ABSTRACT Electronic voting (also known as e-voting) is a term encompassing several different types of voting, embracing both electronic means of casting a vote and electronic means of counting votes. Electronic voting technology can include punch cards, optical scan voting systems and specialized voting kiosks (including self-contained Direct-recording electronic (DRE) voting systems). It can also involve transmission of ballots and votes via telephones, private computer networks, or the Internet. Electronic voting systems may offer advantages compared to other voting techniques. An electronic voting system can be involved in any one of a number of steps in the setup, distributing, voting, collecting, and counting of ballots, and thus may or may not introduce advantages into any of these steps. The main aim of this project is develop a Electronic Voting Machine with maximum security facilities. i
Transcript
ABSTRACT
Electronic voting (also known as e-voting) is a term encompassing
several different types of voting, embracing both electronic means of casting a
vote and electronic means of counting votes. Electronic voting technology can
include punch cards, optical scan voting systems and specialized voting kiosks
(including self-contained Direct-recording electronic (DRE) voting systems). It
can also involve transmission of ballots and votes via telephones, private
computer networks, or the Internet.
Electronic voting systems may offer advantages compared to other voting
techniques. An electronic voting system can be involved in any one of a number
of steps in the setup, distributing, voting, collecting, and counting of ballots, and
thus may or may not introduce advantages into any of these steps.
The main aim of this project is develop a Electronic Voting Machine with
maximum security facilities.
i
TABLE OF CONTENTSTABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
ii
ABSTRACT vii
LIST OF FIGURES xiii
LIST OF ABBREVATION xiv
1. INTRODUCTION 02
1.1 Block Diagram Description 02
1.2 Block Diagram 03
1.3 Circuit Diagram 04
1.4 Circuit Diagram Description 05
2. POWER SUPPLY UNIT 07
2.1 Circuit Diagram 07
2.1.1 Working Principle 07
2.1.2 Transformer 08
2.1.3 Bridge Rectifier 08
2.1.4 IC Voltage Regulators 10
3. MICROCONTROLLER 12
3.1 Description 12
3.2 Pin Diagram 14
3.2.1 8051 Pin Functions 15
3.2.1.1 I/O PORTS 15
3.2.1.2 Port0 15
3
3.2.1.3 Port1 16
3.2.1.4 Port2 16
3.2.1.5 Port3 17
3.2.1.6 Oscillator inputs 19
3.2.1.7 RESET Line (RST) 19
3.2.1.8Address Latch Enable (ALE) 19
3.2.1.9 Program Store Enable (PSEN) 20
3.2.1.10 External Access (EA) 20
3.2.1.11 Memory Organization 21
3.2.1.12 Common Memory Space 25
3.3 Block Diagram 26
3.3.1Oscillator characteristics 26
3.3.2 8051 CLOCK 27
3.3.3 IDLE mode 27
3.3.4 Power down mode 28
3.3.5 8051 RESET 28
3.3.6 Central Processing Unit 29
3.3.7 The Accumulator 29
3.3.8 The "R" Register 29
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3.3.9 The "B" Register 30
3.3.10 The Program Counters (PC) 31
3.3.11 The Data Pointer (DPTR) 31
3.3.12 The Stack Pointer (SP) 32
3.3.13 Input/Output ports 32
3.3.14 Timers/Counters 33
3.3.15 Interrupts 34
3.3.16 Serial port 35
3.3.17 Applications 36
4. SERIAL COMMUNICATION 38
4.1 Introduction 38
4.2 Null MODEM 41
4.3 RS232 42
4.4 Null MODEM without Handshaking 43
4.5 Compatibility issues 44
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5. SOFTWARE CODING 47
6. SOFTWARE TOOLS 56
6.1 Types of Tools
56
6.1.1 KEIL C 56
6.1.2 SigID 57
6.1.3 VISUAL BASIC 58
7. HARDWARE TOOLS 61
7.1 GSM MODEM 66
7.1.1 Definition 66
7.1.2 The GSM Network 67
7.1.3 GSM MODEM 67
7.1.4 GSM MODEM Applications 69
7.1.5 Facts and applications of GSM/GPRS
MODEM 69
7.1.6 Applications 70
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7.1.7 Application suitable for GSM communication 71
7.2 LCD DISPLAY 72
8. CONCLUSION 75
9. APPENDIX 77
10. REFERENCES 79
LIST OF FIGURES
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FIGURE NO. TITLE PAGE NO.
1.1 Block diagram of car security system 03
1.2 Circuit Diagram 04
2.1 Circuit diagram of power supply 07
2.2 Block Diagram of power supply 08
3.1 Pin Diagram of 8051 14
3.2 Program Memory 22
3.3 Main Memory 23
3.4 Internal Data Memory 24
3.5 Block Diagram of the 8051 Core 26
3.6 8051 CLOCK 27
3.7 8051 RESET 28
3.8 Block diagram of timers/counters 34
4.1 Simple null modem without handshaking 44
6.1 Design window of ORCAD 58
7.1 GPS segments 62
7.2 Position of the 28 GPS satellites at 12.00 hrs UTC 63
7.3 GPS Satellite 64
7.4 Block diagram of satellite 65
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LIST OF ABBREVATIONS
MCU Micro Controller Unit
RMS Root Mean Square
CMOS Complementary Metal Oxide Semiconductor
CPU Central Processing Unit
RAM Random Access Memory
ALU Arithmetic Logic Unit
SP Stack Pointer
PSW Program Status Word
PC Program Counter
DPTR Data Pointer Register
UART Universal Asynchronous Receiver Transmitter
CD Carrier Detect Signal
RI Ring Indicator
DSR Data Set Ready
CTS Clear To Send
DTR Data Terminal Ready
DCE Data Communication Equipment
RX Receiver
TX Transmitter
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CHAPTER-1
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CHAPTER-1
INTRODUCTION
E-voting has been a very controversial topic ever since the presidential elections in
the U.S. in 2000.Many security flaws were found . the standards for the
implementation of e-voting systems were shown to be too weak and many
(scientific) experts expressed their negative opinions on e-voting .
Nevertheless, efforts are still made to introduce evoting in countries that use
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traditional paper ballots. E-voting is an election method in which the votes
are cast or collected electronically . A computer system whose main
element is an software component that maps the voting procedure
electronically is called an e-voting system. A direct recording electronic (DRE)
machine is a special case of such a system as it implements all steps in the voting
process, from registration and ballot casting to counting.
There are two different forms of voting: distance and presence voting .
In presence voting, a voter can cast his or her vote in a polling station under
the supervision of the election's administration. Examples for presence voting are
conventional elections in polling stations or voting with e-voting machines. In
distance voting, the voter acts without the supervision of the electoral
commission and casts his or her vote from a place other than a polling booth,
such as casting absentee ballots via mail or internetvoting.
1.1 BLOCK DIAGRAM:
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RTC RTCDriver OSC
Display Unit
Polling Switches
MCU
MAX232
Transformer Rectifier
RegulatorFilter
1.2 BLOCK DIAGRAM DESCRIPTION:
The finger print sensor gets the finger print of the voters and sends to the PC. In PC the finger print image is compared with existing image
If the image is matched, the computer sends the command the person is valid to the micro controller and displayed.
If any one try to poll their vote beyond the time limit, system will be blocked.
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1.3 EXISTING SYSTEM:
The system allows the Evil Practices held in the manual Voting system. Electronic voting systems may offer advantages compared to other voting
techniques. An electronic voting system can be involved in any one of a number of steps in
the setup, distributing, voting, collecting, and counting of ballots, and thus may or may not introduce advantages into any of these steps.
1.4 PROPOSED SYSTEM:
Electronic voting (also known as e-voting) is a term encompassing several
different types of voting, embracing both electronic means of casting a vote
and electronic means of counting votes.
It can also involve transmission of ballots and votes via telephones, private
Of the 40 pins of the typical 8052, 32 of them are
dedicated to I/O lines that have a one-to-one relation with SFRs P0, P1, P2, and P3.
The developer may raise and lower these lines by writing 1s or 0s to the
corresponding bits in the SFRs. Likewise; the current state of these lines may be
read by reading the corresponding bits of the SFRs. All of the ports have internal
pull-up resistors except for port 0.
3.2.1.2 PORT 0:
Port 0 is dual-function in that it in some designs port 0ís I/O
lines are available to the developer to access external devices while in other
designs it is used to access external memory. If the circuit requires external RAM
or ROM, the microcontroller will automatically use port 0 to clock in/out the 8-bit
data word as well as the low 8 bits of the address in response to a MOVX
instruction and port 0 I/O lines may be used for other functions as long as external
RAM isn’t being accessed at the same time. If the circuit requires external code
memory, the microcontroller will automatically use the port 0 I/O lines to access
each instruction that is to be executed. In this case, port 0 cannot be utilized for
other purposes since the state of the I/O lines are constantly being modified to
access external code memory.
Note that there are no pull-up resistors on port 0, so it may be necessary to
include your own pull-up resistors depending on the characteristics of the parts you
will be driving via port 0.here small decoupling capacitor is connected in this port
0.
3.2.1.3 PORT 1:
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Port 1 consists of 8 I/O lines that you may use exclusively to interface to
external parts. Unlike port 0, typical derivatives do not use port 1 for any functions
themselves. Port 1 is commonly used to interface to external hardware such as
LCDs, keypads, and other devices. With 8052 derivatives, two bits of port 1 are
optionally used as described for extended timer 2 functions. These two lines are
not assigned these special functions on 8051ís since 8051ís don’t have a timer 2.
Further, these lines can still be used for your own purposes if you don’t need these
features of timer 2.
P1.0 (T2): If T2CON.1 is set (C/T2), then timer 2 will be incremented
whenever there is a 1-0 transition on this line. With C/T2 set, P1.0 is the clock
source for timer 2. P1.1 (T2EX): If timer 2 is in auto-reload mode and T2CON.3
(EXEN2) is set, a 1-0 transition on this line will cause timer 2 to be reloaded with
the auto-reload value. This will also cause the T2CON.6 (EXF2) external flag to be
set, which may cause an interrupt if so enabled.
3.2.1.4 PORT 2:
Like port 0, port 2 is dual-function. In some circuit designs it is available for
accessing devices while in others it is used to address external RAM or external
code memory. When the MOVX @DPTR instruction is used, port 2 is used to
output the high byte of the memory address that is to be accessed. In these cases,
port 2 may be used to access other devices as long as the devices are not being
accessed at the same time a MOVX instruction is using port 2 to address external
RAM. If the circuit requires external code memory, the microcontroller will
automatically use the port 2 I/O lines to access each instruction that is to be
executed.
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In this case, port 2 cannot be utilized for other purposes since the state of the
I/O lines are constantly being modified to access external code memory.
3.2.1.5 PORT 3:
Port 3 consists entirely of dual-function I/O lines. While the developer may
access all these lines from their software by reading/writing to the P3 SFR, each
pin has a pre-defined function that the microcontroller handles automatically when
configured to do so and/or when necessary. P3.0 (RXD): The UART/serial port
uses P3.0 as the receive line. In circuit designs that will be using the
microcontroller’s internal serial port, this is the line into which serial data will be
clocked. Note that when interfacing an 8052 to an RS-232 port that you may not
connect this line directly to the RS-232 pin; rather, you must pass it through a part
such as the MAX232 to obtain the correct voltage levels. This pin is available for
any use the developer may assign it if the circuit has no need to receive data via the
integrated serial port.
P3.1 (TXD): The UART/serial port uses P3.1 as the ‘transmit line.’ In circuit
designs that will be using the microcontroller’s internal serial port, this is the line
that the microcontroller will clock out all data which is written to the SBUF SFR.
Note that when interfacing an 8052 to an RS-232 port that you may not connect
this line directly to the RS-232 pin; rather, you must pass it through a part such as
the MAX232 to obtain the correct voltage levels. This pin is available for any use
the developer may assign it if the circuit has no need to transmit data via the
integrated serial port.
P3.2 (-INT0): When so configured, this line is used to trigger an ‘External 0
Interrupt.’ This may either be low-level triggered or may be triggered on a 1-0
transition. Please see the chapter on interrupts for details. This pin is available for
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any use the developer may assign it if the circuit does not need to trigger an
external 0 interrupt.
P3.3 (-INT1): When so configured, this line is used to trigger an ‘External 1
Interrupt.’ This may either be low-level triggered or may be triggered on a 1-0
transition. Please see the chapter on interrupts for details. This pin is available for
any use the developer may assign it if the circuit does not need to trigger an
external 1 interrupt.
P3.4 (T0): When so configured, this line is used as the clock source for timer
0. Timer 0 will be incremented either every instruction cycle that T0 is high or
every time there is a 1-0 transition on this line, depending on how the timer is
configured. Please see the chapter on timers for details. This pin is available for
any use the developer may assign it if the circuit does not to control timer 0
externally.
P3.5 (T1): When so configured, this line is used as the clock source for timer
1. Timer 1 will be incremented either every instruction cycle that T1 is high or
every time there is a 1-0 transition on this line, depending on how the timer is
configured. Please see the chapter on timers for details. This pin is available for
any use the developer may assign it if the circuit does not to control timer 1
externally.
P3.6 (-WR): This is external memory write strobe line. This line will be
asserted low by the microcontroller whenever a MOVX instruction writes to
external RAM. This line should be connected to the RAM’s write (-W) line. This
pin is available for any use the developer may assign it if the circuit does not write
to external RAM using MOVX.
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P3.7 (-RD): This is external memory write strobe line. This line will be
asserted low by the microcontroller whenever a MOVX instruction writes to
external RAM. This line should be connected to the RAM’s write (-W) line. This
pin is available for any use the developer may assign it if the circuit does not read
from external RAM using MOVX.
3.2.1.6 OSCILLATOR INPUTS (XTAL1, XTAL2):
The 8052 is typically driven by a crystal connected to pins 18 (XTAL2) and
19 (XTAL1). Common crystal frequencies are 11.0592Mhz as well as 12Mhz,
although many newer derivatives are capable of accepting frequencies as high as
40Mhz.
While a crystal is the normal clock source, this isn’t necessarily the case. A
TTL clock source may also be attached to XTAL1 and XTAL2 to provide the
microcontroller’s clock.
3.2.1.7 RESET LINE (RST):
Pin 9 is the master reset line for the microcontroller. When this pin is
brought high for two instruction cycles, the microcontroller is effectively reset.
SFRs, including the I/O ports, are restored to their default conditions and the
program counter will be reset to 0000h. Keep in mind that Internal RAM is not
affected by a reset. The microcontroller will begin executing code at 0000h when
pin 9 returns to a low state.
The reset line is often connected to a reset button/switch that the user may
press to reset the circuit. It is also common to connect the reset line to a watchdog
IC or a supervisor IC (such as MAX707).
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3.2.1.8 ADDRESS LATCH ENABLE (ALE):
The ALE at pin 30 is an output-only pin that is controlled entirely by the
microcontroller and allows the microcontroller to multiplex the low-byte of a
memory address and the 8-bit data itself on port 0. This is because, while the high-
byte of the memory address is sent on port 2, port 0 is used both to send the low
byte of the memory address and the data itself. This is accomplished by placing the
low-byte of the address on port 0, exerting ALE high to latch the low-byte of the
address into a latch IC (such as the 74HC573), and then placing the 8 data-bits on
port 0. In this way the 8052 is able to output a 16-bit address and an 8-bit data
word with 16 I/O lines instead of 24.
The ALE line is used in this fashion both for accessing external RAM with
MOVX @DPTR as well as for accessing instructions in external code memory.
When your program is executed from external code memory, ALE will pulse at a
rate of 1/6th that of the oscillator frequency. Thus if the oscillator is operating at
11.0592 MHz, ALE will pulse at a rate of 1,843,200 times per second. The only
exception is when the MOVX instruction is executed one ALE pulse is missed in
lieu of a pulse on WR or RD.
3.2.1.9 PROGRAM STORE ENABLE (PSEN):
The Program Store Enable (PSEN) line at pin 29 is exerted low
automatically by the microcontroller whenever it accesses external code memory.
This line should be attached to the Output Enable (-OE) pin of the EPROM that
contains your code memory.
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PSEN will not be exerted by the microcontroller and will remain in a high
state if your program is being executed from internal code memory.
3.2.1.10 EXTERNAL ACCESS (EA):
The External Access (EA) line at pin 31 is used to determine whether the
8052 will execute your program from external code memory or from internal code
memory.
If EA is tied high (connected to +5V) then the microcontroller will execute
the program it finds in internal/on-chip code memory. If EA is tied low (to ground)
then it will attempt to execute the program it finds in the attached external code
memory EPROM. Of course, your EPROM must be properly connected for the
microcontroller to be able to access your program in external code memory.
3.2.1.11 MEMORY ORGANIZATION:
The 8051 architecture provides both on chip memory as well as off chip
memory expansion capabilities. It supports several distinctive ‘physical’ address
spaces, functionally separated at the hardware level by different addressing
mechanisms, read and write controls signals or both:
On chip Program Memory
On chip Data Memory
Off chip Program Memory
Off chip Data Memory
On chip Special Function Registers
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The Program Memory area (EPROM incase of external memory or
Flash/EPROM incase of internal one) is extremely large and never lose
information when the power is removed. Program Memory is used for information
needed each time power is applied: Initialization values, Calibration data,
Keyboard lookup tables etc along with the program itself. The Program Memory
has a 16 bit address and any particular memory location is addressed using the 16
bit Program Counter and instructions which generate a 16 bit address.
On chip Data memory is smaller and therefore quicker than Program
Memory and it goes into a random state when power is removed. On chip RAM is
used for variables which are calculated when the program is executed.
In contrast to the Program Memory, on chip Data Memory accesses need a
single 8 bit value (may be a constant or another variable) to specify a unique
location. Since 8 bits are more than sufficient to address 128 RAM locations, the
on chip RAM address generating register is single byte wide.
Different addressing mechanisms are used to access these different memory
spaces and this greatly contributes to microcomputer’s operating efficiency.
The 64K byte Program Memory space consists of an internal and an external
memory portion. If the EA pin is held high, the 8051 executes out of internal
Program Memory unless the address exceeds 0FFFH and locations 1000H through
FFFFH are then fetched from external Program Memory. If the EA pin is held low,
the 8031 fetches all instructions from the external Program Memory. In either case,
the 16 bit Program Counter is the addressing mechanism.
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Figure.3.2 - Program Memory
The Data Memory address space consists of an internal and an external
memory space. External Data Memory is accessed when a MOVX instruction is
executed.
Apart from on chip Data Memory of size 128/256 bytes, total size of Data
Memory can be expanded up to 64K using external RAM devices.
Total internal Data Memory is divided into three blocks:
Lower 128 bytes.
Higher 128 bytes
Special Function Register space.
Higher 128 bytes are available only in 8032/8052 devices.
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Fig.3.3. Main Memory
Even though the upper RAM area and SFR area share same address
locations, they are accessed through different addressing modes. Direct addresses
higher than 7FH access SFR memory space and indirect addressing above 7FH
access higher 128 bytes (in 8032/8052).
Fig.3.4. Internal Data Memory
The next figure indicates the layout of lower 128 bytes. The lowest 32 bytes
(from address 00H to 1FH) are grouped into 4 banks of 8 registers. Program
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instructions refer these registers as R0 through R7. Program Status Word indicates
which register bank is being used at any point of time.
The next 16 bytes above these register banks form a block of bit addressable
memory space. The instruction set of 8031 contains a wide range of single bit
processing instructions and these instructions can directly access the 128 bits of
this area.
The SFR space includes port latches, timer and peripheral control registers.
All the members of 8031 family have same SFR at the same SFR locations. There
are some 16 unique locations which can be accessed as bytes and as bits.
3.21.12 COMMON MEMORY SPACE:
The 8031’s Data Memory may not be used for program storage. So it means
you can’t execute instructions out of this Data Memory. But, there is a way to have
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a single block of off chip memory acting as both Program and Data Memory. By
gating together both memory read controls (RD and PSEN) using an AND gate, a
common memory read control signal can be generated.
In this arrangement, both memory spaces are tied together and total
accessible memory is reduced from 128 Kbytes to 64 Kbytes.
The 8031 can read and write into this common memory block and it can be
used as Program and Data Memory.
You can use this arrangement during program development and debugging
phase. Without taking Microcontroller off the socket to program its internal ROM
(EPROM/Flash ROM), you can use this common memory for frequent program
storage and code modifications.
Basically, 8031’s assembly language instruction set consists of an operation
mnemonic and zero to three operands separated by commas. In two byte
instructions the destination is specified first, and then the source. Byte wide
mnemonics like ADD or MOV use the Accumulator as a source operand and also
to receive the result.
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3.3 BLOCK DIAGRAM:
Fig.3.5. Block Diagram of the 8051 Core
3.3.1 OSCILLATOR CHARACTERISTICS:
XTAL1 and XTAL2 are the input and output, respectively, of an inverting
amplifier which can be configured for use as an on chip oscillator, as shown in
Figure 1. Either a quartz crystal or ceramic resonator may be used. To drive the
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device from an external clock source, XTAL2 should be left unconnected while
XTAL1 is driven as shown in Figure 2.
There are no requirements on the duty cycle of the external clock signal,
since the input to the internal clocking circuitry is through a divide-by two flip-
flop, but minimum and maximum voltage high and low time specifications must be
observed.
3.3.2 8051 CLOCK:
8051 has an on-chip oscillator
It needs an external crystal
Crystal decides the operating frequency of the 8051
3.3.3 IDLE MODE:
In idle mode, the CPU puts itself to sleep while all the on-chip peripherals
remain active. The mode is invoked by software. The content of the on-chip RAM
and all the special functions registers remain unchanged during this mode. The idle
mode can be terminated by any enabled interrupt or by a hardware reset. It should
be noted that when idle is terminated by a hardware reset, the device normally
resumes program execution, from where it left off, up to two machine cycles
before the internal reset algorithm takes control. On-chip hardware inhibits access
to internal RAM in this event, but access to the port pins is not inhibited. To
eliminate the possibility of an unexpected write to a port pin when Idle is
terminated by reset, the instruction following the one that invokes Idle should not
be one that writes to a port pin or to external memory.
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3.3.4 POWER DOWN MODE:
In the power down mode the oscillator is stopped, and the instruction that
invokes power down is the last instruction executed. The on-chip RAM and
Special Function Registers retain their values until the power down mode is
terminated. The only exit from power down is a hardware reset. Reset redefines the
SFRs but does not change the on-chip RAM. The reset should not be activated
before VCC is restored to its normal operating level and must be held active long
enough to allow the oscillator to restart and stabilize.
3.3.5 8051 RESET:
RESET is an active High input
When RESET is set to High, 8051 goes back to the power on state
Power-On Reset
Push PB and active High on RST
Release PB, Capacitor discharges and RST goes low
RST must stay high for a min of 2 machine cycles
Fig.3.7.8051 RESET
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3.3.6 CENTRAL PROCESSING UNIT:
The CPU is the brain of the microcontrollers reading user’s programs and
executing the expected task as per instructions stored there in. Its primary elements
are an 8 bit Arithmetic Logic Unit (ALU), Accumulator (Acc), few more 8 bit
registers, B register, Stack Pointer (SP), Program Status Word (PSW) and 16 bit
registers, Program Counter (PC) and Data Pointer Register (DPTR).
3.3.7 THE ACCUMULATOR:
If worked with any other assembly language you will be familiar with the
concept of an accumulator register. The Accumulator, as its name suggests, is used
as a general register to accumulate the results of a large number of instructions. It
can hold an 8-bit (1-byte) value and is the most versatile register the 8052 has due
to the sheer number of instructions that make use of the accumulator. More than
half of the 8052ís 255 instructions manipulate or use the Accumulator in some
way.
For example, if you want to add the number 10 and 20, the resulting 30 will
be stored in the Accumulator. Once you have a value in the Accumulator you may
continue processing the value or you may store it in another register or in memory.
3.3.8 THE "R" REGISTERS:
The "R" registers are sets of eight registers that are named R0, R1, through
R7. These registers are used as auxiliary registers in many operations. To continue
with the above example, perhaps you are adding 10 and 20.
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The original number 10 may be stored in the Accumulator whereas the value
20 may be stored in, say, register R4. To process the addition you would execute
the command:
As mentioned earlier, there are four sets of ‘R’ registers, register bank 0, 1,
2, and 3. When the 8052 is first powered up, register bank 0 (addresses 00h
through 07h) is used by default.
In this case, for example, R4 is the same as Internal RAM address 04h.
However, your program may instruct the 8052 to use one of the alternate register
banks; i.e., register banks 1, 2, or 3. In this case, R4 will no longer be the same as
Internal RAM address 04h. For example, if your program instructs the 8052 to use
register bank 1, register R4 will now be synonymous with Internal RAM address
0Ch. If you select register bank 2, R4 is synonymous with 14h, and if you select
register bank 3 it is synonymous with address 1Ch.
The concept of register banks adds a great level of flexibility to the 8052,
especially when dealing with interrupts (we'll talk about interrupts later). However,
always remember that the register banks really reside in the first 32 bytes of
Internal RAM.
3.3.9 THE "B" REGISTER:
The "B" register is very similar to the Accumulator in the sense that it may
hold an 8-bit (1-byte) value. The "B" register is only used implicitly by two 8052
instructions: MUL AB and DIV AB. Thus, if you want to quickly and easily
multiply or divide A by another number, you may store the other number in "B"
and make use of these two instructions. Aside from the MUL and DIV an
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instruction, the “B” register is often used as yet another temporary storage register
much like a ninth "R" register.
3.3.10 THE PROGRAM COUNTER (PC):
The Program Counter (PC) is a 2-byte address that tells the 8052 where the
next instruction to execute is found in memory. When the 8052 is initialized PC
always starts at 0000h and is incremented each time an instruction is executed. It is
important to note that PC isn’t always incremented by one. Since some instructions
are 2 or 3 bytes in length the PC will be incremented by 2 or 3 in these cases.
The Program Counter is special in that there is no way to directly modify its
value. That is to say, you can’t do something like PC=2430h. On the other hand, if
you execute LJMP 2430h you’ve effectively accomplished the same thing.
It is also interesting to note that while you may change the value of PC (by
executing a jump instruction, etc.) there is no way to read the value of PC. That is
to say, there is no way to ask the 8052 "What address are you about to execute?"
As it turns out, this is not completely true: There is one trick that may be used to
determine the current value of PC.
3.3.11 THE DATA POINTER (DPTR):
The Data Pointer (DPTR) is the 8052ís only user-accessible 16-bit (2-byte)
register. The Accumulator, "R" registers, and "B" register are all 1-byte values.
The PC just described is a 16-bit value but isn’t directly user-accessible as a
working register. DPTR, as the name suggests, is used to point to data. It is used by
a number of commands that allow the 8052 to access external memory. When the
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8052 accesses external memory it accesses the memory at the address indicated by
DPTR.
While DPTR is most often used to point to data in external memory or code
memory, many developers take advantage of the fact that it’s the only true 16-bit
register available. It is often used to store 2-byte values that have nothing to do
with memory locations.
3.3.12 THE STACK POINTER (SP):
The Stack Pointer, like all registers except DPTR and PC, may hold an 8-bit
(1-byte) value. The Stack Pointer is used to indicate where the next value to be
removed from the stack should be taken from. When you push a value onto the
stack, the 8052 first increments the value of SP and then stores the value at the
resulting memory location. When you pop a value off the stack, the 8052 returns
the value from the memory location indicated by SP, and then decrements the
value of SP.
This order of operation is important. When the 8052 is initialized SP will be
initialized to 07h. If you immediately push a value onto the stack, the value will be
stored in Internal RAM address 08h. This makes sense taking into account what
was mentioned two paragraphs above: First the 8051 will increment the value of
SP (from 07h to 08h) and then will store the pushed value at that memory address
(08h). SP is modified directly by the 8052 by six instructions: PUSH, POP,
ACALL, LCALL, RET, and RETI. It is also used intrinsically whenever an
interrupt is triggered (more on interrupts later. Don’t worry about them for now!).
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3.3.13 INPUT / OUTPUT PORTS:
The 8031’s I/O port structure is extremely versatile and flexible. The device
has 32 I/O pins configured as four eight bit parallel ports (P0, P1, P2 and P3). Each
pin can be used as an input or as an output under the software control. These I/O
pins can be accessed directly by memory instructions during program execution to
get required flexibility.
These port lines can be operated in different modes and all the pins can be
made to do many different tasks apart from their regular I/O function executions.
Instructions, which access external memory, use port P0 as a multiplexed
address/data bus. At the beginning of an external memory cycle, low order 8 bits of
the address bus are output on P0. The same pins transfer data byte at the later stage
of the instruction execution.
Also, any instruction that accesses external Program Memory will output the
higher order byte on P2 during read cycle. Remaining ports, P1 and P3 are
available for standard I/O functions. But all the 8 lines of P3 support special
functions: Two external interrupt lines, two counter inputs, serial port’s two data
lines and two timing control strobe lines are designed to use P3 port lines. When
you don’t use these special functions, you can use corresponding port lines as a
standard I/O.
Even within a single port, I/O operations may be combined in many ways.
Different pins can be configured as input or outputs independent of each other or
the same pin can be used as an input or as output at different times. You can
comfortably combine I/O operations and special operations for Port 3 lines.
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3.3.14 TIMERS / COUNTERS:
8031 has two 16 bit Timers/Counters capable of working in different modes.
Each consists of a ‘High’ byte and a ‘Low’ byte which can be accessed under
software. There is a mode control register and a control register to configure these
timers/counters in number of ways.
These timers can be used to measure time intervals, determine pulse widths
or initiate events with one microsecond resolution up to a maximum of 65
millisecond (corresponding to 65, 536 counts). Use software to get longer delays.
Working as counter, they can accumulate occurrences of external events (from DC
to 500 KHz) with 16 bit precision.
3.3.15 INTERRUPTS:
The 8031 has five interrupt sources: one from the serial port when a
transmission or reception operation is executed; two from the timers when
overflow occurs and two come from the two input pins INT0, INT1.
Each interrupt may be independently enabled or disabled to allow polling on
same sources and each may be classified as high or low priority.
A high priority source can override a low priority service routine. These
options are selected by interrupt enable and priority control registers, IE and IP.
When an interrupt is activated, then the program flow completes the
execution of the current instruction and jumps to a particular program location
where it finds the interrupt service routine. After finishing the interrupt service
routine, the program flows return to back to the original place.
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The Program Memory address, 0003H is allotted to the first interrupt and
next seven bytes can be used to do any task associated with that interrupt.
Interrupt Source Service routine starting address:
External 0 0003H
Timer/Counter 0 000BH
External 1 0013H
Timer/counter 1 001BH
Serial port 0023H
3.3.16 SERIAL PORT:
Each 8031 microcomputer contains a high speed full duplex (means you can
simultaneously use the same port for both transmitting and receiving purposes)
serial port which is software configurable in 4 basic modes: 8 bit UART; 9 bit
UART; Interprocessor Communications link or as shift register I/O expander.
For the standard serial communication facility, 8031 can be programmed for
UART operations and can be connected with regular personal computers, teletype
writers, modem at data rates between 122 bauds and 31 kilo bauds.
Getting this facility is made very simple using simple routines with option to
select even or odd parity. You can also establish a kind of Interprocessor
communication facility among many microcomputers in a distributed environment
with automatic recognition of address/data.
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Apart from all above, you can also get super fast I/O lines using low cost
simple TTL or CMOS shift registers.
3.3.17APPLICATIONS:
Security applications
Image processing applications
Banking applications
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CHAPTER-4
CHAPTER-4
SERIAL COMMUNICATION
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4.1 INTRODUCTION:
Serial communication is basically the transmission or reception of data one
bit at a time. Today's computers generally address data in bytes or some multiple
thereof. A byte contains 8 bits. A bit is basically either a logical 1 or zero. Every
character on this page is actually expressed internally as one byte. The serial port is
used to convert each byte to a stream of ones and zeroes as well as to convert a
stream of ones and zeroes to bytes. The serial port contains a electronic chip called
a Universal Asynchronous Receiver/Transmitter (UART) that actually does the
conversion.
The serial port has many pins. We will discuss the transmit and receive pin
first. Electrically speaking, whenever the serial port sends a logical one (1) a
negative voltage is effected on the transmit pin. Whenever the serial port sends a
logical zero (0) a positive voltage is affected. When no data is being sent, the serial
port's transmit pin's voltage is negative (1) and is said to be in a MARK state. Note
that the serial port can also be forced to keep the transmit pin at a positive voltage
(0) and is said to be the SPACE or BREAK state. (The terms MARK and SPACE
are also used to simply denote a negative voltage (1) or a positive voltage (0) at the
transmit pin respectively).
When transmitting a byte, the UART (serial port) first sends a START BIT
which is a positive voltage (0), followed by the data (general 8 bits, but could be 5,
6, 7, or 8 bits) followed by one or two STOP Bits which is a negative(1) voltage.
The sequence is repeated for each byte sent. Figure 1 shows a diagram of what a
byte transmission would look like.
At this point you may want to know what the duration of a bit is. In other
words, how long does the signal stay in a particular state to define a bit. The
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answer is simple. It is dependent on the baud rate. The baud rate is the number of
times the signal can switch states in one second. Therefore, if the line is operating
at 9600 baud, the line can switch states 9,600 times per second. This means each
bit has the duration of 1/9600 of a second or about 100µsec.
when transmitting a character there are other characteristics other than the
baud rate that must be known or that must be setup. These characteristics define
the entire interpretation of the data stream. The first characteristic is the length of
the byte that will be transmitted. This length in general can be anywhere from 5 to
8 bits.
The second characteristic is parity. The parity characteristic can be even,
odd, mark, space, or none. If even parity, then the last data bit transmitted will be a
logical 1 if the data transmitted had an even amount of 0 bits. If odd parity, then
the last data bit transmitted will be a logical 1 if the data transmitted had an odd
amount of 0 bits. If MARK parity, then the last transmitted data bit will always be
a logical 1. If SPACE parity, then the last transmitted data bit will always be a
logical 0. If no parity then there is no parity bit transmitted.
The third characteristic is the amount of stop bits. This value in general is 1
or 2. Assume we want to send the letter 'A' over the serial port. The binary
representation of the letter 'A' is 01000001. Remembering that bits are transmitted
from least significant bit (LSB) to most significant bit (MSB), the bit stream
transmitted would be as follows for the line characteristics 8 bits, no parity, 1 stop
bit and 9600 baud.
LSB (0 1 0 0 0 0 0 1 0 1) MSB
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The above represents (Start Bit) (Data Bits) (Stop Bit). To calculate the
actual byte transfer rate simply divide the baud rate by the number of bits that must
be transferred for each byte of data. In the case of the above example, each
character requires 10 bits to be transmitted for each character. As such, at 9600
baud, up to 960 bytes can be transferred in one second.
The above discussion was concerned with the "electrical/logical"
characteristics of the data stream. We will expand the discussion to line protocol.
Serial communication can be half duplex or full duplex. Full duplex
communication means that a device can receive and transmit data at the same time.
Half duplex means that the device cannot send and receive at the same time. It can
do them both, but not at the same time. Half duplex communication is all but
outdated except for a very small focused set of applications.
Half duplex serial communication needs at a minimum two wires, signal
ground and the data line. Full duplex serial communication needs at a minimum
three wires, signal ground, transmit data line, and receive data line. The RS232
specification governs the physical and electrical characteristics of serial
communications. This specification defines several additional signals that are
asserted (set to logical 1) for information and control beyond the data signal
These signals are the Carrier Detect Signal (CD), asserted by modems to
signal a successful connection to another modem, Ring Indicator (RI), asserted by
modems to signal the phone ringing, Data Set Ready (DSR), asserted by modems
to show their presence, Clear To Send (CTS), asserted by modems if they can
receive data, Data Terminal Ready (DTR), asserted by terminals to show their
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presence, Request To Send (RTS), asserted by terminals if they can receive data.
The section RS232 Cabling describes these signals and how they are connected.
The above paragraph alluded to hardware flow control. Hardware flow
control is a method that two connected devices use to tell each other electronically
when to send or when not to send data. A modem in general drops (logical 0) its
CTS line when it can no longer receive characters. It re-asserts it when it can
receive again. A terminal does the same thing instead with the RTS signal. Another
method of hardware flow control in practice is to perform the same procedure in
the previous paragraph except that the DSR and DTR signals.
Note that hardware flow control requires the use of additional wires. The
benefit to this however is crisp and reliable flow control. Another method of flow
control used is known as software flow control. This method requires a simple 3
wire serial communication link, transmit data, receive data, and signal ground. If
using this method, when a device can no longer receive, it will transmit a character
that the two devices agreed on. This character is known as the XOFF character.
This character is generally a hexadecimal 13. When a device can receive again it
transmits an XON character that both devices agreed to. This character is generally
a hexadecimal 11.
4.2 NULL MODEM:
Serial communications with RS232. One of the oldest and most widely
spread communication methods in computer world. The way this type of
communication can be performed is pretty well defined in standards. I.e. with one
exception. The standards show the use of DTE/DCE communication, the way a
computer should communicate with a peripheral device like a modem. For your
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information, DTE means Data Terminal Equipment (computers etc.) where DCE
is the abbreviation of Data Communication Equipment (modems).
One of the main uses of serial communication today where no modem is
involved—a serial null modem configuration with DTE/DTE communication—is
not so well defined, especially when it comes to flow control. The terminology null
modem for the situation where two computers communicate directly is so often
used nowadays, that most people don't realize anymore the origin of the phrase and
that a null modem connection is an exception, not the rule.
In history, practical solutions were developed to let two computers talk with
each other using a null modem serial communication line. In most situations, the
original modem signal lines are reused to perform some sort of handshaking.
Handshaking can increase the maximum allowed communication speed because it
gives the computers the ability to control the flow of information. A high amount
of incoming data is allowed if the computer is capable to handle it, but not if it is
busy performing other tasks. If no flow control is implemented in the null modem
connection, communication is only possible at speeds at which it is sure the
receiving side can handle the amount information even under worst case
conditions.
4.3 RS232:
When we look at the connector pin out of the RS232 port, we see two pins
which are certainly used for flow control. These two pins are RTS, request to send
and CTS, clear to send. With DTE/DCE communication (i.e. a computer
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communicating with a modem device) RTS is an output on the DTE and input on
the DCE. CTS are the answering signal coming from the DCE.
Before sending a character, the DTE asks permission by setting its RTS
output. No information will be sent until the DCE grants permission by using the
CTS line.
If the DCE cannot handle new requests, the CTS signal will go low. A
simple but useful mechanism allowing flow control in one direction. The
assumption is that the DTE can always handle incoming information faster than
the
DCE can send it. In the past, this was true. Modem speeds of 300 baud were
common and 1200 baud was seen as a high speed connection.
For further control of the information flow, both devices have the ability to
signal their status to the other side. For this purpose, the DTR data terminal ready
and DSR data set ready signals are present. The DTE uses the DTR signal to
signal that it is ready to accept information, whereas the DCE uses the DSR signal
for the same purpose. Using these signals involves not a small protocol of
requesting and answering as with the RTS/CTS handshaking. These signals are in
one direction only.
The last flow control signal present in DTE/DCE communication is the CD
carrier detect. It is not used directly for flow control, but mainly an indication of
the ability of the modem device to communicate with its counter part. This signal
indicates the existence of a communication link between two modem devices.
4.4 NULL MODEM WITHOUT HANDSHAKING:
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How to use the handshaking lines in a null modem configuration? The
simplest way is to don't use them at all. In that situation, only the data lines and
signal ground are cross connected in the null modem communication cable. All
other pins have no connection. An example of such a null modem cable without
handshaking can be seen in the figure below.
Connector 1Connector
2Function
2 3 Rx TX
3 2 TX Rx
5 5 Signal ground
Fig.4.1. Simple null modem without handshaking
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4.5 COMPATIBILITY ISSUES:
If you read about null modems, this three wire null modem cable is often
talked about. Yes, it is simple but can we use it in all circumstances? There is a
problem, if either of the two devices checks the DSR or CD inputs. These signals
normally define the ability of the other side to communicate. As they are not
connected, their signal level will never go high. This might cause a problem.
The same holds for the RTS/CTS handshaking sequence. If the software on
both sides is well structured, the RTS output is set high and then a waiting cycle is
started until a ready signal is received on the CTS line. This causes the software to
hang because no physical connection is present to either CTS line to make this
possible. The only type of communication which is allowed on such a null modem
line is data-only traffic on the cross connected Rx/TX lines.
This does however not mean that this null modem cable is useless.
Communication links like present in the Norton Commander program can use this
null modem cable. This null modem cable can also be used when communicating
with devices which do not have modem control signals like electronic measuring
equipment etc.
As you can imagine, with this simple null modem cable no hardware flow control
can be implemented. The only way to perform flow control is with software flow
control using the XOFF and XON characters.
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CHAPTER-5
SOFTWARE CODING
61
6.1 TYPES OF TOOLS:
KEIL C
SigID
VISUAL BASIC
6.1.1 KEIL C:
Keil software is the leading vendor for 8/16-bit development tools (ranked at
first position in the 2004 embedded market study of the embedded system and EE
times magazine).
Keil software is represented world wide in more than 40 countries, since the
market introduction in 1988; the keil C51 compiler is the de facto industry standard
and supports more than 500 current 8051 device variants. Now, keil software
offers development tools for ARM.
Keil software makes C compilers, macro assemblers, real-time kernels,
debuggers, simulators, integrated environments, and evaluation boards for 8051,
251, ARM and XC16x/C16x/ST10 microcontroller families.
The Keil C51 C Compiler for the 8051 microcontroller is the most popular
8051 C compiler in the world. It provides more features than any other 8051 C
compiler available today.
The C51 Compiler allows you to write 8051 microcontroller applications in
C that, once compiled, have the efficiency and speed of assembly language.
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Language extensions in the C51 Compiler give you full access to all resources of
the 8051.
The C51 Compiler translates C source files into relocatable object modules
which contain full symbolic information for debugging with the µVision Debugger
or an in-circuit emulator. In addition to the object file, the compiler generates a
listing file which may optionally include symbol table and cross reference
Nine basic data types, including 32-bit IEEE floating-point,
Flexible variable allocation with bit, data, bdata, idata, xdata, and pdata memory types,
Interrupt functions may be written in C, Full use of the 8051 register banks,
Complete symbol and type information for source-level debugging,
Use of AJMP and ACALL instructions,
Bit-addressable data objects, Built-in interface for the RTX51 real time kernels,
Support for the Philips 8xC750, 8xC751, and 8xC752 limited instruction sets,
Support for the Infineon 80C517 arithmetic unit.
6.1.2 SigID :
SigID.ocx is an Active-X control that allows the developer to capture encrypted fingerprint templates, store them, and use them later to compare against newly-captured fingerprints on-the-fly.
Each fingerprint template is automatically encrypted prior to its delivery to the developer.
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NOTE: It’s important to understand there are two possible ways to use the SigID ActiveX control:
1-Portable: The developer is handed back the fingerprint template with which to compare later fingerprints in a portable file format (.TFT) or ASCII hex string (for easy database storage).
This allows maximum flexibility in terms of storing fingerprint templates, but certain fingerprint comparisons are not possible using this approach (namely one-to-many searches).
2-Maximized: A proprietary, encrypted database (a DAT file) is used to store the fingerprint templates.
Whereas this approach limits the storage flexibility of approach 1, it maximizes fingerprint comparisons in terms of speed and possible search options (namely one-to-many searches).
These approaches are mutually exclusive, and the developer must decide which approach best suits the application.
Methods beginning with the prefix pr (portable) signify methods falling under approach #1, the most portable option.
Methods beginning with the prefix db (database) signify methods falling under approach #2, the maximized proprietary database option.
Methods that begin with neither prefix are neutral methods, and another dependent upon one approach another.
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As the user places their finger on the sensor the image will appear in the olive box. To enroll a fingerprint for a file (and string) the user will need to place their finger on the sensor three times as SigID instructs. After the third scan the fingerprint will be enrolled.
65
Finger Alignment: The ID Gem fingerprint sensor is a reliable and high-quality electronic fingerprint capture device. To capture the best fingerprint image, it is important for the user to align the center of the fingertip’s whorl in the center of the sensor. The fingerprint alignment guide on the ID Gem sensor is designed to fit an average adult thumb. Persons with small fingers, such as children, may instinctively align their fingers with the top of the alignment guide, resulting in a low-quality image that doesn’t fully capture the finger’s
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6.1.3 VISUAL BASIC:
Visual Basic for Applications (VBA) is an implementation of Microsoft's event-driven programming language Visual Basic 6, and associated integrated development environment (IDE), which is built into most Microsoft Office applications.
VBA enables developers to build user defined functions, automate processes, and access Win32 and other low-level functionality through DLLs. It was also built into Office applications apart from version 2008 for Apple's Mac OS X, other Microsoft applications such as Microsoft MapPoint and Microsoft Visio; as well as being at least partially implemented in some other applications such as AutoCAD, WordPerfect, and ArcGIS. It supersedes and expands on the capabilities of earlier application-specific macro programming languages such as Word's WordBasic, and can be used to control many aspects of the host application, including manipulating user interface features, such as menus and toolbars, and working with
67
custom user forms or dialog boxes. VBA can also be used to create import and export filters for various file formats, such as ODF.
As its name suggests, VBA is closely related to Visual Basic and uses the Visual Basic Runtime, but can normally only run code within a host application rather than as a standalone application. It can, however, be used to control one application from another using OLE Automation. For example, it is used to automatically create a Word report from Excel data, in turn automatically collected by Excel from polled observation sensors. The VBA IDE is reached from within an Office document by pressing the key sequence Alt+F11.
VBA is functionally rich and flexible but it does have some important limitations, such as restricted support for function pointers which are used as callback functions in the Windows API. It has the ability to use (but not create) (ActiveX/COM) DLLs, and later versions add support for class modules.
Language
Code written in VBA is compiled to a proprietary intermediate language called P-code (packed code), which the hosting applications (Access, Excel, Word, and PowerPoint) store as a separate stream in COM Structured Storage files (e.g., .doc or .xls) independent of the document streams.
The intermediate code is then executed by a virtual machine (hosted by the hosting application). Despite its resemblance to many old BASIC dialects (particularly Microsoft BASIC, from which it is indirectly derived), VBA is not compatible with any of them except Microsoft Visual Basic, where source-code of VBA Modules and Classes can be directly imported, and which shares the same library and virtual machine.
Compatibility ends with Visual Basic version 6; VBA is not compatible with VB.NET. VBA is proprietary to Microsoft and, apart from the COM interface, is not an open standard.
Object models
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To use VBA with an application such as Access, Word, or Excel, terminology and language constructions are needed to interact with the applicationThis portion of VBA is called the Object Model for the application. A map of the object model is online for Excel and for Word.
A listing of the object model is found by opening the Macro/VBA editor in the target application and then using "View" to open the "Object Browser" (F2).
Much of the difficulty in using VBA is related to learning the object model, which uses names invented by the originators of the model that may be less than transparent to a new user.
One way to learn the terms and syntax of the object model is to use the macro recorder to record the steps taken to achieve a desired result using the mouse and menus of the application. Once this is done, the VBA code constructed by the recorder can be viewed in the VBA editor, and often greatly streamlined or generalized with only a modicum of understanding of VBA itself. Unfortunately, the macro recorder does not always record everything (particularly for graphs), and some applications employing VBA do not provide a recorder at all.
Use of debugging tools to discover VBA constructs for some cases where the macro recorder does not work are described by Jelen and Syrstad,[5] but some steps may remain obscure.
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CHAPTER-7
CHAPTER-7
HARDWARE TOOLS
Microcontroller(DS89C450)
LCD
RS232 Serial Communication
Keypad
Finger Print sensor
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GSM Modem
7.1 GSM MODEM:
7.1.1 DEFINITION:
Global system for mobile communication (GSM) is a globally accepted
standard for digital cellular communication. GSM is the name of a standardization
group established in 1982 to create a common European mobile telephone standard
that would formulate specifications for a pan-European mobile cellular radio
system operating at 900 MHz.
7.1.2 THE GSM NETWORK
GSM provides recommendations, not requirements. The GSM specifications
define the functions and interface requirements in detail but do not address the
hardware. The reason for this is to limit the designers as little as possible but still to
make it possible for the operators to buy equipment from different suppliers. The
GSM network is divided into three major systems: the switching system (SS), the
base station system (BSS), and the operation and support system (OSS). The basic
GSM network elements
7.1.3 GSM MODEM:
A GSM modem is a wireless modem that works with a GSM wireless
network. A wireless modem behaves like a dial-up modem. The main difference
between them is that a dial-up modem sends and receives data through a fixed
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telephone line while a wireless modem sends and receives data through radio
waves.
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.
As mentioned in earlier sections of this SMS tutorial, computers use AT
commands to control modems. Both GSM modems and dial-up modems support a
common set of standard AT commands. You can use a GSM modem just like a
dial-up modem.
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, you can do things like:
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.
The number of SMS messages that can be processed by a GSM modem per
minute is very low -- only about six to ten SMS messages per minute.
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7.1.4 GSM MODEM APPLICATIONS:
7.1.5 FACTS AND APPLICATIONS OF GSM/GPRS MODEM:
The GSM/GPRS Modem comes with a serial interface through which the
modem can be controlled using AT command interface. An antenna and a power
adapter are provided. The basic segregation of working of the modem is as under
• Voice calls
• SMS
• GSM Data calls
• GPRS
Voice calls:
Voice calls are not an application area to be targeted. In future if interfaces
like a microphone and speaker are provided for some applications then this can be
considered.
SMS:
SMS is an area where the modem can be used to provide features like:
• Pre-stored SMS transmission
• These SMS can be transmitted on certain trigger events in an automation
system
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• SMS can also be used in areas where small text information has to be sent.
The transmitter can be an automation system or machines like vending machines,
collection machines or applications like positioning systems where
The navigator keeps on sending SMS at particular time intervals. SMS can be a
solution where GSM data call or GPRS services are not available
7.1.6 APPLICATIONS:
Access control devices:
Now access control devices can communicate with servers and security staff
through SMS messaging. Complete log of transaction is available at the head-
office Server instantly without any wiring involved and device can instantly alert
security personnel on their mobile phone in case of any problem. RaviRaj
Technologies is introducing this technology in all Fingerprint Access control and
time attendance products.
Transaction terminals:
EDC machines, POS terminals can use SMS messaging to confirm
transactions from central servers. The main benefit is that central server can be
anywhere in the world. Today you need local servers in every city with multiple
telephone lines. You save huge infrastructure costs as well as per transaction cost.
Supply Chain Management:
Today SCM require huge IT infrastructure with leased lines, networking
devices, data centre, workstations and still you have large downtimes and high
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costs. You can do all this at a fraction of the cost with GSM M2M technology.
A central server in your head office with GSM capability is the answer; you can
receive instant transaction data from all your branch officers, warehouses and
business associates with nil downtime, Low cost
7.1.7 APPLICATIONS SUITABLE FOR GSM COMMUNICATION:
If your application needs one or more of the following features, GSM will be
more cost-effective then other communication systems.
Short Data Size:
You data size per transaction should be small like 1-3 lines. e.g. banking
transaction data, sales/purchase data, consignment tracking data, updates. These
small but important transaction data can be sent through SMS messaging which
cost even less then a local telephone call or sometimes free of cost worldwide.
Hence with negligible cost you are able to send critical information to your head
office located anywhere in the world from multiple points.
You can also transfer faxes, large data through GSM but this will be as or
more costly compared to landline networks.
Multiple remote data collection points:
If you have multiple data collections points situated all over your city, state,
country or worldwide you will benefit the most. The data can be sent from multiple
points like your branch offices, business associates, warehouses, and agents with
devices like GSM modems connected to PCs, GSM electronic terminals and
Mobile phones. Many a times some places like warehouses may be situated at
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remote location may not have landline or internet but you will have GSM network
still available easily.
High uptime:
If your business require high uptime and availability GSM is best suitable
for you as GSM mobile networks have high uptime compared to landline, internet
and other communication mediums. Also in situations where you expect that
someone may sabotage your communication systems by cutting wires or taping
landlines, you can depend on GSM wireless communication.
Large transaction volumes:
GSM SMS messaging can handle large number of transaction in a very
short time. You can receive large number SMS messages on your server like e-
mails without internet connectivity. E-mails normally get delayed a lot but SMS
messages are almost instantaneous for instant transactions. Consider situation like
shop owners doing credit card transaction with GSM technology instead of
conventional landlines. time you find local transaction servers busy as these
servers use multiple telephone lines to take care of multiple transactions, whereas
one GSM connection is enough to handle hundreds of transaction.
Mobility, Quick installation:
GSM technology allows mobility, GSM terminals, modems can be just
picked and installed at other location unlike telephone lines. Also you can be
mobile with GSM terminals and can also communicate with server using your
mobile phone. You can just purchase the GSM hardware like modems, terminals
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and mobile handsets, insert SIM cards, configure software and your are ready for
GSM communication.
7.2 RS 232
When we look at the connector pin out of the RS232 port, we see
two pins which are certainly used for flow control. These two pins are RTS,
request to send and CTS, clear to send. With DTE/DCE communication (i.e. a
computer communicating with a modem device) RTS is an output on the DTE and
input on the DCE. CTS are the answering signal coming from the DCE.
Before sending a character, the DTE asks permission by setting its RTS
output. No information will be sent until the DCE grants permission by using the
CTS line.
If the DCE cannot handle new requests, the CTS signal will go low. A
simple but useful mechanism allowing flow control in one direction. The
assumption is that the DTE can always handle incoming information faster than
the DCE can send it. In the past, this was true. Modem speeds of 300 baud were
common and 1200 baud was seen as a high speed connection.
For further control of the information flow, both devices have the ability to
signal their status to the other side. For this purpose, the DTR data terminal ready
and DSR data set ready signals are present. The DTE uses the DTR signal to
signal that it is ready to accept information, whereas the DCE uses the DSR signal
for the same purpose. Using these signals involves not a small protocol of
requesting and answering as with the RTS/CTS handshaking. These signals are in
one direction only.
The last flow control signal present in DTE/DCE communication is the CD
carrier detect. It is not used directly for flow control, but mainly an indication of
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the ability of the modem device to communicate with its counter part. This signal
indicates the existence of a communication link between two modem devices.
7.2.1 MAX 232
Introduction
MAX-232 is primary used for people building electronics with an RS-232
interface. Serial RS-232 communication works with voltages (-15V ... -3V for
high) and +3V ... +15V for low) which are not compatible with normal computer
logic voltages. To receive serial data from an RS-232 interface the voltage has to
be reduced, and the low and high voltage level inverted. In the other direction
(sending data from some logic over RS-232) the low logic voltage has to be
"bumped up", and a negative voltage has to be generated, too.
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Fig 5.11 Pin Diagram Of Max 232
RS232 COMMUNICATION
Introduction
In telecommunications, RS-232 is a standard for serial binary data interconnection
between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating
Equipment). It is commonly used in computer serial ports.
Scope of the Standard:
The Electronic Industries Alliance (EIA) standard RS-232-C [3] as of 1969
defines:
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Electrical signal characteristics such as voltage levels, signaling rate, timing and
slew-rate of signals, voltage withstand level, short-circuit behavior, maximum
stray capacitance and cable length
Interface mechanical characteristics, pluggable connectors and pin
identification
Functions of each circuit in the interface connector
Standard subsets of interface circuits for selected telecom applications
The standard does not define such elements as character encoding (for example,
ASCII, Baudot or EBCDIC), or the framing of characters in the data stream (bits
per character, start/stop bits, parity). The standard does not define protocols for
error detection or algorithms for data compression.
The standard does not define bit rates for transmission, although the standard says
it is intended for bit rates lower than 20,000 bits per second. Many modern devices
can exceed this speed (38,400 and 57,600 bit/s being common, and 115,200 and
230,400 bit/s making occasional appearances) while still using RS-232 compatible
signal levels.
Details of character format and transmission bit rate are controlled by the serial
port hardware, often a single integrated circuit called a UART that converts data
from parallel to serial form. A typical serial port includes specialized driver and
receiver integrated circuits to convert between internal logic levels and RS-232
compatible signal levels.
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Circuit Working Description
In this circuit the MAX 232 IC used as level logic converter. The MAX232 is a
dual driver/receiver that includes a capacive voltage generator to supply EIA 232
voltage levels from a single 5v supply. Each receiver converts EIA-232 to 5v
TTL/CMOS levels. Each driver converts TLL/CMOS input levels into EIA-232
levels.
In this circuit the microcontroller transmitter pin is connected in the MAX232
T2IN pin which converts input 5v TTL/CMOS level to RS232 level. Then T2OUT
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pin is connected to reviver pin of 9 pin D type serial connector which is directly
connected to PC.
In PC the transmitting data is given to R2IN of MAX232 through transmitting pin
of 9 pin D type connector which converts the RS232 level to 5v TTL/CMOS level.
The R2OUT pin is connected to receiver pin of the microcontroller. Likewise the
data is transmitted and received between the microcontroller and PC or other
device vice versa.
7.2 LCD DISPLAY
Pin 1 - GND
Pin 2 - VCC (+5V)
Pin 3 – Contrast
Pin 4 – RS
Pin 5 – R/W
Pin 6 – Enable
Pin 7-14 – Data(DB7-DB14)
Pin 15 – LED+
Pin 16 – LED-
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The HD44780U dot-matrix liquid crystal display controller and driver LSI displays alphanumeric, Japanese kana characters, and symbols. It can be configured to drive a dot-matrix liquid crystal display under the control of a 4- or 8-bit microprocessor. Since all the functions such as display RAM, character generator, and liquid crystal driver, required for driving a dot-matrix liquid crystal display are internally provided on one chip, a minimal system can be interfaced with this controller/driver
