automatic college bell ring system

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AUTOMATIC COLLEGE BELL RING SYSTEM

DESCRIPTION:

Manual operation of school bell / college bell is a mundane task prone to human errors. If

the bell operator forgets to ring it for a specific period, or delayed to ring the bell, it will create

disturbances for the entire institution. Automatic Periodic College Bell is the only solution to

avoid all these problems.

This project is very useful in schools, colleges and educational / academic institutions for

automation of periodic class bell. This bell rings only at preprogrammed timings. As the C# front

end is used, the entire calendar can be programmed into the C# application. User set the alarm in

software. According to that set values alarm will on. Microcontroller is connected to PC through

serial communication. C# application always interact with serial port and according to alarm set

values application gives signals to microcontroller. Microcontroller takes values from serial port

and generates alarm through buzzer (or relay). In C# application we can set 10 alarms at a time.

This project uses regulated 5V, 500mA power supply. Unregulated 12V DC is used for

relay. 7805 three terminal voltage regulator is used for voltage regulation. Full wave bridge

rectifier is used to rectify the ac output of secondary of 230/12V step down transformer. Max-

232 is used as a serial driver. It supports different types of baud rates (1200, 2400, 4800,

9600……) in kbps.

H-no: 8-3-800/6/B, First floor, PJR statue lane, Yella reddy Guda, Ameerpet, Hyderabad-73

Mobile: +91 8142 56 63 12, 9704 83 68 91, 9490 37 27 73. Website: www.amvitech.com

E-mail: [email protected], [email protected]

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TECHNICAL SPECIFICATIONS:

HARDWARE:

Micro controller : AT89X series

Crystal : 11.0592 MHz

Serial driver : Max-232

Buzzer

Power supply

Transformer : 12V step down

Filter : 1000uf/25V

Voltage Regulator : 7805

SOFTWARE:

Keil micro vision

Proteus

UC flash

C# .net application




Step down Transformer Filter Regulator Output Bridge Rectifier

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BLOCK DIAGRAM:

POWER SUPPLY BLOCK DIAGRM:




8

05

1

Power Supply PC(C# .net application)

BUZZER

Or Relay

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Schematic:




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EMBEDDED SYSTEMS:

Introduction:

An embedded system is a system which is going to do a predefined specified task

is the embedded system and is even defined as combination of both software and hardware. A

general-purpose definition of embedded systems is that they are devices used to control, monitor

or assist the operation of equipment, machinery or plant. "Embedded" reflects the fact that they

are an integral part of the system. At the other extreme a general-purpose computer may be used

to control the operation of a large complex processing plant, and its presence will be obvious.

All embedded systems are including computers or microprocessors. Some of

these computers are however very simple systems as compared with a personal computer.

The very simplest embedded systems are capable of performing only a single

function or set of functions to meet a single predetermined purpose. In more complex systems an

application program that enables the embedded system to be used for a particular purpose in a

specific application determines the functioning of the embedded system. The ability to have

programs means that the same embedded system can be used for a variety of different purposes.

In some cases a microprocessor may be designed in such a way that application software for a

particular purpose can be added to the basic software in a second process, after which it is not

possible to make further changes. The applications software on such processors is sometimes

referred to as firmware.

The simplest devices consist of a single microprocessor (often called a "chip”),

which may itself be packaged with other chips in a hybrid system or Application Specific

Integrated Circuit (ASIC). Its input comes from a detector or sensor and its output goes to a

switch or activator which (for example) may start or stop the operation of a machine or, by

operating a valve, may control the flow of fuel to an engine.




Software Hardware

ALPCVB Etc.,

ProcessorPeripheralsmemory

Embedded System

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As the embedded system is the combination of both software and hardware

Figure: Block diagram of Embedded System

Software deals with the languages like ALP, C, and VB etc., and Hardware deals with

Processors, Peripherals, and Memory.

Memory: It is used to store data or address.

Peripherals: These are the external devices connected

Processor: It is an IC which is used to perform some task

Applications of embedded systems

Manufacturing and process control

Construction industry

Transport

Buildings and premises

Domestic service




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Communications

Office systems and mobile equipment

Banking, finance and commercial

Medical diagnostics, monitoring and life support

Testing, monitoring and diagnostic systems

Processors are classified into four types like:

Micro Processor (µp)

Micro controller (µc)

Digital Signal Processor (DSP)

Application Specific Integrated Circuits (ASIC)

Micro Processor (µp):

A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor

and CPU are used interchangeably. At the heart of all personal computers and most workstations

sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from

clock radios to fuel-injection systems for automobiles.

Three basic characteristics differentiate microprocessors:

Instruction set: The set of instructions that the microprocessor can execute.

Bandwidth : The number of bits processed in a single instruction.

Clock speed : Given in megahertz (MHz), the clock speed determines how many

instructions per second the processor can execute.

In both cases, the higher the value, the more powerful the CPU. For example, a 32-bit

microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at

25MHz. In addition to bandwidth and clock speed, microprocessors are classified as being either

RISC (reduced instruction set computer) or CISC (complex instruction set computer).




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A microprocessor has three basic elements, as shown above. The ALU performs all

arithmetic computations, such as addition, subtraction and logic operations (AND, OR, etc). It is

controlled by the Control Unit and receives its data from the Register Array. The Register Array

is a set of registers used for storing data. These registers can be accessed by the ALU very

quickly. Some registers have specific functions - we will deal with these later. The Control Unit

controls the entire process. It provides the timing and a control signal for getting data into and

out of the registers and the ALU and it synchronizes the execution of instructions (we will deal

with instruction execution at a later date).

Three Basic Elements of a Microprocessor

Micro Controller (µc):

A microcontroller is a small computer on a single integrated circuit containing a processor core,

memory, and programmable input/output peripherals. Program memory in the form of NOR

flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM.




http://en.wikipedia.org/wiki/Programmable_read-only_memory

http://en.wikipedia.org/wiki/NOR_flash

http://en.wikipedia.org/wiki/NOR_flash

http://en.wikipedia.org/wiki/Input/output

http://en.wikipedia.org/wiki/Integrated_circuit

Timer, Counter, serial communication ROM, ADC, DAC, Timers, USART, Oscillators

Etc.,

ALU

CU

Memory

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Microcontrollers are designed for embedded applications, in contrast to the microprocessors used

in personal computers or other general purpose applications.

Figure: Block Diagram of Micro Controller (µc)

Digital Signal Processors (DSPs):

Digital Signal Processors is one which performs scientific and mathematical operation. Digital

Signal Processor chips - specialized microprocessors with architectures designed specifically for

the types of operations required in digital signal processing. Like a general-purpose

microprocessor, a DSP is a programmable device, with its own native instruction code. DSP

chips are capable of carrying out millions of floating point operations per second, and like their

better-known general-purpose cousins, faster and more powerful versions are continually being

introduced. DSPs can also be embedded within complex "system-on-chip" devices, often

containing both analog and digital circuitry.

Application Specific Integrated Circuit (ASIC)

ASIC is a combination of digital and analog circuits packed into an IC to achieve the desired

control/computation function




http://en.wikipedia.org/wiki/Personal_computer

http://en.wikipedia.org/wiki/Microprocessor

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ASIC typically contains

CPU cores for computation and control

Peripherals to control timing critical functions

Memories to store data and program

Analog circuits to provide clocks and interface to the real world which is analog in

nature

I/Os to connect to external components like LEDs, memories, monitors etc.

Computer Instruction Set

There are two different types of computer instruction set there are:

1. RISC (Reduced Instruction Set Computer) and

2. CISC (Complex Instruction Set computer)

Reduced Instruction Set Computer (RISC)

A RISC (reduced instruction set computer) is a microprocessor that is designed to perform a

smaller number of types of computer instruction so that it can operate at a higher speed (perform

more million instructions per second, or millions of instructions per second). Since each

instruction type that a computer must perform requires additional transistors and circuitry, a

larger list or set of computer instructions tends to make the microprocessor more complicated

and slower in operation.




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Besides performance improvement, some advantages of RISC and related design improvements

are:

A new microprocessor can be developed and tested more quickly if one of its aims is to

be less complicated.

Operating system and application programmers who use the microprocessor's instructions

will find it easier to develop code with a smaller instruction set.

The simplicity of RISC allows more freedom to choose how to use the space on a

microprocessor.

Higher-level language compilers produce more efficient code than formerly because they have

always tended to use the smaller set of instructions to be found in a RISC computer.

RISC characteristics

Simple instructions.

In a RISC machine, the instruction set contains simple, basic instructions, from which more

complex instructions can be composed.

Same length instructions.

Each instruction is the same length, so that it may be fetched in a single operation.

1machine-cycle instructions.

Most instructions complete in one machine cycle, which allows the processor to handle several

instructions at the same time. This pipelining is a key technique used to speed up RISC

machines.

Complex Instruction Set Computer (CISC)




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CISC, which stands for Complex Instruction Set Computer, is a philosophy for designing

chips that are easy to program and which make efficient use of memory. Each instruction in a

CISC instruction set might perform a series of operations inside the processor. This reduces the

number of instructions required to implement a given program, and allows the programmer to

learn a small but flexible set of instructions.

The advantages of CISC

At the time of their initial development, CISC machines used available technologies to optimize

Computer performance.

Microprogramming is as easy as assembly language to implement, and much less

expensive than hardwiring a control unit.

The ease of micro-coding new instructions allowed designers to make CISC machines

upwardly compatible: a new computer could run the same programs as earlier computers because

the new computer would contain a superset of the instructions of the earlier computers.

As each instruction became more capable, fewer instructions could be used to implement

a given task. This made more efficient use of the relatively slow main memory.

Because micro program instruction sets can be written to match the constructs of high-

level languages, the compiler does not have to be as complicated.

The disadvantages of CISC

Still, designers soon realized that the CISC philosophy had its own problems, including:

Earlier generations of a processor family generally were contained as a subset in every

new version --- so instruction set & chip hardware become more complex with each generation

of computers.

So that as many instructions as possible could be stored in memory with the least possible

wasted space, individual instructions could be of almost any length---this means that different




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instructions will take different amounts of clock time to execute, slowing down the overall

performance of the machine.

Many specialized instructions aren't used frequently enough to justify their existence ---

approximately 20% of the available instructions are used in a typical program.

CISC instructions typically set the condition codes as a side effect of the instruction. Not

only does setting the condition codes take time, but programmers have to remember to examine

the condition code bits before a subsequent instruction changes them.

Memory Architecture

There two different type’s memory architectures there are:

Harvard Architecture

Von-Neumann Architecture

Harvard Architecture

Computers have separate memory areas for program instructions and data. There are two or more

internal data buses, which allow simultaneous access to both instructions and data. The CPU

fetches program instructions on the program memory bus.

The Harvard architecture is a computer architecture with physically separate storage and signal

pathways for instructions and data. The term originated from the Harvard Mark I relay-based

computer, which stored instructions on punched tape (24 bits wide) and data in electro-




http://en.wikipedia.org/wiki/Punched_tape

http://en.wikipedia.org/wiki/Harvard_Mark_I

http://en.wikipedia.org/wiki/Computer_storage

http://en.wikipedia.org/wiki/Computer_architecture

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mechanical counters. These early machines had limited data storage, entirely contained within

the central processing unit, and provided no access to the instruction storage as data. Programs

needed to be loaded by an operator, the processor could not boot itself.

Figure: Harvard Architecture

Modern uses of the Harvard architecture:

The principal advantage of the pure Harvard architecture - simultaneous access to more than one

memory system - has been reduced by modified Harvard processors using modern CPU cache

systems. Relatively pure Harvard architecture machines are used mostly in applications where

tradeoffs, such as the cost and power savings from omitting caches, outweigh the programming

penalties from having distinct code and data address spaces.

Digital signal processors (DSPs) generally execute small, highly-optimized audio or

video processing algorithms. They avoid caches because their behavior must be extremely

reproducible. The difficulties of coping with multiple address spaces are of secondary concern to

speed of execution. As a result, some DSPs have multiple data memories in distinct address

spaces to facilitate SIMD and VLIW processing. Texas Instruments TMS320 C55x processors,

as one example, have multiple parallel data busses (two write, three read) and one instruction

bus.




http://en.wikipedia.org/wiki/Texas_Instruments_TMS320

http://en.wikipedia.org/wiki/VLIW

http://en.wikipedia.org/wiki/SIMD

http://en.wikipedia.org/wiki/Digital_signal_processors

http://en.wikipedia.org/wiki/CPU_cache

http://en.wikipedia.org/wiki/Booting

http://en.wikipedia.org/wiki/Central_processing_unit

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Microcontrollers are characterized by having small amounts of program (flash memory)

and data (SRAM) memory, with no cache, and take advantage of the Harvard architecture to

speed processing by concurrent instruction and data access. The separate storage means the

program and data memories can have different bit depths, for example using 16-bit wide

instructions and 8-bit wide data. They also mean that instruction pre-fetch can be performed in

parallel with other activities. Examples include, the AVR by Atmel Corp, the PIC by Microchip

Technology, Inc. and the ARM Cortex-M3 processor (not all ARM chips have Harvard

architecture).

Even in these cases, it is common to have special instructions to access program memory as data

for read-only tables, or for reprogramming.

Von-Neumann Architecture

A computer has a single, common memory space in which both program instructions and data

are stored. There is a single internal data bus that fetches both instructions and data. They cannot

be performed at the same time

The von Neumann architecture is a design model for a stored-program digital computer that

uses a central processing unit (CPU) and a single separate storage structure ("memory") to hold

both instructions and data. It is named after the mathematician and early computer scientist John

von Neumann. Such computers implement a universal Turing machine and have a sequential

architecture.

A stored-program digital computer is one that keeps its programmed instructions, as well as its

data, in read-write, random-access memory (RAM). Stored-program computers were

advancement over the program-controlled computers of the 1940s, such as the Colossus and the

ENIAC, which were programmed by setting switches and inserting patch leads to route data and

to control signals between various functional units. In the vast majority of modern computers, the




http://en.wikipedia.org/wiki/ARM_architecture

http://en.wikipedia.org/wiki/Microchip_Technology

http://en.wikipedia.org/wiki/Microchip_Technology

http://en.wikipedia.org/wiki/PIC_microcontroller

http://en.wikipedia.org/wiki/Atmel

http://en.wikipedia.org/wiki/Atmel_AVR

http://en.wikipedia.org/wiki/Instruction_prefetch

http://en.wikipedia.org/wiki/SRAM

http://en.wikipedia.org/wiki/Flash_memory

http://en.wikipedia.org/wiki/Microcontrollers

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same memory is used for both data and program instructions. The mechanisms for transferring

the data and instructions between the CPU and memory are, however, considerably more

complex than the original von Neumann architecture.

The terms "von Neumann architecture" and "stored-program computer" are generally used

interchangeably, and that usage is followed in this article.

Figure: Schematic of the Von-Neumann Architecture.

Basic Difference between Harvard and Von-Neumann Architecture

The primary difference between Harvard architecture and the Von Neumann architecture

is in the Von Neumann architecture data and programs are stored in the same memory and

managed by the same information handling system.

Whereas the Harvard architecture stores data and programs in separate memory devices

and they are handled by different subsystems.

In a computer using the Von-Neumann architecture without cache; the central processing

unit (CPU) can either be reading and instruction or writing/reading data to/from the memory.

Both of these operations cannot occur simultaneously as the data and instructions use the same

system bus.




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In a computer using the Harvard architecture the CPU can both read an instruction and

access data memory at the same time without cache. This means that a computer with Harvard

architecture can potentially be faster for a given circuit complexity because data access and

instruction fetches do not contend for use of a single memory pathway.

Today, the vast majority of computers are designed and built using the Von Neumann

architecture template primarily because of the dynamic capabilities and efficiencies gained in

designing, implementing, operating one memory system as opposed to two. Von Neumann

architecture may be somewhat slower than the contrasting Harvard Architecture for certain

specific tasks, but it is much more flexible and allows for many concepts unavailable to Harvard

architecture such as self programming, word processing and so on.

Harvard architectures are typically only used in either specialized systems or for very

specific uses. It is used in specialized digital signal processing (DSP), typically for video and

audio processing products. It is also used in many small microcontrollers used in electronics

applications such as Advanced RISK Machine (ARM) based products for many vendors.




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THE MICROCONTROLLER:

A microcontroller is a general purpose device, but that is meant to read data, perform

limited calculations on that data and control its environment based on those calculations. The

prime use of a microcontroller is to control the operation of a machine using a fixed program that

is stored in ROM and that does not change over the lifetime of the system.

The microcontroller design uses a much more limited set of single and double byte

instructions that are used to move data and code from internal memory to the ALU. The

microcontroller is concerned with getting data from and to its own pins; the architecture and

instruction set are optimized to handle data in bit and byte size.

The AT89C51 is a low-power, high-performance CMOS 8-bit microcontroller with 4k

bytes of Flash Programmable and erasable read only memory (EROM). The device is

manufactured using Atmel’s high-density nonvolatile memory technology and is functionally

compatible with the industry-standard 80C51 microcontroller instruction set and pin out. By

combining versatile 8-bit CPU with Flash on a monolithic chip, the Atmel’s AT89c51 is a

powerful microcomputer, which provides a high flexible and cost- effective solution to many

embedded control applications.

AT89C51 MICROCONTROLLER

FEATURES

80C51 based architecture

4-Kbytes of on-chip Reprogrammable Flash Memory

128 x 8 RAM

Two 16-bit Timer/Counters




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Full duplex serial channel

Boolean processor

Four 8-bit I/O ports, 32 I/O lines

Memory addressing capability

– 64K ROM and 64K RAM

Power save modes:

– Idle and power-down

Six interrupt sources

Most instructions execute in 0.3 us

CMOS and TTL compatible

Maximum speed: 40 MHz @ Vcc = 5V

Industrial temperature available

Packages available:

– 40-pin DIP

– 44-pin PLCC

– 44-pin PQFP




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Pin configuration:




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AT89C51 Block Diagram




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PIN DESCRIPTION:

VCC

Supply voltage

GND

Ground

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 can also be configured to be the multiplexed low order address/data bus during

access to external program and data memory. In this mode, P 0 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 1output buffers

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

internal pull-ups can be used as inputs. As inputs, Port 1 pins that are externally being pulled low

will source current (1) because of the internal pull-ups.

Port 2




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



will source current because of the internal pull-ups.

Port 2 emits the high-order address byte during fetches from external program memory

and during access to DPTR. In this application Port 2 uses strong internal pull-ups when emitting

1s. During accesses to external data memory that use 8-bit data address (MOVX@R1), 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 3 output buffers



will source current because of the internal pull-ups.

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

Port pin Alternate Functions

P3.0 RXD(serial input port)

P3.1 TXD(serial input port)




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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)

P3.6 WR(external data memory write strobe)

P3.7 RD(external data memory read strobe)

RST

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

ALE/PROG:

Address Latch Enable is an output pulse for latching the low byte of the address during

access 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 1/16 the oscillator frequency and may be

used for external timing or clocking purpose. Note, however, that one ALE pulse is skipped

during each access to external Data memory.

PSEN




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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 when 12-volt programming is selected.

XTAL1

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

XTAL 2

Output from the inverting oscillator amplifier.

OPERATING DESCRIPTION

The detail description of the AT89C51 included in this description is:

• Memory Map and Registers

• Timer/Counters

• Interrupt System




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MEMORY MAP AND REGISTERS

Memory

The AT89C51 has separate address spaces for program and data memory. The program

and data memory can be up to 64K bytes long. The lower 4K program memory can reside on-

chip. The AT89C51 has 128 bytes of on-chip RAM.

The lower 128 bytes can be accessed either by direct addressing or by indirect

addressing. The lower 128 bytes of RAM can be divided into 3 segments as listed below

1. Register Banks 0-3: locations 00H through 1FH (32 bytes). The device after reset defaults to

register bank 0. To use the other register banks, the user must select them in software. Each

register bank contains eight 1-byte registers R0-R7. Reset initializes the stack point to location

07H, and is incremented once to start from 08H, which is the first register of the second register

bank.

2. Bit Addressable Area: 16 bytes have been assigned for this segment 20H-2FH. Each one of

the 128 bits of this segment can be directly addressed (0-7FH). Each of the 16 bytes in this

segment can also be addressed as a byte.

3. Scratch Pad Area: 30H-7FH are available to the user as data RAM. However, if the data

pointer has been initialized to this area, enough bytes should be left aside to prevent SP data

destruction.




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SPECIAL FUNCTION REGISTERS:

The Special Function Registers (SFR's) are located in upper 128 Bytes direct addressing

area. The SFR Memory Map in shows that.

Not all of the addresses are occupied. Unoccupied addresses are not implemented on the

chip. Read accesses to these addresses in general return random data, and write accesses have no

effect. User software should not write 1s to these unimplemented locations, since they may be

used in future microcontrollers to invoke new features. In that case, the reset or inactive values of

the new bits will always be 0, and their active values will be 1.

The functions of the SFR’s are outlined in the following sections.




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Accumulator (ACC)

ACC is the Accumulator register. The mnemonics for Accumulator-specific instructions,

however, refer to the Accumulator simply as A.

B Register (B)

The B register is used during multiply and divide operations. For other instructions it can be

treated as another scratch pad register.

Program Status Word (PSW)

The PSW register contains program status information.

Stack Pointer (SP)

The Stack Pointer Register is eight bits wide. It is incremented before data is stored during

PUSH and CALL executions. While the stack may reside anywhere in on chip RAM, the Stack

Pointer is initialized to 07H after a reset. This causes the stack to begin at location 08H.

Data Pointer (DPTR)

The Data Pointer consists of a high byte (DPH) and a low byte (DPL). Its function is to hold a

16-bit address. It may be manipulated as a 16-bit register or as two independent 8-bit registers.

Serial Data Buffer (SBUF)

The Serial Data Buffer is actually two separate registers, a transmit buffer and a receive buffer

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




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transmission. (Moving a byte to SBUF initiates the transmission.) When data is moved from

SBUF, it comes from the receive buffer.

Timer Registers

Register pairs (TH0, TL0) and (TH1, TL1) are the 16-bit Counter registers for Timer/Counters 0

and 1, respectively.

Control Registers

Special Function Registers IP, IE, TMOD, TCON, SCON, and PCON contain control and status

bits for the interrupt system, the Timer/Counters, and the serial port.

TIMER/COUNTERS

The IS89C51 has two 16-bit Timer/Counter registers: Timer 0 and Timer 1. All two can

be configured to operate either as Timers or event counters. As a Timer, the register is

incremented every machine cycle. Thus, the register counts machine cycles. Since a machine

cycle consists of 12 oscillator periods, the count rate is 1/12 of the oscillator frequency.

As a Counter, the register is incremented in response to a 1-to-0 transition at its

corresponding external input pin, T0 and T1. The external input is sampled during S5P2 of every

machine cycle. When the samples show a high in one cycle and a low in the next

cycle, the count is incremented. The new count value appears in the register during S3P1 of the

cycle following the one in which the transition was detected. Since two machine cycles (24

oscillator periods) are required to recognize a 1-to-0 transition, the maximum count rate is 1/24

of the oscillator frequency. There are no restrictions on the duty cycle of the external input




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signal, but it should be held for at least one full machine cycle to ensure that a given level is

sampled at least once before it changes.

In addition to the Timer or Counter functions, Timer 0 and Timer 1 have four operating modes:

13-bit timer, 16-bit timer, 8-bit auto-reload, split timer.

TIMERS:

SFR’S USED IN TIMERS

The special function registers used in timers are,

TMOD Register

TCON Register

Timer(T0) & timer(T1) Registers

(i) TMOD Register:




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TMOD is dedicated solely to the two timers (T0 & T1).

The timer mode SFR is used to configure the mode of operation of each of the two

timers. Using this SFR your program may configure each timer to be a 16-bit timer, or 13

bit timer, 8-bit auto reload timer, or two separate timers. Additionally you may configure

the timers to only count when an external pin is activated or to count “events” that are

indicated on an external pin.

It can consider as two duplicate 4-bit registers, each of which controls the action of one

of the timers.

(ii) TCON Register:

The timer control SFR is used to configure and modify the way in which the 8051’s two

timers operate. This SFR controls whether each of the two timers is running or stopped

and contains a flag to indicate that each timer has overflowed. Additionally, some non-

timer related bits are located in TCON SFR.

These bits are used to configure the way in which the external interrupt flags are

activated, which are set when an external interrupt occurs.

(iii) TIMER 0 (T0):

TO (Timer 0 low/high, address 8A/8C h)

These two SFR’s taken together represent timer 0. Their exact behavior depends

on how the timer is configured in the TMOD SFR; however, these timers always count

up. What is configurable is how and when they increment in value.




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(iv) TIMER 1 (T1):

T1 (Timer 1 Low/High, address 8B/ 8D h)

These two SFR’s, taken together, represent timer 1. Their exact behavior depends on how the

timer is configured in the TMOD SFR; however, these timers always count up. What is

Configurable is how and when they increment in value.

The Timer or Counter function is selected by control bits C/T in the Special Function Register

TMOD. These two Timer/Counters have four operating modes, which are selected by bit pairs

(M1, M0) in TMOD. Modes 0, 1, and 2 are the same for both Timer/Counters, but Mode 3 is

different.

The four modes are described in the following sections.

Mode 0:

Both Timers in Mode 0 are 8-bit Counters with a divide-by-32 pre scalar. Figure 8 shows

the Mode 0 operation as it applies to Timer 1. In this mode, the Timer register is configured as a

13-bit register. As the count rolls over from all 1s to all 0s, it sets the Timer interrupt flag TF1.

The counted input is enabled to the Timer when TR1 = 1 and either GATE = 0 or INT1 = 1.

Setting GATE = 1 allows the Timer to be controlled by external input INT1, to facilitate pulse

width measurements. TR1 is a control bit in the Special Function Register TCON. Gate is in

TMOD.




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The 13-bit register consists of all eight bits of TH1 and the lower five bits of TL1.

The upper three bits of TL1 are indeterminate and should be ignored. Setting the run flag (TR1)

does not clear the registers.

Mode 0 operation is the same for Timer 0 as for Timer 1, except that TR0, TF0 and INT0

replace the corresponding Timer 1 signals. There are two different GATE bits, one for Timer 1

(TMOD.7) and one for Timer 0 (TMOD.3).

Mode 1

Mode 1 is the same as Mode 0, except that the Timer register is run with all 16 bits. The

clock is applied to the combined high and low timer registers (TL1/TH1). As clock pulses are

received, the timer counts up: 0000H, 0001H, 0002H, etc. An overflow occurs on the FFFFH-to-

0000H overflow flag. The timer continues to count. The overflow flag is the TF1 bit in TCON

that is read or written by software

Mode 2

Mode 2 configures the Timer register as an 8-bit Counter (TL1) with automatic reload, as

shown in Figure 10. Overflow from TL1 not only sets TF1, but also reloads TL1 with the

contents of TH1, which is preset by software. The reload leaves the TH1 unchanged. Mode 2

operation is the same for Timer/Counter 0.

Mode 3

Timer 1 in Mode 3 simply holds its count. The effect is the same as setting TR1 = 0.

Timer 0 in Mode 3 establishes TL0and TH0 as two separate counters. The logic for Mode 3 on

Timer 0 is shown in Figure 11. TL0 uses the Timer 0 control bits: C/T, GATE, TR0, INT0, and




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TF0. TH0 is locked into a timer function (counting machine cycles) and over the use of TR1 and

TF1 from Timer 1. Thus, TH0 now controls the Timer 1 interrupt.

Mode 3 is for applications requiring an extra 8-bit timer or counter. With Timer 0 in

Mode 3, the AT89C51 can appear to have three Timer/Counters. When Timer 0 is in Mode 3,

Timer 1 can be turned on and off by switching it out of and into its own Mode 3. In this case,

Timer 1 can still be used by the serial port as a baud rate generator or in any application not

requiring an interrupt.

INTERRUPT SYSTEM

An interrupt is an external or internal event that suspends the operation of micro

controller to inform it that a device needs its service. In interrupt method, whenever any device

needs its service, the device notifies the micro controller by sending it an interrupt signal. Upon

receiving an interrupt signal, the micro controller interrupts whatever it is doing and serves the

device. The program associated with interrupt is called as interrupt service subroutine

(ISR).Main advantage with interrupts is that the micro controller can serve many devices.

Baud Rate

The baud rate in Mode 0 is fixed as shown in the following equation. Mode 0 Baud Rate

= Oscillator Frequency /12 the baud rate in Mode 2 depends on the value of the SMOD bit in

Special Function Register PCON. If SMOD = 0 the baud rate is 1/64 of the oscillator frequency.

If SMOD = 1, the baud rate is 1/32 of the oscillator frequency.

Mode 2 Baud Rate = 2SMODx (Oscillator Frequency)/64.

In the IS89C51, the Timer 1 overflow rate determines the baud rates in Modes 1 and 3.

NUMBER OF INTERRUPTS IN 89C51:




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There are basically five interrupts available to the user. Reset is also considered as an

interrupt. There are two interrupts for timer, two interrupts for external hardware interrupt and

one interrupt for serial communication.

Memory location Interrupt name

0000H Reset

0003H External interrupt 0

000BH Timer interrupt 0

0013H External interrupt 1

001BH Timer interrupt 1

0023H Serial COM interrupt

Lower the vector, higher the priority. The External Interrupts INT0 and 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 the IE0 and IE1 bits in TCON. When the

service routine is vectored, hardware clears the flag that generated an external interrupt only if

the interrupt was transition-activated. If the interrupt was level-activated, then the external

requesting source (rather than the on-chip hardware) controls the request flag.

The Timer 0 and Timer 1 Interrupts are generated by TF0and TF1, which are set by a

rollover in their respective Timer/Counter registers (except for Timer 0 in Mode 3).When a timer

interrupt is generated, the on-chip hardware clears the flag that is generated.




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The Serial Port Interrupt is generated by the logical OR of RI and TI. The service routine

normally must determine whether RI or TI generated the interrupt, and the bit must be cleared in

software.

All of the bits that generate interrupts can be set or cleared by software, with the same

result as though they had been set or cleared by hardware. That is, interrupts can be generated

and pending interrupts can be canceled in software.

Each of these interrupt sources can be individually enabled or disabled by setting or

clearing a bit in Special Function Register IE (interrupt enable) at address 0A8H. There is a

global enable/disable bit that is cleared to disable all interrupts or to set the interrupts.

IE (Interrupt enable register):

Steps in enabling an interrupt:

Bit D7 of the IE register must be set to high to allow the rest of register to take effect. If

EA=1, interrupts are enabled and will be responded to if their corresponding bits in IE are high.

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

Description of each bit in IE register:

D7 bit: Disables all interrupts. If EA =0, no interrupt is acknowledged, if EA=1 each

interrupt source is individually enabled or disabled by setting or clearing its enable bit.

D6 bit: Reserved.

D5 bit: Enables or disables timer 2 over flow interrupt (in 8052).

D4 bit: Enables or disables serial port interrupt.

D3 bit: Enables or disables timer 1 over flow interrupt.




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D2 bit: Enables or disables external interrupt 1.

D1 bit: Enables or disables timer 0 over flow interrupt.

D0 bit: Enables or disables external interrupt 0.

Interrupt priority in 89C51:

There is one more SRF to assign priority to the interrupts which is named as interrupt

priority (IP). User has given the provision to assign priority to one interrupt. Writing one to that

particular bit in the IP register fulfils the task of assigning the priority.

Description of each bit in IP register:

D7 bit: Reserved.

D6 bit: Reserved.

D5 bit: Timer 2 interrupt priority bit (in 8052).

D4 bit: Serial port interrupt priority bit.

D3 bit: Timer 1 interrupt priority bit.

D2 bit: External interrupt 1 priority bit.

D1 bit: Timer 0 interrupt priority bit.

D0 bit: External interrupt 0 priority bit.




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POWER SUPPLY:

Block diagram:

Figure: Power Supply

Circuit diagram:




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Description:

Transformer:

A transformer is a device that transfers electrical energy from one circuit to another through

inductively coupled conductors—the transformer's coils. A varying current in the first or primary

winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic




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field through the secondary winding. This varying magnetic field induces a varying

electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual

induction.

Figure: Transformer Symbol

(or)

Transformer is a device that converts the one form energy to another form of energy like a

transducer.

Figure: Transformer




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Basic Principle:

A transformer makes use of Faraday's law and the ferromagnetic properties of an iron core to

efficiently raise or lower AC voltages. It of course cannot increase power so that if the voltage is

raised, the current is proportionally lowered and vice versa.




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Figure: Basic Principle

Transformer Working:

A transformer consists of two coils (often called 'windings') linked by an iron core, as shown in

figure below. There is no electrical connection between the coils; instead they are linked by a

magnetic field created in the core.

Figure: Basic Transformer

Transformers are used to convert electricity from one voltage to another with minimal loss of

power. They only work with AC (alternating current) because they require a changing magnetic

field to be created in their core. Transformers can increase voltage (step-up) as well as reduce

voltage (step-down).




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Alternating current flowing in the primary (input) coil creates a continually changing magnetic

field in the iron core. This field also passes through the secondary (output) coil and the changing

strength of the magnetic field induces an alternating voltage in the secondary coil. If the

secondary coil is connected to a load the induced voltage will make an induced current flow. The

correct term for the induced voltage is 'induced electromotive force' which is usually abbreviated

to induced e.m.f.

The iron core is laminated to prevent 'eddy currents' flowing in the core. These are currents

produced by the alternating magnetic field inducing a small voltage in the core, just like that

induced in the secondary coil. Eddy currents waste power by needlessly heating up the core but

they are reduced to a negligible amount by laminating the iron because this increases the

electrical resistance of the core without affecting its magnetic properties.

Transformers have two great advantages over other methods of changing voltage:

1. They provide total electrical isolation between the input and output, so they can be safely

used to reduce the high voltage of the mains supply.

2. Almost no power is wasted in a transformer. They have a high efficiency (power out /

power in) of 95% or more.

Classification of Transformer:

Step-Up Transformer

Step-Down Transformer




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Step-Down Transformer:

Step down transformers are designed to reduce electrical voltage. Their primary voltage is

greater than their secondary voltage. This kind of transformer "steps down" the voltage applied

to it. For instance, a step down transformer is needed to use a 110v product in a country with a

220v supply.

Step down transformers convert electrical voltage from one level or phase configuration usually

down to a lower level. They can include features for electrical isolation, power distribution, and

control and instrumentation applications. Step down transformers typically rely on the principle

of magnetic induction between coils to convert voltage and/or current levels.

Step down transformers are made from two or more coils of insulated wire wound around a core

made of iron. When voltage is applied to one coil (frequently called the primary or input) it

magnetizes the iron core, which induces a voltage in the other coil, (frequently called the

secondary or output). The turn’s ratio of the two sets of windings determines the amount of

voltage transformation.

Figure: Step-Down Transformer




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An example of this would be: 100 turns on the primary and 50 turns on the secondary, a ratio of

2 to 1.

Step down transformers can be considered nothing more than a voltage ratio device.

With step down transformers the voltage ratio between primary and secondary will mirror the

"turn’s ratio" (except for single phase smaller than 1 kva which have compensated secondary). A

practical application of this 2 to 1 turn’s ratio would be a 480 to 240 voltage step down. Note that

if the input were 440 volts then the output would be 220 volts. The ratio between input and

output voltage will stay constant. Transformers should not be operated at voltages higher than

the nameplate rating, but may be operated at lower voltages than rated. Because of this it is

possible to do some non-standard applications using standard transformers.

Single phase step down transformers 1 kva and larger may also be reverse connected to step-

down or step-up voltages. (Note: single phase step up or step down transformers sized less than 1

KVA should not be reverse connected because the secondary windings have additional turns to

overcome a voltage drop when the load is applied. If reverse connected, the output voltage will

be less than desired.)

Step-Up Transformer:

A step up transformer has more turns of wire on the secondary coil, which makes a larger

induced voltage in the secondary coil. It is called a step up transformer because the voltage

output is larger than the voltage input.

Step-up transformer 110v 220v design is one whose secondary voltage is greater than its primary

voltage. This kind of transformer "steps up" the voltage applied to it. For instance, a step up

transformer is needed to use a 220v product in a country with a 110v supply.




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A step up transformer 110v 220v converts alternating current (AC) from one voltage to another

voltage. It has no moving parts and works on a magnetic induction principle; it can be designed

to "step-up" or "step-down" voltage. So a step up transformer increases the voltage and a step

down transformer decreases the voltage.

The primary components for voltage transformation are the step up transformer core and coil.

The insulation is placed between the turns of wire to prevent shorting to one another or to

ground. This is typically comprised of Mylar, nomex, Kraft paper, varnish, or other materials. As

a transformer has no moving parts, it will typically have a life expectancy between 20 and 25

years.

Figure: Step-Up Transformer

Applications

Generally these Step-Up Transformers are used in industries applications only.

Turns Ratio and Voltage




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The ratio of the number of turns on the primary and secondary coils determines the ratio of the

voltages...

...where Vp is the primary (input) voltage, Vs is the secondary (output) voltage, Np is the number

of turns on the primary coil, and Ns is the number of turns on the secondary coil.

Diodes:

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the

direction in which the current can flow. Diodes are the electrical version of a valve and early

diodes were actually called valves.

Figure: Diode Symbol

A diode is a device which only allows current to flow through it in one direction. In this

direction, the diode is said to be 'forward-biased' and the only effect on the signal is that there

will be a voltage loss of around 0.7V. In the opposite direction, the diode is said to be 'reverse-

biased' and no current will flow through it.

Rectifier




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The purpose of a rectifier is to convert an AC waveform into a DC waveform (OR) Rectifier

converts AC current or voltages into DC current or voltage. There are two different rectification

circuits, known as 'half-wave' and 'full-wave' rectifiers. Both use components called diodes to

convert AC into DC.

The Half-wave Rectifier

The half-wave rectifier is the simplest type of rectifier since it only uses one diode, as shown in

figure .

Figure: Half Wave Rectifier

Figure 2 shows the AC input waveform to this circuit and the resulting output. As you can see,

when the AC input is positive, the diode is forward-biased and lets the current through. When

the AC input is negative, the diode is reverse-biased and the diode does not let any current

through, meaning the output is 0V. Because there is a 0.7V voltage loss across the diode, the




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Peak output voltage will be 0.7V less than Vs.

Figure: Half-Wave Rectification

While the output of the half-wave rectifier is DC (it is all positive), it would not be suitable as a

power supply for a circuit. Firstly, the output voltage continually varies between 0V and Vs-

0.7V, and secondly, for half the time there is no output at all.

The Bridge Rectifier

The circuit in figure 3 addresses the second of these problems since at no time is the output

voltage 0V. This time four diodes are arranged so that both the positive and negative parts of the

AC waveform are converted to DC. The resulting waveform is shown in figure 4.




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Figure: Bridge Rectifier

Figure: Bridge Rectification




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When the AC input is positive, diodes A and B are forward-biased, while diodes C and D are

reverse-biased. When the AC input is negative, the opposite is true - diodes C and D are

forward-biased, while diodes A and B are reverse-biased.

While the full-wave rectifier is an improvement on the half-wave rectifier, its output still isn't

suitable as a power supply for most circuits since the output voltage still varies between 0V and

Vs-1.4V. So, if you put 12V AC in, you will 10.6V DC out.

Capacitor Filter

The capacitor-input filter, also called "Pi" filter due to its shape that looks like the Greek letter

pi, is a type of electronic filter. Filter circuits are used to remove unwanted or undesired

frequencies from a signal.

Figure: Capacitor Filter

A typical capacitor input filter consists of a filter capacitor C1, connected across the rectifier

output, an inductor L, in series and another filter capacitor connected across the load.

1. The capacitor C1 offers low reactance to the AC component of the rectifier output while

it offers infinite reactance to the DC component. As a result the capacitor shunts an




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appreciable amount of the AC component while the DC component continues its journey

to the inductor L

2. The inductor L offers high reactance to the AC component but it offers almost zero

reactance to the DC component. As a result the DC component flows through the

inductor while the AC component is blocked.

3. The capacitor C2 bypasses the AC component which the inductor had failed to block. As

a result only the DC component appears across the load RL.

Figure: Centered Tapped Full-Wave Rectifier with a Capacitor Filter

Voltage Regulator:

A voltage regulator is an electrical regulator designed to automatically maintain a constant

voltage level. It may use an electromechanical mechanism, or passive or active electronic

components. Depending on the design, it may be used to regulate one or more AC or DC

voltages. There are two types of regulator are they.

Positive Voltage Series (78xx) and

Negative Voltage Series (79xx)




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78xx:’78’ indicate the positive series and ‘xx’ indicates the voltage rating. Suppose 7805

produces the maximum 5V.’05’indicates the regulator output is 5V.

79xx:’78’ indicate the negative series and ‘xx’ indicates the voltage rating. Suppose 7905

produces the maximum -5V.’05’indicates the regulator output is -5V.

These regulators consists the three pins there are

Pin1: It is used for input pin.

Pin2: This is ground pin for regulator

Pin3: It is used for output pin. Through this pin we get the output.

Figure: Regulator




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SERIAL COMMUNICATION

THEORY:

In order to connect micro controller to a modem or a pc to modem a serial port is used.

Serial is a very common protocol for device communication that is standard on almost every PC.

Most computers include two RS-232 based serial ports. Serial is also a common communication

protocol that is used by many devices for instrumentation; numerous GPIB-compatible devices

also come with an RS-232 port. Furthermore, serial communication can be used for data

acquisition in conjunction with a remote sampling device.

The concept of serial communication is simple. The serial port sends and receives bytes

of information one bit at a time. Although this is slower than parallel communication, which

allows the transmission of an entire byte at once, it is simpler and can be used over longer

distances. For example, the IEEE 488 specifications for parallel communication state that the

cabling between equipment can be no more than 20 meters total, with no more than 2 meters

between any two devices. Serial, however, can extend as much as 1200 meters.

Typically, serial is used to transmit ASCII data. Communication is completed using 3

transmission lines: (1) Ground, (2) Transmit, and (3) Receive. Since serial is asynchronous, the

port is able to transmit data on one line while receiving data on another. Other lines are available

for handshaking, but are not required. The important serial characteristics are baud rate, data bits,

stop bits, and parity. For two ports to communicate, these parameters must match.

Baud rate: It is a speed measurement for communication. It indicates the number of bit

transfers per second. For example, 300 baud is 300 bits per second. When a clock cycle is

referred it means the baud rate. For example, if the protocol calls for a 4800 baud rate, then the

clock is running at 4800Hz. This means that the serial port is sampling the data line at 4800Hz.




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Common baud rates for telephone lines are 14400, 28800, and 33600. Baud rates greater than

these are possible, but these rates reduce the distance by which devices can be separated. These

high baud rates are used for device communication where the devices are located together, as is

typically the case with GPIB devices.

Data bits: Measurement of the actual data bits in a transmission. When the computer sends a

packet of information, the amount of actual data may not be a full 8 bits. Standard values for the

data packets are 5, 7, and 8 bits. Which setting chosen depends on what information transferred

For example, standard ASCII has values from 0 to 127 (7 bits). Extended ASCII uses 0 to 255 (8

bits). If the data being transferred is simple text (standard ASCII), then sending 7 bits of data per

packet is sufficient for communication. A packet refers to a single byte transfer, including

start/stop bits, data bits, and parity. Since the number of actual bits depends on the protocol

selected, the term packet is used to cover all instances.

Stop bits: used to signal the end of communication for a single packet. Typical values are 1,

1.5, and 2 bits. Since the data is clocked across the lines and each device has its own clock, it is

possible for the two devices to become slightly out of sync. Therefore, the stop bits not only

indicate the end of transmission but also give the computers some room for error in the clock

speeds. The more bits that are used for stop bits, the greater the lenience in synchronizing the

different clocks, but the slower the data transmission rate.

Parity: A simple form of error checking that is used in serial communication. There are four

types of parity: even, odd, marked, and spaced. The option of using no parity is also available.

For even and odd parity, the serial port sets the parity bit (the last bit after the data bits) to a

value to ensure that the transmission has an even or odd number of logic high bits. For example,

if the data is 011, then for even parity, the parity bit is 0 to keep the number of logic-high bits

even. If the parity is odd, then the parity bit is 1, resulting in 3 logic-high bits. Marked and




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spaced parity does not actually check the data bits, but simply sets the parity bit high for marked

parity or low for spaced parity. This allows the receiving device to know the state of a bit to

enable the device to determine if noise is corrupting the data or if the transmitting and receiving

device clocks are out of sync.

WHAT IS RS –232C

RS-232 (ANSI/EIA-232 Standard) is the serial connection found on IBM-compatible

PCs. It is used for many purposes, such as connecting a mouse, printer, or modem, as well as

industrial instrumentation. Because of improvements in line drivers and cables, applications

often increase the performance of RS-232 beyond the distance and speed listed in the standard.

RS-232 is limited to point-to-point connections between PC serial ports and devices. RS-232

hardware can be used for serial communication up to distances of 50 feet.

DB-9 pin connector

1 2 3 4 5

6 7 8 9

(Out of computer and exposed end of cable)

Pin Functions:

Data: TxD on pin 3, RxD on pin 2

Handshake: RTS on pin 7, CTS on pin 8, DSR on pin 6,




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CD on pin 1, DTR on pin 4

Common: Common pin 5(ground)

Other: RI on pin 9

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

Connection Diagram:

Figure: Interfacing to MCU RS 232

SFRs Used for Serial Communication:

SCON:




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TMOD:

T1:

CONNECTIONS IN MAX 232:

If you wanted to do a general RS-232 connection, you could take a bunch of long wires

and solder them directly to the electronic circuits of the equipment you are using, but this tends

to make a big mess and often those solder connections tend to break and other problems can

develop. To deal with these issues, and to make it easier to setup or take down equipment, some

standard connectors have been developed that is commonly found on most equipment using the

RS-232 standards.

These connectors come in two forms: A male and a female connector. The female connector has

holes that allow the pins on the male end to be inserted into the connector.

This is a female "DB-9" connector (properly known as DE9F):




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Female Connector

The female DB-9 connector is typically used as the "plug" that goes into a typical PC. If you see

one of these on the back of your computer, it is likely not to be used for serial communication,

but rather for things like early VGA or CGA monitors (not SVGA) or for some special control

joystick equipment.

And this is a male "DB-9" connector (properly known as DE9M):

Male Connector

This is the connector that you are more likely to see for serial communications on a "generic"

PC. Often you will see two of them side by side (for COM1 and COM2). Special equipment that




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you might communicate with would have either connector, or even one of the DB-25 connectors

listed below.

The wiring of RS-232 devices involves first identifying the actual pins that are being used. Here

is how a female DB-9 connector is numbered:

Figure: Front View

If the numbers are hard to read, it starts at the top-right corner as "1", and goes left until the end

of the row and then starts again as pin 6 on the next row until you get to pin 9 on the bottom-left

pin. "Top" is defined as the row with 5 pins.

The male connector (like what you have on your PC) is simply this same order, but reversed

from right to left.

Here each pin is usually defined as:

9-pin 25-pin pin definition

1 8 DCD (Data Carrier Detect)

2 3 RX (Receive Data)

3 2 TX (Transmit Data)

4 20 DTR (Data Terminal Ready)




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5 7 GND (Signal Ground)

6 6 DSR (Data Set Ready)

7 4 RTS (Request To Send)

8 5 CTS (Clear To Send))

9 22 RI (Ring Indicator)

Pin Definition of Connectors

One thing to keep in mind when discussing these pins and their meaning is that they are very

closely tied together with modems and modem protocols. Often you don't have a modem

attached in the loop, but you still treat the equipment as if it were a modem on a theoretical level.

MAX232:

Max 232 is a communications device used mainly for serial commands to and from a flash

ROM.The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to

signals suitable for use in TTL compatible digital logic circuits. The MAX232 is a dual

driver/receiver and typically converts the RX, TX, CTS and RTS signals. The drivers provide

RS-232 voltage level outputs (approx. ± 7.5 V) from a single + 5 V supply via on-chip charge

pumps and external capacitors. This makes it useful for implementing RS-232 in devices that

otherwise do not need any voltages outside the 0 V to + 5 V range, as power supply design does

not need to be made more complicated just for driving the RS-232 in this case.




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The receivers reduce RS-232 inputs (which may be as high as ± 25 V), to standard 5 V TTL

levels. These receivers have a typical threshold of 1.3 V, and a typical hysteresis of 0.5 V.

The later MAX232A is backwards compatible with the original MAX232 but may operate at

higher baud rates and can use smaller external capacitors – 0.1 μF in place of the 1.0 μF

capacitors used with the original device.

The newer MAX3232 is also backwards compatible, but operates at a broader voltage range,

from 3 to 5.5V.

Voltage levels

It is helpful to understand what occurs to the voltage levels. When a MAX232 IC receives a TTL

level to convert, it changes a TTL Logic 0 to between +3 and +15V, and changes TTL Logic 1 to

between -3 to -15V, and vice versa for converting from RS232 to TTL. This can be confusing

when you realize that the RS232 Data Transmission voltages at a certain logic state are opposite

from the RS232 Control Line voltages at the same logic state. To clarify the matter, see the table

below. For more information see RS-232 Voltage Levels.

RS232 Line Type & Logic Level RS232 Voltage TTL Voltage to/from MAX232

Data Transmission (Rx/Tx) Logic 0 +3V to +15V 0V

Data Transmission (Rx/Tx) Logic 1 -3V to -15V 5V

Control Signals (RTS/CTS/DTR/DSR) Logic 0 -3V to -15V 5V

Control Signals (RTS/CTS/DTR/DSR) Logic 1 +3V to +15V 0V




http://en.wikipedia.org/wiki/RS-232#Voltage_levels

http://en.wikipedia.org/wiki/Farad

http://en.wikipedia.org/wiki/Baud

http://en.wikipedia.org/wiki/Hysteresis

http://en.wikipedia.org/wiki/Transistor-transistor_logic

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Standard serial interfacing of microcontroller

(TTL) with PC or any RS232C Standard device ,

requires TTL to RS232 Level converter . A

MAX232 is used for this purpose. It provides 2-

channel RS232C port and requires external 10uF

capacitors. The driver

requires a single supply of

+5V.

BUZZER:

1. Magnetic Transducer

Magnetic transducers

contain magnetic circuit

consisting of iron core with

wound coil and a yoke

plate, a permanent magnet

and a vibrating diaphragm

with a movable iron piece. The diaphragm is slightly

pulled towards the top of the core by the magnet's

magnetic field. When a positive AC signal is

applied, the current flowing through the excitation coil

produces a fluctuating magnetic field, which

causes the diaphragm to vibrate up and down, thus




Figure 13:MAX 232 Pin Diagram

http://www.bsc.nodak.edu/electron/rs232.htm

http://www.arcelect.com/rs232.htm

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vibrating air. Resonance amplifies vibration through resonator consisting of sound hole(s) and

cavity and produces a loud sound.

2. Magnetic Buzzer (Sounder)

Buzzers like the TMB-series are magnetic audible signal devices with

built-in oscillating circuits. The construction combines an oscillation

circuit unit with a detection coil, a drive coil and a magnetic

transducer. Transistors, resistors, diodes and other small devices act as

circuit devices for driving sound generators. With the application of

voltage, current flows to the drive coil on primary side and to the

detection coil on the secondary side. The amplification circuit,

including the transistor and the feedback circuit, causes vibration. The

oscillation current excites the coil and the unit generates an AC magnetic field corresponding to

an oscillation frequency. This AC magnetic field magnetizes the yoke comprising the magnetic

circuit. The oscillation from the intermittent magnetization prompts the vibration diaphragm to

vibrate up and down, generating buzzer sounds through the resonator.




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Recommended Driving Circuit for Magnetic Transducer

ntroduction of Magnetic Buzzer (Transducer)




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Specifications:

Rated Voltage: A magnetic buzzer is driven

by 1/2 square waves (V o-p).

Operating Voltage: For normal operating.

But it is not guaranteed to make the

minimum Sound Pressure Level (SPL) under

the rated voltage.

Consumption Current: The current is

stably consumed under the regular operation.

However, it normally takes three times of

current at the moment of starting to work.

Direct Current Resistance: The direct current resistance is measured by ammeter directly.

Sound Output: The sound output is measured by decibel meter. Applying rated voltage and 1/2

square waves, and the distance of 10 cm.

Rated Frequency: A buzzer can make sound on any frequencies, but we suggest that the highest

and the most stable SPL comes from the rated frequency.

Operating Temp : Keep working well between -30℃ and +70℃.

How to choose:

Driving methods: AX series with built drive circuit will be the best choice when we cannot

provide frequency signal to a buzzer, it only needs direct current.

Dimension: Dimension affects frequency, small size result in high frequency.

Voltage: Depend on V o-p (1/2 square waves)

Fixed methods: From the highest cost to the lowest- DIP, wires/ connector, SMD.

Soldering methods: AS series is soldered by hand, the frequency is lower because of the holes




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on the bottom. On the other hand, we suggest AC series for the reflow soldering, the reliability is

better.

How to choose a buzzer

There are many different kinds of buzzer to choose, first we need to know a few parameters,

such as voltage, current, drive method, dimension, mounting type, and the most important thing

is how much SPL and frequency we want.

Operating voltage: Normally, the operating voltage for a magnetic buzzer is from 1.5V to 24V,

for a piezo buzzer is from 3V to 220V. However, in order to get enough SPL, we suggest giving

at least 9V to drive a piezo buzzer.

Consumption current: According to the different voltage, the consumption current of a

magnetic buzzer is from dozens to hundreds of mill amperes; oppositely, the piezo type saves

much more electricity, only needs a few mill amperes, and consumes three times current when

the buzzer start to work.

Driving method: Both magnetic and piezo buzzer have self drive type to choose. Because of the

internal set drive circuit, the self drive buzzer can emit sound as long as connecting with the

direct current. Due to the different work principle, the magnetic buzzer need to be driven by 1/2

square waves, and the piezo buzzer need square waves to get better sound output.

Dimension: The dimension of the buzzer affects its SPL and the frequency, the dimension of the

magnetic buzzer is from 7 mm to 25 mm; the piezo buzzer is from 12 mm to 50 mm, or even

bigger.

Connecting way: Dip type, Wire type, SMD type, and screwed type for big piezo buzzer are




http://www.buzzer-speaker.com/manufacturer/magnetic%20buzzer/smd%20magnetic%20buzzer.htm

http://www.buzzer-speaker.com/manufacturer/piezo%20buzzer.htm

http://www.buzzer-speaker.com/manufacturer/magnetic%20buzzer.htm

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usually seen.

Sound Pressure Level (SPL): Buzzer is usually tested the SPL at the distance of 10 cm, if

distance double, the SPL will decay about 6 dB; oppositely, the SPL will increase 6 dB when the

distance is shortened by one time. The SPL of the magnetic buzzer can reach to around 85 dB/

10 cm; the piezo buzzer can be designed to emit very loud sound, for example, the common

siren, are mostly made of piezo buzzer.

Introduction of Piezo Buzzer

Specifications:

Rated Voltage: A piezo buzzer is driven by square waves (V p-p).

Operating Voltage: For normal operating. But it is not guaranteed to make the minimum SPL

under the rated voltage.




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Consumption Current: The current is stably consumed under the regular operation. However, it

normally takes three times of current at the moment of starting to work.

Capacitance: A piezo buzzer can make higher SPL with higher capacitance, but it consumes

more electricity.

Sound Output: The sound output is measured by decibel meter. Applying rated voltage and

square waves, and the distance of 10 cm.

Rated Frequency: A buzzer can make sound on any frequencies, but we suggest that the highest

and the most stable SPL comes from the rated frequency.

Operating Temp.: Keep working well between -30℃ and +70℃.

How to choose:

Driving methods: AZ-xxxxS-x series with built drive circuit will be the best choice when we

cannot provide frequency signal to a buzzer, it only needs direct current. Besides, there are

different tone nature for you to choose, such as continuous, fast pulse, and slow pulse.

Dimension: Dimension affects frequency, small size result in high frequency.

Voltage: Driven by square waves (V p-p), the higher voltage results in the higher SPL.

Pin Pitch: The numerous spec. for the piezo buzzers lead to the difficulty in finding a spec. in

facsimile, therefore we suggest that you can firstly choose a spec. with the same pitch and similar

frequency.

Introduction of Micro Speaker

How to choose:

The factors which affect the SPL: the

square measure of diaphragm, the

amplitude of vibration, magnetic field

intensity, power, impedance, resonant

chamber, the pattern and the thickness




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of diaphragm, and the holes.

Power vs. SPL: Suppose all the conditions are the same, increasing the power does not mean the

SPL will increase as well. We need to revise the diaphragm and the sound coil to load the higher

power, but it leads to lower SPL instead.

Dimension vs. SPL: A larger speaker can vibrate more air, therefore it provides higher SPL. In

addition, the thicker speaker can give wider amplitude of vibration which also leads to higher

SPL.

Acoustics: What we request most is how much SPL a micro speaker can output.

Matching: It will be better to provide the power slight higher than the rated power for the

enlarged circuit.

Question for mechanism:

The volume of the resonant chamber: The general problem of the consuming products is that

the resonant chambers are not big enough. We can only try to find space to enlarge the volume of

the resonant chamber.

Sound Hole: Must be more than 1/8 of the diaphragm’s area at least.

Airtight: The front and back sound fields of the speaker should be separated to avoid

neutralization.

Shock absorber: When a speaker works the vibration will also happen at the same time. In order

to reduce interference, it will do good to have some material between speaker and case to absorb

theshock.

Mounting: The speakers are usually fixed on the case. Firmly fixed is important especially for

the iron housing or the large size to avoid separating in the drop test.

How to choose the speaker




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Dimension: To the micro speaker, size has decisive influence on its volume. 5mm difference of

diameter might result in double or half area of diaphragm, therefore the SPL is quite different.

Besides, the thicker speaker has more space to vibrate the air, and usually has bigger magnet, so

it will be more powerful to push the air and emit louder sound.

Power: Mainly refer to how much power can a speaker bear, there is no direct relation to the

SPL. The speaker with larger power needs to use thicker diaphragm and sound coil to bear larger

power, which will lead to lower efficiency (SPL). Therefore, according to the mechanical design,

try to select a larger speaker which matches the outputting power from the amplified circuit, then

the best SPL would be emitted.

Impedance: Higher impedance can save more electricity, however, the SPL and the loaded

power will go down. The reason is that we have to use thinner wire or to coil more, the front

makes the power lower, and the after leads to heaviness and low efficiency.

The material of diaphragm: Most speakers (diameter less than 50mm) use mylar diaphragms,

which are easily finished, cheaper and waterproof. However, mylar diaphragm is not good at

Heatproof and the sound is stiff.

The patterns of diaphragm: The speaker with concentric circles diaphragm is good for the speech

sounds. Generally, the SPL is good at the frequency before 5-6 KHz, but will dramatically

decrease after 6 KHz. On the other hand, the speaker with radiate diaphragm has average

frequency response. Supposing other conditions are all the same, the SPL of radiate diaphragm

will lower than the concentric circles one at the frequency before 6 KHz.




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Keil

Software Explanation:

A) About Software:

Software’s used are:

*Keil software for c programming

*Express PCB for lay out design

*Express SCH for schematic design

What's New in µVision3?

µVision3 adds many new features to the Editor like Text Templates, Quick Function Navigation,

and Syntax Coloring with brace high lighting Configuration Wizard for dialog based startup and

debugger setup. µVision3 is fully compatible to µVision2 and can be used in parallel with

µVision2.




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What is µVision3?

µVision3 is an IDE (Integrated Development Environment) that helps you write, compile, and

debug embedded programs. It encapsulates the following components:

A project manager.

A make facility.

Tool configuration.

Editor.

A powerful debugger.

To help you get started, several example programs (located in the \C51\Examples, \C251\

Examples, \C166\Examples, and \ARM\...\Examples) are provided.

HELLO is a simple program that prints the string "Hello World" using the Serial

Interface.

MEASURE is a data acquisition system for analog and digital systems.

TRAFFIC is a traffic light controller with the RTX Tiny operating system.

SIEVE is the SIEVE Benchmark.

DHRY is the Dhrystone Benchmark.

WHETS are the Single-Precision Whetstone Benchmark.

Additional example programs not listed here are provided for each device architecture.

Building an Application in µVision2

To build (compile, assemble, and link) an application in µVision2, you must:

1. Select Project -(forexample,166\EXAMPLES\HELLO\HELLO.UV2).

2. Select Project - Rebuild all target files or Build target.

µVision2 compiles, assembles, and links the files in your project.




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Creating Your Own Application in µVision2

To create a new project in µVision2, you must:

1. Select Project - New Project.

2. Select a directory and enter the name of the project file.

3. Select Project - Select Device and select an 8051, 251, or C16x/ST10 device from the

Device Database™.

4. Create source files to add to the project.

5. Select Project - Targets, Groups, Files. Add/Files, select Source Group1, and add the

source files to the project.

6. Select Project - Options and set the tool options. Note when you select the target device

from the Device Database™ all special options are set automatically. You typically only

need to configure the memory map of your target hardware. Default memory model

settings are optimal for most applications.

7. Select Project - Rebuild all target files or Build target.

Debugging an Application in µVision2

To debug an application created using µVision2, you must:

1. Select Debug - Start/Stop Debug Session.

2. Use the Step toolbar buttons to single-step through your program. You may enter G,

main in the Output Window to execute to the main C function.

3. Open the Serial Window using the Serial #1 button on the toolbar.

Debug your program using standard options like Step, Go, Break, and so on.

Starting µVision2 and Creating a Project




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µVision2 is a standard Windows application and started by clicking on the program icon. To

create a new project file select from the µVision2 menu

Project – New Project…. This opens a standard Windows dialog that asks you

for the new project file name.

We suggest that you use a separate folder for each project. You can simply use

the icon Create New Folder in this dialog to get a new empty folder. Then

select this folder and enter the file name for the new project, i.e. Project1.

µVision2 creates a new project file with the name PROJECT1.UV2 which contains

a default target and file group name. You can see these names in the Project

Window – Files.

Now use from the menu Project – Select Device for Target and select a CPU

for your project. The Select Device dialog box shows the µVision2 device

database. Just select the micro controller you use. We are using for our examples the Philips

80C51RD+ CPU. This selection sets necessary tool

options for the 80C51RD+ device and simplifies in this way the tool Configuration

Building Projects and Creating a HEX Files

Typical, the tool settings under Options – Target are all you need to start a new

application. You may translate all source files and line the application with a




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click on the Build Target toolbar icon. When you build an application with

syntax errors, µVision2 will display errors and warning messages in the Output

Window – Build page. A double click on a message line opens the source file

on the correct location in a µVision2 editor window.

Once you have successfully generated your application you can start debugging.

After you have tested your application, it is required to create an Intel HEX file to

download the software into an EPROM programmer or simulator. µVision2 creates HEX files

with each build process when Create HEX files under Options for Target – Output is enabled.

You may start your PROM programming utility after the make process when you specify the

program under the option Run User Program #1.

CPU Simulation

µVision2 simulates up to 16 Mbytes of memory from which areas can be

Mapped for read, write, or code execution access. The µVision2 simulator traps

And reports illegal memory accesses.

In addition to memory mapping, the simulator also provides support for the

integrated peripherals of the various 8051 derivatives. The on-chip peripherals

Of the CPU you have selected are configured from the Device

Database selection

you have made when you create your project target. Refer to page 58 for more




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Information about selecting a device. You may select and display the on-chip peripheral

components using the Debug menu. You can also change the aspects of each peripheral using the

controls in the dialog boxes.

Start Debugging

You start the debug mode of µVision2 with the Debug – Start/Stop Debug

Session command. Depending on the Options for Target – Debug

Configuration, µVision2 will load the application program and run the startup

Code µVision2 saves the editor screen layout and restores the screen layout of the last debug

session. If the program execution stops, µVision2 opens an

Editor window with the source text or shows CPU instructions in the disassembly window. The

next executable statement is marked with a yellow arrow. During debugging, most editor

features are still available.

For example, you can use the find command or correct program errors. Program source text of

your application is shown in the same windows. The µVision2 debug mode differs from the edit

mode in the following aspects:

_ The “Debug Menu and Debug Commands” described on page 28 are

Available. The additional debug windows are discussed in the following.

_ The project structure or tool parameters cannot be modified. All build

Commands are disabled.

Disassembly Window




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The Disassembly window shows your target program as mixed source and assembly program or

just assembly code. A trace history of previously executed instructions may be displayed with

Debug – View Trace Records. To enable the trace history, set Debug – Enable/Disable Trace

Recording.

If you select the Disassembly Window as the active window all program step commands work

on CPU instruction level rather than program source lines. You can select a text line and set or

modify code breakpoints using toolbar buttons or the context menu commands.

You may use the dialog Debug – Inline Assembly… to modify the CPU instructions.

That allows you to correct mistakes or to make temporary changes to the target program you are

debugging.

B) Keil Software

Installing the Keil software on a Windows PC

Insert the CD-ROM in your computer’s CD drive

On most computers, the CD will “auto run”, and you will see the Keil installation menu.

If the menu does not appear, manually double click on the Setup icon, in the root

directory: you will then see the Keil menu.

On the Keil menu, please select “Install Evaluation Software”. (You will not require a

license number to install this software).

Follow the installation instructions as they appear.

Loading the Projects




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The example projects for this book are NOT loaded automatically when you install the Keil

compiler.

These files are stored on the CD in a directory “/Pont”. The files are arranged by chapter: for

example, the project discussed in Chapter 3 is in the directory “/Pont/Ch03_00-Hello”.

Rather than using the projects on the CD (where changes cannot be saved), please copy the files

from CD onto an appropriate directory on your hard disk.

Note: you will need to change the file properties after copying: file transferred from the CD will

be ‘read only’.

Configuring the Simulator

Open the Keil Vision2

Go to Project – Open Project and browse for Hello in Ch03_00 in Pont and open it.

Keilsoftwaretool(Steps)

1. Click on the Keil uVision Icon on DeskTop

2. The following fig will appear




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3. Click on the Project menu from the title bar

4. Then Click on New Project




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5. Save the Project by typing suitable project name with no extension in u r own folder

sited in either C:\ or D:\




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6. Then Click on Save button above.

7. Select the component for u r project. i.e. Atmel……

8. Click on the + Symbol beside of Atmel




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9. Select AT89C52 as shown below




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10. Then Click on “OK”

11. The Following fig will appear




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12. Then Click either YES or NO………mostly “NO”

13. Now your project is ready to USE

14. Now double click on the Target1, you would get another option “Source group 1” as

shown in next page.




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15. Click on the file option from menu bar and select “new”




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16. The next screen will be as shown in next page, and just maximize it by double

clicking on its blue boarder.

17. Now start writing program in either in “C” or “ASM”

18. For a program written in Assembly, then save it with extension “. asm” and for “C”

based program save it with extension “ .C”




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19. Now right click on Source group 1 and click on “Add files to Group Source”




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20. Now you will get another window, on which by default “C” files will appear.




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21. Now select as per your file extension given while saving the file

22. Click only one time on option “ADD”

23. Now Press function key F7 to compile. Any error will appear if so happen.

24. If the file contains no error, then press Control+F5 simultaneously.

25. The new window is as follows




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26. Then Click “OK”

27. Now Click on the Peripherals from menu bar, and check your required port as shown

in fig below

28. Drag the port a side and click in the program file.




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29. Now keep Pressing function key “F11” slowly and observe.

30. You are running your program successfully




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Code:

#include<reg51.h>

sbit buz=P0^7;void delay(unsigned int v){unsigned int i,j;for(i=0;i<=v;i++)for(j=0;j<=1275;j++); }unsigned char receive() { unsigned char rx; while(RI == 0); rx=SBUF; RI=0; return rx; }void tx(unsigned char *tx) { for(;*tx != '\0';tx++) {

SBUF=*tx; while(TI == 0); TI=0; }

}void tx1(unsigned char tx) { SBUF=tx; while(TI == 0); TI=0; }

void main(){ unsigned char rcv; buz=0;




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TMOD=0x20; TH1=0xFD; SCON=0x50; TR1=1;

while(1) {

rcv=receive(); if(rcv=='1') { buz=1; delay(250); buz=0; }

}}

Conclusion:




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The project titled with “AUTOMATIC COLLEGE BELL RING SYSTEM” is successfully

designed and implemented.

Applications:




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Schools

Colleges

Educational institutes

Limitations:




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Future scope:




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Bibliography:




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The 8051 Micro controller and Embedded Systems

o MuhammadAliMazidi

o JaniceGillispieMazidi

The8051MicrocontrollerArchitecture,Programming& Applications

o KennethJ.Ayala

Fundamentals of Micro processors and Micro computers

o B. Ram

Electronic Components

D.V.Prasad

References on the Web:

www.national.com

www.atmel.com

www.microsoftsearch.com

www.geocities.com




http://www.geocities.com/

http://www.microsoftsearch.com/

http://www.atmel.com/

http://www.national.com/