an embedded systems and rfid solution for transport related issues
TRANSCRIPT
AN EMBEDDED SYSTEMS AND RFID SOLUTION FOR TRANSPORT RELATED ISSUES
CHAPTER -1
INTRODUCTION TO EMBEDDED SYSTEMS
1.1 WHAT IS AN EMBEDDED SYSTEM?
An embedded system can be defined as a computing device that does a specific
focused job. Appliances such as the air-conditioner, VCD player, DVD player, printer, fax
machine, mobile phone etc. are examples of embedded systems. Each of these appliances will
have a processor and special hardware to meet the specific requirement of the application
along with the embedded software that is executed by the processor for meeting that specific
requirement. The embedded software is also called “firm ware”. The desktop/laptop computer
is a general purpose computer. You can use it for a variety of applications such as playing
games, word processing, accounting, software development and so on. In contrast, the
software in the embedded systems is always fixed.
1.1.1 HISTORY
In the earliest years of computers in the 1940s, computers were sometimes dedicated
to a single task, but were too large to be considered "embedded". Over time however, the
concept of programmable controllers developed from a mix of computer technology, solid
state devices, and traditional electromechanical sequences.
The first recognizably modern embedded system was the Apollo Guidance Computer,
developed by Charles Stark Draper at the MIT Instrumentation Laboratory. At the project's
inception, the Apollo guidance computer was considered the riskiest item in the Apollo
project. The use of the then new monolithic integrated circuits, to reduce the size and weight,
increased this risk.
The first mass-produced embedded system was the Autonetics D-17 guidance computer for
the Minuteman (missile), released in 1961. It was built from transistor logic and had a hard
disk for main memory. When the Minuteman II went into production in 1966, the D-17 was
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replaced with a new computer that was the first high-volume use of integrated circuits. This
program alone reduced prices on quad nand gate ICs from $1000/each to $3/each, permitting
their use in commercial products.
Since these early applications in the 1960s, embedded systems have come down in
price. There has also been an enormous rise in processing power and functionality. For
example the first microprocessor was the Intel 4004, which found its way into calculators and
other small systems, but required external memory and support chips.
In 1978 National Engineering Manufacturers Association released the standard for a
programmable microcontroller. The definition was an almost any computer-based controller.
They included single board computers, numerical controllers, and sequential controllers in
order to perform event-based instructions.
By the mid-1980s, many of the previously external system components had been
integrated into the same chip as the processor, resulting in integrated circuits called
microcontrollers, and widespread use of embedded systems became feasible.
As the cost of a microcontroller fell below $1, it became feasible to replace expensive
knob-based analog components such as potentiometers and variable capacitors with digital
electronics controlled by a small microcontroller with up/down buttons or knobs. By the end
of the 80s, embedded systems were the norm rather than the exception for almost all
electronics devices, a trend which has continued since.
1.2 EMBEDDED SYSTEMS ARE CHARACTERIZED BY SOME
SPECIAL FEATURES LISTED BELOW
Embedded systems do a very specific task; they cannot be programmed to do different
things. . Embedded systems have very limited resources, particularly the memory.
Generally, they do not have secondary storage devices such as the C DROM or the
floppy disk. Embedded systems have to work against some deadlines. A specific job
has to be completed within a specific time. In some embedded systems, called real-
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time systems, the deadlines are stringent. Missing a deadline may cause a catastrophe-
loss of life or damage to property. Embedded systems are constrained for power. As
many embedded systems operate through a battery, the power consumption has to be
very low.
Embedded systems need to be highly reliable. Once in a while, pressing ALT-CTRL-
OEL is OK on your desktop, but you cannot afford to reset your embedded system.
Some embedded systems have to operate in extreme environmental conditions such as
very high temperatures and humidity.
Embedded systems that address the consumer market (for exam-ple, electronic toys)
are very cost-sensitive: Even a reduction of $0.1 is lot of cost saving, because
thousands or millions systems may be sold.
Unlike desktop computers in which the hardware platform is dominated by Intel and
the operating system is dominated by Microsoft, there is a wide variety of processors
and operating systems for the embedded systems. So, choosing the right plat-form is
the most complex task.
1.2.1 APPLICATION AREAS
Nearly 99 per cent of the processors manufactured end up in embedded systems. The
embedded system market is one of the highest growth areas as these systems are used in very
market segment- consumer electronics, office automation, industrial automation, biomedical
engineering, wireless communication, data communication, telecommunications,
transportation, military and so on.
1.2.2 CONSUMER APPLIANCES
At home we use a number of embedded systems which include digital camera, digital
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diary, DVD player, electronic toys, microwave oven, remote controls for TV and air-
conditioner, VCO player, video game consoles, video recorders etc. Today’s high-tech car has
about 20 embedded systems for transmission control, engine spark control, air-conditioning,
navigation etc. Even wristwatches are now becoming embedded systems. The palmtops are
powerful embedded systems using which we can carry out many general-purpose tasks such
as playing games and word processing.
1.2.3 OFFICE AUTOMATION
The office automation products using embedded systems are copying machine, fax
machine, key telephone, modem, printer, scanner etc. Industrial automation: Today a lot of
industries use embedded systems for process control. These include pharmaceutical, cement,
sugar, oil exploration, nuclear energy, electricity generation and transmission. The embedded
systems for industrial use are designed to carry out specific tasks such as monitoring the
temperature, pressure, humidity, voltage, current etc., and then take appropriate action based
on the monitored levels to control other devices or to send information to a centralized
monitoring station. In hazardous industrial environment, where human presence has to be
avoided, robots are used, which are programmed to do specific jobs. The robots are now
becoming very powerful and carry out many interesting and complicated tasks such as
hardware assembly.
1.3 CATEGORIES OF EMBEDDED SYSTEMS
Based on functionality and performance requirements, embedded systems can be
categorized as:
Stand-alone embedded systems
Real-time systems
Networked information appliances
Mobile devices
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1.3.1 STAND ALONE EMBEDDED SYSTEMS
As the name implies, stand-alone systems work in stand-alone mode. They take inputs,
process them and produce the desired output. The input can be electrical signals from
transducers or commands from a human being such as the pressing of a button. The output
can be electrical signals to drive another system, an LED display or LCD display for
displaying of information to the users. Embedded systems used in process co~1’rol,
automobiles, consumer electronic items etc. fall into this category. In a process control
system, the inputs are from sensors that convert a physical entity such as temperature or
pressure into its equivalent electrical signal. These electrical signals are processed by the
system and the appropriate electrical signals are produced using which an action is taken such
as opening a valve. A few embedded systems used at home are shown in fig
Figure1-1 stand alone embedded systems at home
1.3.2 REAL TIME SYSTEMS
Embedded systems in which some specific work has to be done in a specific time
period are called real-time systems. For example: consider a system that has to open a valve
within 30milliseconds when the humidity crosses a particular threshold. If the valve is not
opened within 30 milliseconds, a catastrophe may occur. Such systems with strict deadlines
are called hard real-time systems. In some embedded systems, deadlines are imposed, but not
adhering to them once in a while may not lead to a catastrophe. For example, consider a DVD
player. Suppose, you give a command to the DVD player from are mote control, and there is a
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delay of a few milliseconds in executing that command. But, this delay won’t lead to a serious
simplification. Such systems are called soft real-time systems.
Figure 1-2 Hard Real Time embedded Systems
1.3.3 NETWORKED INFORMATION APPLIANCES
Embedded systems that are provided with network interfaces and accessed by
networks such as Local Area Network or the Internet are called networked information
appliances. Such embedded systems are connected to a network, typically a network running
TCP/IP (Transmission Control Protocol! Internet Protocol) protocol suite, such as the Internet
or a company’s Intranet. These systems have emerged in recent years These systems run the
protocol TCP/IP stack and get connected either through PPP or Ethernet to a network and
communicate with other nodes in the network. Here are some examples of such systems:
Figure 1-3 Networked Information Appliance
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1.3.4 MOBILE DEVICES
Mobile devices such as mobile phones, Personal Digital Assistants (PDAs), smart
phones etc. are a special category of embedded systems. Though the PDAs do many general
purpose tasks, they need to be designed just like the ‘conventional’ embedded systems. The
limitations of –the mobile devices- memory constraints, small size, lack of good user
interfaces such as full-fledged keyboard and display etc.-are same as those found in the
embedded systems discussed above. Hence, mobile devices are considered as embedded
systems. However, the PDAs are now capable of supporting general-purpose application
software such as word processors, games, etc.
User Interfaces
Embedded systems range from no user interface at all - dedicated only to one task - to
full user interfaces similar to desktop operating systems in devices such as PDAs.
Simple Systems
Simple embedded devices use buttons, LEDs, and small character- or digit-only
displays, often with a simple menu system.
In More Complex Systems
A full graphical screen, with touch sensing or screen-edge buttons provides flexibility
while minimizing space used: the meaning of the buttons can change with the screen, and
selection involves the natural behavior of pointing at what's desired. Handheld systems often
have a screen with a "joystick button" for a pointing device.
The rise of the World Wide Web has given embedded designers another quite different
option: providing a web page interface over a network connection. This avoids the cost of a
sophisticated display, yet provides complex input and display capabilities when needed, on
another computer. This is successful for remote, permanently installed equipment. In
particular, routers take advantage of this ability.
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CPU Platform
Embedded processors can be broken into two distinct categories: microprocessors (μP)
and micro controllers (μC). Micro controllers have built-in peripherals on the chip, reducing
size of the system.
There are many different CPU architectures used in embedded designs such as ARM,
MIPS, Coldfire/68k, PowerPC, x86, PIC, 8051, Atmel AVR, Renesas H8, SH, V850, FR-V,
M32R, Z80, Z8, etc. A common configuration for very-high-volume embedded systems is
the system on a chip (SoC), an application-specific integrated circuit (ASIC), for which the
CPU core was purchased and added as part of the chip design. A related scheme is to use a
field-programmable gate array (FPGA), and program it with all the logic, including the CPU.
1.4 PERIPHERALS
Embedded Systems talk with the outside world via peripherals, such as:
Serial Communication Interfaces (SCI): RS-232, RS-422, RS-485 etc
Synchronous Serial Communication Interface: I2C, JTAG, SPI, SSC and ESSI
Universal Serial Bus (USB)
Networks: Controller Area Network, Lan Works, etc
Timers: PLL(s), Capture/Compare and Time Processing Units
Discrete IO: aka General Purpose Input Output (GPIO)
1.4.1 TOOLS
As for other software, embedded system designers use compilers, assemblers, and
debuggers to develop embedded system software. However, they may also use some more
specific tools:
An in-circuit emulator (ICE) is a hardware device that replaces or plugs into the
microprocessor, and provides facilities to quickly load and debug experimental code in
the system.
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Utilities to add a checksum or CRC to a program, so the embedded system can check
if the program is valid.
For systems using digital signal processing, developers may use a math workbench
such as MathCAD or Mathematic to simulate the mathematics.
Custom compilers and linkers may be used to improve optimization for the particular
hardware.
An embedded system may have its own special language or design tool, or add
enhancements to an existing language.
Software tools can come from several sources:
Software companies that specialize in the embedded market
Ported from the GNU software development tools
Sometimes, development tools for a personal computer can be used if the embedded
processor is a close relative to a common PC processor
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CHAPTER -2
INTRODUCTION TO MICROCONTROLLERS
2.1 MICROCONTROLLER
Microprocessors and microcontrollers are widely used in embedded systems products.
Microcontroller is a programmable device. A microcontroller has a CPU in addition to a fixed
amount of RAM, ROM, I/O ports and a timer embedded all on a single chip. The fixed
amount of on-chip ROM, RAM and number of I/O ports in microcontrollers makes them ideal
for many applications in which cost and space are critical.
The Intel 8051 is Harvard architecture, single chip microcontroller (µC) which was
developed by Intel in 1980 for use in embedded systems. It was popular in the 1980s and
early 1990s, but today it has largely been superseded by a vast range of enhanced devices with
8051-compatible processor cores that are manufactured by more than 20 independent
manufacturers including Atmel, Infineon Technologies and Maxim Integrated Products.
8051 is an 8-bit processor, meaning that the CPU can work on only 8 bits of data at a
time. Data larger than 8 bits has to be broken into 8-bit pieces to be processed by the CPU.
8051 is available in different memory types such as UV-EPROM, Flash and NV-RAM.
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2.2 FEATURES OF AT89S52
8K Bytes of Re-programmable Flash Memory.
RAM is 256 bytes.
4.0V to 5.5V Operating Range.
Fully Static Operation: 0 Hz to 33 MHz’s
Three-level Program Memory Lock.
256 x 8-bit Internal RAM.
32 Programmable I/O Lines.
Three 16-bit Timer/Counters.
Eight Interrupt Sources.
Full Duplex UART Serial Channel.
Low-power Idle and Power-down Modes.
Interrupt recovery from power down mode.
Watchdog timer.
Dual data pointer.
Power-off flag.
Fast programming time.
Flexible ISP programming (byte and page mode).
2.3 DESCRIPTION OF MICROCONTROLLER
The AT89s52 is a low-voltage, high-performance CMOS 8-bit microcomputer with
8K bytes of Flash programmable memory. The device is manufactured using Atmel’s high
density nonvolatile memory technology and is compatible with the industry-standard MCS-51
instruction set. The on chip flash allows the program memory to be reprogrammed in system
or by a conventional non volatile memory programmer. By combining a versatile 8-bit CPU
with Flash on a monolithic chip, the Atmel AT89s52 is a powerful microcomputer, which
provides a highly flexible and cost-effective solution to many embedded control applications.
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In addition, the AT89s52 is designed with static logic for operation down to zero
frequency and supports two software selectable power saving modes. The Idle Mode stops the
CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue
functioning. The power-down mode saves the RAM contents but freezes the oscillator
disabling all other chip functions until the next hardware reset.
Figure 2-1 Pin Diagram
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Figure 2-2 Block Diagram
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2.3 PIN DESCRIPTION
VCC Pin 40 provides supply voltage to the chip. The voltage source is +5V.
GND Pin 20 is the ground.
PORT 0
Port 0 is an 8-bit open drain bidirectional 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
accesses to external program and data memory. In this mode, P0 has internal pull-ups. Port 0
also receives the code bytes during Flash programming and outputs the code bytes during
Program verification. External pull-ups are required during program verification.
PORT 1
Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output
buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled
high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are
externally being pulled low will source current (IIL) because of the internal pull-ups. In
addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input
(P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX), respectively, as shown in the
following table.
Port 1 also receives the low-order address bytes during Flash programming and verification.
Table 2-1 Description Of Port 1 Pins
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PORT 2
Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output
buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled
high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are
externally being pulled low will source current (IIL) because of the internal pull-ups.
Port 2 emits the high-order address byte during fetches from external program
memory and during accesses to external data memory that uses 16-bit addresses (MOVX @
DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. During
accesses to external data memory that uses 8-bit addresses (MOVX @ RI), Port 2 emits the
contents of the P2 Special Function Register. The port also receives the high-order address
bits and some control signals during Flash programming and verification.
PORT 3
Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output
buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled
high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are
externally being pulled low will source current (IIL) because of the pull-ups. Port 3 receives
some control signals for Flash programming and verification. Port 3 also serves the functions
of various special features of the AT89S52, as shown in the following table.
Table 2-2 Description of Port 3 Pins
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RST
Reset input A high on this pin for two machine cycles while the oscillator is running
resets the device. This pin drives high for 98 oscillator periods after the Watchdog times out.
The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the
default state of bit DISRTO, the RESET HIGH out feature is enabled.
ALE / PROG
Address Latch Enable (ALE) is an output pulse for latching the low byte of the
address during accesses to external memory. This pin is also the program pulse input (PROG)
during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6 the
oscillator frequency and may be used for external timing or clocking purposes. Note,
however, that one ALE pulse is skipped during each access to external data memory.
PSEN
Program Store Enable (PSEN) is the read strobe to external program memory. When
the AT89S52 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.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
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Oscillator Connections
C1, C2 = 30 pF ± 10 pF for Crystals = 40 pF ± 10 pF for Ceramic Resonators
External Clock Drive Configuration
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier
that can be configured for use as an on-chip oscillator. Either a quartz crystal or ceramic
resonator may be used. To drive the device from an external clock source, XTAL2 should be
left unconnected while XTAL1 is driven. There are no requirements on the duty cycle of the
external clock signal, since the input to the internal clocking circuitry is through a divide-by-
two flip-flop, but minimum and maximum voltage high and low time specifications must be
observed.
2.4 SPECIAL FUNCTION REGISTERS
A map of the on-chip memory area called the Special Function Register (SFR) space
is shown in the following table. It should be noted that not all of the addresses are occupied
and unoccupied addresses may not be implemented on the chip. Read accesses to these
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addresses will in general return random data, and write accesses will have an indeterminate
effect.
User software should not write 1s to these unlisted locations, since they may be used
in future products to invoke new features. In that case, the reset or inactive values of the new
bits will always be 0.
Table 2-3 AT89S52 SFR Map and Reset Values
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Power off Flag
The Power Off Flag (POF) is located at bit 4 (PCON.4) in the PCON SFR. POF is set
to “1” during power up. It can be set and rest under software control and is not affected by
reset.
Memory Organization
MCS-51 devices have a separate address space for Program and Data Memory. Up to
64K bytes each of external Program and Data Memory can be addressed.
Program Memory
If the EA pin is connected to GND, all program fetches are directed to external
memory. On the AT89S52, if EA is connected to VCC, program fetches to addresses 0000H
through 1FFFH are directed to internal memory and fetches to addresses 2000H through
FFFFH are to external memory.
Data Memory
The AT89S52 implements 256 bytes of on-chip RAM. The upper 128 bytes occupy a
parallel address space to the Special Function Registers. This means that the upper 128 bytes
have the same addresses as the SFR space but are physically separate from SFR space. When
an instruction accesses an internal location above address 7FH, the address mode used in the
instruction specifies whether the CPU accesses the upper 128 bytes of RAM or the SFR
space. Instructions which use direct addressing access the SFR space.
For example, the following direct addressing instruction accesses the SFR at location 0A0H
(which is P2).
MOV 0A0H, #data
The instructions that use indirect addressing access the upper 128 bytes of RAM. For
example, the following indirect addressing instruction, where R0 contains 0A0H, accesses the
data byte at address 0A0H, rather than P2 (whose address is 0A0H).
MOV @R0, #data
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It should be noted that stack operations are examples of indirect addressing, so the
upper 128 bytes of data RAM are available as stack space.
UART
The Atmel 8051 Microcontrollers implement three general purpose, 16-bit timers/
counters. They are identified as Timer 0, Timer 1 and Timer 2 and can be independently
configured to operate in a variety of modes as a timer or as an event counter. When operating
as a timer, the timer/counter runs for a programmed length of time and then issues an interrupt
request. When operating as a counter, the timer/counter counts negative transitions on an
external pin. After a preset number of counts, the counter issues an interrupt request. The
various operating modes of each timer/counter are described in the following sections.
A basic operation consists of timer registers THx and TLx (x= 0, 1) connected in
cascade to form a 16-bit timer. Setting the run control bit (TRx) in TCON register turns the
timer on by allowing the selected input to increment TLx. When TLx overflows it increments
THx; when THx overflows it sets the timer overflow flag(TFx) in TCON register. Setting the
TRx does not clear the THx and TLx timer registers. Timer registers can be accessed to obtain
the current count or to enter preset values. They can be read at any time but TRx bit must be
cleared to preset their values, otherwise the behavior of the timer/counter is unpredictable.
The C/T control bit (in TCON register) selects timer operation or counter operation,
by selecting the divided-down peripheral clock or external pin Tx as the source for the
counted signal. TRx bit must be cleared when changing the mode of operation, otherwise the
behavior of the timer/counter is unpredictable. For timer operation (C/Tx# = 0), the timer
register counts the divided-down peripheral clock. The timer register is incremented once
every peripheral cycle (6 peripheral clock periods). The timer clock rate is FPER / 6, i.e.
FOSC / 12 in standard mode or FOSC / 6 inX2 mode For counter operation (C/Tx# = 1), the
timer register counts the negative transitions on the Tx external input pin. The external input
is sampled every peripheral cycle. When the sample is high in one cycle and low in the next
one, the counter is incremented.
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Since it takes 2 cycles (12 peripheral clock periods) to recognize a negative transition, the
maximum count rate is FPER / 12, i.e. FOSC / 24 in standard mode or FOSC / 12 in X2mode.
There are no restrictions on the duty cycle of the external input signal, but to ensure that a
given level is sampled at least once before it changes, it should be held forat least one full
peripheral cycle. In addition to the “timer” or “counter” selection, Timer 0 and Timer 1 have
four operating modes from which to select which are selected by bit-pairs (M1, M0) in
TMOD. Modes 0, 1and 2 are the same for both timer/counters. Mode 3 is different.
The four operating modes are described below. Timer 2, has three modes of operation:
‘capture’, ‘auto-reload’ and ‘baud rate generator’.
TIMER 0
Timer 0 functions as either a timer or event counter in four modes of operation. Timer
0 is controlled by the four lower bits of the TMOD register and bits0, 1, 4 and 5 of the TCON
register. TMOD register selects the method of timer gating (GATE0), timer or counter
operation (T/C0#) and mode of operation (M10and M00). The TCON register provides timer
0 control functions: overflow flag (TF0), run control bit (TR0), interrupt flag (IE0) and
interrupt type control bit (IT0).
For normal timer operation (GATE0= 0), setting TR0 allows TL0 to be incremented
by the selected input. Setting GATE0 and TR0 allows external pin INT0# to control timer
operation.
Timer 0 overflow(count rolls over from all 1s to all 0s) sets TF0 flag, generating an
interrupt request. It is important to stop timer/counter before changing mode.
Mode 0 (13-bit timer)
Mode 0 configures timer 0 as a 13-bit timer which is set up as an 8-bit timer (TH0
register)with a modulo-32 prescaler implemented with the lower five bits of the TL0 register.
The upper three bits of TL0 register are indeterminate and should be ignored. Prescaler
overflow increments the TH0 register.
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As the count rolls over from all 1’s to all 0’s, it sets the timer interrupt flag TF0. The counted
input is enabled to the Timer when TR0 = 1 and either GATE = 0 or INT0 = 1.(Setting GATE
= 1 allows the Timer to be controlled by external input INT0, to facilitate pulse width
measurements). TR0 is a control bit in the Special Function register TCON. GATE is in
TMOD.
The 13-bit register consists of all 8 bits of TH0 and the lower 5 bits of TL0. The upper
3bits of TL0 are indeterminate and should be ignored. Setting the run flag (TR0) does not
clear the registers. Mode 0 operation is the same for Timer 0 as for Timer 1. There are two
different GATE bits, one for Timer 1 (TMOD.7) and one for Timer 0 (TMOD.3).
Timer/Counter x (x = 0 or 1) in Mode 0
Figure 2-4 Timer/Counter in Mode 0
Mode 1 (16-bitTimer)
Mode 1 is the same as Mode 0, except that the Timer register is being run with all
16bits.Mode 1 configures timer 0 as a 16-bit timer with the TH0 and TL0 registers connected
in cascade. The selected input increments the TL0 register.
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Timer/Counter x (x = 0 or 1) in Mode 1
Figure 2-5 Timer/counter in mode1
Mode 2 (8-bit Timer with Auto-Reload)
Mode 2 configures timer 0 as an 8-bit timer (TL0 register) that automatically reloads
from the TH0 register. TL0 overflow sets TF0 flag in the TCON register and reloads TL0
with the contents of TH0, which is preset by software.
When the interrupt request is serviced, hardware clears TF0. The reload leaves
TH0unchanged. The next reload value may be changed at any time by writing it to the
TH0register.Mode 2 operation is the same for Timer/Counter 1.
Timer/Counter x (x = 0 or 1) in Mode 2
Figure 2-6 Timer/Counter in mode2
Mode 3 (Two 8-bitTimers)
Mode 3 configures timer 0 so that registers TL0 and TH0 operate as separate 8-bit
timers. This mode is provided for applications requiring an additional 8-bittimer or counter.
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TL0 uses the timer 0 control bits C/T0# and GATE0 in the TMOD register, and TR0
and TF0 in the TCON register in the normal manner. TH0 is locked into a timer function
(counting FPER /6) and takes over use of the timer 1 interrupt (TF1) and run control (TR1)
bits. Thus, operation of timer 1 is restricted when timer 0 is in mode 3.
Timer/Counter 0 in Mode 3: Two 8-bit Counters
Figure 2-7 Timer/Counter in Mode 3
Timer 1:
Timer 1 is identical to timer 0, except for mode 3, which is a hold-count mode. The
following comments help to understand the differences:
• Timer 1 functions as either a timer or event counter in three modes of operation.
Timer1’s mode 3 is a hold-count mode.
• Timer 1 is controlled by the four high-order bits of the TMOD register and bits 2, 3,
6 and 7 of the TCON register.
The TMOD register selects the method of timer gating (GATE1), timer or counter
operation (C/T1#) and mode of operation (M11 and M01). The TCON register provides timer
1 control functions: overflow flag (TF1), run control bit (TR1), interrupt flag (IE1) and
interrupt type control bit (IT1).
Timer 1 can serve as the baud rate generator for the serial port. Mode 2 is best suited
for this purpose.
For normal timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented
by the selected input. Setting GATE1 and TR1 allows external pin INT1# to control
timer operation.
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Timers 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag generating
an interrupt request.
When timer 0 is in mode 3, it uses timer 1’s overflow flag (TF1) and run control bit
(TR1). For this situation, use timer 1 only for applications that do not require an
interrupt (such as a baud rate generator for the serial port) and switch timer 1 in and
out of mode 3 to turn it off and on.
It is important to stop timer/counter before changing modes.
Mode 0 (13-bitTimer)
Mode 0 configures Timer 1 as a 13-bit timer, which is set up as an 8-bit timer (TH1
register)with a modulo-32 prescaler implemented with the lower 5 bits of the TL1 register.
The upper 3 bits of the TL1 register are ignored. Prescaler overflowincrements the TH1
register.
Mode 1 (16-bitTimer)
Mode 1 configures Timer 1 as a 16-bit timer with the TH1 and TL1 registers
connected in cascade. The selected input increments the TL1 register.
Mode 2 (8-bit Timer with Auto Reload)
Mode 2 configures Timer 1 as an 8-bit timer (TL1 register) with automatic reload
from the TH1 register on overflow. TL1 overflow sets the TF1 flag in the TCON register and
reloads TL1 with the contents of TH1, which is preset by software. The reload leaves TH1
unchanged.
Mode 3 (Halt)
Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt
Timer 1 when TR1 run control bit is not available i.e., when Timer 0 is in mode 3.
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Timer 2
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event
counter. The type of operation is selected by bit C/T2 in the SFR T2CON. Timer 2 has three
operating modes: capture, auto-reload (up or down counting), and baud rate generator. The
modes are selected by bits in T2CON. Timer 2 consists of two 8-bit registers, TH2 and TL2.
In the Timer function, the TL2 register is incremented every machine cycle. Since a machine
cycle consists of 12 oscillator periods, the count rate is 1/12 of the oscillator frequency.
Table 2-4 Timer 2 Operating Modes
In the Counter function, the register is incremented in response to a 1-to-0 transition at
its corresponding external input pin, T2. In this function, 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. To ensure that a given level is sampled at least once before it
changes, the level should be held for at least one full machine cycle.
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CHAPTER -3
DESCRIPTION OF MODULES
3.1 BLOCK DIAGRAM
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3.2 POWER SUPPLY
There are many types of power supply. Most are designed to convert high voltage AC
mains electricity to a suitable low voltage supply for electronics circuits and other devices. A
power supply can by broken down into a series of blocks, each of which performs a particular
function.
For example a 5V regulated supply:
Figure 3-1 Block Diagram of a Regulated power Supply System
Each of the blocks is described in more detail below:
Transformer - steps down high voltage AC mains to low voltage AC.
Rectifier - converts AC to DC, but the DC output is varying.
Smoothing - smoothes the DC from varying greatly to a small ripple.
Regulator - eliminates ripple by setting DC output to a fixed voltage.
Power supplies made from these blocks are described below with a circuit diagram and a
graph of their output:
Transformer only
Transformer + Rectifier
Transformer + Rectifier + Smoothing
Transformer + Rectifier + Smoothing + Regulator
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3.2.1 DUAL SUPPLIES
Some electronic circuits require a power supply with positive and negative outputs as
well as zero volts (0V). This is called a 'dual supply' because it is like two ordinary supplies
connected together as shown in the diagram. Dual supplies have three outputs, for example a
±9V supply has +9V, 0V and -9V outputs
TRANSFORMER ONLY
The low voltage AC output is suitable for lamps, heaters and special AC motors. It is
not suitable for electronic circuits unless they include a rectifier and a smoothing capacitor.
Transformer + Rectifier
The varying DC output is suitable for lamps, heaters and standard motors. It is not
suitable for electronic circuits unless they include a smoothing capacitor.
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Transformer + Rectifier + Smoothing
The smooth DC output has a small ripple. It is suitable for most electronic circuits.
TRANSFORMER + RECTIFIER + SMOOTHING + REGULATOR
The Regulated DC output is very smooth with no ripple. It is suitable for all
electronic circuits.
3.2.2 TRANSFORMER
Transformers convert AC electricity from one voltage to another with little loss of
power. Transformers work only with AC and this is one of the reasons why mains electricity
is AC. Step-up transformers increase voltage, step-down transformers reduce voltage. Most
power supplies use a step-down transformer to reduce the dangerously high mains voltage
(230V in UK) to a safer low voltage.
The input coil is called the primary and the output coil is called the secondary. There
is no electrical connection between the two coils, instead they are linked by an alternating
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magnetic field created in the soft-iron core of the transformer. The two lines in the middle of
the circuit symbol represent the core.
Transformers waste very little power so the power out is (almost) equal to the power
in. Note that as voltage is stepped down current is stepped up. The ratio of the number of
turns on each coil, called the turns ratio, determines the ratio of the voltages. A step-down
transformer has a large number of turns on its primary (input) coil which is connected to the
high voltage mains supply, and a small number of turns on its secondary (output) coil to give
a low output voltage.
turns ratio = Vp
= Np
and power out = power in
Vs Ns Vs × Is = Vp × Ip
Figure 3-2 Transformer circuit symbol
3.2.3 RECTIFIER
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Vp = primary (input) voltage
Np = number of turns on primary coil
Ip = primary (input) current
Vs = secondary (output) voltage
Ns = number of turns on secondary coil
Is = secondary (output) current
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There are several ways of connecting diodes to make a rectifier to convert AC to DC.
The bridge rectifier is the most important and it produces full-wave varying DC. A full-wave
rectifier can also be made from just two diodes if a centre-tap transformer is used, but this
method is rarely used now that diodes are cheaper. A single diode can be used as a rectifier
but it only uses the positive (+) parts of the AC wave to produce half-wave varying DC.
3.2.4 BRIDGE RECTIFIER
A bridge rectifier can be made using four individual diodes, but it is also available in
special packages containing the four diodes required. It is called a full-wave rectifier because
it uses all the AC wave (both positive and negative sections). 1.4V is used up in the bridge
rectifier because each diode uses 0.7V when conducting and there are always two diodes
conducting, as shown in the diagram below. Bridge rectifiers are rated by the maximum
current they can pass and the maximum reverse voltage they can withstand (this must be at
least three times the supply RMS voltage so the rectifier can withstand the peak voltages).
Please see the Diodes page for more details, including pictures of bridge rectifiers.
Figure 3-3 Bridge rectifier
Output: full-wave varying DC
3.2.5 SINGLE DIODE RECTIFIER
A single diode can be used as a rectifier but this produces half-wave varying DC
which has gaps when the AC is negative. It is hard to smooth this sufficiently well to supply
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electronic circuits unless they require a very small current so the smoothing capacitor does not
significantly discharge during the gaps. Please see the Diodes page for some examples of
rectifier diodes.
Single diode rectifierOutput: half-wave varying DC
(using only half the AC wave)
Figure 3-4 Single diode rectifier
3.2.6 SMOOTHING
Smoothing is performed by a large value electrolytic capacitor connected across the
DC supply to act as a reservoir, supplying current to the output when the varying DC voltage
from the rectifier is falling. The diagram shows the unsmoothed varying DC (dotted line) and
the smoothed DC (solid line). The capacitor charges quickly near the peak of the varying DC,
and then discharges as it supplies current to the output.
Note that smoothing significantly increases the average DC voltage to almost the peak
value (1.4 × RMS value). For example 6V RMS AC is rectified to full wave DC of about
4.6V RMS (1.4V is lost in the bridge rectifier), with smoothing this increases to almost the
peak value giving 1.4 × 4.6 = 6.4V smooth DC.
Smoothing is not perfect due to the capacitor voltage falling a little as it discharges,
giving a small ripple voltage. For many circuits a ripple which is 10% of the supply voltage
is satisfactory and the equation below gives the required value for the smoothing capacitor. A
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larger capacitor will give less ripple. The capacitor value must be doubled when smoothing
half-wave DC.
Figure 3-5 Smoothing circuit diagram
Smoothing capacitor for 10% ripple, C = 5 × Io
Vs × f
C = smoothing capacitance in farads (F)
Io = output current from the supply in amps (A)
Vs = supply voltage in volts (V), this is the peak value of the unsmoothed DC
f = frequency of the AC supply in hertz (Hz), 50Hz in the UK
3.2.7 REGULATORS
Voltage regulator ICs are available with fixed (typically 5, 12 and 15V) or variable
output voltages. They are also rated by the maximum current they can pass. Negative voltage
regulators are available, mainly for use in dual supplies. Most regulators include some
automatic protection from excessive current ('overload protection') and overheating ('thermal
protection'). Many of the fixed voltage regulator ICs have 3 leads and look like power
transistors, such as the 7805 +5V 1A regulator shown on the right. They include a hole for
attaching a heat sink if necessary.
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Figure 3-6 Regulator circuit
3.3 LCD DISPLAY
Liquid Crystal Display also called as LCD is very helpful in providing user interface
as well as for debugging purpose. The most common type of LCD controller is HITACHI
44780 which provides a simple interface between the controller & an LCD. These LCD's are
very simple to interface with the controller as well as are cost effective.
The most commonly used ALPHANUMERIC displays are 1x16 (Single Line & 16
characters), 2x16 (Double Line & 16 character per line) & 4x20 (four lines & Twenty
characters per line). The LCD requires 3 control lines (RS, R/W & EN) & 8 (or 4) data lines.
The number on data lines depends on the mode of operation.
If operated in 8-bit mode then 8 data lines + 3 control lines i.e. total 11 lines are
required. And if operated in 4-bit mode then 4 data lines + 3 control lines i.e. 7 lines are
required. How do we decide which mode to use? It’s simple if you have sufficient data lines
you can go for 8 bit mode & if there is a time constrain i.e. display should be faster then we
have to use 8-bit mode because basically 4-bit mode takes twice as more time as compared to
8-bit mode.
Most projects you create with the 8051 CPU require some form of display. The most
common way to accomplish this is with the LCD (Liquid Crystal Display). LCDs have
become a cheap and easy way to get text display for embedded system Common displays are
set up as 16 to 20 characters by 1 to 4 lines.
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When RS is low (0), the data is to be treated as a command. When RS is high (1), the
data being sent is considered as text data which should be displayed on the screen.
When R/W is low (0), the information on the data bus is being written to the LCD. When RW
is high (1), the program is effectively reading from the LCD. Most of the times there is no
need to read from the LCD so this line can directly be connected to Gnd thus saving one
controller line.
The ENABLE pin is used to latch the data present on the data pins. A HIGH - LOW
signal is required to latch the data. The LCD interprets and executes our command at the
instant the EN line is brought low. If you never bring EN low, your instruction will never be
executed.
Figure 3-7 Pindiagram of LCD
UNDERSTANDING LCD
Pin outline
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• 8 data pins D7:D0
Bi-directional data/command pins.
Alphanumeric characters are sent in
ASCII format.
• RS: Register Select
RS = 0 -> Command Register is selected
RS = 1 -> Data Register is selected
• R/W: Read or Write
0 -> Write, 1 -> Read
• E: Enable (Latch data)
Used to latch the data present on the data
pins. A high-to-low edge is needed to
latch the data.
• VEE: contrast control
NOTE: When writing to the display, data is transferred only on the high to low
transition of this signal. However, when reading from the display, data will become
available shortly after the low to high transition and remain available until the signal falls
low again.
3.3.1 Display Data RAM (DDRAM)
Display data RAM (DDRAM) is where you send the characters (ASCII code) you
want to see on the LCD screen. It stores display data represented in 8-bit character codes.
Its capacity is 80 characters (bytes). Below you see DD RAM address layout of a 2*16
LCD.
In the above memory map, the area shaded in black is the visible display (For
16x2 displays). For first line addresses for first 15 characters is from 00h to 0Fh. But for
second line address of first character is 40h and so on up to 4Fh for the 16th character. So
if you want to display the text at specific positions of LCD , we require to manipulate
address and then to set cursor position accordingly .
3.3.2 Character Generator RAM (CGRAM)-User defined character RAM
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In the character generator RAM, we can define our own character patterns by
program. CG RAM is 64 bytes ,allowing for eight 5*8 pixel, character patterns to be
defined. However how to define this and use it is out of scope of this tutorial. So I will
not talk any more about CGRAM
3.3.3 Registers
The HD44780 has two 8-bit registers, an instruction register (IR) and a data
register (DR). The IR stores instruction codes. The DR temporarily stores data to be
written into DDRAM or CGRAM and temporarily stores data to be read from DDRAM
or CGRAM. Data written into the DR is automatically written into DDRAM or CGRAM
by an internal operation. . These two registers can be selected by the register selector
(RS) signal. See the table below:
Register Selection
RS R/WOperation
0 0 IR write as an internal operation (display clear, etc.)
0 1 Read busy flag (DB7) and address counter (DB0 to DB6)
1 0 DR write as an internal operation (DR to DDRAM or CGRAM)
1 1 DR read as an internal operation (DDRAM or CGRAM to DR)
Table 3-1 Register selection
Busy Flag (BF)
When the busy flag is 1, the LCD is in the internal operation mode, and the next
instruction will not be accepted. When RS = 0 and R/W = 1 (see the table above), the
busy flag is output to DB7 (MSB of LCD data bus). The next instruction must be written
after ensuring that the busy flag is 0.
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3.3.4 LCD Commands
The LCD’s internal controller accept several commands and modify the display
accordingly. These commands would be things like:
– Clear screen
– Return home
– Shift display right/left
Instruction Decimal HEX
Function set (8-bit interface, 2 lines, 5*7 Pixels) 56 38
Function set (8-bit interface, 1 line, 5*7 Pixels) 48 30
Function set (4-bit interface, 2 lines, 5*7 Pixels) 40 28
Function set (4-bit interface, 1 line, 5*7 Pixels) 32 20
Entry mode set See Below See Below
Scroll display one character right (all lines) 28 1E
Scroll display one character left (all lines) 24 18
Home (move cursor to top/left character position) 2 2
Move cursor one character left 16 10
Move cursor one character right 20 14
Turn on visible underline cursor 14 0E
Turn on visible blinking-block cursor 15 0F
Make cursor invisible 12 0C
Blank the display (without clearing) 8 08
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Restore the display (with cursor hidden) 12 0C
Clear Screen 1 01
Set cursor position (DDRAM address) 128 + addr 80+ addr
Set pointer in character-generator RAM (CG RAM address) 64 + addr 40+ addr
Table 3-1 Instructions
3.3.5 INTERFACING LCD TO 8051
Figure 3-8 Interfacing LCD to 8051
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Figure 3-9 Interfacing HD44780 LCD to 8051
The 44780 standard requires 3 control lines as well as either 4 or 8 I/O lines for
the data bus. The user may select whether the LCD is to operate with a 4-bit data bus or
an 8-bit data bus.
If a 4-bit data bus is used, the LCD will require a total of 7 data lines.
If an 8-bit data bus is used, the LCD will require a total of 11 data lines.
The three control lines are EN, RS, and RW.
Note that the EN line must be raised/lowered before/after each instruction sent to
the LCD regardless of whether that instruction is read or write, text or instruction. In
short, you must always manipulate EN when communicating with the LCD. EN is the
LCD's way of knowing that you are talking to it. If you don't raise/lower EN, the LCD
doesn't know you're talking to it on the other lines.
3.3.6 CHECKING THE BUSY FLAG
You can use subroutine for checking busy flag or just a big (and safe) delay.
1. Set R/W Pin of the LCD HIGH(read from the LCD)
2. Select the instruction register by setting RS pin LOW
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3. Enable the LCD by Setting the enable pin HIGH
4. The most significant bit of the LCD data bus is the state of the busy
flag(1=Busy,0=ready to accept instructions/data). The other bits hold the current
value of the address counter.
If the LCD never come out from "busy" status because of some problems ,The
program will "hang," waiting for DB7 to go low. So in a real applications it would be
wise to put some kind of time limit on the delay--for example, a maximum of 100
attempts to wait for the busy signal to go low. This would guarantee that even if the LCD
hardware fails, the program would not lock up.
CODE EXAMPLE
It is easy (and clean tech. ) to make different subroutines and then call them as we
need.
Busy flag checking
ready:
setb P1.7 ;D7 as input
clr P3.6 ;RS=0 cmd
setb P3.5 ;RW=1 for read
again:
setb P3.7 ;H->L pulse on E
clr P3.7
jb P1.7, again
ret
Data write Routine
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data:
mov P1, A ;move acc. data to port
setb P3.6 ;RS=1 data
clr P3.5 ;RW=0 for write
setb P3.7 ;H->L pulse on E
clr P3.7
lcall ready
ret
Command write Routine
command:
mov P1, A ;move acc. data to port
clr P3.6 ;RS=0 for cmd
clr P3.5 ;RW=0 for write
setb P3.7 ;H->L pulse on E
clr P3.7
lcall ready
ret
Initialization
mov A, #38H ; Initialize, 2-lines, 5X7
matrix.
lcall Command
mov A, #0EH ; LCD on, cursor on
lcall Command
mov A, #01H ; Clear LCD Screen
lcall Command
mov A, #06H ; Shift cursor right
lcall Command
Display clear
clear:
setb p3.7 ;enable EN
clr 3.6 ;RS=0 for cmd.
mov DATA,#01h
clr p3.7 ;disable EN
lcall ready
RET
Note- As we need to clear the LCD
frequently and not the whole
initialisation , it is better to use this
routine separately.
Displaying "HI"
lcall initialization
lcall clear
mov A,#'H'
acall data
mov A,#'I'
lcall data
Let's now try code for displaying text at specific positions.
I want to display "MAHESH" in message "Hi MAHESH" at the right corner of first line
then I should start from 10th character.
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So referring to table 80h+0Ah= 8Ah.
So below is code and I don's think that you will need explanation comments.
ASSEMBLY LANGUAGE
lcall Initialization
lcall clear
mov a,#'H'
lcall data
mov a,#'I'
lcall data
mov a,#8ah
lcall command
mov a,#'M'
lcall data
mov a,#'A'
lcall data
mov a,#'H'
lcall data
mov a,#'E'
lcall data
mov a,#'S'
lcall data
mov a,#'H'
lcall data
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3.4 MAX232
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. 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.
3.4.1VOLTAGE 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.
Figure 3-10 Pin diagram of MAX232
APPLICATIONS
Portable Computers
Low-Power Modems
Interface Translation
Battery-Powered RS-232 Systems
Multi drop RS-232 Networks
3.5 INTERFACING THE SERIAL / RS232 PORT
The Serial Port is harder to interface than the Parallel Port. In most cases, any device
you connect to the serial port will need the serial transmission converted back to parallel so
that it can be used. This can be done using a UART. On the software side of things, there are
many more registers that you have to attend to than on a Standard Parallel Port. (SPP) So
what are the advantages of using serial data transfer rather than parallel?
1. Serial Cables can be longer than Parallel cables. The serial port transmits a '1' as -3 to -25
volts and a '0' as +3 to +25 volts where as a parallel port transmits a '0' as 0v and a '1' as 5v.
Therefore the serial port can have a maximum swing of 50V compared to the parallel port
which has a maximum swing of 5 Volts. Therefore cable loss is not going to be as much of
a problem for serial cables than they are for parallel.
2. You don't need as many wires than parallel transmission. If your device needs to be
mounted a far distance away from the computer then 3 core cable (Null Modem
Configuration) is going to be a lot cheaper that running 19 or 25 core cable. However you
must take into account the cost of the interfacing at each end.
3. Infra Red devices have proven quite popular recently. You may of seen many electronic
diaries and palmtop computers which have infra red capabilities build in. However could
you imagine transmitting 8 bits of data at the one time across the room and being able to
(from the devices point of view) decipher which bits are which? Therefore serial
transmission is used where one bit is sent at a time. IrDA-1 (The first infra red
specifications) was capable of 115.2k baud and was interfaced into a UART. The pulse
length however was cut down to 3/16th of a RS232 bit length to conserve power
considering these devices are mainly used on diaries, laptops and palmtops.
4. Microcontrollers have also proven to be quite popular recently. Many of these have in built
SCI (Serial Communications Interfaces) which can be used to talk to the outside world.
Serial Communication reduces the pin count of these MPU's. Only two pins are commonly
used, Transmit Data (TXD) and Receive Data (RXD) compared with at least 8 pins if you
use a 8 bit Parallel method
Devices which use serial cables for their communication are split into two categories.
These are DCE (Data Communications Equipment) and DTE (Data Terminal Equipment.)
Data Communications Equipment are devices such as your modem, TA adapter, plotter etc
while Data Terminal Equipment is your Computer or Terminal. The electrical specification of
the serial port is contained in the EIA (Electronics Industry Association) RS232C standard. It
states many parameters such as –
1. A "Space" (logic 0) will be between +3 and +25 Volts.
2. A "Mark" (Logic 1) will be between -3 and -25 Volts.
3. The region between +3 and -3 volts is undefined.
4. An open circuit voltage should never exceed 25 volts. (In Reference to
GND)
5. A short circuit current should not exceed 500mA. The driver should be
able to handle this without damage. (Take note of this one!)
Above is no where near a complete list of the EIA standard. Line Capacitance,
Maximum Baud Rates etc are also included. For more information please consult the EIA
RS232-C standard. It is interesting to note however, that the RS232C standard specifies a
maximum baud rate of 20,000 BPS!, which is rather slow by today's standards. A new
standard, RS-232D has been recently released.
Serial Ports come in two "sizes", There are the D-Type 25 pin connector and the D-
Type 9 pin connector both of which are male on the back of the PC, thus you will require a
female connector on your device. Below is a table of pin connections for the 9 pin and 25 pin
D-Type connectors.
3.5.1 HARDWARE PROPERTIES
Devices which use serial cables for their communication are split into two categories.
These are DCE (Data Communications Equipment) and DTE (Data Terminal Equipment.)
Data Communications Equipment are devices such as your modem, TA adapter, plotter etc
while Data Terminal Equipment is your Computer or Terminal.
The electrical specifications of the serial port is contained in the EIA (Electronics
Industry Association) RS232C standard. It states many parameters such as - Above is no
where near a complete list of the EIA standard. Line Capacitance, Maximum Baud Rates etc
are also included. For more information please consult the EIA RS232-C standard. It is
interesting to note however, that the RS232C standard specifies a maximum baud rate of
20,000 BPS!, which is rather slow by today's standards.
A new standard, RS-232D has been recently released.Serial Ports come in two "sizes",
There are the D-Type 25 pin connector and the D-Type 9 pin connector both of which are
male on the back of the PC, thus you will require a female connector on your device. Below is
a table of pin connections for the 9 pin and 25 pin D-Type connectors
3.5.2 DB9 CONNECTOR
1. A "Space" (logic 0) will be between +3 and +25 Volts.
2. A "Mark" (Logic 1) will be between -3 and -25 Volts.
3. The region between +3 and -3 volts is undefined.
4. An open circuit voltage should never exceed 25 volts. (In Reference to GND)
5. A short circuit current should not exceed 500mA. The driver should be able to handle
this without damage.
DB9 CONNECTOR
Figure 3-11 RS232 DB9Connector Pin out
DB-9M Function Abbreviation Pin #1 Data Carrier Detect CD Pin #2 Receive Data RD or RX or RXD Pin #3 Transmitted Data TD or TX or TXD Pin #4 Data Terminal Ready DTR Pin #5 Signal Ground GND Pin #6 Data Set Ready DSR Pin #7 Request to Send RTS Pin #8 Clear To Send CTS Pin #9 Ring Indicator RI.
3.6 GSM Technology:
3.6.1 INTRODUCTION TO THE GSM STANDARD
The GSM (Global System for Mobile communications) network is at the start of the
21st century, the most commonly used mobile telephony standard in Europe. It is called as
Second Generation (2G) standard because communications occur in an entirely digital mode,
unlike the first generation of portable telephones.
When it was first standardized in 1982, it was called as Group Special Mobile and
later, it became an international standard called "Global System for Mobile
communications" in 1991. In Europe, the GSM standard uses the 900 MHz and 1800 MHz
frequency bands. In the United States, however, the frequency band used is the 1900 MHz
band. For this reason, portable telephones that are able to operate in both Europe and the
United States are called tri-band while those that operate only in Europe are called bi-band.
The GSM standard allows a maximum throughput of 9.6 kbps which allows
transmission of voice and low-volume digital data like text messages (SMS, for Short
Message Service) or multimedia messages (MMS, for Multimedia Message Service).
GSM STANDARDS
GSM uses narrowband TDMA, which allows eight simultaneous calls on the same
radio frequency. There are three basic principles in multiple access, FDMA (Frequency
Division Multiple Access), TDMA (Time Division Multiple Access), and CDMA (Code
Division Multiple Access). All three principles allow multiple users to share the same
physical channel. But the two competing technologies differ in the way user sharing the
common resource.
TDMA allows the users to share the same frequency channel by dividing the signal
into different time slots. Each user takes turn in a round robin fashion for transmitting and
receiving over the channel. Here, users can only transmit in their respective time slot. CDMA
uses a spread spectrum technology that is it spreads the information contained in a particular
signal of interest over a much greater bandwidth than the original signal. Unlike TDMA, in
CDMA several users can transmit over the channel at the same time.
DEFINITION OF GSM
GSM (Global System for Mobile communications) is an open, digital cellular
technology used for transmitting mobile voice and data services. GSM (Global System for
Mobile communication) is a digital mobile telephone system that is widely used in Europe
and other parts of the world. GSM uses a variation of Time Division Multiple Access
(TDMA) and is the most widely used of the three digital wireless telephone technologies
(TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a
channel with two other streams of user data, each in its own time slot. It operates at either the
900 MHz or 1,800 MHz frequency band. It supports voice calls and data transfer speeds of up
to 9.6 kbit/s, together with the transmission of SMS (Short Message Service).
HISTORY
In 1982, the European Conference of Postal and Telecommunications Administrations
(ECPT) created the Group Special Mobile (GSM) to develop a standard for a mobile
telephone system that could be used across Europe. In 1987, a memorandum of
understanding was signed by 13 countries to develop a common cellular telephone system
across Europe. Finally the system created by SINTEF lead by Torleiv Maseng was selected.
In 1989, GSM responsibility was transferred to the European Telecommunications
Standards Institute (ETSI) and phase I of the GSM specifications were published in 1990. The
first GSM network was launched in 1991 by Radiolinja in Finland with joint technical
infrastructure maintenance from Ericsson.
By the end of 1993, over a million subscribers were using GSM phone networks being
operated by 70 carriers across 48 countries. As of the end of 1997, GSM service was available
in more than 100 countries and has become the de facto standard in Europe and Asia.
GSM FREQUENCIES
GSM networks operate in a number of different frequency ranges (separated into GSM
frequency ranges for 2G and UMTS frequency bands for 3G). Most 2G GSM networks
operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including
Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and
1800 MHz frequency bands were already allocated. Most 3G GSM networks in Europe
operate in the 2100 MHz frequency band. The rarer 400 and 450 MHz frequency bands are
assigned in some countries where these frequencies were previously used for first-generation
systems.
GSM-900 uses 890–915 MHz to send information from the mobile station to the base
station (uplink) and 935–960 MHz for the other direction (downlink), providing 124 RF
channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used.
In some countries the GSM-900 band has been extended to cover a larger frequency range.
This 'extended GSM', E-GSM, uses 880–915 MHz (uplink) and 925–960 MHz (downlink),
adding 50 channels (channel numbers 975 to 1023 and 0) to the original GSM-900 band.
Time division multiplexing is used to allow eight full-rate or sixteen half-rate speech
channels per radio frequency channel. There are eight radio timeslots (giving eight burst
periods) grouped into what is called a TDMA frame. Half rate channels use alternate frames
in the same timeslot. The channel data rate for all 8 channels is 270.833 Kbit/s, and the frame
duration is 4.615 ms.
The transmission power in the handset is limited to a maximum of 2 watts in
GSM850/900 and 1 watt in GSM1800/1900. GSM operates in the 900MHz and 1.8GHz
bands in Europe and the 1.9GHz and 850MHz bands in the US. The 850MHz band is also
used for GSM and 3G in Australia, Canada and many South American countries. By having
harmonized spectrum across most of the globe, GSM’s international roaming capability
allows users to access the same services when travelling abroad as at home. This gives
consumers seamless and same number connectivity in more than 218 countries.
Terrestrial GSM networks now cover more than 80% of the world’s population. GSM
satellite roaming has also extended service access to areas where terrestrial coverage is not
available.
Mobile Telephony Standards
Standard Generation Frequency band Throughput
GSM 2GAllows transfer of voice or low-volume digital data. 9.6 kbps
9.6 kbps
GPRS 2.5GAllows transfer of voice or moderate-volume digital data.
21.4-171.2 kbps
48 kbps
EDGE 2.75GAllows simultaneous transfer of voice and digital data.
43.2-345.6 kbps
171 kbps
UMTS 3GAllows simultaneous transfer of voice and high-speed digital data. 0.144-2 Mbps
384 kbps
Table 3-3 Mobile telephony standards
3.6.2 1G
The first generation of mobile telephony (written 1G) operated using analogue
communications and portable devices that were relatively large. It used primarily the
following standards:
AMPS (Advanced Mobile Phone System), which appeared in 1976 in the United
States, was the first cellular network standard. It was used primarily in the Americas,
Russia and Asia. This first-generation analogue network had weak security
mechanisms which allowed hacking of telephones lines.
TACS (Total Access Communication System) is the European version of the AMPS
model. Using the 900 MHz frequency band, this system was largely used in England
and then in Asia (Hong-Kong and Japan).
ETACS (Extended Total Access Communication System) is an improved version of
the TACS standard developed in the United Kingdom that uses a larger number of
communication channels.
The first-generation cellular networks were made obsolete by the appearance of an entirely
digital second generation.
3.6.3 SECOND GENERATION OF MOBILE NETWORKS (2G)
The second generation of mobile networks marked a break with the first generation of
cellular telephones by switching from analogue to digital. The main 2G mobile telephony
standards are:
GSM (Global System for Mobile communications) is the most commonly used
standard in Europe at the end of the 20th century and supported in the United States.
This standard uses the 900 MHz and 1800 MHz frequency bands in Europe. In the
United States, however, the frequency band used is the 1900 MHz band. Portable
telephones that are able to operate in Europe and the United States are therefore
called tri-band.
CDMA (Code Division Multiple Access) uses a spread spectrum technique that allows
a radio signal to be broadcast over a large frequency range.
TDMA (Time Division Multiple Access) uses a technique of time division of
communication channels to increase the volume of data transmitted simultaneously.
TDMA technology is primarily used on the American continent, in New Zealand and
in the Asia-Pacific region.
With the 2G networks, it is possible to transmit voice and low volume digital data, for
example text messages (SMS, for Short Message Service) or multimedia messages (MMS,
for Multimedia Message Service). The GSM standard allows a maximum data rate of 9.6
kbps.
Extensions have been made to the GSM standard to improve throughput. One of these
is the GPRS (General Packet Radio System) service which allows theoretical data rates on the
order of 114 Kbit/s but with throughput closer to 40 Kbit/s in practice. As this technology
does not fit within the "3G" category, it is often referred to as 2.5G
The EDGE (Enhanced Data Rates for Global Evolution) standard, billed as 2.75G,
quadruples the throughput improvements of GPRS with its theoretical data rate of 384 Kbps,
thereby allowing the access for multimedia applications. In reality, the EDGE standard allows
maximum theoretical data rates of 473 Kbit/s, but it has been limited in order to comply with
the IMT-2000(International Mobile Telecommunications-2000) specifications from the ITU
(International Telecommunications Union).
3.6.4 3G
The IMT-2000 (International Mobile Telecommunications for the year 2000)
specifications from the International Telecommunications Union (ITU) defined the
characteristics of 3G (third generation of mobile telephony). The most important of these
characteristics are:
1. High transmission data rate.
2. 144 Kbps with total coverage for mobile use.
3. 384 Kbps with medium coverage for pedestrian use.
4. 2 Mbps with reduced coverage area for stationary use.
5. World compatibility.
6. Compatibility of 3rd generation mobile services with second generation networks.
3G offers data rates of more than 144 Kbit/s, thereby allowing the access to
multimedia uses such as video transmission, video-conferencing or high-speed internet
access. 3G networks use different frequency bands than the previous networks: 1885-2025
MHz and 2110-2200 MHz.
The main 3G standard used in Europe is called UMTS (Universal Mobile
Telecommunications System) and uses WCDMA (Wideband Code Division Multiple Access)
encoding. UMTS technology uses 5 MHz bands for transferring voice and data, with data
rates that can range from 384 Kbps to 2 Mbps. HSDPA (High Speed Downlink Packet
Access) is a third generation mobile telephony protocol, (considered as "3.5G"), which is able
to reach data rates on the order of 8 to 10 Mbps. HSDPA technology uses the 5 GHz
frequency band and uses WCDMA encoding.
THE CONCEPT OF CELLULAR NETWORK
Mobile telephone networks are based on the concept of cells, circular zones that
overlap to cover a geographical area.
Figure 3-12 Cellular Network
Cellular networks are based on the use of a central transmitter-receiver in each cell,
called a "base station" (or Base Transceiver Station, written BTS). The smaller the radius of
a cell, the higher is the available bandwidth. So, in highly populated urban areas, there are
cells with a radius of a few hundred meters, while huge cells of up to 30 kilometers provide
coverage in rural areas. In a cellular network, each cell is surrounded by 6 neighbouring cells
(thus a cell is generally drawn as a hexagon). To avoid interference, adjacent cells cannot use
the same frequency. In practice, two cells using the same frequency range must be separated
by a distance of two to three times the diameter of the cell.
3.6.5 ARCHITECTURE OF THE GSM NETWORK
In a GSM network, the user terminal is called a mobile station. A mobile station is
made up of a SIM (Subscriber Identity Module) card allowing the user to be uniquely
identified and a mobile terminal. The terminals (devices) are identified by a unique 15-digit
identification number called IMEI (International Mobile Equipment Identity). Each SIM card
also has a unique (and secret) identification number called IMSI (International Mobile
Subscriber Identity). This code can be protected using a 4-digit key called a PIN code.
The SIM card therefore allows each user to be identified independently of the terminal
used during communication with a base station. Communications occur through a radio link
(air interface) between a mobile station and a base station.
Figure 3-13 Architecture of the GSM Network
All the base stations of a cellular network are connected to a base station
controller (BSC) which is responsible for managing distribution of the resources. The system
consisting of the base station controller and its connected base stations is called the Base
Station Subsystem (BSS).
Finally, the base station controllers are themselves physically connected to the Mobile
Switching Centre (MSC), managed by the telephone network operator, which connects them
to the public telephone network and the Internet. The MSC belongs to a Network Station
Subsystem (NSS), which is responsible for managing user identities, their location and
establishment of communications with other subscribers. The MSC is generally connected to
databases that provide additional functions:
1. The Home Location Register (HLR) is a database containing information
(geographic position, administrative information etc.) of the subscribers registered in
the area of the switch (MSC).
2. The Visitor Location Register (VLR) is a database containing information of users
other than the local subscribers. The VLR retrieves the data of a new user from the
HLR of the user's subscriber zone. The data is maintained as long as the user is in the
zone and is deleted when the user leaves or after a long period of inactivity (terminal
off).
3. The Equipment Identify Register (EIR) is a database listing the mobile terminals.
4. The Authentication Centre (AUC) is responsible for verifying user identities.
5. The cellular network formed in this way is designed to support mobility via
management of handovers (movements from one cell to another).
Finally, GSM networks support the concept of roaming i.e., movement from one operator
network to another.
Figure 3-14 GSM Modem
A GSM modem can be an external device or a PC Card / PCMCIA Card. Typically, an
external GSM modem is connected to a computer through a serial cable or a USB cable. A
GSM modem in the form of a PC Card / PCMCIA Card is designed for use with a laptop
computer. It should be inserted into one of the PC Card / PCMCIA Card slots of a laptop
computer.
Like a GSM mobile phone, a GSM modem requires a SIM card from a wireless carrier in
order to operate.
A SIM card contains the following information:
Subscriber telephone number (MSISDN)
International subscriber number (IMSI, International Mobile Subscriber Identity)
State of the SIM card
Service code (operator)
Authentication key
PIN (Personal Identification Code)
PUK (Personal Unlock Code)
Computers use AT commands to control modems. Both GSM modems and dial-up
modems support a common set of standard AT commands. In addition to the standard AT
commands, GSM modems support an extended set of AT commands. These extended AT
commands are defined in the GSM standards. With the extended AT commands, the
following operations can be performed:
Reading, writing and deleting SMS messages.
Sending SMS messages.
Monitoring the signal strength.
Monitoring the charging status and charge level of the battery.
Reading, writing and searching phone book entries.
Figure 3-15 Connection between PC and GSM Modem
The number of SMS messages that can be processed by a GSM modem per minute is very
low i.e., about 6 to 10 SMS messages per minute.
3.6.6 Introduction to AT Commands
AT commands are instructions used to control a modem. AT is the abbreviation of
ATtention. Every command line starts with "AT" or "at". That's the reason, modem
commands are called AT commands. Many of the commands that are used to control wired
dial-up modems, such as ATD (Dial), ATA (Answer), ATH (Hook control) and ATO (Return
to online data state) are also supported by GSM modems and mobile phones.
Besides this common AT command set, GSM modems and mobile phones support an
AT command set that is specific to the GSM technology, which includes SMS-related
commands like AT+CMGS (Send SMS message), AT+CMSS (Send SMS message from
storage), AT+CMGL (List SMS messages) and AT+CMGR (Read SMS messages).
It should be noted that the starting "AT" is the prefix that informs the modem about
the start of a command line. It is not part of the AT command name. For example, D is the
actual AT command name in ATD and +CMGS is the actual AT command name in
AT+CMGS. Some of the tasks that can be done using AT commands with a GSM modem or
mobile phone are listed below:
Get basic information about the mobile phone or GSM modem. For example, name of
manufacturer (AT+CGMI), model number (AT+CGMM), IMEI number (International
Mobile Equipment Identity) (AT+CGSN) and software version (AT+CGMR).
Get basic information about the subscriber. For example, MSISDN (AT+CNUM) and
IMSI number (International Mobile Subscriber Identity) (AT+CIMI).
Get the current status of the mobile phone or GSM/GPRS modem. For example,
mobile phone activity status (AT+CPAS), mobile network registration status
(AT+CREG), radio signal strength (AT+CSQ), battery charge level and battery
charging status (AT+CBC).
Establish a data connection or voice connection to a remote modem (ATD, ATA, etc).
Send and receive fax (ATD, ATA, AT+F*).
Send (AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write (AT+CMGW)
or delete (AT+CMGD) SMS messages and obtain notifications of newly received
SMS messages (AT+CNMI).
Read (AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook entries.
Perform security-related tasks, such as opening or closing facility locks (AT+CLCK),
checking whether a facility is locked (AT+CLCK) and changing
passwords(AT+CPWD).
(Facility lock examples: SIM lock [a password must be given to the SIM card every
time the mobile phone is switched on] and PH-SIM lock [a certain SIM card is
associated with the mobile phone. To use other SIM cards with the mobile phone, a
password must be entered.])
Control the presentation of result codes / error messages of AT commands. For
example, the user can control whether to enable certain error messages (AT+CMEE)
and whether error messages should be displayed in numeric format or verbose format
(AT+CMEE=1 or AT+CMEE=2).
Get or change the configurations of the mobile phone or GSM/GPRS modem. For
example, change the GSM network (AT+COPS), bearer service type (AT+CBST),
radio link protocol parameters (AT+CRLP), SMS center address (AT+CSCA) and
storage of SMS messages (AT+CPMS).
Save and restore configurations of the mobile phone or GSM/GPRS modem. For
example, save (AT+CSAS) and restore (AT+CRES) settings related to SMS
messaging such as the SMS center address.
It should be noted that the mobile phone manufacturers usually do not implement all AT
commands, command parameters and parameter values in their mobile phones. Also, the
behavior of the implemented AT commands may be different from that defined in the
standard. In general, GSM modems, designed for wireless applications, have better support of
AT commands than ordinary mobile phones.
3.6.7 BASIC CONCEPTS OF SMS TECHNOLOGY
1. Validity Period of an SMS Message
An SMS message is stored temporarily in the SMS center if the recipient mobile
phone is offline. It is possible to specify the period after which the SMS message will be
deleted from the SMS center so that the SMS message will not be forwarded to the recipient
mobile phone when it becomes online. This period is called the validity period. A mobile
phone should have a menu option that can be used to set the validity period. After setting it,
the mobile phone will include the validity period in the outbound SMS messages
automatically.
2. Message Status Reports
Sometimes the user may want to know whether an SMS message has reached the
recipient mobile phone successfully. To get this information, you need to set a flag in the
SMS message to notify the SMS center that a status report is required about the delivery of
this SMS message. The status report is sent to the user mobile in the form of an SMS
message. A mobile phone should have a menu option that can be used to set whether the
status report feature is on or off. After setting it, the mobile phone will set the corresponding
flag in the outbound SMS messages for you automatically. The status report feature is turned
off by default on most mobile phones and GSM modems.
3. Message Submission Reports
After leaving the mobile phone, an SMS message goes to the SMS center. When it
reaches the SMS center, the SMS center will send back a message submission report to the
mobile phone to inform whether there are any errors or failures (e.g. incorrect SMS message
format, busy SMS center, etc). If there is no error or failure, the SMS center sends back a
positive submission report to the mobile phone. Otherwise it sends back a negative
submission report to the mobile phone. The mobile phone may then notify the user that the
message submission was failed and what caused the failure.
If the mobile phone does not receive the message submission report after a period of
time, it concludes that the message submission report has been lost. The mobile phone may
then send the SMS message again to the SMS center. A flag will be set in the new SMS
message to inform the SMS center that this SMS message has been sent before. If the
previous message submission was successful, the SMS center will ignore the new SMS
message but send back a message submission report to the mobile phone. This mechanism
prevents the sending of the same SMS message to the recipient multiple times. Sometimes the
message submission report mechanism is not used and the acknowledgement of message
submission is done in a lower layer.
4. Message Delivery Reports
After receiving an SMS message, the recipient mobile phone will send back a message
delivery report to the SMS center to inform whether there are any errors or failures (example
causes: unsupported SMS message format, not enough storage space, etc). This process is
transparent to the mobile user. If there is no error or failure, the recipient mobile phone sends
back a positive delivery report to the SMS center. Otherwise it sends back a negative delivery
report to the SMS center. If the sender requested a status report earlier, the SMS center sends
a status report to the sender when it receives the message delivery report from the recipient. If
the SMS center does not receive the message delivery report after a period of time, it
concludes that the message delivery report has been lost. The SMS center then ends the SMS
message to the recipient for the second time.
Sometimes the message delivery report mechanism is not used and the
acknowledgement of message delivery is done in a lower layer.
3.7 RFID READER & TAG
3.7.1 What is RFID?
RFID stands for Radio-Frequency Identification. The acronym refers to small
electronic devices that consist of a small chip and an antenna. The chip typically is capable of
carrying 2,000 bytes of data or less. The RFID device serves the same purpose as a bar code
or a magnetic strip on the back of a credit card or ATM card; it provides a unique identifier
for that object. And, just as a bar code or magnetic strip must be scanned to get the
information, the RFID device must be scanned to retrieve the identifying information.
“RFID Works Better Than Barcodes”
A significant advantage of RFID devices over the others mentioned above is that the
RFID device does not need to be positioned precisely relative to the scanner. We're all
familiar with the difficulty that store checkout clerks sometimes have in making sure that a
barcode can be read. And obviously, credit cards and ATM cards must be swiped through a
special reader.
In contrast, RFID devices will work within a few feet (up to 20 feet for high-frequency
devices) of the scanner. For example, you could just put all of your groceries or purchases in a
bag, and set the bag on the scanner. It would be able to query all of the RFID devices and total
your purchase immediately. (Read a more detailed article on RFID compared to barcodes.)
RFID technology has been available for more than fifty years. It has only been
recently that the ability to manufacture the RFID devices has fallen to the point where they
can be used as a "throwaway" inventory or control device. Alien Technologies recently sold
500 million RFID tags to Gillette at a cost of about ten cents per tag.
One reason that it has taken so long for RFID to come into common use is the lack of
standards in the industry. Most companies invested in RFID technology only use the tags to
track items within their control; many of the benefits of RFID come when items are tracked
from company to company or from country to country.
“Common Problems with RFID’
Some common problems with RFID are reader collision and tag collision. Reader
collision occurs when the signals from two or more readers overlap. The tag is unable to
respond to simultaneous queries. Systems must be carefully set up to avoid this problem. Tag
collision occurs when many tags are present in a small area; but since the read time is very
fast, it is easier for vendors to develop systems that ensure that tags respond one at a time.
3.7.2 How does RFID work?
A Radio-Frequency Identification system has three parts:
A scanning antenna
A transceiver with a decoder to interpret the data
A transponder - the RFID tag - that has been programmed with information.
The scanning antenna puts out radio-frequency signals in a relatively short range. The RF
radiation does two things: It provides a means of communicating with the transponder (the
RFID tag) AND it provides the RFID tag with the energy to communicate (in the case of
passive RFID tags).
This is an absolutely key part of the technology; RFID tags do not need to contain
batteries, and can therefore remain usable for very long periods of time (maybe decades). The
scanning antennas can be permanently affixed to a surface; handheld antennas are also
available. They can take whatever shape you need; for example, you could build them into a
door frame to accept data from persons or objects passing through.
When an RFID tag passes through the field of the scanning antenna, it detects the
activation signal from the antenna. That "wakes up" the RFID chip, and it transmits the
information on its microchip to be picked up by the scanning antenna. In addition, the RFID
tag may be of one of two types. Active RFID tags have their own power source; the advantage
of these tags is that the reader can be much farther away and still get the signal. Even though
some of these devices are built to have up to a 10 year life span, they have limited life spans.
Passive RFID tags, however, do not require batteries, and can be much smaller and have a
virtually unlimited life span.
RFID tags can be read in a wide variety of circumstances, where barcodes or other
optically read technologies are useless. The tag need not be on the surface of the object (and
is therefore not subject to wear) The read time is typically less than 100 milliseconds Large
numbers of tags can be read at once rather than item by item.
3.7.3 Is RFID Technology Secure and Private?
Unfortunately, not very often in the systems to which consumers are likely to be
exposed. Anyone with an appropriately equipped scanner and close access to the RFID device
can activate it and read its contents. Obviously, some concerns are greater than others. If
someone walks by your bag of books from the bookstore with a 13.56 Mhz "sniffer" with an
RF field that will activate the RFID devices in the books you bought, that person can get a
complete list of what you just bought. That's certainly an invasion of your privacy, but it
could be worse. Another scenario involves a military situation in which the other side scans
vehicles going by, looking for tags that are associated with items that only high-ranking
officers can have, and targeting accordingly.
Companies are more concerned with the increasing use of RFID devices in company
badges. An appropriate RF field will cause the RFID chip in the badge to "spill the beans" to
whomever activates it. This information can then be stored and replayed to company scanners,
allowing the thief access - and your badge is the one that is "credited" with the access.
The smallest tags that will likely be used for consumer items don't have enough
computing power to do data encryption to protect your privacy. The most they can do is PIN-
style or password-based protection.
3.7.4 Next-Generation Uses of RFID?
Some vendors have been combining RFID tags with sensors of different kinds. This
would allow the tag to report not simply the same information over and over, but identifying
information along with current data picked up by the sensor. For example, an RFID tag
attached to a leg of lamb could report on the temperature readings of the past 24 hours, to
ensure that the meat was properly kept cool.
Over time, the proportion of "scan-it-yourself" aisles in retail stores will increase.
Eventually, we may wind up with stores that have mostly "scan-it-yourself" aisles and only a
few checkout stations for people who are disabled or unwilling.
3.7.5 Problems with RFID
RFID problems can be divided into several categories:
Technical problems with RFID
Privacy and ethics problems with RFID
Technical problems with RFID
Problems with RFID Standards
RFID has been implemented in different ways by different manufacturers; global
standards are still being worked on. It should be noted that some RFID devices are never
meant to leave their network (as in the case of RFID tags used for inventory control within a
company). This can cause problems for companies.
Consumers may also have problems with RFID standards. For example, ExxonMobil's
Speed Pass system is a proprietary RFID system; if another company wanted to use the
convenient Speed Pass (say, at the drive-in window of your favorite fast food restaurant) they
would have to pay to access it - an unlikely scenario. On the other hand, if every company had
their own "Speed Pass" system, a consumer would need to carry many different devices with
them.
3.7.6 RFID systems can be easily disrupted
Since RFID systems make use of the electromagnetic spectrum (like Wi-Fi networks
or cell phones), they are relatively easy to jam using energy at the right frequency. Although
this would only be an inconvenience for consumers in stores (longer waits at the checkout), it
could be disastrous in other environments where RFID is increasingly used, like hospitals or
in the military in the field. Also, active RFID tags (those that use a battery to increase the
range of the system) can be repeatedly interrogated to wear the battery down, disrupting the
system.
3.7.7 RFID Reader Collision
Reader collision occurs when the signals from two or more readers overlap. The tag is
unable to respond to simultaneous queries. Systems must be carefully set up to avoid this
problem; many systems use an anti-collision protocol (also called a singulation protocol.
Anti-collision protocols enable the tags to take turns in transmitting to a reader. (Learn more
about RFID reader collision.)
3.7.8 RFID Tag Collision
Tag collision occurs when many tags are present in a small area; but since the read
time is very fast, it is easier for vendors to develop systems that ensure that tags respond one
at a time. (Learn more about RFID tag collision.) Security, privacy and ethics problems with
RFID.
The following problems with RFID tags and readers have been reported.
The contents of an RFID tag can be read after the item leaves the supply chain. An
RFID tag cannot tell the difference between one reader and another. RFID scanners are very
portable; RFID tags can be read from a distance, from a few inches to a few yards. This
allows anyone to see the contents of your purse or pocket as you walk down the street. Some
tags can be turned off when the item has left the supply chain; see zombie RFID tags.
3.7.9 RFID tags are difficult to remove
RFID tags are difficult to for consumers to remove; some are very small (less than a
half-millimeter square, and as thin as a sheet of paper) - others may be hidden or embedded
inside a product where consumers cannot see them. New technologies allow RFID
tags to be "printed" right on a product and may not be removable at all (see Printing RFID
Tags With Magic Ink).
3.7.10 RFID tags can be read without your knowledge
Since the tags can be read without being swiped or obviously scanned (as is the case
with magnetic strips or barcodes), anyone with an RFID tag reader can read the tags
embedded in your clothes and other consumer products without your knowledge. For
example, you could be scanned before you enter the store, just to see what you are carrying.
You might then be approached by a clerk who knows what you have in your backpack or
purse, and can suggest accessories or other items.
3.7.11 RFID tags can be read greater distances with a high-gain antenna
For various reasons, RFID reader/tag systems are designed so that distance between
the tag and the reader is kept to a minimum (see the material on tag collision above).
However, a high-gain antenna can be used to read the tags from much further away, leading to
privacy problems.
RFID tags with unique serial numbers could be linked to an individual credit card number
At present, the Universal Product Code (UPC) implemented with barcodes allows
each product sold in a store to have a unique number that identifies that product. Work is
proceeding on a global system of product identification that would allow each individual item
to have its own number. When the item is scanned for purchase and is paid for, the RFID tag
number for a particular item can be associated with a credit card number.
3.8 Advantages of RFID versus Barcodes
RFID tags and barcodes both carry information about products. However, there are
important differences between these two technologies:
Barcode readers require a direct line of sight to the printed barcode; RFID readers do
not require a direct line of sight to either active RFID tags or passive RFID tags.
RFID tags can be read at much greater distances; an RFID reader can pull information
from a tag at distances up to 300 feet. The range to read a barcode is much less,
typically no more than fifteen feet.
RFID readers can interrogate, or read, RFID tags much faster; read rates of forty or
more tags per second are possible. Reading barcodes is much more time-consuming;
due to the fact that a direct line of sight is required, if the items are not properly
oriented to the reader it may take seconds to read an individual tag. Barcode readers
usually take a half-second or more to successfully complete a read.
Line of sight requirements also limit the ruggedness of barcodes as well as the
reusability of barcodes. (Since line of sight is required for barcodes, the printed barcode
must be exposed on the outside of the product, where it is subject to greater wear and tear.)
RFID tags are typically more rugged, since the electronic components are better protected in a
plastic cover. RFID tags can also be implanted within the product itself, guaranteeing greater
ruggedness and reusability.
Barcodes have no read/write capability; that is, you cannot add to the information written
on a printed barcode. RFID tags, however, can be read/write devices; the RFID reader can
communicate with the tag, and alter as much of the information as the tag design will allow.
RFID tags are typically more expensive than barcodes, in some cases, much more so.
3.9 Contactless Credit Card Advantages
Credit card companies are claiming the following advantages for contactless credit cards:
The card is faster to use. To make a purchase, the card owner just waves his card over
the RFID reader, waits for the acceptance indicator - and goes on his way. American Express,
Visa and MasterCard have all agreed to waive the signature requirement for contactless credit
card transactions under $25. If you want to look at the numbers, here is where this technology
is taking us in our need for speed (average transaction speeds):
Contactless credit card transaction: 15 seconds
Magnetic strip card transaction: 25 seconds
Cash transaction: 34 seconds
The contactless cards use highly secure data transmission standards.
Contactless cards make use of the most secure encryption standards practical with current
technology. 128-bit and triple DES encryptions make it nearly impossible for thieves to steal
your data. The contactless card never transmits your card number
Instead, the RFID chip within the card creates a unique number for the transaction; if a
criminal intercepted the number, it would be useless even if successfully decrypted.
Contactless cards probably use other measures although this is just speculation, there are
certainly other ways to secure the data on the card. For example, the RFID reader that sits on
the merchant's counter may use some sort of special signal, or offer a special set of
frequencies, that would be difficult for a thief with an off-the-shelf reader to duplicate.
One additional fact that is known about contactless cards is definitely an advantage for
merchants - consumers may feel otherwise. In a 2004 study, the average number of
transactions at a retail location rose by about one percent, and the average "spend" rose fifteen
percent for all contactless credit card users. So, it appears that there is a correlation between
ease of use and total spending. Consumers, take note!
3.10 Contactless Credit Card Disadvantages
The following disadvantages have been noted with contactless credit cards:
Contactless cards are more exposed than regular credit cards.
If you want to keep your credit card secure, you could keep it safely in an enclosed
wallet or purse; thieves would have absolutely no way to even know if you have a
credit card. However, a thief armed with a suitable reader, within a few feet of you,
would be able to interrogate all of the cards in your wallet or purse without your
knowledge.
Also, a regular credit card transaction is fairly secure; the magnetic strip is swiped at
very close range (less than a millimeter). However, a thief with a suitable reader could
monitor your contactless card transaction while standing at the counter with you, or
just behind you.
These concerns have, of course, been carefully noted by credit card companies. The
RFID chip in the contactless credit card responds to the merchant reader with a unique
number used for that transaction only; it does not simply transmit the consumer's
account number. This number is also encrypted.
It is easier to spend. Studies have demonstrated that consumers will be more likely to
spend, and will spend more frequently, with contactless credit cards.
Privacy advocates are particularly concerned about this technology; it is feared that
having this muchc information available "in the open air" will lead inevitably to problems.
CHAPTER -4
SOFTWARE USAGE
4.1 KEIL
This software is used to write the microcontroller code and to simulate it on the
computer itself. It is also used to generate the hex code for the code written in ALP or C.
User Vs machine (microcontroller): as the microcontroller know only about the digital
value (i.e. either logic zero or one), so we need to convert the written code in the sets of zero n
one. The KEIL environment provide us the facility to convert the code written in C or ALP to
sets of zero n one (i.e. called hex code).
Keil Vision2
Open the Keil Vision2
Go to Project – Open Project and browse for Hello in Ch03_00 in Pont and open it.
Go to Project – Select Device for Target ‘Target1’
Select 8052(all variants) and click OK
Now we need to check the oscillator frequency:
Go to project – Options for Target ‘Target1’
Make sure that the oscillator frequency is 12MHz.
Building the Target
Build the target as illustrated in the figure below
RUNNING THE SIMULATION
Having successfully built the target, we are now ready to start the debug session and run the simulator.
First start a debug session
The flashing LED we will view will be connected to Port 1. We therefore want to observe the activity on this port
To ensure that the port activity is visible, we need to start the ‘periodic window update’ flag
Go to Debug – Go
While the simulation is running, view the performance analyzer to check the delay durations.
Go to Debug – Performance Analyzer and click on it
Double click on DELAY_LOOP_Wait in Function Symbols: and click Define button
Here we need to change the ‘Xtal (MHz): ‘. Here fill the frequency of crystal which
we are going to use. For the microcontroller which we are using the crystal that we are
using is having crystal frequency 12MHz.and click the option for ‘Use On-chip
ROM(0x0-0xFFFF)’.then click the option ‘Output’ where we have to select the option
‘Create HEX File’. After that we can translate the current file n built target will
generate the HEX code automatically.
4.2 Flash magic
Flash Magic is Windows software from that microcontroller is easyly programmed
using In-System Programming technology to all the ISP feature empowered devices.
After installing the software when we click on the icon of the software the window
will open on the screen as shown in figure. We need to change the device and have to select
the device 89V51RD2, and then we set to ‘erase all flash’ option on the flash magic window.
If we need to verify the proper dumping of the program in the microcontroller then we
need to set the ‘verify after program’ option.
Loading of hex file: After selecting device we load the hex file in the given block by using
the ‘browse’ option on the ‘FLASH MAGIC’ window..
Programming of device
After loading the file next step is dumping of code in microcontroller. For that we
first connect the computer’s serial port to your controller board through serial cable. Then
after give the power supply to the controller board..
Now its time to dump the code in controller.. Press the start option on your flash magic
window. Then your microcontroller will be programmed in few seconds..
CHAPTER-5
CIRCUIT DIAGRAM AND CODE
5.1CIRCUIT DIAGRAM
5.2 CODE
#include<reg51.h>void UART_init(void);
void send_to_modem (unsigned char s[]);void enter (void);void ch_send_to_modem (unsigned char single_char);
void UART_init(void) { TMOD=0x20; TH1=0xFD; SCON=0x50; TR1=1; }
void send_to_modem (unsigned char s[]) { unsigned char r;
for(r=0;s[r]!='\0';r++) // to send the command to GSM modem to avoid echo signal { // the command is "ate0", SBUF=s[r]; while(TI==0); TI=0; delay(20); } // enter(); }
void enter (void) { SBUF=13; // Enter ASC values are 13 and 10, while(TI==0); // After sending commands to GSM modem you must be send Enter's ASC values. TI=0; SBUF=10; while(TI==0); TI=0; }
void ch_send_to_modem (unsigned char single_char) {
SBUF=single_char; while(TI==0); TI=0; delay(10); } //#include<reg51.h>
#define lcd_data P1#define lcd_cont() ((lcd_en=1),(delay(3)),(lcd_en=0))
sbit lcd_rs = P1^2; // Here we are using LCD in four bit mode that's why LCD's Data pins and control sbit lcd_en = P1^3; void lcd_init (void); void lcdcmd (unsigned char value); void lcddata (unsigned char value); void msgdisplay (unsigned char b[]); void delay (unsigned int value);
void lcd_init (void){ lcdcmd(0x02); lcdcmd(0x02); lcdcmd(0x02); lcdcmd(0x28); lcdcmd(0x28); lcdcmd(0x28); lcdcmd(0x0e); lcdcmd(0x06); lcdcmd(0x01);
}
void lcdcmd (unsigned char value) // LCD COMMAND { lcd_data=value&(0xf0); lcd_rs=0; lcd_cont(); lcd_data=((value<<4)&(0xf0)); lcd_rs=0; lcd_cont(); }
void lcddata(unsigned char value)
{ lcd_data=value&(0xf0);
lcd_rs=1; lcd_cont(); delay(3); lcd_data=((value<<4)&(0xf0)); lcd_rs=1; lcd_cont(); delay(3); }
void msgdisplay(unsigned char b[]) {unsigned char s,count=0;for(s=0;b[s]!='\0';s++) { if(s==16) lcdcmd(0xc0); lcddata(b[s]); }}
void delay(unsigned int value)
{ unsigned int x,y; for(x=0;x<200;x++) for(y=0;y<value;y++); }
/*******************/ #include<reg51.h> #include"lcddisplay.h" #include"UART.h"
#include<string.h> #include<intrins.h>
sbit buz = P3^4;
sbit gsm = P3^3;sbit rfid = P3^2;
sbit accidentsw = P2^7;
unsigned char mobilenum[]="9985784340"; //user number
unsigned char msg[10],rfiddata[15];unsigned char XX,newmsg=0,a,j,msgtype;
/****** interrupt function to recieve the data from GSM or RFID *****/
void serintr(void) interrupt 4{if(RI==1){ XX=SBUF; if(XX=='+') newmsg=1; else rfiddata[j]=XX;j=j+1;
RI=0;
}
}
void main(){ delay(50); lcd_init(); /*****lcd intialization**/
UART_init(); ////////UART intialization for 9600 baud rate lcdcmd(0x85); gsm=0; //selcet gsm modem rfid=1; //deselcet rfid modem RI=0; lcdcmd(0x01); msgdisplay("searching for"); lcdcmd(0xc0); msgdisplay("GSM modem"); delay(300); send_to_modem("ate0"); //to avoid echo signals, enter();again: send_to_modem("at"); // TO CHECKING GSM MODEM... enter(); if(!RI) // Here we are waiting for data whitch is sending by GSM modem goto again;
RI=0; EA=1;
ES=1; lcdcmd(0x01); msgdisplay("SYSTEM"); lcdcmd(0xc3); msgdisplay("CONNECTED"); delay(100); send_to_modem("at+creg=0"); // enter(); delay(300);
xxx: lcdcmd(0x01); msgdisplay("CHEKING SIM"); send_to_modem("AT+CPIN?"); // enter();
delay(500); if(newmsg==0) goto xxx; lcdcmd(0xC0);
msgdisplay("SIM CONNECTED"); delay(500);
send_to_modem("at+cmgf=1"); // tr set message format astext mode enter();
st: RI=0; lcdcmd(0x01);
msgdisplay(" Accident "); lcdcmd(0xC0); msgdisplay("Intmation Systm"); delay(500);
newmsg=0; rfid=0;
gsm=1; RI=0;
while(1){ while(j==0) //check for switch till we get data from RFID { if(accidentsw==0) //if switch is pressed then send message goto sendmsg; } if(!strcmp(rfiddata,"25001C01B4")) //compare the rFId data {
msgtype=0;
lcdcmd(0x01); msgdisplay("authorized");
delay(500); lcdcmd(0x01);
msgdisplay("expiry date "); lcdcmd(0xc0);
msgdisplay("20/12/2012"); delay(500);
} else { buz=0;
msgtype=1; lcdcmd(0x01); msgdisplay("unauthorized");
lcdcmd(0xc0);
msgdisplay("Card Expired");delay(500);
} goto st; } sendmsg:gsm=0;lcdcmd(0x01);msgdisplay("sending message");send_to_modem("at+cmgs=");send_to_modem(mobilenum);enter();delay(100);send_to_modem("vehicle met with an accident!!!"); ch_send_to_modem(0x1a);lcdcmd(0x01);msgdisplay("MESSAGE SENT");delay(500);goto st;}
APPLICATIONS
Through GSM we control the house hold appliances.
We can control the devices from remote places
We can use in industrial appliances also.
RFID applications help in tracking goods in the supply chain and during the
manufacturing process. Another useful RFID application is one that allows controlled
access to buildings and networks. Low frequency RFID applications are ideal for
scanning objects with high water content at close range. UHF tags are best for
scanning boxes of goods. Any company seeking to implement RFID applications must
choose the right frequency. RFID applications extend to triggering equipment deep
down in the oil wells as well as reusable containers and high value tools.
CONCLUSION
The main aim of the project is to develop a module that helps in controlling the devices using
the GSM technology. In this project we control the operation of the devices remotely Here
when we type the MESSAGE to the system.
In terms of tracking capabilities, though, by employing GSM and using detailed street
level mapping system it would be possible to obtain geographical location accuracy within
about 300 metres. Ongoing development within the mobile telephone networks is expected to
reduce this to 50 metres soon. In the case of the theft of a valuable item or a kidnapping, for
example, the radio beacon contained within the tracking device can be activated by SMS and
tracking can begin.
Of course the distance at which the radio signal may be picked up by the receiver
depends on topographical conditions. Under normal conditions the signal may be received 2 -
3 kilometres away from the tracking device. But if height can be gained (using a tall building
or a helicopter, for example) the distance can be increased greatly. Using radio detection
methods the accuracy of such devices are very accurate, generally within 1 metre or less.