2.pc based controlling devices in industriesabstract
TRANSCRIPT
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COMMAND BASED STREET LIGHT CONTROLLINGTHROUGH PC
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INDEX
CONTENTS
1. Abbreviations2. Figures locations
3. Introduction
4. Block Diagram
5. Block Diagram Description
6. Schematic
7. Schematic Description
8. Hardware Components
Power supply
Microcontroller
Max232
relays
pc
9. Circuit Description
10. Software componentsa. About Kielb. Embedded C
11. KEIL procedure description12. Conclusion (or) Synopsis13. Future Aspects
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14. Bibliography
Abbreviations
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Symbo
l
Name
ACC Accumulator
B B register
PSW Program status word
SP Stack pointer
DPTR Data pointer 2 bytes
DPL Low byte
DPH High byte
P0 Port0
P1 Port1
P2 Port2
P3 Port3
IP Interrupt priority control
IE Interrupt enable control
TMOD Timer/counter mode control
TCON Timer/counter control
T2CON Timer/counter 2 control
T2MOD Timer/counter mode2 control
TH0 Timer/counter 0high byte
TL0 Timer/counter 0 low byte
TH1 Timer/counter 1 high byte
TL1 Timer/counter 1 low byte
TH2 Timer/counter 2 high byte
TL2 Timer/counter 2 low byte
SCON Serial control
SBUF Serial data buffer
MAX MAXIM (IC manufacturer )
TTL Transistor to Transistor Logic
ATM Automatic Teller Machine
RS 232 Recommended Standard
AC Alternating Current
DC Direct Current
LCD Li uid Cr stal Dis la
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Figure Locations
S.No. Figure Page No.
1
Components of Typical Linear Power
Supply
2 An Electrical Transformer
3 Bridge Rectifier
4 Bridge Rectifier Positive Cycle
5 Bridge Rectifier Negative Cycle
6 Three terminal voltage Regulator
7 Functional Diagram of Microcontroller
8 Pin Diagram of Microcontroller
9 Oscillator connections
10 External clock drive connections
11 A register
12 B register
13 RAM
14 RAM Allocation15 Register Banks
16 PSW
17 DPTR
18 SP
19 PORT 0
20 TL0 and TH0
21 DB9
22 Connecting Microcontroller to PC
23 Types of SIM Structures
24 Smart Card Pin-out
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25 Smart Card Reader
26 LCD
27 MAX 232 Pin-out
28 MAX 232 Operating circuit
29 MAX 232 Logic output
30 Project
31 New Project
32 Select Target device
33 Select device for Target
34 Copy 8051 startup code
35 Source group 1
36 New file
37 Opened new file
38 File Save
39 Add files to the source group
40 Adding files to the source group
41 Compilation
42 After Compilation
43 Build
44 Selecting the Ports to be visualized
45 Start Debugging
INTRODUCTION
EMBEDDED SYSTEMS
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Embedded systems are designed to do some specific task, rather than be a general-
purpose computer for multiple tasks. Some also have real time performance constraints that must
be met, for reason such as safety and usability; others may have low or no performance
requirements, allowing the system hardware to be simplified to reduce costs.
An embedded system is not always a separate block - very often it is physically built-
in to the device it is controlling.
The software written for embedded systems is often called firmware, and is stored in read-only
memory or flash convector chips rather than a disk drive. It often runs with limited computer
hardware resources: small or no keyboard, screen, and little memory.
Now a day's every system is automated in order to face new challenges. In the present
days Automated systems have less manual operations, flexibility, reliability and accurate. Due tothis demand every field prefers automated control systems. Especially in the field of electronics
automated systems are giving good performance. In the present scenario of war situations,
unmanned systems plays very important role to minimize human losses.
Today, there exists no well-defined body of knowledge a student must learn to become
proficient in communications and information systems. This is an emerging field, and builds on
data communications, computer networks, distributed systems, information management, and
applications.
PC control has become an indispensable item of every days life. Starting from routines
like gate openers, window shutters through metering and PC fire alarms to automotive
applications like remote keyless entry and tire pressure monitoring systems. Wireless control
devices have established themselves as a cost-efficient and robust solution for a broad range of
control applications.
In this project we are controlling various devices i.e. various street lights through PC justby typing the commands in communication terminal, in which PC is interfaced with the
microcontroller serially. According to commands given by PC the controller makes the devices
ON or OFF.
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BLOCDIAGRAM:
Block diagram explanation:
This Project mainly consists of Power Supply section, Microcontroller section,
Energy Meter, Smart Card Reader section, LCD display section, Max 232 serial
driver section, Relay section and latch section, GSM modem section, Load sections.
Power supply:
MICRO
CONTROLLE
R
LIGHTING
SYSTEM
PC
MA
X
2
3
2
RELAYS
CIRCUIT
POWER
SUPPLY
DC MOTOR
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In this system we are using 5V power supply for microcontroller of Transmitter section as well
as receiver section. We use rectifiers for converting the A.C. into D.C and a step down
transformer to step down the voltage. The full description of the Power supply section is given in
this documentation in the following sections i.e. hardware components.
Microcontroller (8051):
In this project work the micro-controller is playing a major role. Micro-controllers were
originally used as components in complicated process-control systems. However, because of
their small size and low price, Micro-controllers are now also being used in regulators for
individual control loops. In several areas Micro-controllers are now outperforming their analog
counterparts and are cheaper as well.
Relay Section:This section is nothing but driving circuitry needed to drive the
DEVICES. So this section basically includes a Relay with its protection circuitry. This
section is responsible to drive the Normal devices.
MAX 232 Sections:The microcontroller can communicate with the serial devices
using its single Serial Port. The logic levels at which this serial port operates is TTL
logics. But some of the serial devices operate at RS 232 Logic levels. For example
PC and Smart Card Reader etc. So in order to communicate the Microcontroller witheither Smart Card Reader or PC, a mismatch between the Logic levels occurs. In
order to avoid this mismatch, in other words to match the Logic levels, a Serial
driver is used. And MAX 232 is a Serial Line Driver used to establish communication
between microcontroller and PC (or Smart Card Reader)
SCHEMATIC DIAGRAM:
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SCHEMATIC DESCRIPTION:
Firstly, the required operating voltage for Microcontroller 89C51 is 5V. Hence the 5V
D.C. power supply is needed by the same. This regulated 5V is generated by first stepping down
the 230V to 18V by the step down transformer.
In the both the Power supplies the step downed a.c. voltage is being rectified by the
Bridge Rectifier. The diodes used are 1N4007. The rectified a.c voltage is now filtered using a
C filter. Now the rectified, filtered D.C. voltage is fed to the Voltage Regulator. This voltage
regulator allows us to have a Regulated Voltage. In Power supply given to Microcontroller 5V is
generated using 7805 and in other two power supply 12V is generated using 7812. The rectified;
filtered and regulated voltage is again filtered for ripples using an electrolytic capacitor 100F.
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Now the output from the first section is fed to 40th pin of 89c51 microcontroller to supply
operating voltage and from other power supply to circuitry.
The microcontroller 89C51 with Pull up resistors at Port0 and crystal oscillator of
11.0592 MHz crystal in conjunction with couple of capacitors of is placed at 18th
& 19th
pins of89C51 to make it work (execute) properly.
In this Schematic, P2.0 is connected to relay for device1.P1.0 TO p1.3 are connected to TheLEDS.P3.0, P3.1 are connected to the Max 10,11 pins and 14, 13 pins are connected to the
PC by using DB 9 connector.
20th pin connected to GROUND
40th pin is connected to Vcc
HARDWARE COMPONENTS:
Power supply
Microcontroller
Max232
relays
pc
HARDWARE EXPLANANATION:
MICRO CONTROLLER 89C51
Introduction
A Micro controller consists of a powerful CPU tightly coupled with memory, various I/O
interfaces such as serial port, parallel port timer or counter, interrupt controller, data acquisition
interfaces-Analog to Digital converter, Digital to Analog converter, integrated on to a single
silicon chip.
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If a system is developed with a microprocessor, the designer has to go for external
memory such as RAM, ROM, EPROM and peripherals. But controller is provided all these
facilities on a single chip. Development of a Micro controller reduces PCB size and cost of
design.
One of the major differences between a Microprocessor and a Micro controller is that a
controller often deals with bits not bytes as in the real world application.
Intel has introduced a family of Micro controllers called the MCS-51.
The Major Features:
Compatible with MCS-51 products
4k Bytes of in-system Reprogrammable flash memory
Fully static operation: 0HZ to 24MHZ
Three level programmable clock
128 * 8 bit timer/counters
Six interrupt sources
Programmable serial channel
Low power idle power-down modes
Why AT 89C51
The system requirements and control specifications clearly rule out the use
of 16, 32 or 64 bit micro controllers or microprocessors. Systems using these may
be earlier to implement due to large number of internal features. They are also
faster and more reliable but, 8-bit micro controller satisfactorily serves the above
application. Using an inexpensive 8-bit Microcontroller will doom the 32-bit productfailure in any competitive market place.
Coming to the question of why to use AT89C51 of all the 8-bit microcontroller available
in the market the main answer would be because it has 4 Kb on chip flash memory which is just
sufficient for our application. The on-chip Flash ROM allows the program memory to be
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reprogrammed in system or by conventional non-volatile memory Programmer. Moreover
ATMEL is the leader in flash technology in todays market place and hence using AT 89C51 is
the optimal solution.
AT89C51 MICROCONTROLLER ARCHITECTURE
The 89C51 architecture consists of these specific features:
Eight bit CPU with registers A (the accumulator) and B
Sixteen-bit program counter (PC) and data pointer (DPTR) Eight- bit stack pointer (PSW)
Eight-bit stack pointer (Sp)
Internal ROM or EPROM (8751) of 0(8031) to 4K (89C51)
Internal RAM of 128 bytes:
1. Four register banks, each containing eight registers
2. Sixteen bytes, which maybe addressed at the bit level
3. Eighty bytes of general- purpose data memory
Thirty two input/output pins arranged as four 8-bit ports:p0-p3
Two 16-bit timer/counters: T0 and T1
Full duplex serial data receiver/transmitter: SBUF
Control registers: TCON, TMOD, SCON, PCON, IP, and IE
Two external and three internal interrupts sources.
Oscillator and clock circuits.
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Functional block diagram of micro controller
The 89C51 oscillator and clock:
The heart of the 89C51 circuitry that generates the clock pulses by which all the internal
all internal operations are synchronized. Pins XTAL1 And XTAL2 is provided for connecting a
resonant network to form an oscillator. Typically a quartz crystal and capacitors are employed.
The crystal frequency is the basic internal clock frequency of the microcontroller. The
manufacturers make 89C51 designs that run at specific minimum and maximum frequencies
typically 1 to 16 MHz.
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Fig 3.7.2: - Oscillator and timing circuit
Types of memory:
The 89C51 have three general types of memory. They are on-chip memory,
external Code memory and external Ram. On-Chip memory refers to physically
existing memory on the micro controller itself. External code memory is the code
memory that resides off chip. This is often in the form of an external EPROM.
External RAM is the Ram that resides off chip. This often is in the form of standard
static RAM or flash RAM.
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a) Code memory
Code memory is the memory that holds the actual 89C51 programs that is to
be run. This memory is limited to 64K. Code memory may be found on-chip or off-
chip. It is possible to have 4K of code memory on-chip and 60K off chip memory
simultaneously. If only off-chip memory is available then there can be 64K of off
chip ROM. This is controlled by pin provided as EA
b) Internal RAM
The 89C51 have a bank of 128 of internal RAM. The internal RAM is found on-
chip. So it is the fastest Ram available. And also it is most flexible in terms of
reading and writing. Internal Ram is volatile, so when 89C51 is reset, this memory is
cleared. 128 bytes of internal memory are subdivided. The first 32 bytes are divided
into 4 register banks. Each bank contains 8 registers. Internal RAM also contains
128 bits, which are addressed from 20h to 2Fh. These bits are bit addressed i.e.
each individual bit of a byte can be addressed by the user. They are numbered 00hto 7Fh. The user may make use of these variables with commands such as SETB
and CLR.
FLASH MEMORY:
Flash memory (sometimes called "flash RAM") is a type of constantly-powered non volatile that can be erased and reprogrammed in units of memory
called blocks. It is a variation of electrically erasable programmable read-only
memory (EEPROM) which, unlike flash memory, is erased and rewritten at the byte
level, which is slower than flash memory updating. Flash memory is often used to
hold control code such as the basic input/output system (BIOS) in a personal
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computer. When BIOS needs to be changed (rewritten), the flash memory can be
written to in block (rather than byte) sizes, making it easy to update. On the other
hand, flash memory is not useful as random access memory (RAM) because RAM
needs to be addressable at the byte (not the block) level.
Flash memory gets its name because the microchip is organized so that a
section of memory cells are erased in a single action or "flash." The erasure is
caused by Fowler-Nordheim tunneling in which electrons pierce through a thin
dielectric material to remove an electronic charge from a floating gate associated
with each memory cell. Intel offers a form of flash memory that holds two bits
(rather than one) in each memory cell, thus doubling the capacity of memory
without a corresponding increase in price.
Flash memory is used in digital cellular phones, digital cameras, LAN
switches, PC Cards for notebook computers, digital set-up boxes, embedded
controllers, and other devices.
Memory Type
Features
FLASH Low-cost, high-density, high-speed
architecture; low power; high
reliability
ROM
Read-Only Memory
Mature, high-density, reliable, low
cost; time-consuming mask
required, suitable for high
production with stable code
SRAM
Static Random-Access Memory
Highest speed, high-power, low-
density memory; limited density
drives up cost
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EPROM
Electrically Programmable Read-
Only Memory
High-density memory; must be
exposed to ultraviolet light for
erasure
EEPROMorE2
PROMElectrically Erasable Programmable
Read-Only Memory
Electrically byte-erasable; lowerreliability, higher cost, lowest
density
DRAM
Dynamic Random Access Memory
High-density, low-cost, high-speed,
high-power
Technical Overview of Flash Memory
Flash memory is a nonvolatile memory using NOR technology, which allows the user
to electrically program and erase information. Intel Flash memory uses memory
cells similar to an EPROM, but with a much thinner, precisely grown oxide between
the floating gate and the source (see Figure 2). Flash programming occurs when
electrons are placed on the floating gate. The charge is stored on the floating gate,
with the oxide layer allowing the cell to be electrically erased through the source.
Intel Flash memory is an extremely reliable nonvolatile memory architecture.
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Fig 3.7.3: - Pin diagram of AT89C51
Pin Description:
VCC: Supply voltage.
GND: Ground.
Port 0:
Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink
eight TTL inputs. When ones are written to port 0 pins, the pins can be used as high impedance
inputs. Port 0 may also be configured to be the multiplexed low order address/data bus during
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accesses to external program and data memory. In this mode P0 has internal pull-ups. Port 0 also
receives the code bytes during Flash programming, and outputs the code bytes during program
verification. External pull-ups are required during program verification.
Port 1:
Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers
can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled
low will source current (IIL) because of the internal pull-ups. Port 1 also receives the low-order
address bytes during Flash programming and verification.
Port 2:
Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers
can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled
low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address
byte during fetches from external program memory and during accesses to external data
memories that use 16-bit addresses (MOVX @DPTR). In this application, it uses strong internal
pull-ups when emitting 1s. During accesses to external data memories that use 8-bit addresses
(MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also
receives the high-order address bits and some control signals during Flash programming and
verification.
Port 3:
Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins
they are pulled high by the internal pull-ups and can be used as inputs. As inputs,
Port 3 pins that are externally being pulled low will source current (IIL) because of
the pull-ups.
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Port 3 also serves the functions of various special features of the AT89C51 as listed
below:
Port 3 also receives some control signals for Flash programming and verification
Tab 6.2.1 Port pins and their alternate functions
RST:
Reset input. A high on this pin for two machine cycles while the oscillator is
running resets the device.
ALE/PROG:
Address Latch Enable output pulse for latching the low byte of the address during
accesses to external memory. This pin is also the program pulse input (PROG) during Flashprogramming. In normal operation ALE is emitted at a constant rate of 1/6the oscillator
frequency, and may be used for external timing or clocking purposes. Note, however, that one
ALE pulse is skipped during each access to external Data Memory.
If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With
the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the
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pin is pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in
external execution mode.
PSEN:
Program Store Enable is the read strobe to external program memory. When the
AT89C51 is executing code from external program memory, PSEN is activated twice each
machine cycle, except that two PSEN activations are skipped during each access to external data
memory.
EA/VPP:
External Access Enable EA must be strapped to GND in order to enable the
device to fetch code from external program memory locations starting at 0000H up
to FFFFH.
Note, however, that if lock bit 1 is programmed, EA will be internally latched
on reset.
EA should be strapped to VCC for internal program executions. This pin also
receives the 12-volt programming enable voltage (VPP) during Flash programming,
for parts that require 12-volt VPP.
XTAL1:
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2:
It is the Output from the inverting oscillator amplifier.
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Oscillator Characteristics:
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier
which can be configured for use as an on-chip oscillator, as shown in Figs 6.2.3. Either a quartz
crystal or ceramic resonator may be used. To drive the device from an external clock source,XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.2.4.There are
no requirements on the duty cycle of the external clock signal, since the input to the internal
clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high
and low time specifications must be observed.
Fig 6.2.3 Oscillator Connections Fig 6.2.4 External Clock Drive
Configuration
Notes:
1. Under steady state (non-transient) conditions, IOL must be externally
limited as follows:
Maximum IOL per port pin: 10 mA
Maximum IOL per 8-bit port: Port 0: 26 mA
Ports 1, 2, 3: 15 mA
Maximum total IOL for all output pins: 71 mA
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If IOL exceeds the test condition, VOL may exceed the related
specification. Pins are not guaranteed to sink current greater than the
listed test conditions.
2. Minimum VCC for Power-down is 2V.
REGISTERS:
In the CPU, registers are used to store information temporarily. That
information could be a byte of data to be processed, or an address pointing to the
data to be fetched. The vast majority of 8051 registers are 8bit registers. In the
8051 there is only one data type: 8bits. The 8bits of a register are shown in the
diagram from the MSB (most significant bit) D7 to the LSB (least significant bit) D0.
With an 8-bit data type, any data larger than 8bits must be broken into 8-bit chunks
before it is processed. Since there are a large number of registers in the 8051, we
will concentrate on some of the widely used general-purpose registers and cover
special registers in future chapters.
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
The most widely used registers of the 8051 are A (accumulator), B, R0, R1,
R2, R3, R4, R5, R6, R7, DPTR (data pointer), and PC (program counter). All of the
above registers are 8-bits, except DPTR and the program counter. The
accumulator, register A, is used for all arithmetic and logic instructions.
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SFRs (Special Function Registers)
Among the registers R0-R7 is part of the 128 bytes of RAM memory. What about
registers A, B, PSW, and DPTR? Do they also have addresses? The answer is yes. In the 8051,
registers A, B, PSW and DPTR are part of the group of registers commonly referred to as SFR
(special function registers). There are many special function registers and they are widely used.
The SFR can be accessed by the names (which is much easier) or by their addresses. For
example, register A has address E0h, and register B has been ignited the address F0H, as shown
in table.
The following two points should noted about the SFR addresses.
1. The Special function registers have addresses between 80H and FFH. These
addresses are above 80H, since the addresses 00 to 7FH are addresses of RAM
memory inside the 8051.
2. Not all the address space of 80H to FFH is used by the SFR. The unused locations
80H to FFH are reserved and must not be used by the 8051 programmer.
Regarding direct addressing mode, notice the following two points: (a) the address value
is limited to one byte, 00-FFH, which means this addressing mode is limited to accessing RAM
locations and registers located inside the 8051. (b) If you examine the l st file for an assembly
language program, you will see that the SFR registers names are replaced with their addresses as
listed in table.
Symb
ol
Name Addre
ss
ACC Accumulator 0E0H
B B register 0F0H
PSW Program status word 0D0H
SP Stack pointer 81H
DPTR Data pointer 2 bytes
DPL Low byte 82H
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DPH High byte 83H
P0 Port0 80H
P1 Port1 90H
P2 Port2 0A0HP3 Port3 0B0H
IP Interrupt priority control 0B8H
IE Interrupt enable control 0A8H
TMOD Timer/counter mode
control
89H
TCON Timer/counter control 88H
T2CO
N
Timer/counter 2 control 0C8H
T2MO
D
Timer/counter mode2
control
0C9H
TH0 Timer/counter 0high byte 8CH
TL0 Timer/counter 0 low byte 8AH
TH1 Timer/counter 1 high
byte
8DH
TL1 Timer/counter 1 low byte 8BH
TH2 Timer/counter 2 high
byte
0CDH
TL2 Timer/counter 2 low byte 0CCH
RCAP
2H
T/C 2 capture register
high byte
0CBH
RCAP
2L
T/C 2 capture register
low byte
0CAH
SCON Serial control 98H
SBUF Serial data buffer 99H
PCON Power control 87H
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Table: 8051 Special function register Address
A Register (Accumulator)
This is a general-purpose register which serves for storing intermediate results during operating.
A number (an operand) should be added to the accumulator prior to execute an instruction upon
it. Once an arithmetical operation is preformed by the ALU, the result is placed into the
accumulator. If a data should be transferred from one register to another, it must go throughaccumulator. For such universal purpose, this is the most commonly used register that none
microcontroller can be imagined without (more than a half 8051 microcontroller's instructions
used use the accumulator in some way).
B Register
B register is used during multiply and divide operations which can be performed only upon
numbers stored in the A and B registers. All other instructions in the program can use thisregister as a spare accumulator (A).
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During programming, each of registers is called by name so that
their exact address is not so important for the user. During compiling into machine
code (series of hexadecimal numbers recognized as instructions by the
microcontroller), PC will automatically, instead of registers name, write necessary
addresses into the microcontroller.
R Registers (R0-R7)
This is a common name for the total 8 general purpose registers (R0, R1, and R2 ...R7). Even
they are not true SFRs, they deserve to be discussed here because of their purpose. The bank is
active when the R registers it includes are in use. Similar to the accumulator, they are used for
temporary storing variables and intermediate results. Which of the banks will be active depends
on two bits included in the PSW Register. These registers are stored in four banks in the scope ofRAM.
The following example best illustrates the useful purpose of these registers. Suppose that
mathematical operations on numbers previously stored in the R registers should be performed:
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(R1+R2) - (R3+R4). Obviously, a register for temporary storing results of addition is needed.
Everything is quite simple and the program is as follows:
MOV A, R3; Means: move number from R3 into accumulator
ADD A, R4; Means: add number from R4 to accumulator (result remains in accumulator)
MOV R5, A; Means: temporarily moves the result from accumulator into R5
MOV A, R1; Means: move number from R1 into accumulator
ADD A, R2; Means: add number from R2 to accumulator
SUBB A, R5; Means: subtract number from R5 (there are R3+R4)
8051 Register Banks and Stack
RAM memory space allocation in the 8051
There are 128 bytes of RAM in the 8051. The 128 bytes of RAM inside the
8051 are assigned addresses 00 to7FH. These 128 bytes are divided into three
different groups as follows:
1. A total of 32 bytes from locations 00 to 1FH hex are set aside for registerbanks and the stack.
2. A total of 16 bytes from locations 20 to 2FH hex are set aside for bit-
addressable read/write memory.
3. A total of 80 bytes from locations 30H to 7FH are used for read and write
storage, or what is normally called Scratch pad. These 80 locations of
RAM are widely used for the purpose of storing data and parameters nu
8051 programmers.
Register banks in the 8051
A total of 32bytes of RAM are set aside for the register banks and stack.
These 32 bytes are divided into 4 banks of registers in which each bank has
registers, R0-R7. RAM locations 0 to 7 are set aside for bank 0 of R0-R7 where R0 is
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RAM location 0, R1 is RAM location 1, and R2 is location 2, and so on, until memory
location7, which belongs to R7 of bank0. The second bank of registers R0-R7 starts
at RAM location 08 and goes to location 0FH. The third bank of R0-R7 starts at
memory location 10H and goes to location 17H. Finally, RAM locations 18H to 1FH
are set aside for the fourth bank of R0-R7. Fig shows how the 32 bytes are allocated
into 4 banks.
As we can see from fig 1, the bank 1 uses the same RAM space as the
stack. This is a major problem in programming the 8051. we must either not use
register bank1, or allocate another area of RAM for the stack.
Default register bank
If RAM locations 00-1F are set aside for the four register banks, whichregister bank of R0-R7 do we have access to when the 8051 is powered up? The
answer is register bank 0; that is , RAM locations 0, 1,2,3,4,5,6, and 7 are accessed
with the names R0, R1, R2, R3, R4, R5, R6, and R7 when programming the 8051. It
is much easier to refer to these RAM locations with names such as R0, R1 and so on,
than by their memory locations as shown in fig 2.
The register banks are switched by using the D3 & D4 bits of register PSW.
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FIG: RAM Allocation in the 8051
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Fig: 8051 Register Banks and their RAM Addresses
PSW Register (Program Status Word)
This is one of the most important SFRs. The Program Status Word (PSW) contains several status
bits that reflect the current state of the CPU. This register contains: Carry bit, Auxiliary Carry,
two register bank select bits, Overflow flag, parity bit, and user-definable status flag. The ALU
automatically changes some of registers bits, which is usually used in regulation of the program
performing.
P - Parity bit. If a number in accumulator is even then this bit will be automatically set (1),
otherwise it will be cleared (0). It is mainly used during data transmission and receiving via
serial communication.
- Bit 1. This bit is intended for the future versions of the microcontrollers, so it is not supposed to
be here.
OV Overflow occurs when the result of arithmetical operation is greater than 255 (decimal), so
that it can not be stored in one register. In that case, this bit will be set (1). If there is no
overflow, this bit will be cleared (0).
RS0, RS1 - Register bank selects bits. These two bits are used to select one of the four register
banks in RAM. By writing zeroes and ones to these bits, a group of registers R0-R7 is stored in
one of four banks in RAM.
RS1 RS2 Space in RAM
0 0 Bank0 00h-07h
0 1 Bank1 08h-0Fh
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1 0 Bank2 10h-17h
1 1 Bank3 18h-1Fh
F0 - Flag 0. This is a general-purpose bit available to the user.
AC - Auxiliary Carry Flag is used for BCD operations only.
CY - Carry Flag is the (ninth) auxiliary bit used for all arithmetical operations and shift
instructions.
DPTR Register (Data Pointer)
These registers are not true ones because they do not physically exist. They consist of two
separate registers: DPH (Data Pointer High) and (Data Pointer Low). Their 16 bits are used for
external memory addressing. They may be handled as a 16-bit register or as two independent 8-
bit registers. Besides, the DPTR Register is usually used for storing data and intermediate results
which have nothing to do with memory locations.
SP Register (Stack Pointer)
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The stack is a section of RAM used by the CPU to store information temporarily. This
information could be data or an address. The CPU needs this storage area since there are only a
limited number of registers.
How stacks are accessed in the 8051
If the stack is a section of RAM, there must be registers inside the CPU to point to it.
The register used to access the stack is called the SP (Stack point) Register. The stack pointer in
the 8051 is only 8 bits wide; which means that it can take values of 00 to FFH. When the 8051 is
powered up, the SP register contains value 07. This means that RAM location 08 is the first
location used for the stack by the 8051. The storing of a CPU register in the stack is called a
PUSH, and pulling the contents off the stack back into a CPU register is called a POP. In other
words, a register is pushed onto the stack to save it and popped off the stack to retrieve it. The
job of the SP is very critical when push and pop actions are performed.
Pushing onto the stack
In the 8051 the stack pointer (SP) points to the last used location of the stack. As we
push data onto the stack, the stack pointer is incremented by one. Notice that this different frommany microprocessors, notably x86 processors in which the SP is decremented when data is
pushed onto the stack. As each PUSH is executed, the contents of the register are saved on the
stack and SP is incremented by 1. Notice that for every byte of data saved on the stack and then
SP is incremented only once. Notice also that to push the registers onto the stack we must use
their RAM addresses. For example, the instruction PUSH pushes register R1 onto the stack.
Popping from the stack
Popping the contents of the stack back into a given register is the opposite process of
pushing. With every pop, the top byte of the stack is copied to the register specified by the
instruction and the stack pointer is decremented once.
The upper limit of the stack
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As, mentioned earlier, locations 08 to 1FH in the 8051 RAM can be used for the stack.
This is because locations 20-2FH of RAM are reserved for bit-addressable memory and must not
be used by the stack. If in a program we need more than 24 bytes (08 to 1FH=24bytes) of stack,
we can change the SP to point to RAM locations 30-7FH. This is done with the instruction
MOV SP, #XX.
P0, P1, P2, P3 - Input/Output Registers
In case that external memory and serial communication system are not in use then, 4 ports with
in total of 32 input-output lines are available to the user for connection to peripheral
environment. Each bit inside these ports corresponds to the appropriate pin on the
microcontroller. This means that logic state written to these ports appears as a voltage on the pin
(0 or 5 V). Naturally, while reading, the opposite occurs voltage on some input pins is reflected
in the appropriate port bit.
The state of a port bit, besides being reflected in the pin, determines at the same time whether it
will be configured as input or output. If a bit is cleared (0), the pin will be configured as output.
In the same manner, if a bit is set to 1 the pin will be configured as input. After reset, as well as
when turning the microcontroller ON, all bits on these ports are set to one (1). This means that
the appropriate pins will be configured as inputs.
Program counter:
The important register in the 8051 is the PC (Program counter). The program counter
points to the address of the next instruction to be executed. As the CPU fetches the OPCODE
from the program ROM, the program counter is incremented to point to the next instruction. The
program counter in the 8051 is 16bits wide. This means that the 8051 can access program
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addresses 0000 to FFFFH, a total of 64k bytes of code. However, not all members of the 8051
have the entire 64K bytes of on-chip ROM installed, as we will see soon.
Types of instructions
Depending on operation they perform, all instructions are divided in several groups:
Arithmetic Instructions
Branch Instructions
Data Transfer Instructions
Logical Instructions
Logical Instructions with bits
The first part of each instruction, called MNEMONIC refers to the operation an instruction
performs (copying, addition, logical operation etc.). Mnemonics commonly are shortened form
of name of operation being executed. For example:
INC R1; Increment R1 (increment register R1)
LJMP LAB5 ;Long Jump LAB5 (long jump to address specified as LAB5)
JNZ LOOP ;Jump if Not Zero LOOP (if the number in the accumulator is not 0, jump to
address specified as LOOP)
Another part of instruction, called OPERAND is separated from mnemonic at least by one empty
space and defines data being processed by instructions. Some instructions have no operand; some
have one, two or three. If there is more than one operand in instruction, they are separated by
comma. For example:
RET - (return from sub-routine)
JZ TEMP - (if the number in the accumulator is not 0, jump to address specified as
TEMP)
ADD A,R3 - (add R3 and accumulator)
CJNE A,#20,LOOP - (compare accumulator with 20. If they are not equal, jump to
address specified as LOOP)
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Arithmetic instructions
These instructions perform several basic operations (addition, subtraction, division,
multiplication etc.) After execution, the result is stored in the first operand. For example:
ADD A, R1 - The result of addition (A+R1) will be stored in the accumulator.
Arithmetical Instructions
Mnemonic DescriptionByte
Number
Oscillator
Period
ADD A,Rn Add R Register to accumulator 1 1
ADD A,RxAdd directly addressed Rx Register to
accumulator2 2
ADD A,@RiAdd indirectly addressed Register to
accumulator1 1
ADD A,#X Add number X to accumulator 2 2
ADDC A,RnAdd R Register with Carry bit to
accumulator1 1
Branch Instructions
There are two kinds of these instructions:
Unconditional jump instructions: After their execution a jump to a new location from where
the program continues execution is executed.
Conditional jump instructions: If some condition is met - a jump is executed. Otherwise, the
program normally proceeds with the next instruction.
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Branch Instruction
Mnemonic DescriptionByte
Number
Oscillator
Period
ACALL
adr11
Call subroutine located at address within 2 K
byte Program Memory space2 3
LCALL
adr16
Call subroutine located at any address within
64 K byte Program Memory space3 4
RET Return from subroutine 1 4
RETI Return from interrupt routine 1 4
AJMP adr11Jump to address located within 2 K byte
Program Memory space2 3
LJMP adr16Jump to any address located within 64 K byte
Program Memory space3 4
Data Transfer Instructions
These instructions move the content of one register to another one. The register which content is
moved remains unchanged. If they have the suffix X (MOVX), the data is exchanged with
external memory.
Data Transfer Instruction
Mnemonic DescriptionByte
Number
Cycle
Number
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MOV A,Rn Move R register to accumulator 1 1
MOV A,RxMove directly addressed Rx register to
accumulator2 2
MOV A,@RiMove indirectly addressed register to
accumulator1 1
MOV A,#X Move number X to accumulator 2 2
Logical Instructions
These instructions perform logical operations between corresponding bits of two registers. After
execution, the result is stored in the first operand.
Logical Instructions
Mnemonic DescriptionByte
Number
Cycle
Number
ANL A,RnLogical AND between accumulator and R
register1 1
ANL A,RxLogical AND between accumulator and
directly addressed register Rx2 2
ANL A,@RiLogical AND between accumulator and
indirectly addressed register1 1
ANL A,#XLogical AND between accumulator and
number X2 2
Logical Operations on Bits
Similar to logical instructions, these instructions perform logical operations. The difference is
that these operations are performed on single bits.
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Logical operations on bits
Mnemonic DescriptionByte
Number
Cycle
Number
CLR C Clear Carry bit 1 1
CLR bit Clear directly addressed bit 2 2
SETB C Set Carry bit 1 1
SETB bit Set directly addressed bit 2 2
CPL C Complement Carry bit 1 1
CPL bit Complement directly addressed bit 2 2
TIMERSOn-chip timing/counting facility has proved the capabilities of the
microcontroller for implementing the real time application. These includes pulse
counting, frequency measurement, pulse width measurement, baud rate
generation, etc,. Having sufficient number of timer/counters may be a need in a
certain design application. The 8051 has two timers/counters. They can be usedeither as timers to generate a time delay or as counters to count events happening
outside the microcontroller. Let discuss how these timers are used to generate time
delays and we will also discuss how they are been used as event counters.
PROGRAMMING 8051 TIMERS
The 8051 has timers: Timer 0 and Timer1.they can be used either as timers or
as event counters. Let us first discuss about the timers registers and how to
program the timers to generate time delays.
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BASIC RIGISTERS OF THE TIMER
Both Timer 0 and Timer 1 are 16 bits wide. Since the 8051 has an 8-bit
architecture, each 16-bit timer is accessed as two separate registers of low byte
and high byte.
TIMER 0 REGISTERS
The 16-bit register of Timer 0 is accessed as low byte and high byte. the
low byte register is called TL0(Timer 0 low byte)and the high byte register is
referred to as TH0(Timer 0 high byte).These register can be accessed like any other
register, such as A,B,R0,R1,R2,etc.for example, the instruction MOV TL0,
#4Fmoves the value 4FH into TL0,the low byte of Timer 0.These registers can also
be read like any other register.
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TIMER 1 REGISTERS
Timer 1 is also 16-bit register is split into two bytes, referred to as TL1
(Timer 1 low byte) and TH1 (Timer 1 high byte).these registers are accessible n the
same way as the register of Timer 0.
TMOD (timer mode) REGISTER
Both timers TIMER 0 and TIMER 1 use the same register, called TMOD, to set
the various timer operation modes. TMOD is an 8-bit register in which the lower 4
bits are set aside for Timer 0 and the upper 4 bits for Timer 1.in each case; thelower 2 bits are used to set the timer mode and the upper 2 bits to specify the
operation.
MODES:
M1, M0:
M0 and M1 are used to select the timer mode. There are three modes: 0, 1,
2.Mode 0 is a 13-bit timer, mode 1 is a 16-bit timer, and mode 2 is an 8-bit timer.
We will concentrate on modes 1 and 2 since they are the ones used most widely.
We will soon describe the characteristics of these modes, after describing the reset
of the TMOD register.
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GATE Gate control when set. The timer/counter is enabled
only
While the INTx pin is high and the TRx control
pin is.
Set. When cleared, the timer is enabled.
C/T Timer or counter selected cleared for timer
operation
(Input from internal system clock).set for counter
Operation (input TX input pin).
M 1 Mode bit 1
M0 Mode bit 0
M1 M0 MODE Operating Mode
0 0 0 13-bit timer mode
8-bit timer/counter THx with TLx as
5 - Bit pre-scaler.
0 1 1 16-bit timer mode
16-bit timer/counters THx with TLx
are
Cascaded; there is no prescaler
1 0 2 8-bit auto reload
8-bit auto reload timer/counter;THx
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Holds a value that is to be reloaded
into
TLx each time it overflows.
1 1 3 Split timer mode.
C/T (clock/timer)
This bit in the TMOD register is used to decide whether the timer is used as a
delay generator or an event counter. If C/T=0, it is used as a timer for time delay
generation. The clock source for the time delay is the crystal frequency of the 8051.
This section is concerned with this choice. The timers use as an event counter is
discussed in the next section.
Serial Communication:
Computers can transfer data in two ways: parallel and serial. In parallel data
transfers, often 8 or more lines (wire conductors) are used to transfer data to a
device that is only a few feet away. Examples of parallel data transfer are printers
and hard disks; each uses cables with many wire strips. Although in such cases a
lot of data can be transferred in a short amount of time by using many wires in
parallel, the distance cannot be great. To transfer to a device located many meters
away, the serial method is used. In serial communication, the data is sent one bit at
a time, in contrast to parallel communication, in which the data is sent a byte or
more at a time. Serial communication of the 8051 is the topic of this chapter. The
8051 has serial communication capability built into it, there by making possible fast
data transfer using only a few wires.
If data is to be transferred on the telephone line, it must be converted from
0s and 1s to audio tones, which are sinusoidal-shaped signals. A peripheral device
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called a modem, which stands for modulator/demodulator, performs this
conversion.
Serial data communication uses two methods, asynchronous and
synchronous. The synchronous method transfers a block of data at a time, while
the asynchronous method transfers a single byte at a time.
In data transmission if the data can be transmitted and received, it is a
duplex transmission. This is in contrast to simplex transmissions such as with
printers, in which the computer only sends data. Duplex transmissions can be half
or full duplex, depending on whether or not the data transfer can be simultaneous.
If data is transmitted one way at a time, it is referred to as half duplex. If the data
can go both ways at the same time, it is full duplex. Of course, full duplex requires
two wire conductors for the data lines, one for transmission and one for reception,
in order to transfer and receive data simultaneously.
Asynchronous serial communication and data framing
The data coming in at the receiving end of the data line in a serial data
transfer is all 0s and 1s; it is difficult to make sense of the data unless the sender
and receiver agree on a set of rules, a protocol, on how the data is packed, how
many bits constitute a character, and when the data begins and ends.
Start and stop bits
Asynchronous serial data communication is widely used for character-
oriented transmissions, while block-oriented data transfers use the synchronous
method. In the asynchronous method, each character is placed between start and
stop bits. This is called framing. In the data framing for asynchronous
communications, the data, such as ASCII characters, are packed between a start bit
and a stop bit. The start bit is always one bit, but the stop bit can be one or two bits.
The start bit is always a 0 (low) and the stop bit (s) is 1 (high).
Data transfer rate
The rate of data transfer in serial data communication is stated in bps (bits
per second). Another widely used terminology for bps is baud rate. However, the
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baud and bps rates are not necessarily equal. This is due to the fact that baud rate
is the modem terminology and is defined as the number of signal changes per
second. In modems a single change of signal, sometimes transfers several bits of
data. As far as the conductor wire is concerned, the baud rate and bps are the
same, and for this reason we use the bps and baud interchangeably.
The data transfer rate of given computer system depends on
communication ports incorporated into that system. For example, the early
IBMPC/XT could transfer data at the rate of 100 to 9600 bps. In recent years,
however, Pentium based PCS transfer data at rates as high as 56K bps. It must be
noted that in asynchronous serial data communication, the baud rate is generally
limited to 100,000bps.
RS232 Standards
To allow compatibility among data communication equipment made by
various manufacturers, an interfacing standard called RS232 was set by the
Electronics Industries Association (EIA) in 1960. In 1963 it was modified and called
RS232A. RS232B AND RS232C were issued in 1965 and 1969, respectively. Today,
RS232 is the most widely used serial I/O interfacing standard. This standard is used
in PCs and numerous types of equipment. However, since the standard was set
long before the advert of the TTL logic family, its input and output voltage levels arenot TTL compatible. In RS232, a 1 is represented by -3 to -25V, while a 0 bit is +3
to +25V, making -3 to +3 undefined. For this reason, to connect any RS232 to a
microcontroller system we must use voltage converters such as MAX232 to convert
the TTL logic levels to the RS232 voltage levels, and vice versa. MAX232 IC chips
are commonly referred to as line drivers.
RS232 pins
RS232 cable is commonly referred to as the DB-25 connector. In labeling, DB-25Prefers to the plug connector (male) and DB-25S is for the socket connector (female). Since not
all the pins are used in PC cables, IBM introduced the DB-9 Version of the serial I/O standard,
which uses 9 pins only, as shown in table.
DB-9 pin connector
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1 2 3 4 5
6 7 8 9
(Out of computer and exposed end of cable)
Pin Functions:
Pin Description1 Data carrier detect (DCD)2 Received data (RXD)3 Transmitted data (TXD)4 Data terminal ready(DTR)
5 Signal ground (GND)6 Data set ready (DSR)7 Request to send (RTS)8 Clear to send (CTS)9 Ring indicator (RI)
Note: DCD, DSR, RTS and CTS are active low pins.
The method used by RS-232 for communication allows for a simple connection of three lines:
Tx, Rx, and Ground. The three essential signals for 2-way RS-232
Communications are these:
TXD: carries data from DTE to the DCE.
RXD: carries data from DCE to the DTE
SG: signal ground
8051 connection to RS232
The RS232 standard is not TTL compatible; therefore, it requires a line
driver such as the MAX232 chip to convert RS232 voltage levels to TTL levels, and
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vice versa. The interfacing of 8051 with RS232 connectors via the MAX232 chip is
the main topic.
The 8051 has two pins that are used specifically for transferring
and receiving data serially. These two pins are called TXD and RXD and a part of the
port 3 group (P3.0 and P3.1). Pin 11 of the 8051 is assigned to TXD and pin 10 is
designated as RXD. These pins are TTL compatible; therefore, they require a line
driver to make them RS232 compatible. One such line driver is the MAX232 chip.
MAX232 converts from RS232 voltage levels to TTL voltage
levels, and vice versa. One advantage of the MAX232 chip is that it uses a +5V
power source which, is the same as the source voltage for the 8051. In the other
words, with a single +5V power supply we can power both the 8051 and MAX232,
with no need for the power supplies that are common in many older systems. The
MAX232 has two sets of line drivers for transferring and receiving data. The line
drivers used for TXD are called T1 and T2, while the line drivers for RXD are
designated as R1 and R2. In many applications only one of each is used.
Embedded
Controller
RXD
TXD
TXD
RXD2
3
5
GND
MAX 232
CONNECTING C to PC using MAX 232
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INTERRUPTS
A single microcontroller can serve several devices. There are two ways to do that:INTERRUPTS or POLLING.
POLLING:
In polling the microcontroller continuously monitors the status of a given device; when the status
condition is met, it performs the service .After that, it moves on to monitor the next device untileach one is serviced. Although polling can monitor the status of several devices and serve each
of them as certain condition are met.
INTERRUPTS:
In the interrupts method, whenever any device needs its service, the device
notifies the microcontroller by sending it an interrupts signal. Upon receiving an interrupt signal,
the microcontroller interrupts whatever it is doing and serves the device. The program associated
with the interrupts is called the interrupt service routine (ISR).or interrupt handler.
INTERRUPTS Vs POLLING:
The advantage of interrupts is that the microcontroller can serve many devices (not all the
same time, of course); each device can get the attention of the microcontroller based on the
priority assigned to it. The polling method cannot assign priority since it checks all devices in
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round-robin fashion. More importantly, in the interrupt method the microcontroller can also
ignore (mask) a device request for service. This is again not possible with the polling
method. The most important reason that the interrupt method is preferable is that the polling
method wastes much of the microcontrollers time by polling devices that do not need
service. So, in order to avoid tying down the microcontroller, interrupts are used.
INTERRUPT SERVICE ROUTINE
For every interrupt, there must be an interrupt service routine (ISR), or interrupt
handler. When an interrupt is invoked, the microcontroller runs the interrupts
service routine. For every interrupt, there is a fixed location in memory that holds
the address of its ISR. The group of memory location set aside to hold the addresses
of ISR and is called the Interrupt Vector Table. Shown below:
Interrupt Vector Table for the 8051:
S.No. INTERRUPT ROM
LOCATION
(HEX)
PIN FLAG
CLEARING
1. Reset 0000 9 Auto
2. External
hardware
Interrupt 0
0003 P3.2 (12) Auto
3. Timers 0 000B Auto
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interrupt
(TF0)
4. External
hardware
Interrupt
1(INT1)
0013 P3.3 (13) Auto
5. Timers 1
interrupt
(TF1)
001B Auto
6. Serial COM
(RI and TI)
0023 Programmer
clears it
Six Interrupts in the 8051:
In reality, only five interrupts are available to the user in the 8051, but many
manufacturers data sheets state that there are six interrupts since they include
reset .the six interrupts in the 8051 are allocated as above.
1. Reset. When the reset pin is activated, the 8051 jumps to address location
0000.this is the power-up reset.
2. Two interrupts are set aside for the timers: one for Timer 0 and one for Timer
1.Memory location 000BH and 001BH in the interrupt vector table belong to
Timer 0 and Timer 1, respectively.
3. Two interrupts are set aside for hardware external harder interrupts. Pin
number 12(P3.2) and 13(P3.3) in port 3 are for the external hardware
interrupts INT0 and INT1,respectively.These external interrupts are alsoreferred to as EX1 and EX2.Memory location 0003H and 0013H in the
interrupt vector table are assigned to INT0 and INT1, respectively.
4. Serial communication has a single interrupt that belongs to both receive and
transmit. The interrupt vector table location 0023H belongs to this interrupt.
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Notice that a limited number of bytes are set aside for each interrupt. For example,
a total of 8 bytes from location 0003 to 000A is set aside for INT0, external
hardware interrupt 0.similarly,a total of 8 bytes from location 00BH to 0012H is
reserved for TF0, Timer 0 interrupt. If the service routine for a given interrupt is
short enough to fit in the memory space allocated to it, it is placed in the vector
table; otherwise, and an LJMP instruction is placed in the vector table to point to the
address of the ISR. In that rest of the bytes allocated to that interrupt are unused.
From the above table also notice that only three bytes of ROM space are assigned
to the reset pin. they are ROM address location 0,1 and2.address location 3
belongs to external hardware interrupt 0.for this reason, in our program we put the
LJMP as the first instruction and redirect the processor away from the interrupt
vector table, as shown below
Steps in executing an interrupt
Upon activation of an interrupt, the microcontroller goes through the following
steps.
1. It finishes the instruction it is executing and saves the address of the next
instruction (PC) on the stack.
2. It also saves the current status of all the interrupts internally (i.e., not on the
stack).
3. It jumps to a fixed location in memory called the interrupt vector table that
holds the address of the interrupts service routine.
4. The microcontroller gets the address of the ISR from the interrupt vector
table and jumps to it. It starts to execute the interrupt service subroutine
until it reaches the last instruction of the subroutine, which is RETI (return
from interrupt).
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5. Upon executing the RETI instruction, the microcontroller returns to the place
where it was interrupted. First, it gets the program counter (PC) address from
the stack by popping the top two bytes of the stack into the PC. Then it starts
to execute from that address.
Notice from step 5 the critical role of the stack. For this reason, we must be
careful in manipulating the stack contents in the ISR. Specifically, in the ISR, just as
in any CALL subroutine, the number of pushes and pops must be equal.
Enabling and disabling an interrupt:
Upon reset, all interrupt are disabled (masked), meaning that none will be
responded to by the microcontroller if they are activated. The interrupt must be
enabled by software in order for the microcontroller to respond to them. There is a
register called IE (interrupt enable) that is responsible for enabling (unmasking) and
disabling (masking) the interrupts.
Notice that IE is a bit-addressable register.
Steps in enabling an interrupt:
To enable an interrupt, we take the following steps:
1. Bit D7 of the IE register (EA) must be set to high to allow the reset to take
effect.If EA=1, interrupts are enabled and will be responded to if their corresponding bit in
IE are high. If EA=0, no interrupt will be responded to, even if the associated bit in
the IE register is high.
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Interrupt Enable Register
D7 D6 D5 D4 D3 D2 D1 D0
EA IE.7 disables all interrupts. If EA=0, no interrupts is acknowledged.
If EA=1, each interrupt source is individually enabled disabled
By setting or clearing its enable bit.
-- IE.6 Not implemented, reserved for future use.*
ET2 IE.5 Enables or disables Timer 2 overflow or capture interrupt (8052
Only)
ES IE.4 Enables or disables the serial port interrupts.
ET1 IE.3 Enables or disables Timers 1 overflow interrupt
EX1 IE.2 Enables or disables external interrupt 1.
ET0 IE.1 Enables or disables Timer 0 overflow interrupt.
EX0 IE.0 Enables or disables external interrupt.
Power supply
EA -- ET2 ES ET1 EX1 ET0
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The power supplies are designed to convert high voltage AC mains
electricity to a suitable low voltage supply for electronics circuits and other devices. A power
supply can by broken down into a series of blocks, each of which performs a particular function.
A d.c power supply which maintains the output voltage constant irrespective of a.c mains
fluctuations or load variations is known as Regulated D.C Power Supply
For example a 5V regulated power supply system as shown below:
Transformer:
A transformer is an electrical device which is used to convert
electrical power from one Electrical circuit to another without change in frequency.
Transformers convert AC electricity from one voltage to another with little loss of power.
Transformers work only with AC and this is one of the reasons why mains electricity is AC.
Step-up transformers increase in output voltage, step-down transformers decrease in output
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voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains
voltage to a safer low voltage. The input coil is called the primary and the output coil is called
the secondary. There is no electrical connection between the two coils; instead they are linked by
an alternating magnetic field created in the soft-iron core of the transformer. The two lines in the
middle of the circuit symbol represent the core. Transformers waste very little power so the
power out is (almost) equal to the power in. Note that as voltage is stepped down current is
stepped up. The ratio of the number of turns on each coil, called the turns ratio, determines the
ratio of the voltages. A step-down transformer has a large number of turns on its primary (input)
coil which is connected to the high voltage mains supply, and a small number of turns on its
secondary (output) coil to give a low output voltage.
An Electrical Transformer
Turns ratio = Vp/ VS = Np/NS
Power Out= Power In
VS X IS=VP X IP
Vp = primary (input) voltage
Np = number of turns on primary coilIp = primary (input) current
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RECTIFIER:
A circuit which is used to convert a.c to dc is known as RECTIFIER. The
process of conversion a.c to d.c is called rectification
TYPES OF RECTIFIERS:
Half wave Rectifier Full wave rectifier
1. Centre tap full wave rectifier.
2. Bridge type full bridge rectifier.
Comparison of rectifier circuits:
Parameter
Type of Rectifier
Half wave Full wave
Bridge
Number of diodes
1
2
4
PIV of diodes
Vm
2Vm Vm
D.C output voltage
Vm/
2Vm/
2Vm/
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Vdc,at
no-load
0.318Vm
0.636Vm 0.636Vm
Ripple factor
1.21
0.482
0.482
Ripple
frequency
f 2f
2f
Rectification
efficiency
0.406
0.812
0.812
Transformer
Utilization
Factor(TUF)
0.287 0.693 0.812
RMS voltage Vrms Vm/2 Vm/2 Vm/2
Full-wave Rectifier:
From the above comparision we came to know that full wave bridge rectifier as
more advantages than the other two rectifiers. So, in our project we are using full
wave bridge rectifier circuit.
Bridge Rectifier: A bridge rectifier makes use of four diodes in a bridge arrangement to achieve
full-wave rectification. This is a widely used configuration, both with individual diodes
wired as shown and with single component bridges where the diode bridge is wired
internally.
A bridge rectifier makes use of four diodes in a bridge arrangement as shown
in fig(a) to achieve full-wave rectification. This is a widely used configuration, both
with individual diodes wired as shown and with single component bridges where the
diode bridge is wired internally.
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Fig(A)
Operation:
During positive half cycle of secondary, the diodes D2 and D3 are in forward biased
while D1 and D4 are in reverse biased as shown in the fig(b). The current flow
direction is shown in the fig (b) with dotted arrows.
Fig(B)
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During negative half cycle of secondary voltage, the diodes D1 and D4 are in
forward biased while D2 and D3 are in reverse biased as shown in the fig(c). The
current flow direction is shown in the fig (c) with dotted arrows.
Fig(C)
Filter:
A Filter is a device which removes the a.c component of rectifier
output
but allows the d.c component to reach the load
Capacitor Filter:
We have seen that the ripple content in the rectified output of half waverectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48%
such high percentages of ripples is not acceptable for most of the applications.
Ripples can be removed by one of the following methods of filtering.
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(a) A capacitor, in parallel to the load, provides an easier by pass for the ripples
voltage though it due to low impedance. At ripple frequency and leave the d.c.to
appears the load.
(b) An inductor, in series with the load, prevents the passage of the ripple current
(due to high impedance at ripple frequency) while allowing the d.c (due to low
resistance to d.c)
(c) various combinations of capacitor and inductor, such as L-section filter
section filter, multiple section filter etc. which make use of both the properties
mentioned in (a) and (b) above. Two cases of capacitor filter, one applied on half
wave rectifier and another with full wave rectifier.
Filtering is performed by a large value electrolytic capacitor connected across the DC
supply to act as a reservoir, supplying current to the output when the varying DC voltage from
the rectifier is falling. The capacitor charges quickly near the peak of the varying DC, and then
discharges as it supplies current to the output. Filtering significantly increases the average DC
voltage to almost the peak value (1.4 RMS value).
To calculate the value of capacitor(C),
C = *3*f*r*Rl
Where,
f = supply frequency,
r = ripple factor,
Rl = load resistance
Note: In our circuit we are using 1000F Hence large value of capacitor is placed to
reduce ripples and to improve the DC component.
Regulator:
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Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable
output voltages. The maximum current they can pass also rates them. Negative
voltage regulators are available, mainly for use in dual supplies. Most regulators
include some automatic protection from excessive current ('overload protection')
and overheating ('thermal protection'). Many of the fixed voltage regulator ICs have
3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown
on the right. The LM7805 is simple to use. You simply connect the positive lead of
your unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin,
connect the negative lead to the Common pin and then when you turn on the
power, you get a 5 volt supply from the output pin.
Fig 6.1.6 A Three Terminal Voltage Regulator
78XX:
The Bay Linear LM78XX is integrated linear positive regulator with three
terminals. The LM78XX offer several fixed output voltages making them useful in
wide range of applications. When used as a zener diode/resistor combination
replacement, the LM78XX usually results in an effective output impedance
improvement of two orders of magnitude, lower quiescent current. The LM78XX is
available in the TO-252, TO-220 & TO-263packages,
Features:
Output Current of 1.5A
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Output Voltage Tolerance of 5%
Internal thermal overload protection
Internal Short-Circuit Limited
No External Component
Output Voltage 5.0V, 6V, 8V, 9V, 10V,12V, 15V, 18V, 24V
Offer in plastic TO-252, TO-220 & TO-263
Direct Replacement for LM78XX
MAX-232:The MAX232 from Maxim was the first IC which in one package contains the necessary drivers(two) and receivers (also two), to adapt the RS-232 signal voltage levels to TTL logic. It becamepopular, because it just needs one voltage (+5V) and generates the necessary RS-232 voltagelevels (approx. -10V and +10V) internally. This greatly simplified the design of circuitry.Circuitry designers no longer need to design and build a power supply with three voltages (e.g.-12V, +5V, and +12V), but could just provide one +5V power supply, e.g. with the help of asimple 78x05 voltage converter.
The MAX232 has a successor, the MAX232A. The ICs are almost identical, however, the
MAX232A is much more often used (and easier to get) than the original MAX232, and theMAX232A only needs external capacitors 1/10th the capacity of what the original MAX232needs.
It should be noted that the MAX 232(A) is just a driver/receiver. It does not generate thenecessary RS-232 sequence of marks and spaces with the right timing, it does not decode the RS-232 signal, it does not provide a serial/parallel conversion. All it does is to convert signalvoltage levels. Generating serial data with the right timing and decoding serial data has to bedone by additional circuitry, e.g. by a 16550 UART or one of these small micro controllers (e.g.Atmel AVR, Microchip PIC) getting more and more popular.
The MAX232 and MAX232A were once rather expensive ICs, but today they are cheap. It hasalso helped that many companies now produce clones (ie. Sipex). These clones sometimes needdifferent external circuitry, e.g. the capacities of the external capacitors vary. It is recommendedto check the data sheet of the particular manufacturer of an IC instead of relying on Maxim'soriginal data sheet.
The original manufacturer (and now some clone manufacturers, too) offers a large series ofsimilar ICs, with different numbers of receivers and drivers, voltages, built-in or external
http://www.maxim-ic.com/http://en.wikibooks.org/wiki/Serial_Programming:8250_UART_Programminghttp://en.wikibooks.org/wiki/Atmel_AVRhttp://en.wikibooks.org/wiki/Embedded_Systems/PIC_Microcontrollerhttp://www.sipex.com/products/interface.htmhttp://www.maxim-ic.com/http://en.wikibooks.org/wiki/Serial_Programming:8250_UART_Programminghttp://en.wikibooks.org/wiki/Atmel_AVRhttp://en.wikibooks.org/wiki/Embedded_Systems/PIC_Microcontrollerhttp://www.sipex.com/products/interface.htm -
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capacitors, etc. E.g. The MAX232 and MAX232A need external capacitors for the internalvoltage pump, while the MAX233 has these capacitors built-in. The MAX233 is also betweenthree and ten times more expensive in electronic shops than the MAX232A because of itsinternal capacitors. It is also more difficult to get the MAX233 than the garden varietyMAX232A.
A Typical Application
The MAX 232(A) has two receivers (converts from RS-232 to TTL voltage levels) and twodrivers (converts from TTL logic to RS-232 voltage levels). This means only two of the RS-232signals can be converted in each direction. The old MC1488/1498 combo provided four driversand receivers.
Typically a pair of a driver/receiver of the MAX232 is used for
TX and RX
And the second one for
CTS and RTS.
There are not enough drivers/receivers in the MAX232 to also connect the DTR, DSR, and DCDsignals. Usually these signals can be omitted when e.g. communicating with a PC's serialinterface. If the DTE really requires these signals either a second MAX232 is needed, or someother IC from the MAX232 family can be used (if it can be found in consumer electronic shopsat all). An alternative for DTR/DSR is also given below.
Maxim's data sheet explains the MAX232 family in great detail, including the pin configurationand how to connect such an IC to external circuitry. This information can be used as-is in owndesign to get a working RS-232 interface. Maxim's data just misses one critical piece ofinformation: How exactly to connect the RS-232 signals to the IC. So here is one possibleexample:
MAX232 to RS232 DB9 Connection as a DCE
MAX232 Pin
Nbr.
MAX232 Pin
Name
Sign
al
Volta
ge
DB9
Pin
7 T2out CTSRS-
2327
8 R2in RTSRS-
2328
http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdfhttp://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf -
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9 R2out RTS TTL n/a
10 T2in CTS TTL n/a
11 T1in TX TTL n/a
12 R1out RX TTL n/a
13 R1in TXRS-
2323
14 T1out RXRS-
2322
15 GND GND 0 5
In addition one can directly wire DTR (DB9 pin 4) to DSR (DB9 pin 6) without going throughany circuitry. This gives automatic (brain dead) DSR acknowledgment of an incoming DTRsignal.
Sometimes pin 6 of the MAX232 is hard wired to DCD (DB9 pin 1). This is not recommended.Pin 6 is the raw output of the voltage pump and inverter for the -10V voltage. Drawing currents
from the pin leads to a rapid breakdown of the voltage, and as a consequence to a breakdown ofthe output voltage of the two RS-232 drivers. It is better to use software which doesn't care aboutDCD, but does hardware-handshaking via CTS/RTS only.
The circuitry is completed by connecting five capacitors to the IC as it follows. The MAX232needs 1.0F capacitors, the MAX232A needs 0.1F capacitors. MAX232 clones show similardifferences. It is recommended to consult the corresponding data sheet. At least 16V capacitortypes should be used. If electrolytic or tantalic capacitors are used, the polarity has to beobserved. The first pin as listed in the following table is always where the plus pole of thecapacitor should be connected to.
MAX232(A) external Capacitors
Capaci
tor
+
Pin
-
PinRemark
C1 1 3
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C2 4 5
C3 2 16
C4GN
D6
This looks non-intuitive, but becausepin 6 is
on -10V, GND gets the + connector, and
not the -
C5 16GN
D
The 5V power supply is connected to
+5V: Pin 16 GND: Pin 15
Features
Meet or Exceed TIA/EIA-232-F and ITURecommendation V.28
Operate With Single 5-V Power Supply Operate Up to 120 kbit/s Two Drivers and Two Receivers 30-V Input Levels Low Supply Current . . . 8 mA Typical
Designed to be Interchangeable WithMaxim MAX232
ESD Protection Exceeds JESD 222000-V Human-Body Model (A114-A)
ApplicationsTIA/EIA-232-F
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Battery-Powered Systems
Terminals
Modems
Computers
Description/ordering information
The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to supply EIA-232
voltage levels from a single 5-V supply. Each receiver converts EIA-232 inputs to 5-V TTL/CMOS levels.
These receivers have a typical threshold of 1.3 V and a typical hysteresis of 0.5 V, and can accept 30-V
inputs. Each driver converts TTL/CMOS input levels into EIA-232 levels. The driver, receiver, and voltage-
generator functions are available as cells in the Texas Instruments Lin ASIC library.
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RELAYS
Relay is an electrically operated switch. Current flowing through the coil of the
relay creates a magnetic field which attracts a lever and changes the switch
contacts. The coil current can be on or off so relays have two switch positions and
they are double throw (changeover) switches.
Relays allow one circuit to switch a second circuit which can be completely
separate from the first. For example a low voltage battery circuit can use a relay to
switch a 230V AC mains circuit. There is no electrical connection inside the relay
between the two circuits; the link is magnetic and mechanical.
The coil of a relay passes a relatively large current, typically 30mA for a 12V
relay, but it can be as much as 100mA for relays designed to operate from lower
voltages. Most ICs (chips) cannot provide this current and a transistor is usually
used to amplify the small IC current to the larger value required for the relay coil.
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The maximum output current for the popular 555 timer IC is 200mA so these
devices can supply relay coils directly without amplification.
Relays are usually SPDT or DPDT but they can have many more sets of switch
contacts, for example relays with 4 sets of changeover contacts are readilyavailable. For further information about switch contacts and the terms used to
describe them please see the page on switches.
Most relays are designed for PCB mounting but you can solder wires directly
to the pins providing you take care to avoid melting the plastic case of the relay.
The supplier's catalogue should show you the relay's connections. The coil will be
obvious and it may be connected either way round. Relay coils produce brief high
voltage 'spikes' when they are switched off and this can destroy transistors and ICs
in the circuit. To prevent damage you must connect a protection diode across the
relay coil.
The animated picture shows a working relay with its coil and switch contacts.
You can see a lever on the left being attracted by magnetism when the coil is
switched on. This lever moves the switch contacts. There is one set of contacts
(SPDT) in the foreground and another behind them, making the relay DPDT.
The relay's switch connections are usually labelled COM, NC and
NO:
COM = Common, always connect to this, it is the moving part of the switch.
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NC = Normally Closed, COM is connected to this when the relay coil is off.
NO = Normally Open, COM is connected to this when the relay coil is on.
Connect to COM and NO if you want the switched circuit to be on when the
relay coil is on.
Connect to COM and NC if you want the switched circuit to be on when the
relay coil is off.
Choosing a relay
You need to consider several features when choosing a relay:
1. Physical size and pin arrangement If you are choosing a relay for an existing
PCB you will need to ensure that its dimensions and pin arrangement are
suitable. You should find this information in the supplier's catalogue.
2. Coil voltage the relay's coil voltage rating and resistance must suit the circuit
powering the relay coil. Many relays have a coil rated for a 12V supply but 5V
and 24V relays are also readily available. Some relays operate perfectly well
with a supply voltage which is a little lower than their rated value.
3. Coil resistance the circuit must be able to supply the current required by the
relay coil. You can use Ohm's law to calculate the current:
Relay coil
current =
supplyvoltage
coil
resistance
4. For example: A 12V supply relay with a coil resistance of 400 passes a
current of 30mA. This is OK for a 555 timer IC (maximum output current
200mA), but it is too much for most ICs and they will require a transistor to
amplify the current.
5. Switch ratings (voltage and current) the relay's switch contacts must be
suitable for the circuit they are to control. You will need to check the voltage
and current ratings. Note that the voltage rating is