Embedded Documentation

7/28/2019 Embedded Documentation

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One of the tools we use most when debugging our projects isserialinput/output. Serial is very easy to

implement, and it allows you to send/receive any data you need from your microcontroller to a

computer's serial port so it can be viewed using aterminal emulator. These two devices are compatible

from a software perspective, however you can't just hook a microcontroller up to a computer because the

hardware interfaces are not compatible.

Most microcontrollers these days have built in UARTs (universally asynchronous receiver/transmitter)

that can be used to receive and transmit data serially. UARTs transmit one bit at a time at a specified data

rate (i.e. 9600bps, 115200bps, etc.). This method of serial communication is sometimes referred to

as TTL serial (transistor-transistor logic). Serial communication at aTTLlevel will always remain

between the limits of0V and Vcc, which is often 5V or 3.3V. A logic high ('1') is represented by Vcc, while

a logic low ('0') is 0V.

The serial port on your computer (if it's lucky enough to have one, they're quickly becoming a relic)

complies with theRS-232(Recommended Standard 232) telecommunications standard. RS-232 signals

are similar to your microcontroller's serial signals in that they transmit one bit at a time, at aspecificbaudrate, with or withoutparityand/or stop bits. The two differ solely at a hardware level. By the

RS-232 standard a logic high ('1') is represented by a negative voltage anywhere from -3 to -25V while

a logic low ('0') transmits a positive voltage that can be anywhere from +3 to +25V. On most PCs these

signals swing from -13 to +13V.

More recent laptop computers have USB ports instead of serial ports. This converter will plug into your

USB port and provide a COM port for your GPS receiver. Use with a USB hub to get multiple com ports .

Introduction:

Microcontroller:

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.

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

in personal computers or other general purpose applications.

Microcontrollers are used in automatically controlled products and devices, such as

automobile engine control systems, implantable medical devices, remote controls, office

machines, appliances, power tools, toys and other embedded systems. By reducing the size and

cost compared to a design that uses a separate microprocessor, memory, and input/output

devices, microcontrollers make it economical to digitally control even more devices and
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processes. Mixed signal microcontrollers are common, integrating analog components needed to

control non-digital electronic systems.

Some microcontrollers may use four-bit words and operate at clock rate frequencies as

low as 4 kHz, for low power consumption (single-digit milliwatts or microwatts). They willgenerally have the ability to retain functionality while waiting for an event such as a button press

or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may

be just nanowatts, making many of them well suited for long lasting battery applications. Other

microcontrollers may serve performance-critical roles, where they may need to act more like

a digital signal processor(DSP), with higher clock speeds and power consumption.

The first single-chip microprocessor was the 4-bit Intel 4004 released in 1971, with the Intel

8008 and other more capable microprocessors becoming available over the next several years.

However, both processors required external chips to implement a working system, raising total

system cost, and making it impossible to economically computerize appliances.

The Smithsonian Institution says engineers Gary Boone and Michael Cochran succeeded in

creating the first microcontroller in 1971. The result of their work was the TMS 1000, which

went commercial in 1974. It combined read-only memory, read/write memory, processor and

clock on one chip and was targeted at embedded systems.

Partly in response to the existence of the single-chip TMS 1000, Intel developed a computersystem on a chip optimized for control applications, the Intel 8048, with commercial parts first

shipping in 1977. It combined RAM and ROM on the same chip. This chip would find its way

into over one billion PC keyboards, and other numerous applications. At that time Intel's

President, Luke J. Valenter, stated that the microcontroller was one of the most successful in the

company's history, and expanded the division's budget over 25%.

Most microcontrollers at this time had two variants. One had an erasable EPROM program

memory, with a transparent quartz window in the lid of the package to allow it to be erased byexposure to ultraviolet light. The other was a PROM variant which was only programmable

once; sometimes this was signified with the designation OTP, standing for "one-time

programmable". The PROM was actually exactly the same type of memory as the EPROM, but

because there was no way to expose it to ultraviolet light, it could not be erased. The erasable

versions required ceramic packages with quartz windows, making them significantly more


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expensive than the OTP versions, which could be made in lower-cost opaque plastic packages.

For the erasable variants, quartz was required, instead of less expensive glass, for its

transparency to ultravioletglass is largely opaque to UVbut the main cost differentiator was

the ceramic package itself.

In 1993, the introduction of EEPROM memory allowed microcontrollers (beginning with the

Microchip PIC16x84)to be electrically erased quickly without an expensive package as required

for EPROM, allowing both rapid prototyping, and In System Programming. (EEPROM

technology had been available prior to this time, but the earlier EEPROM was more expensive

and less durable, making it unsuitable for low-cost mass-produced microcontrollers.) The same

year, Atmel introduced the first microcontroller using Flash memory, a special type of

EEPROM. Other companies rapidly followed suit, with both memory types.

Cost has plummeted over time, with the cheapest 8-bit microcontrollers being available for under

$0.25 in quantity (thousands) in 2009 and some 32-bit microcontrollers around $1 for similar

quantities.

Nowadays microcontrollers are cheap and readily available for hobbyists, with large online

communities around certain processors.

In the future, MRAM could potentially be used in microcontrollers as it has infinite endurance

and its incremental semiconductor wafer process cost is relatively low.

EMBEDDED SYSTEM DESIGN:

A microcontroller can be considered a self-contained system with a processor, memory and

peripherals and can be used as an embedded system. The majority of microcontrollers in use

today are embedded in other machinery, such as automobiles, telephones, appliances, and

peripherals for computer systems. While some embedded systems are very sophisticated, many

have minimal requirements for memory and program length, with no operating system, and low

software complexity. Typical input and output devices include

switches, relays, solenoids, LED's, small or custom LCD displays, radio frequency devices, and

sensors for data such as temperature, humidity, light level etc. Embedded systems usually have

no keyboard, screen, disks, printers, or other recognizable I/O devices of a personal computer,

and may lack human interaction devices of any kind.


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Interrupts:

Microcontrollers must provide real time (predictable, though not necessarily fast) response to

events in the embedded system they are controlling. When certain events occur,

an interrupt system can signal the processor to suspend processing the current instruction

sequence and to begin an interrupt service routine (ISR, or "interrupt handler"). The ISR will

perform any processing required based on the source of the interrupt before returning to the

original instruction sequence. Possible interrupt sources are device dependent, and often include

events such as an internal timer overflow, completing an analog to digital conversion, a logic

level change on an input such as from a button being pressed, and data received on a

communication link. Where power consumption is important as in battery operated devices,

interrupts may also wake a microcontroller from a low power sleep state where the processor is

halted until required to do something by a peripheral event.

Programs:

Typically microcontroller programs must fit in the available on-chip program memory, since it

would be costly to provide a system with external, expandable, memory. Compilers and

assemblers are used to convert high-level language and assembler language codes into a

compact machine code for storage in the microcontroller's memory. Depending on the device,

the program memory may be permanent, read-only memory that can only be programmed at the

factory, or program memory may be field-alterable flash or erasable read-only memory.

Manufacturers have often produced special versions of their microcontrollers in order to help the

hardware and software development of the target system. Originally these included EPROM

versions that have a "window" on the top of the device through which program memory can be

erased by ultraviolet light, ready for reprogramming after a programming ("burn") and test cycle.

Since 1998, EPROM versions are rare and have been replaced by EEPROM and flash, which are

easier to use (can be erased electronically) and cheaper to manufacture.

Other versions may be available where the ROM is accessed as an external device rather than as

internal memory, however these are becoming increasingly rare due to the widespread

availability of cheap microcontroller programmers.


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The use of field-programmable devices on a microcontroller may allow field update of

the firmware or permit late factory revisions to products that have been assembled but not yet

shipped. Programmable memory also reduces the lead time required for deployment of a new

product.

Where hundreds of thousands of identical devices are required, using parts programmed at the

time of manufacture can be an economical option. These "mask programmed" parts have the

program laid down in the same way as the logic of the chip, at the same time.

A customizable microcontroller incorporates a block of digital logic that can be personalized in

order to provide additional processing capability, peripherals and interfaces that are adapted to

the requirements of the application. For example, the AT91CAP from Atmel has a block of logic

that can be customized during manufacture according to user requirements.

Other microcontroller features:

Microcontrollers usually contain from several to dozens of general

purpose input/output pins (GPIO). GPIO pins are software configurable to either an input or an

output state. When GPIO pins are configured to an input state, they are often used to read sensors

or external signals. Configured to the output state, GPIO pins can drive external devices such as

LEDs or motors.

Many embedded systems need to read sensors that produce analog signals. This is the purpose of

the analog to digital converter (ADC). Since processors are built to interpret and process digital

data, i.e. 1s and 0s, they are not able to do anything with the analog signals that may be sent to it

by a device. So the analog to digital converter is used to convert the incoming data into a form

that the processor can recognize. A less common feature on some microcontrollers is a digital to

analog (DAC) that allows the processor to output analog signals or voltage levels.

In addition to the converters, many embedded microprocessors include a variety of timers as

well. One of the most common types of timers is the Programmable Interval Timer (PIT). A PITmay either count down from some value to zero, or up to the capacity of the count register,

overflowing to zero. Once it reaches zero, it sends an interrupt to the processor indicating that it

has finished counting. This is useful for devices such as thermostats, which periodically test the

temperature around them to see if they need to turn the air conditioner on, the heater on, etc.


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A dedicated Pulse Width Modulation (PWM) block makes it possible for the CPU to control

power converters, resistive loads, motors, etc., without using lots of CPU resources in tight

timer loops.

Universal Asynchronous Receiver/Transmitter (UART) block makes it possible to receive andtransmit data over a serial line with very little load on the CPU.

Higher Integration:

Micro-controllers may not implement an external address or data bus as they integrate RAM and

non-volatile memory on the same chip as the CPU. Using fewer pins, the chip can be placed in a

much smaller, cheaper package.

Integrating the memory and other peripherals on a single chip and testing them as a unit

increases the cost of that chip, but often results in decreased net cost of the embedded system as

a whole. Even if the cost of a CPU that has integrated peripherals is slightly more than the cost of

a CPU and external peripherals, having fewer chips typically allows a smaller and cheaper circuit

board, and reduces the labor required to assemble and test the circuit board, in addition to

tending to decrease the defect rate for the finished assembly.

A micro-controller is a single integratedcircuit, commonly with the following features:

central processing unit - ranging from small and simple 4-bit processors to complex 32- or

64-bit processors

volatile memory (RAM) for data storage

ROM, EPROM, EEPROM orFlash memory for program and operating parameter storage

discrete input and output bits, allowing control or detection of the logic state of an individual

package pin

serial input/output such as serial ports (UARTs)

otherserial communications interfaces like IC, Serial Peripheral Interface and Controller

Area Networkfor system interconnect

peripherals such as timers, event counters, PWM generators, and watchdog
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clock generator- often an oscillator for a quartz timing crystal, resonator orRC circuit

many include analog-to-digital converters, some include digital-to-analog converters

in-circuit programming and debugging support

This integration drastically reduces the number of chips and the amount of wiring and circuitboard space that would be needed to produce equivalent systems using separate chips.

Furthermore, on low pin count devices in particular, each pin may interface to several internal

peripherals, with the pin function selected by software. This allows a part to be used in a wider

variety of applications than if pins had dedicated functions. Micro-controllers have proved to be

highly popular in embedded systems since their introduction in the 1970s.

Some microcontrollers use a Harvard architecture: separate memory buses for instructions and

data, allowing accesses to take place concurrently. Where a Harvard architecture is used,instruction words for the processor may be a different bit size than the length of internal memory

and registers; for example: 12-bit instructions used with 8-bit data registers.

The decision of which peripheral to integrate is often difficult. The microcontroller vendors often

trade operating frequencies and system design flexibility against time-to-market requirements

from their customers and overall lower system cost. Manufacturers have to balance the need to

minimize the chip size against additional functionality.

Microcontroller architectures vary widely. Some designs include general-purposemicroprocessor cores, with one or more ROM, RAM, or I/O functions integrated onto the

package. Other designs are purpose built for control applications. A micro-controller instruction

set usually has many instructions intended for bit-wise operations to make control programs

more compact. For example, a general purpose processor might require several instructions to

test a bit in a register and branch if the bit is set, where a micro-controller could have a single

instruction to provide that commonly required function.

Microcontrollers typically do not have a math coprocessor, so floating point arithmetic isperformed by software.

Accelerometer ADXL335:
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GENERAL DESCRIPTION :

The ADXL335 is a small, thin, low power, complete 3-axis accelerometer with signal

conditioned voltage outputs. The product measures acceleration with a minimum full-scale range

of 3 g. It can measure the static acceleration of gravity in tilt-sensing applications, as well asdynamic acceleration resulting from motion, shock, or vibration.

The user selects the bandwidth of the accelerometer using the CX, CY, and CZ capacitors at the

XOUT, YOUT, and ZOUT pins. Bandwidths can be selected to suit the application, with a range

of 0.5 Hz to 1600 Hz for the X and Y axes, and a range of 0.5 Hz to 550 Hz for the Z axis.

The ADXL335 is available in a small, low profile, 4 mm 4 mm 1.45 mm, 16-lead, plastic

lead frame chip scale package (LFCSP_LQ)

FEATURES: 3-axis sensing

Small, low profile package

4 mm 4 mm 1.45 mm LFCSP

Low power : 350 A (typical)

Single-supply operation: 1.8 V to 3.6 V


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10,000gshock survival

Excellent temperature stability

BW adjustment with a single capacitor per axis

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS OF ADXL335:

Pin Function Descriptions Pin No. Mnemonic Description

1 NC No Connect1.

2 ST Self-Test.

3 COM Common.

4 NC No Connect1.

5 COM Common.

6 COM Common.

7 COM Common.

8 ZOUT Z Channel Output.

9 NC No Connect1.


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10 YOUT Y Channel Output.

11 NC No Connect1.

12 XOUT X Channel Output.

13 NC No Connect1.

14 VS Supply Voltage (1.8 V to 3.6 V).

15 VS Supply Voltage (1.8 V to 3.6 V).

16 NC No Connect1.

EP Exposed Pad Not internally connected. Solder

for mechanical integrity.

APPLICATIONS:

Cost sensitive, low power, motion- and tilt-sensing applications

Mobile devices

Gaming systems

Disk drive protection

Image stabilization

Sports and health devices

HARDWARE COMPONETS:

ATMEGA8:

PINDIAGRAM:


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.BLOCK DIAGRAM


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FEATURES:

High-performance, Low-power AVR 8-bit Microcontroller


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Advanced RISC Architecture

130 Powerful InstructionsMost Single-clock Cycle Execution

32 x 8 General Purpose Working Registers

Fully Static Operation

Up to 16 MIPS Throughput at 16 MHz

On-chip 2-cycle Multiplier

High Endurance Non-volatile Memory segments

8K Bytes of In-System Self-programmable Flash program memory

512 Bytes EEPROM

1K Byte Internal SRAM

Write/Erase Cycles: 10,000 Flash/100,000 EEPROM

Data retention: 20 years at 85C/100 years at 25C

Optional Boot Code Section with Independent Lock Bits

In-System Programming by On-chip Boot Program

True Read-While-Write Operation

Programming Lock for Software Security

Peripheral Features

Two 8-bit Timer/Counters with Separate Prescaler, one Compare Mode

One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture

Mode

Real Time Counter with Separate Oscillator

Three PWM Channels

8-channel ADC in TQFP and QFN/MLF package

Eight Channels 10-bit Accuracy

6-channel ADC in PDIP package

Six Channels 10-bit Accuracy

Byte-oriented Two-wire Serial Interface

Programmable Serial USART

Master/Slave SPI Serial Interface

Programmable Watchdog Timer with Separate On-chip Oscillator

On-chip Analog Comparator


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Special Microcontroller Features

Power-on Reset and Programmable Brown-out Detection

Internal Calibrated RC Oscillator

External and Internal Interrupt Sources

Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, and

Standby

I/O and Packages

23 Programmable I/O Lines

28-lead PDIP, 32-lead TQFP, and 32-pad QFN/MLF

Operating Voltages

2.7 - 5.5V (ATmega8L)

4.5 - 5.5V (ATmega8)

Speed Grades

0 - 8 MHz (ATmega8L)

0 - 16 MHz (ATmega8)

Power Consumption at 4 MHz, 3V, 25C

Active: 3.6 mA

Idle Mode: 1.0 mA

Power-down Mode: 0.5 A

Pin Descriptions

VCC Digital supply voltage.

GND Ground.

Port B (PB7..PB0)

XTAL1/XTAL2/TOSC1/

TOSC2

Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The

Port B output buffers have symmetrical drive characteristics with both high sink and source

capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up

resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,

even if the clock is not running.


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Depending on the clock selection fuse settings, PB6 can be used as input to the inverting

Oscillator

amplifier and input to the internal clock operating circuit.

Depending on the clock selection fuse settings, PB7 can be used as output from the inverting

Oscillator amplifier.

If the Internal Calibrated RC Oscillator is used as chip clock source, PB7..6 is used as TOSC2..1

input for the Asynchronous Timer/Counter2 if the AS2 bit in ASSR is set.

Port C (PC5..PC0) Port C is an 7-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). The

Port C output buffers have symmetrical drive characteristics with both high sink and source

capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up

resistors are activated. The Port C pins are tri-stated when a reset condition becomes active,


PC6/RESET If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the

electrical characteristics

of PC6 differ from those of the other pins of Port C.

If the RSTDISBL Fuse is unprogrammed, PC6 is used as a Reset input. A low level on this pin

for longer than the minimum pulse length will generate a Reset, even if the clock is not running.

Shorter pulses are not guaranteed to generate a Reset.

Port D (PD7..PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). The

Port D output buffers have symmetrical drive characteristics with both high sink and source

capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up

resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,


RESET- Reset input. A low level on this pin for longer than the minimum pulse length will

generate a

AVCC- AVCC is the supply voltage pin for the A/D Converter, Port C (3..0), and ADC (7..6). It

should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it

should be connected to VCC through a low-pass filter. Note that Port C (5..4) use digital supply

voltage, VCC.


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AREF- AREF is the analog reference pin for the A/D Converter.

ADC7..6 (TQFP and QFN/MLF Package Only)

In the TQFP and QFN/MLF package, ADC7..6 serve as analog inputs to the A/D converter.

These pins are powered from the analog supply and serve as 10-bit ADC channels

UART:

A Universal Asynchronous Receiver/Transmitter, abbreviated UART , is a piece ofcomputer

hardware that translates data between parallel and serial forms. UARTs are commonly used in

conjunction with communication standards such as EIA, RS-232, RS-422 orRS-485.

The universaldesignation indicates that the data format and transmission speeds are

configurable. The electric signaling levels and methods (such as differential signaling etc.) are

handled by a driver circuit external to the UART. A UART is usually an individual (or part of

an) integrated circuit used forserial communications over a computer or peripheral device serial

port. UARTs are now commonly included in microcontrollers. A dual UART, orDUART,

combines two UARTs into a single chip. Many modern ICs now come with a UART that can

also communicate synchronously; these devices are called USARTs (universal

synchronous/asynchronous receiver/transmitter).

RS232:

In telecommunications,RS-232 is the traditional name for a series of standards

forserialbinary single-ended data and control signals connecting between aDTE(Data Terminal

Equipment) and aDCE(Data Circuit-terminating Equipment). It is commonly used

in computerserial ports. The standard defines the electrical characteristics and timing of signals,

the meaning of signals, and the physical size and pinout of connectors.

An RS-232serial portwas once a standard feature of a personal computer, used for connections

to modems, printers, mice, data storage, uninterruptible, and other peripheral devices. However,

the low transmission speed, large voltage swing, and large standard connectors motivated

development of the universal serial bus, which has displaced RS-232 from most of its peripheral

interface roles. Many modern personal computers have no RS-232 ports and must use an external
http://en.wikipedia.org/wiki/Computer_hardwarehttp://en.wikipedia.org/wiki/Computer_hardwarehttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Electronic_Industries_Alliancehttp://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/RS-422http://en.wikipedia.org/wiki/RS-485http://en.wikipedia.org/wiki/Differential_signalinghttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Serial_communicationshttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Telecommunicationshttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Single-ended_signalinghttp://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Signaling_(telecommunications)http://en.wikipedia.org/wiki/Data_Terminal_Equipmenthttp://en.wikipedia.org/wiki/Data_Terminal_Equipmenthttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Pinouthttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Printer_(computing)http://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/Printer_(computing)http://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Personal_computerhttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Pinouthttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Data_Terminal_Equipmenthttp://en.wikipedia.org/wiki/Data_Terminal_Equipmenthttp://en.wikipedia.org/wiki/Signaling_(telecommunications)http://en.wikipedia.org/wiki/Data_transmissionhttp://en.wikipedia.org/wiki/Single-ended_signalinghttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Telecommunicationshttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Serial_communicationshttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Differential_signalinghttp://en.wikipedia.org/wiki/RS-485http://en.wikipedia.org/wiki/RS-422http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/Electronic_Industries_Alliancehttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Computer_hardwarehttp://en.wikipedia.org/wiki/Computer_hardware


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USB-to-RS-232 converter to connect to RS-232 peripherals. RS-232 devices are still found,

especially in industrial machines or scientific instruments.

Pinouts

The following table lists commonly used RS-232 signals and pin assignments.[3]

Signal Origin

D

B-

25

DE-

9

(TI

A-

574)

MM

J

8P8C("RJ45") 10P10C("RJ50")

NameAbbreviat

ion

DT

E

DC

E

TI

A-

561

Yo

st

Cyclade

s[4]

National

Instrumen

ts[5]

Cyclade

s[4]

Digi[

6]

Transmit

ted DataTxD 2 3 2 6 3 3 8 4 5

Received

DataRxD 3 2 5 5 6 6 9 7 6

Data

Terminal

Ready

DTR 20 4 1 3 2 2 7 3 9

Carrier

DetectDCD 8 1 2

7

7 10 8

10

(alt

2)

Data Set

ReadyDSR 6 6 6

1

8 5 92

(alt

10)

Ring

IndicatorRI 22 9 2 10 1

Request RTS 4 7 8 1 1 4 2 3
http://en.wikipedia.org/wiki/Serial_port#cite_note-3http://en.wikipedia.org/wiki/Serial_port#cite_note-3http://en.wikipedia.org/wiki/Serial_port#cite_note-3http://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/Modified_Modular_Jackhttp://en.wikipedia.org/wiki/Modified_Modular_Jackhttp://en.wikipedia.org/wiki/Modified_Modular_Jackhttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#10P10Chttp://en.wikipedia.org/wiki/Modular_connector#10P10Chttp://en.wikipedia.org/wiki/Data_terminal_equipmenthttp://en.wikipedia.org/wiki/Data_terminal_equipmenthttp://en.wikipedia.org/wiki/Data_terminal_equipmenthttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Serial_port#cite_note-niserial-5http://en.wikipedia.org/wiki/Serial_port#cite_note-niserial-5http://en.wikipedia.org/wiki/Serial_port#cite_note-niserial-5http://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Digi_Internationalhttp://en.wikipedia.org/wiki/Digi_Internationalhttp://en.wikipedia.org/wiki/Serial_port#cite_note-digi-6http://en.wikipedia.org/wiki/Serial_port#cite_note-digi-6http://en.wikipedia.org/wiki/Serial_port#cite_note-digi-6http://en.wikipedia.org/wiki/Digi_Internationalhttp://en.wikipedia.org/wiki/Digi_Internationalhttp://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Serial_port#cite_note-niserial-5http://en.wikipedia.org/wiki/Serial_port#cite_note-cyclom-y-4http://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Data_circuit-terminating_equipmenthttp://en.wikipedia.org/wiki/Data_terminal_equipmenthttp://en.wikipedia.org/wiki/Data_terminal_equipmenthttp://en.wikipedia.org/wiki/Modular_connector#10P10Chttp://en.wikipedia.org/wiki/Modular_connector#8P8Chttp://en.wikipedia.org/wiki/Modified_Modular_Jackhttp://en.wikipedia.org/wiki/Modified_Modular_Jackhttp://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/TIA-574http://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/D-subminiaturehttp://en.wikipedia.org/wiki/Serial_port#cite_note-3


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To Send

Clear To

SendCTS 5 8 7 8 5 3 6 8

Common

Ground G common 7 5 3,4 4 4,5 4 6 5 7

Protectiv

e GroundPG common 1 1 4

The signals are named from the standpoint of the DTE, for example, an IBM-PC compatible

serial port. The ground signal is a common return for the other connections; it appears on two

pins in the Yost standard but is the same signal. The DB-25 connector includes a second

"protective ground" on pin 1. Connecting this to pin 7 (signal reference ground) is a common

practice but not essential.

The RS-232 standard is used by many specialized and custom-built devices. This list includes

some of the more common devices that are connected to the serial port on a PC. Some of these

such as modems and serial mice are falling into disuse while others are readily available.

Serial ports are very common on most types ofmicrocontroller, where they can be used to

communicate with a PC or other serial devices.

Dial-up modems

GPS receivers (typically NMEA 0183 at 4,800 bit/s)

Bar code scanners and otherpoint of sale devices

LED and LCD text displays

Satellite phones, low-speed satellite modems and other satellite based transceiver devices

Flat-screen (LCD and Plasma) monitors to control screen functions by external computer,

other AV components or remotes

Test and measuring equipment such as digital multimeters and weighing systems

Updating Firmware on various consumer devices.

Some CNC controllers

Uninterruptible power supply

Stenography orStenotype machines.
http://en.wikipedia.org/wiki/Single-ended_signalinghttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/NMEA_0183http://en.wikipedia.org/wiki/Barcode_readerhttp://en.wikipedia.org/wiki/Point_of_salehttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Liquid_crystal_displayhttp://en.wikipedia.org/wiki/Satellite_phonehttp://en.wikipedia.org/wiki/Multimeterhttp://en.wikipedia.org/wiki/Firmwarehttp://en.wikipedia.org/wiki/Numerical_controlhttp://en.wikipedia.org/wiki/Uninterruptible_power_supplyhttp://en.wikipedia.org/wiki/Stenotypehttp://en.wikipedia.org/wiki/Stenotypehttp://en.wikipedia.org/wiki/Uninterruptible_power_supplyhttp://en.wikipedia.org/wiki/Numerical_controlhttp://en.wikipedia.org/wiki/Firmwarehttp://en.wikipedia.org/wiki/Multimeterhttp://en.wikipedia.org/wiki/Satellite_phonehttp://en.wikipedia.org/wiki/Liquid_crystal_displayhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Point_of_salehttp://en.wikipedia.org/wiki/Barcode_readerhttp://en.wikipedia.org/wiki/NMEA_0183http://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Single-ended_signaling


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Software debuggers that run on a second computer.

Industrial field buses

Printers

Computer terminal, teletype

Olderdigital cameras

Networking (Macintosh AppleTalkusing RS-422 at 230.4 kbit/s)

Serial mouse

OlderGSM mobile phones

Some Telescopes

GSM THEORY:

In recent years, vehicle thefts are increasing at an alarming rate around the world. People

have started to use the theft control systems installed in their vehicles. The commercially

available anti-theft vehicular systems are very expensive. Here, we make a modest attempt to

design & develop a simple, low cost vehicle theft control scheme using an inbuilt

microcontroller. This scheme involves a microcontroller & a mobile for the communication

purposes The Global System for Mobile communications (GSM) is the most popular standard for

mobile phones in the world. Over billion people use GSM service across the world. The usability

of the GSM standard makes international roaming very common between mobile phone

operators, enabling subscribers to use their phones in many parts of the world. GSM differs

significantly from its predecessors in that both signaling and speech channels are digital, which

means that it is considered a second generation (2G) mobile phone system. This fact has also

meant that data communication was built into the system from very early on. We start off

exploring the existing scenarios and later we move towards the proposed architecture, describing

the various modules in detail and the working methodology. Finally we present the simulation

results and the various component details. The concept of this paper has been implemented as a

small prototype model.
http://en.wikipedia.org/wiki/Printer_(computing)http://en.wikipedia.org/wiki/Computer_terminalhttp://en.wikipedia.org/wiki/Teletypehttp://en.wikipedia.org/wiki/Digital_camerahttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/RS-422http://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/Groupe_Sp%C3%A9cial_Mobilehttp://en.wikipedia.org/wiki/Mobile_phone#Software_and_applicationshttp://en.wikipedia.org/wiki/GoTo_(telescopes)http://en.wikipedia.org/wiki/GoTo_(telescopes)http://en.wikipedia.org/wiki/Mobile_phone#Software_and_applicationshttp://en.wikipedia.org/wiki/Groupe_Sp%C3%A9cial_Mobilehttp://en.wikipedia.org/wiki/Mouse_(computing)http://en.wikipedia.org/wiki/RS-422http://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Digital_camerahttp://en.wikipedia.org/wiki/Teletypehttp://en.wikipedia.org/wiki/Computer_terminalhttp://en.wikipedia.org/wiki/Printer_(computing)


20/56

GSM module is used to establish communication between a computer and a GSM-GPRS

system. Global System for Mobile communication (GSM) is an architecture used for mobile

communication in most of the countries. Global Packet Radio Service (GPRS) is an extension

of GSM that enables higher data transmission rate. GSM/GPRS module consists of a

GSM/GPRS modem assembled together with power supply circuit and communication

interfaces (like RS-232, USB, etc) for computer. The MODEM is the soul of such modules.

Wireless MODEMs:

Wireless MODEMs are the MODEM devices that generate, transmit or decode data from acellular network, for establishing communication between the cellular network and the computer.

These are manufactured for specific cellular network (GSM/UMTS/CDMA) or specific cellular

data standard (GSM/UMTS/GPRS/EDGE /HSDPA) or technology (GSM/SIM). Wireless

MODEMs like other MODEM devices use serial communication to interface with and

need Hayes compatible AT Commands for communication with the computer (any

microprocessor or microcontroller system).


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GSM MODEM:

GSM/GPRS MODEM is a class of wireless MODEM devices that are designed for

communication of a computer with the GSM and GPRS network. It requires a SIM (Subscriber

Identity Module) card just like mobile phones to activate communication with the network. Also

they have IMEI (International Mobile Equipment Identity) number similar to mobile phones for

their identification. A GSM/GPRS MODEM can perform the following operations:

1. Receive, send or delete SMS messages in a SIM.

2. Read, add, search phonebook entries of the SIM.

3. Make, Receive, or reject a voice call.

The MODEM needs AT commands, for interacting with processor or controller, which are

communicated through serial communication. These commands are sent by the

controller/processor. The MODEM sends back a result after it receives a command. Different AT

commands supported by the MODEM can be sent by the processor/controller/computer to

interact with the GSM and GPRS cellular network.


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GSM Module:

A GSM/GPRS module assembles a GSM/GPRS modem with standard communication interfaces

like RS-232 (Serial Port), USB etc., so that it can be easily interfaced with a computer or a

microprocessor / microcontroller based system. The power supply circuit is also built in the

module that can be activated by using a suitable adaptor.

Mobile Station (Cell phones and SIM):

A mobile phone and Subscriber Identity Module (SIM) together form a mobile station. It is the

user equipment that communicates with the mobile network. A mobile phone comprises of

Mobile Termination, Terminal Equipment and Terminal Adapter.


23/56

Mobile Termination is interfaced with the GSM mobile network and is controlled by abaseband processor. It handles access to SIM, speech encoding and decoding, signaling and other

network related tasks. The Terminal Equipment is an application processor that deals with

handling operations related to keypad, screen, phone memory and other hardware and software

services embedded into the handset. The Terminal Adapter establishes communication between

the Terminal Equipment and the Mobile Termination using AT commands. The communication

with the network in a GSM/GPRS mobile is carried out by the baseband processor.

Difference between GSM mobile and GSM/GPRS module:

A GSM mobile is a complete system in itself with embedded processors that are dedicated to

provide an interface between the user and the mobile network. The AT commands are served

between the processors of the mobile termination and the terminal equipment. The mobile

handset can also be equipped with a USB interface to connect with a computer, but it may or

may not support AT commands from the computer or an external processor/controller.

The GSM/GPRS module, on the other hand, always needs a computer or external

processor/controller to receive AT commands from. GSM/GPRS module itself does not provide

any interface between the user and the network, but the computer to which module is connected

is the interface between user and network.


24/56

An advantage that GSM/GPRS modules offer is that they support concatenated SMS which may

not be supported in some GSM mobile handsets. Also some mobile handsets cant receive MMS

when connected to a computer.

Applications of GSM/GPRS module:

The GSM/GPRS module demonstrates the use of AT commands. They can feature all the

functionalities of a mobile phone through computer like making and receiving calls, SMS, MMS

etc. These are mainly employed for computer based SMS and MMS services.

AT Commands:

AT commands are used to control MODEMs. AT is the abbreviation for Attention. These

commands come from Hayes commands that were used by the Hayes smart modems. The Hayes

commands started with AT to indicate the attention from the MODEM. The dial up and wireless

MODEMs (devices that involve machine to machine communication) need AT commands to

interact with a computer. These include the Hayes command set as a subset, along with other

extended AT commands.

AT commands with a GSM/GPRS MODEM or mobile phone can be used to access following

information and services:

1. Information and configuration pertaining to mobile device or MODEM and SIM card.

2. SMS services.

3. MMS services.

4. Fax services.

5. Data and Voice link over mobile network.

The Hayes subset commands are called the basic commands and the commands specific to a

GSM network are called extended AT commands.


25/56

Command, Information response and Result Codes:

The AT commands are sent by the computer to the MODEM/ mobile phone. The MODEM sends

back an Information Response i.e. the information requested by or pertaining to the action

initiated by the AT command. This is followed by a Result Code. The result code tells about thesuccessful execution of that command.

EXECUTION OF AT COMMANDS BLOCK DIAGRAM.

There are also unsolicited Result Codes that are returned automatically by the MODEM to notify

the occurrence of an event. For example the reception of a SMS will force MODEM to return anunsolicited result code.


26/56

AT commands' syntax:

Case Sensitivity -

The AT commands are generally used in uppercase letters. However some MODEMs and mobile

phones allow both uppercase and small case letters.Single Command -

The AT commands include a prefix AT which indicates the beginning of the command to

MODEM; and a carriage return which indicates the end of the command.

AT COMMANDS SYNTAX

However string AT itself is not the part of the command. For example in ATD, D is the

command name not ATD.

The extended AT commands have a + in the command name.

For example: AT+CGMI

Command Line -

Multiple AT commands can be sent to MODEM in a single command line. The commands in a

line are separated by a semi-colon (;).

For example: AT+CGMI; +CBS

String in Command Line

Strings in a command line are enclosed in double quotes.


27/56

For example: AT+CGML=ALL

AT COMMAND LINE.

Information Response and Result Code:

The Information Response and Result Codes, returned by the MODEM, have a carriage return

and line feed in the beginning as well as at the end.

For example:

OK

ERROR

+CBC: 0, 60 etc.


28/56

Sequence of Execution -

In the command line, the command appearing first is executed first. The execution then follows

for second appeared command and so on. The execution of commands in a command line takes

place in sequential manner.

If an error occurs in the execution of a command, an error result code is returned by the

MODEM and the execution of the command line is terminated irrespective of presence of other

commands next in the command line.

Types of commands:

There are four types of AT commands:

1) Test commands2) Read commands

3) Set commands

4) Execution commands.

RESULT CODE DESCRIPTION

OK Successful execution of a command

ERROR Execution of a command failed

+CMS ERROR Message service failure with return of a error code

UN SOLICITED RESULT CODES+CDS Notify receipt of SMS status report of a new message to computer

+CMT Notify forwarding of a new SMS to computer

+CMTI Notify recipient of a message status

Interfacing MODEM/Mobile phone with Windows platform:

The Windows (XP and lower versions) comes with an application called HyperTerminal for

data communication through serial port of the computer. The interfacing of the GSM/GPRS

module with the serial port of the computer involves following steps:

Connect RS-232 port of GSM module with the serial port of the computer. Insert a SIM card in

the module.

Open HyperTerminal from Start -> All Programs -> Accessories -> Communications -

> HyperTerminal.

Enter a name for the connection and press OK.


29/56

Now select the communication port (COM) at which GSM module is connected.

Create a new connection set on HyperTerminal. Set parameters, like baud rate as 9600,

handshaking mode as none, parity bit as none, stop bit as 1 and data bit as 8.

GLOBAL POSITIONING SYSTEM

The Global Positioning System (GPS) is a space-based satellite navigation system that provides

location and time information in all weather conditions, anywhere on or near the Earth where

there is an unobstructed line of sight to four or more GPS satellites. The system provides critical

capabilities to military, civil and commercial users around the world. It is maintained by

the United States government and is freely accessible to anyone with a GPS receiver.

The GPS project was developed in 1973 to overcome the limitations of previous navigation

systems,[1]integrating ideas from several predecessors, including a number of classified

engineering design studies from the 1960s. GPS was created and realized by the U.S.

Department of Defense (DoD) and was originally run with 24 satellites. It became fully

operational in 1994. Roger L. Easton is generally credited as its inventor.

Advances in technology and new demands on the existing system have now led to efforts to

modernize the GPS system and implement the next generation of GPS III satellites and Next

Generation Operational Control System (OCX).[2]Announcements from the Vice President and

the White House in 1998 initiated these changes. In 2000, U.S. Congress authorized the

modernization effort, referred to as GPS III.

In addition to GPS, other systems are in use or under development. The Russian Global

Navigation Satellite System (GLONASS) was developed contemporaneously with GPS, but

suffered from incomplete coverage of the globe until the mid-2000s. There are also the planned

European Union Galileo, Chinese Compass navigation system, and Indian Regional Navigational

Satellite System.
http://en.wikipedia.org/wiki/Satellite_navigationhttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/GPS_receiverhttp://en.wikipedia.org/wiki/GPS#cite_note-1http://en.wikipedia.org/wiki/GPS#cite_note-1http://en.wikipedia.org/wiki/GPS#cite_note-1http://en.wikipedia.org/wiki/U.S._Department_of_Defensehttp://en.wikipedia.org/wiki/U.S._Department_of_Defensehttp://en.wikipedia.org/wiki/Roger_L._Eastonhttp://en.wikipedia.org/wiki/GPS#cite_note-losangelesmil-2http://en.wikipedia.org/wiki/GPS#cite_note-losangelesmil-2http://en.wikipedia.org/wiki/GPS#cite_note-losangelesmil-2http://en.wikipedia.org/wiki/GLONASShttp://en.wikipedia.org/wiki/Compass_navigation_systemhttp://en.wikipedia.org/wiki/Indian_Regional_Navigational_Satellite_Systemhttp://en.wikipedia.org/wiki/Indian_Regional_Navigational_Satellite_Systemhttp://en.wikipedia.org/wiki/Indian_Regional_Navigational_Satellite_Systemhttp://en.wikipedia.org/wiki/Indian_Regional_Navigational_Satellite_Systemhttp://en.wikipedia.org/wiki/Compass_navigation_systemhttp://en.wikipedia.org/wiki/GLONASShttp://en.wikipedia.org/wiki/GPS#cite_note-losangelesmil-2http://en.wikipedia.org/wiki/Roger_L._Eastonhttp://en.wikipedia.org/wiki/U.S._Department_of_Defensehttp://en.wikipedia.org/wiki/U.S._Department_of_Defensehttp://en.wikipedia.org/wiki/GPS#cite_note-1http://en.wikipedia.org/wiki/GPS_receiverhttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/Satellite_navigation


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HISTORY

The design of GPS is based partly on similar ground-based radio-navigation systems, such

as LORAN and the Decca Navigatordeveloped in the early 1940s, and used during World War

II.

Predecessors

In 1956, the German-American physicist Friedwardt Winterbergproposed a test ofgeneral

relativity (for time slowing in a strong gravitational field) using accurate atomic clocksplaced in

orbit inside artificial satellites. (To achieve accuracy requirements, GPS uses principles of

general relativity to correct the satellites' atomic clocks.) Additional inspiration for GPS came

when the Soviet Union launched the first man-made satellite, Sputnikin 1957. Two American

physicists, William Guier and George Weiffenbach, at Johns Hopkins's Applied Physics

Laboratory (APL), decided on their own to monitor Sputnik's radio transmissions.[5]Within

hours they realized that, because of the Doppler effect, they could pinpoint where the satellite

was along its orbit from the Doppler shift. The Director of the APL gave them access to

theirUNIVAC to do the heavy calculations required. The following spring, Frank McClure, the

deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem -

pinpointing the user's location given that of the satellite. (The Navy was developing the

submarine-launched Polaris missile, which required them to know the submarine's location.)

This led them and APL to develop the Transit system.

Official logo

for NAVSTAR

GPS

Emblem o

the50th Space

Wing

The first satellite navigation system, Transit, used by the United States Navy, was first

successfully tested in 1960. It used a constellation of five satellites and could provide a

navigational fix approximately once per hour. In 1967, the U.S. Navy developed

the Timation satellite that proved the ability to place accurate clocks in space, a technology
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required by GPS. In the 1970s, the ground-based Omega Navigation System, based on phase

comparison of signal transmission from pairs of stations, became the first worldwide radio

navigation system. Limitations of these systems drove the need for a more universal navigation

solution with greater accuracy.

While there were wide needs for accurate navigation in military and civilian sectors, almost none

of those were seen as justification for the billions of dollars it would cost in research,

development, deployment, and operation for a constellation of navigation satellites. During

the Cold Wararms race, the nuclear threat to the existence of the United States was the one need

that did justify this cost in the view of the United States Congress. This deterrent effect is why

GPS was funded. It is also the reason for the ultra secrecy at that time. The nuclear

triad consisted of the United States Navy's submarine-launched ballistic missiles (SLBMs) along

with United States Air Force (USAF) strategic bombers and intercontinental ballistic

missiles (ICBMs). Considered vital to the nuclear deterrence posture, accurate determination of

the SLBM launch position was a force multiplier.

Precise navigation would enable United States submarines to get an accurate fix of their

positions prior to launching their SLBMs. The USAF with two-thirds of the nuclear triad also

had requirements for a more accurate and reliable navigation system. The Navy and Air Force

were developing their own technologies in parallel to solve what was essentially the same

problem. To increase the survivability of ICBMs, there was a proposal to use mobile launch

platforms (such as Russian SS-24 and SS-25) and so the need to fix the launch position had

similarity to the SLBM situation.

In 1960, the Air Force proposed a radio-navigation system called MOSAIC (Mobile System for

Accurate ICBM Control) that was essentially a 3-D LORAN. A follow-on study called

Project 57 was worked in 1963 and it was "in this study that the GPS concept was born." That

same year the concept was pursued as Project 621B, which had "many of the attributes that you

now see in GPS" and promised increased accuracy for Air Force bombers as well as ICBMs.

Updates from the Navy Transit system were too slow for the high speeds of Air Force operation.

The Navy Research Laboratory continued advancements with their Timation (Time Navigation)

satellites, first launched in 1967, and with the third one in 1974 carrying the first atomic clock

into orbit.
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Another important predecessor to GPS came from a different branch of the United States

military. In 1964, the United States Army orbited its first Sequential Collation of Range

(SECOR) satellite used for geodetic surveying. The SECOR system included three ground-based

transmitters from known locations that would send signals to the satellite transponder in orbit. A

fourth ground-based station at an undetermined position could then use those signals to fix its

location precisely. The last SECOR satellite was launched in 1969. Decades later during the

early years of GPS, civilian surveying became one of the first fields to make use of the new

technology, because they could reap benefits of signals from the less-than-complete GPS

constellation years before it was declared operational. GPS can be thought of as an evolution of

the SECOR system where the ground-based transmitters have been migrated into orbit.

Development

With these parallel developments in the 1960s, it was realized that a superior system

could be developed by synthesizing the best technologies from 621B, Transit, Timation, and

SECOR in a multi-service program.

During Labor Day weekend in 1973, a meeting of about 12 military officers at the Pentagon

discussed the creation of aDefense Navigation Satellite System (DNSS). It was at this meeting

that "the real synthesis that became GPS was created." Later that year, the DNSS program was

namedNavstar. With the individual satellites being associated with the name Navstar (as with

the predecessors Transit and Timation), a more fully encompassing name was used to identify

the constellation of Navstar satellites,Navstar-GPS, which was later shortened simply to GPS.[12]

AfterKorean Air Lines Flight 007, carrying 269 people, was shot down in 1983 after straying

into the USSR's prohibited airspace, in the vicinity ofSakhalin and Moneron Islands, President

Ronald issued a directive making GPS freely available for civilian use, once it was sufficiently

developed, as a common good. The first satellite was launched in 1989, and the 24th satellite was

launched in 1994. Roger L. Easton is widely credited as the primary inventor of GPS.

Initially, the highest quality signal was reserved for military use, and the signal available for

civilian use was intentionally degraded (Selective Availability). This changed with President Bill

Clintonordering Selective Availability to be turned off at midnight May 1, 2000, improving the

precision of civilian GPS from 100 meters (330 ft) to 20 meters (66 ft). The executive order

signed in 1996 to turn off Selective Availability in 2000 was proposed by the US Secretary of
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Defense, William Perry, because of the widespread growth ofdifferential GPS services to

improve civilian accuracy and eliminate the US military advantage. Moreover, the US military

was actively developing technologies to deny GPS service to potential adversaries on a regional

basis.

Over the last decade, the U.S. has implemented several improvements to the GPS service,

including new signals for civil use and increased accuracy and integrity for all users, all while

maintaining compatibility with existing GPS equipment.

GPS modernization has now become an ongoing initiative to upgrade the Global Positioning

System with new capabilities to meet growing military, civil, and commercial needs. The

program is being implemented through a series of satellite acquisitions, including GPS Block III

and the Next Generation Operational Control System (OCX). The U.S. Government continues to

improve the GPS space and ground segments to increase performance and accuracy.

GPS is owned and operated by the United States Government as a national resource. Department

of Defense (DoD) is the steward of GPS.Interagency GPS Executive Board (IGEB) oversaw

GPS policy matters from 1996 to 2004. After that the National Space-Based Positioning,

Navigation and Timing Executive Committee was established by presidential directive in 2004 to

advise and coordinate federal departments and agencies on matters concerning the GPS and

related systems. The executive committee is chaired jointly by the deputy secretaries of defense

and transportation. Its membership includes equivalent-level officials from the departments of

state, commerce, and homeland security, the joint chiefs of staff, and NASA. Components of the

executive office of the president participate as observers to the executive committee, and the

FCC chairman participates as a liaison.

The DoD is required by law to "maintain a Standard Positioning Service (as defined in the

federal radio navigation plan and the standard positioning service signal specification) that will

be available on a continuous, worldwide basis," and "develop measures to prevent hostile use of

GPS and its augmentations without unduly disrupting or degrading civilian uses."
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Basic concept of GPS

A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high

above the Earth. Each satellite continually transmits messages that include

the time the message was transmitted

satellite position at time of message transmission

The receiver uses the messages it receives to determine the transit time of each message and

computes the distance to each satellite using the speed of light. Each of these distances and

satellites' locations define a sphere. The receiver is on the surface of each of these spheres when

the distances and the satellites' locations are correct. These distances and satellites' locations areused to compute the location of the receiver using the navigation equations. This location is then

displayed, perhaps with a moving map display orlatitude and longitude; elevation information

may be included. Many GPS units show derived information such as direction and speed,

calculated from position changes.

In typical GPS operation, four or more satellites must be visible to obtain an accurate result. Four

sphere surfaces typically do not intersect. Because of this we can say with confidence that when

we solve the navigation equations to find an intersection, this solution gives us the position of thereceiver along with accurate time thereby eliminating the need for a very large, expensive, and

power hungry clock. The very accurately computed time is used only for display or not at all in

many GPS applications, which use only the location. A number of applications for GPS do make

use of this cheap and highly accurate timing. These include time transfer, traffic signal timing,

and synchronization of cell phone base stations.

Although four satellites are required for normal operation, fewer apply in special cases. If one

variable is already known, a receiver can determine its position using only three satellites. For

example, a ship or aircraft may have known elevation. Some GPS receivers may use additional

clues or assumptions such as reusing the last known altitude, dead reckoning, inertial navigation,

or including information from the vehicle computer, to give a (possibly degraded) position when

fewer than four satellites are visible
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Structure

The current GPS consists of three major segments. These are the space segment (SS), a

control segment (CS), and a user segment (US). The U.S. Air Force develops, maintains, and

operates the space and control segments. GPS satellites broadcast signals from space, and each

GPS receiver uses these signals to calculate its three-dimensional location (latitude, longitude,

and altitude) and the current time.

The space segment is composed of 24 to 32 satellites in medium Earth orbit and also

includes the payload adapters to the boosters required to launch them into orbit. The control

segment is composed of a master control station, an alternate master control station, and a host of

dedicated and shared ground antennas and monitor stations. The user segment is composed of

hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning

Service, and tens of millions of civil, commercial, and scientific users of the Standard

Positioning Service

Space segment

The space segment (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in

GPS parlance. The GPS design originally called for 24 SVs, eight each in three approximately

circularorbits, but this was modified to six orbital planes with four satellites each. The orbits are

centered on the Earth, not rotating with the Earth, but instead fixed with respect to the distant

stars.[46]The six orbit planes have approximately 55inclination (tilt relative to Earth's equator)

and are separated by 60 right ascension of the ascending node (angle along the equator from a

reference point to the orbit's intersection). The orbital period is one-half a sidereal day, i.e., 11

hours and 58 minutes. The orbits are arranged so that at least six satellites are always within lineof sight from almost everywhere on Earth's surface. The result of this objective is that the four

satellites are not evenly spaced (90 degrees) apart within each orbit. In general terms, the angular

difference between satellites in each orbit is 30, 105, 120, and 105 degrees apart which, of

course, sum to 360 degrees.
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Orbiting at an altitude of approximately 20,200 km (12,600 mi); orbital radius of approximately

26,600 km (16,500 mi), each SV makes two complete orbits each sidereal day, repeating the

same ground track each day. This was very helpful during development because even with only

four satellites, correct alignment means all four are visible from one spot for a few hours each

day. For military operations, the ground track repeat can be used to ensure good coverage in

combat zones.

As of December 2012, there are 32 satellites in the GPS constellation. The additional satellites

improve the precision of GPS receiver calculations by providing redundant measurements. With

the increased number of satellites, the constellation was changed to a non uniform arrangement.

Such an arrangement was shown to improve reliability and availability of the system, relative to

a uniform system, when multiple satellites fail. About nine satellites are visible from any point

on the ground at any one time (see animation at right), ensuring considerable redundancy over

the minimum four satellites needed for a position.

Control segment

The control segment is composed of

1. a master control station (MCS),

2. an alternate master control station,

3. four dedicated ground antennas and

4. six dedicated monitor stations

The MCS can also access U.S. Air Force Satellite Control Network (AFSCN) ground antennas

(for additional command and control capability) and NGA (National Geospatial-Intelligence

Agency) monitor stations. The flight paths of the satellites are tracked by dedicated U.S. Air

Force monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado

Springs, Colorado and Cape Canaveral, along with shared NGA monitor stations operated in

England, Argentina, Ecuador, Bahrain, Australia and Washington DC. The tracking information

is sent to the Air Force Space Command MCS at Schriever Air Force Base 25 km (16 mi) ESE

of Colorado Springs, which is operated by the 2nd Space Operations Squadron(2 SOPS) of the

U.S. Air Force. Then 2 SOPS contacts each GPS satellite regularly with a navigational update

using dedicated or shared (AFSCN) ground antennas (GPS dedicated ground antennas are
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located at Kwajalein, Ascension Island, Diego Garcia, and Cape Canaveral). These updates

synchronize the atomic clocks on board the satellites to within a few nanoseconds of each other,

and adjust the ephemeris of each satellite's internal orbital model. The updates are created by

a Kalman filterthat uses inputs from the ground monitoring stations, space weatherinformation,

and various other inputs.

Satellite maneuvers are not precise by GPS standards. So to change the orbit of a satellite, the

satellite must be marked unhealthy, so receivers will not use it in their calculation. Then the

maneuver can be carried out, and the resulting orbit tracked from the ground. Then the new

ephemeris is uploaded and the satellite marked healthy again.

The Operation Control Segment (OCS) currently serves as the control segment of record. It

provides the operational capability that supports global GPS users and keeps the GPS system

operational and performing within specification.

OCS successfully replaced the legacy 1970s-era mainframe computer at Schriever Air Force

Base in September 2007. After installation, the system helped enable upgrades and provide a

foundation for a new security architecture that supported the U.S. armed forces. OCS will

continue to be the ground control system of record until the new segment, Next Generation GPS

Operation Control System (OCX), is fully developed and functional.

The new capabilities provided by OCX will be the cornerstone for revolutionizing GPSsmission capabilities, and enabling Air Force Space Command to greatly enhance GPS

operational services to U.S. combat forces, civil partners and myriad of domestic and

international users.

The GPS OCX program also will reduce cost, schedule and technical risk. It is designed to

provide 50% sustainment cost savings through efficient software architecture and Performance-

Based Logistics. In addition, GPS OCX expected to cost millions less than the cost to upgrade

OCS while providing four times the capability.

The GPS OCX program represents a critical part of GPS modernization and provides significant

information assurance improvements over the current GPS OCS program.

OCX will have the ability to control and manage GPS legacy satellites as well as the next

generation of GPS III satellites, while enabling the full array of military signals.
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Built on a flexible architecture that can rapidly adapt to the changing needs of todays and

future GPS users allowing immediate access to GPS data and constellations status through

secure, accurate and reliable information.

Empowers the war fighter with more secure, actionable and predictive information to

enhance situational awareness.

Enables new modernized signals (L1C, L2C, and L5) and has M-code capability, which the

legacy system is unable to do.

Provides significant information assurance improvements over the current program including

detecting and preventing cyber attacks, while isolating, containing and operating during such

attacks.

Supports higher volume near real-time command and control capabilities.

On September 14, 2011, the U.S. Air Force announced the completion of GPS OCX Preliminary

Design Review and confirmed that the OCX program is ready for the next phase of development.

The GPS OCX program has achieved major milestones and is on track to support the GPS IIIA

launch in May 2014.

Communication:

Main article: GPS signals

The navigational signals transmitted by GPS satellites encode a variety of information including

satellite positions, the state of the internal clocks, and the health of the network. These signals

are transmitted on two separate carrier frequencies that are common to all satellites in the

network. Two different encodings are used: a public encoding that enables lower resolution

navigation, and an encrypted encoding used by the U.S. military.
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Message format :

GPS message format

Sub frames Description

1Satellite clock,GPS time relationship

23Ephemeris(precise satellite orbit)

45Almanac component(satellite network synopsis,error correction)

Each GPS satellite continuously broadcasts a navigation message on L1 C/A and L2 P/Y

frequencies at a rate of 50 bits per second . Each complete message takes 750 seconds (12

1/2 minutes) to complete. The message structure has a basic format of a 1500-bit-long frame

made up of five s

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