2323

14 T1out RXRS-

2322

15 GND GND 0 5

In addition one can directly wire DTR (DB9 pin 4) to DSR (DB9 pin 6) without going throughany circuitry. This gives automatic (brain dead) DSR acknowledgment of an incoming DTRsignal.

Sometimes pin 6 of the MAX232 is hard wired to DCD (DB9 pin 1). This is not recommended.Pin 6 is the raw output of the voltage pump and inverter for the -10V voltage. Drawing currents

from the pin leads to a rapid breakdown of the voltage, and as a consequence to a breakdown ofthe output voltage of the two RS-232 drivers. It is better to use software which doesn't care aboutDCD, but does hardware-handshaking via CTS/RTS only.

The circuitry is completed by connecting five capacitors to the IC as it follows. The MAX232needs 1.0F capacitors, the MAX232A needs 0.1F capacitors. MAX232 clones show similardifferences. It is recommended to consult the corresponding data sheet. At least 16V capacitortypes should be used. If electrolytic or tantalic capacitors are used, the polarity has to beobserved. The first pin as listed in the following table is always where the plus pole of thecapacitor should be connected to.

MAX232(A) external Capacitors

Capaci

tor

+

Pin

-

PinRemark

C1 1 3


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C2 4 5

C3 2 16

C4GN

D6

This looks non-intuitive, but becausepin 6 is

on -10V, GND gets the + connector, and

not the -

C5 16GN

D

The 5V power supply is connected to

+5V: Pin 16 GND: Pin 15

Features

Meet or Exceed TIA/EIA-232-F and ITURecommendation V.28

Operate With Single 5-V Power Supply Operate Up to 120 kbit/s Two Drivers and Two Receivers 30-V Input Levels Low Supply Current . . . 8 mA Typical

Designed to be Interchangeable WithMaxim MAX232

ESD Protection Exceeds JESD 222000-V Human-Body Model (A114-A)

ApplicationsTIA/EIA-232-F


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Battery-Powered Systems

Terminals

Modems

Computers

Description/ordering information

The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to supply EIA-232

voltage levels from a single 5-V supply. Each receiver converts EIA-232 inputs to 5-V TTL/CMOS levels.

These receivers have a typical threshold of 1.3 V and a typical hysteresis of 0.5 V, and can accept 30-V

inputs. Each driver converts TTL/CMOS input levels into EIA-232 levels. The driver, receiver, and voltage-

generator functions are available as cells in the Texas Instruments Lin ASIC library.


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RELAYS

Relay is an electrically operated switch. Current flowing through the coil of the

relay creates a magnetic field which attracts a lever and changes the switch

contacts. The coil current can be on or off so relays have two switch positions and

they are double throw (changeover) switches.

Relays allow one circuit to switch a second circuit which can be completely

separate from the first. For example a low voltage battery circuit can use a relay to

switch a 230V AC mains circuit. There is no electrical connection inside the relay

between the two circuits; the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V

relay, but it can be as much as 100mA for relays designed to operate from lower

voltages. Most ICs (chips) cannot provide this current and a transistor is usually

used to amplify the small IC current to the larger value required for the relay coil.


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The maximum output current for the popular 555 timer IC is 200mA so these

devices can supply relay coils directly without amplification.

Relays are usually SPDT or DPDT but they can have many more sets of switch

contacts, for example relays with 4 sets of changeover contacts are readilyavailable. For further information about switch contacts and the terms used to

describe them please see the page on switches.

Most relays are designed for PCB mounting but you can solder wires directly

to the pins providing you take care to avoid melting the plastic case of the relay.

The supplier's catalogue should show you the relay's connections. The coil will be

obvious and it may be connected either way round. Relay coils produce brief high

voltage 'spikes' when they are switched off and this can destroy transistors and ICs

in the circuit. To prevent damage you must connect a protection diode across the

relay coil.

The animated picture shows a working relay with its coil and switch contacts.

You can see a lever on the left being attracted by magnetism when the coil is

switched on. This lever moves the switch contacts. There is one set of contacts

(SPDT) in the foreground and another behind them, making the relay DPDT.

The relay's switch connections are usually labelled COM, NC and

NO:

COM = Common, always connect to this, it is the moving part of the switch.
http://www.kpsec.freeuk.com/components/relay.htm#protecthttp://www.kpsec.freeuk.com/components/relay.htm#protect


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NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when the

relay coil is on.

Connect to COM and NC if you want the switched circuit to be on when the

relay coil is off.

Choosing a relay

You need to consider several features when choosing a relay:

1. Physical size and pin arrangement If you are choosing a relay for an existing

PCB you will need to ensure that its dimensions and pin arrangement are

suitable. You should find this information in the supplier's catalogue.

2. Coil voltage the relay's coil voltage rating and resistance must suit the circuit

powering the relay coil. Many relays have a coil rated for a 12V supply but 5V

and 24V relays are also readily available. Some relays operate perfectly well

with a supply voltage which is a little lower than their rated value.

3. Coil resistance the circuit must be able to supply the current required by the

relay coil. You can use Ohm's law to calculate the current:

Relay coil

current =

supplyvoltage

coil

resistance

4. For example: A 12V supply relay with a coil resistance of 400 passes a

current of 30mA. This is OK for a 555 timer IC (maximum output current

200mA), but it is too much for most ICs and they will require a transistor to

amplify the current.

5. Switch ratings (voltage and current) the relay's switch contacts must be

suitable for the circuit they are to control. You will need to check the voltage

and current ratings. Note that the voltage rating is

Documents

2.Pc Based Controlling Devices in Industriesabstract