Cnc Automatoc Drilling Machine

8/11/2019 Cnc Automatoc Drilling Machine

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1. INTRODUCTION

PCB stands for Printed Circuit Board. A Printed Circuit Board is a

thin board made of an insulating material such as a fiber glass or a similar material that

bears all the electronic components of a circuit connected together by very thin copper

tracks. The components of a PCB are held in their respective position by drilling holes at

required places on the board and soldering them.

Drilling operation is one of the important mechanical processes in

manufacture of printed circuited boards. The purpose of this drilling is twofold:

(i) To provide component lead mounting precisely and with

structural integrity.

(ii) To establish electrical connection between top, bottom, and

sometimes intermediate conductor pathways.

Drilling of holes at the required places on the circuit board, so that it

can bear the required components of the circuit at required positions is a significant step in

the manufacturing of Printed Circuit Boards. For manufacture of PCBs in small quantities

drilling of holes is usually done by manual drilling with either an electric or pneumatic

drill, while production of PCBs in large quantity involves the use of Computer Numerical

Controlled (CNC) drilling machines.

A common problem experienced by these smaller manufacturers of

PCBs is that the total turnaround time is impeded by the time spent for the drilling of

PCBs. Moreover the small industries cannot afford the expensive and sophisticatedComputer Numerical Controlled (CNC) Drilling machine.

The ideal solution for this problem is to develop a low cost reliable

Computer Numerical Control (CNC) drilling machine that possesses the capabilities and

versatility of expensive Computer Numerical Control (CNC) drilling machines available.


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1.1 Mechanical operations in fabrication of Printed Circuit Boards:

Shearing :Shearing is the first mechanical operation carried out on PCBs to

give them proper shape or contour. It is basically a cutting method applicable to all kinds

of base materials, generally of less than 2 mm thickness.

Sawing:

In the PCB industry, mostly circular sawing machines of the moving

table type are preferred. The saw blade speed is adjustable between 2000-6000 rpm. This

method is preferred as it gives a smother edge finish and clean cut, though the dimensional

tolerances are similar (0.3-0.5 mm) to that of shearing.

Blanking :

When PCBs are designed to have shapes other than rectangular or

have an odd contour, the use of a blanking die is a faster and more economical method.

Blanking basically consists of a clean cutting operation done with a punching tool rather

than with a saw or a shearing machine. Blanking helps to achieve PCB dimensions within a

tolerance of (0.1 0.2 mm).

Milling:

Milling is a commonly used operation which can be applied for the

clean cutting of PCBs and for obtaining good edge finish and overall dimensions with a

high degree of accuracy. The generally used cutting speeds are in the range of 1000-3000

rpm. They usually employ straight or spiral tooth HSS (high speed steel) milling cutters.


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Routing:

For obtaining superior edge finish and higher dimensional accuracy

than that obtainable from shearing or sawing routing is adopted. Especially for PCBs with

odd contours, routing becomes a better choice. The dimensional tolerances within (0.1-

0.2) mm can be achieved with a much lower cost than blanking. There are three basic

routing systems available. They are:

a) Pin routing b) Tracer or stylus routing and

c) NC routing Drilling:

Drilling operation is one of the important mechanical processes in

the manufacture of printed circuit boards. After the drilling process, the drilled circuit

board undergoes various processes like plating, aging, etching and solder plating.Therefore, care is needed to obtain a good surface on the drilled hole and hence its quality

assumes great significance.

Fig. 1.1 The important steps in the drilling process


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1.3 Drill bits for PCB drilling:

Normally, most PCBs are drilled with carbide bits rather than high-

speed steel (HSS). Carbide bits have good resistance to heat and high hardness. The quality

of cutting edges or drill points of the drill bit are very important. Drill bits should not be

pressed against metallic or hard surfaces to avoid damage to the bit geometry. The drill bit

surface should be cleaned by 1 per cent tri-sodium phosphate in water for 20 to 30 seconds.

This removes the oils and debris from their surface.

The standard PCB drills for holes of 0.024" (0.6 mm) and larger is

composed of wear-resistant cemented tungsten carbide crystals. Their composition, i.e. 94

per cent tungsten carbide (WC) and 6 per cent cobalt (co) provides maximum drilling

speed and tool life for years. For holes with diameters of 0.018" (0.45 mm) or smaller,

several PCB drilling problems are encountered. These include a higher frequency of drill

breakage upon retract, an increase of hole location scrap, and a decrease in output due to a

reduction in the PCB stack height.

1.4 Drill bit geometry:

Drills used for making holes in PCBs are usually made of HighSpeed Steel (HSS) and tungsten carbide (mostly). These drill bits are generally available intwo basic forms:

(i) Common shank(ii) Straight shank

The function of drill bit in PCB drilling is to cut and remove the base material and copper. Most of the drill bits used for PCB drilling are of common shankdesign. This allows a drill machine to use many bit diameters with only one collet. The

point angle determines the ability of the tool to cut the laminate material and it usuallyvaries in the range of 90 to 130.


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Fig. 1.2 Common shank and straight shank drill bits

Fig. 1.3 The geometry of a drill bit.


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2. THE OUTLOOK OF THE PROTOTYPE OF THE

PCB DRILLING MACHINE


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2.1 Mechanical components used:

Stepper Motors:A stepper motor is a widely used device that translates electrical

pulses into mechanical movement. The stepper motor is used for position control in

applications such as disk drivers, dot matrix printers, and robotics, etc. Every stepper

motor has a permanent magnet rotor (also called the shaft) surrounded by a stator.

In our project stepping motors are used to achieve precise positioning of

the table of the drilling machine via digital control. The motor operates by accurately

synchronizing with the pulse signal output from the microcontroller, to the driver circuit.

Stepping motors, with their ability to produce high torque at a low speed while

minimizing vibration, are ideal for applications requiring quick positioning over a short

distance.

Stepping motors enable accurate positioning with ease. They are used in

various types of equipment for accurate rotation angle and speed control using pulse

signals. Stepping motors generate high torque with a compact body, and are ideal for

quick acceleration and response. Stepping motors also hold their position at stop, due to

their mechanical design. Stepping motor functioning consist of a driver (takes pulse

signals in and converts them to motor motion) and a stepping motor.

The stepper motor used to in this project for the positioning of the table is a

VEXTA STEPPING MOTOR, model no. PH266-01.

Fig. 2.1 The VEXTA stepper motor PH266-01


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The specifications of this stepping motor are as follows:

Phase: 2 phase

Input Voltage: 6V Amperes: 1.2A Step Angle: 1.8 Casing Size: NEMA 23

Mechanism of a stepper motor:

Stepper motors consist of a permanent magnet rotating shaft, calledthe rotor, and electromagnets on the stationary portion that surrounds the motor, called the

stator. The following figure illustrates one complete rotation of a stepper motor. At

position 1, we can see that the rotor is beginning at the upper electromagnet, which is

currently active (has voltage applied to it). To move the rotor clockwise, the upper

electromagnet is deactivated and the right electromagnet is activated, causing the rotor to

move 90 degrees clockwise, aligning itself with the active magnet. This process is repeated

in the same manner at the south and west electromagnets until we once again reach the

starting position.

Fig. 2.2 Working of a stepper motor.
http://www.imagesco.com/articles/picstepper/02.html#fig1http://www.imagesco.com/articles/picstepper/02.html#fig1


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In the above example, a motor with a resolution of 90 degrees is illustrated for

demonstration purpose. The resolution (the amount of degrees of rotors rotation for a

single pulse) of VEXTA stepping motor used is much lower than this. This motor has a

resolution of 1.8 degrees, that is, the motor would move its rotor 1.8 degrees per step,

thereby requiring 200 pulses (steps) to complete a full 360 degree rotation.

Accurate Positioning in Fine Steps:

Fig. 2.3 Step angle of a stepper motor.

A stepping motor rotates with a fixed step angle, just like the second hand

of a clock. This angle is called "basic step angle". The stepping motor used is with a basic

step angle 1.8.

Easy Control with Pulse Signals:

The system configuration for high accuracy positioning is shown below.

The rotation angle and speed of the stepping motor can be controlled with precise

accuracy by using pulse signals from the controller.

Fig. 2.3 Controlling of a stepper motor using pulse signal.


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What is a Pulse Signal?

Fig. 2.4 Pulse signal to a stepper motor.

A pulse signal is an electrical signal whose voltage level changes

repeatedly between ON and OFF. Each ON/OFF cycle is counted as one pulse. A

command with one pulse causes the motor output shaft to turn by one step. The signal

levels corresponding to voltage ON and OFF conditions are referred to as "H" and "L"

respectively.

The Amount of Rotation is Proportional to the Number of Pulses:

Fig. 2.5 Angle of rotation for different pulse inputs.

The amount the stepping motor rotates is proportional to the number of

pulse signals (pulse number) given to the driver. The relationship of the stepping motor's


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Fig. 2.7 Step movement of the rotor of the stepper motor.

The Motor Holds Itself at a Stopped Positioning

Stepping motors continue to generate holding torque even at

standstill. This means that the motor can be held at a stopped position without using a

mechanical brake. Once the power is cut off, the self-holding torque of the motor is lost

and the motor can no longer be held at the stopped position in vertical operations or whenan external force is applied. In lift and similar applications, use an electromagnetic brake

type.

Fig. 2.8 Horizontal and vertical implementation of a stepper motor.


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Lead Screw mechanism for table movement:The movement of the table of the PCB drilling machine to required

position is achieved by the lead screw mechanism. Lead screw is a general term for a

threaded rod that translates rotary motion to linear motion. The rod is connected to theshaft of the Stepper motor. Situated along the length of the rod is a nut which is connected

to some platform or a carriage. When the motors shaft rotates, the rod also rotates, and the

nut travels forward or backward depending on the direction of rotation of motor and the

rod. The table which is joined to this nut will move accordingly along with the nut to come

to the required position. The two ends of the threaded rod are held in roller bearings to

constrain any linear movement of it and hence the only resulting motion is the linear travel

of the nut along the threaded rod.

Fig. 2.9 Lead screw mechanism.

Fig. 2.10 Implementation of a lead screw mechanism.


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Spur Gears:The spur gears are used for transmitting the power from the stepper motors

to the threaded rod of the lead screw mechanism. There are a total of 6 gear wheels

employed for transmission, two for each stepper motor and lead screw combination.

Fig. 2.11 Spur gears used in lead screw mechanism.

Ball bearings:The threaded rods of the lead screw are supported by two ball bearings, one

on each side of the threaded rod. So there are totally six bearings supporting the three

threaded rods in each direction of X, Y, Z.

Fig. 2.12 Ball bearings used to support the threaded rod.


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Hand drilling machine:

The hand drilling machine is mounted in the configuration of a pillar

drilling machine on the vertical threaded rod of lead screw mechanism. This is held in its

position on the support of threaded rod with the help of a clamp. The drilling machine is

moved down and up during drilling process for a single hole on the PCB. The following

are the specifications of the hand drilling machine:

Input: 220 V, 50 Hz Speed: 1700 rpm Drill bit range: 1.5 to 10 mm

Make ; Jainpai Electronic drill Model no.: FY-007

Fig. 2.13 Hand drilling machine.


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3.INTRODUCTION TO EMBEDDED SYSTEM

Embedded systems are systems with self contained programs that are

embedded within a piece of hardware. While a regular computer has many different

applications and software that are related to various tasks, embedded systems are usually

set to a specific task that cannot be altered without physically manipulating the circuit. An

embedded system may be considered as a computer system that is created with optimal

efficiency, thereby allowing it to complete specific functions as quickly as possible.

Embedded system literally means that a system in which the

processor is embedded into the required application. An embedded product uses a

microprocessor or microcontroller to do one specific task only. In an embedded system,

there is only one application software that is typically burned into ROM.

An embedded system may have a controller in two forms, either as a

microprocessor or as a microcontroller. A microprocessor a single chip in the electronic

circuit that contains the Central Processing Unit for a system or it is more like a micro-

computer for that system while a microcontroller is a single chip in a circuit used to control

other devices in an electronic circuit.

Microcontroller differs from a microprocessor in many ways. First

and the most important is its functionality. In order for a microprocessor to be used, other

components such as memory, or components for receiving and sending data must be added

to it. In short that means that microprocessor is the very heart of the computer.

On the other hand, microcontroller is designed to be all of that in

one. No other external components are needed for its application because all necessary

peripherals are already built into it. Thus, we save the time and space needed to construct

devices.


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3.1 Microprocessor Vs Microcontroller:

Microprocessor:

CPU is stand-alone, RAM, ROM, I/O, timer are separate

Designer can decide on the amount of ROM, RAM and I/O ports.

expensive

versatility general-purpose

Microcontroller: CPU, RAM, ROM, I/O and timer are all on a single chip Fixed amount of on-chip ROM, RAM, I/O ports for applications in which cost, power and space are critical single-purpose

3.2 What is a microcontroller?

Microcontrollers as the name suggests can be thought of as small

controllers for a system. They may be thought of as single chip computers that are

embedded into other systems to function as processing or controlling units. For example

the remote control of a television has microcontrollers inside it, that perform decoding and

other controlling functions. They are also used in automobiles, washing machines,

microwave ovens, toys etc, where automation of the system is required.

Microcontrollers are useful to the extent that they communicate with

other devices, such as sensors, motors, switches, keypads, displays, memory and even

other microcontrollers. Many interface methods have been developed over the years to

solve the complex problem of balancing circuit design criteria such as features, cost, size,

weight, power consumption, reliability, availability, manufacturability. Many

microcontroller designs typically mix multiple interfacing methods. In a very simplistic

form, a micro-controller system can be viewed as a system that reads from (monitors)

inputs, performs processing and writes to (controls) outputs.


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3.3 General features of 8051 microcontroller:

4KB ROM 128 bytes internal RA 4 register banks of 8 bytes each (R0-R7) 16 bytes of bit-addressable area 80 bytes of general purpose memory Four 8-bit I/O ports (P0-P3) Two 16-bit timers (Timer0 & Timer1) One serial receiver-transmitter interface Five interrupt sources (2 external & 3 internal)

One oscillator (generates clock signal)

3.4 Architecture of a microcontroller 8051

The features of studying the internal hardware design, and todetermine the type, number, size of registers is called Architecture of a device (8051).

Fig. 3.1 Architecture of 8051 microcontroller.


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Central Processing Unit (CPU):The Central Processing Unit is the main unit that receives data,

manipulates the data and processes it and sends it out. It takes a program as an input for

processing of data. This program is written in permanent memory storage, Read OnlyMemory (ROM).

The 8051 contains 34 general purpose or working registers.

Registers A and B comprise the mathematical core of 8051 central processing unit (CPU).

The other 32 are arranged as part of internal RAM in four banks,

The A (Accumulator) register is the most versatile of the two CPU

registers and is used for many operations. The A register is also used for all data transfers

between the 8051 and external memory.

Internal ROM:The 8051 is organized so that data memory and program code

memory can be in two entirely different physical memory entities. Each has same address

ranges.

The corresponding block of internal program code, contained in an

internal ROM, occupies code address space 0000h to 0FFFh. Hence the memory unit in

which, the program that defines the manipulations done in the central processing unit, is

called Read Only Memory (ROM).

Generally the ROM is a permanent storage (i.e) anything written in

it cannot be modified. But the recent advancement is an EPROM- Erasable and

Programmable Read Only Memory, in which the written data can be modified as many

times as required.

Input and Output Port:The Input and output ports are the components of an 8051

microcontroller that connect it to the external world. There are a total of 40 pins for an

8051 microcontroller, but out of these only 32 are used for Input/output purpose. These 32

pins are grouped into 4 ports P0, P1, P2, and P3 with each port having a set of 8 pins. Out

of these 24 pins can be used for dual purpose. They can be used for input and output

purposes or as a control line or as a part of address or date bus. The function that a pin


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performs depends firstly upon, what it is physically connected to and then upon what

software commands are used to program the pin.

Given this pin flexibility the 8051 may be simply applied as a

component for input and output purposes or it may be expanded to include additional

memory, parallel ports, and serial communication of data by using alternate pin

assignments.

Bus Control:A Bus is component of 8051 micro controller that controls the

transmission of data from CPU to other components and vice-versa. The general bus

control has two sections:

Data bus : The CPU either gets data from the device or sends data to it

Control bus : Provides read or write signals to the device to indicate if the

CPU is asking for information from it or sending it

information.

The 8051 Oscillator and Clock:The heart of 8051 is the circuitry that generates clock pulses by

which all the internal operations are synchronized. Pins XTAL1 and XTAL2 are used for

connecting the network to a resonating crystal to form an oscillator. A quartz crystal and a

capacitor are employed for this purpose. The crystal frequency is basic internal clock

frequency of microcontroller. The designs of 8051 microcontroller that are available are

such that they can run at a maximum and minimum frequency, generally the frequency

range is from 1 MHz to 16 MHz. Minimum frequencies imply that some internal memories

are dynamic and must always operate above minimum frequency, or data will be lost.

Serial Port:The microcontroller 8051 has a serial data communication that uses

SBUF register to hold data. Register SCON controls data communication, register PCON

controls data rates and pins RXD (P3.0) and TXD (P3.1) are used for the purpose of serial

communication. The SBUF register is indeed two re3gisters, one is to hold data to be

transmitted out of 8051 through TXD while the other is to read data from external sources

through RXD. Both mutually exclusive registers use address 99H.


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Timers:The basic 8051 has two on-chip timers (Timer 0, Timer 1) that can

be used for timing durations or for counting external events. Interval timing allows the

programmer to perform operations at specific instants in time. For example, in an LEDflashing program the LED was turned on for a specific length of time and then turned off

for a specific length of time.

External Interrupts:An interrupt is the occurrence of an event (Like timer overflow

setting the TF0 or TF1 flags to 1) that causes a temporary suspension of a program whilethe event is serviced by a section of code known as the interrupt service routine. The 8051

has five interrupt sources: Two external interrupts are provided through pins INTO-bar and INT1-bar, which

are the alternate functions of port 3 pin 2 and port 3 pin 3, respectively.

Two internal interrupts are generated by timer 0 overflow and by timer 1 overflow. The serial port on the 8051 can generate an interrupt when a byte has been

transmitted or when a byte is received.

Interrupt Flag Location in

Registers

External 0 IE0 TCON.1

External 1 IE1 TCON.3

Timer 0 TF0 TCON.5

Timer 1 TF1 TCON.7

Serial Port Receive RI SCON.0

Serial Port Transmit TI SCON.1

Table 3.1 Interrupts in microcontroller 8051


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When an interrupt occurs the following happens:

The current instruction completes execution. The Program Counter is saved on the stack (That is, the address of the next

instruction).

The address of the ISR for the interrupt is loaded into the Program Counter.

Interrupt Vectors: When an interrupt occurs, the address of the interrupt service routine is

loaded into the PC. This address is known as the interrupt vector.

Interrupt Flag Vector

System reset RST 0000H

External interrupt 0 IE0 0003H

Timer 0 TF0 000BH

External interrupt 1 IE1 0013H

Timer 1 TF1 001BH

Serial port RI or TI 0023H

Table 3.2 Interrupt flags and vectors.

3.5 Pin Configuration of 8051 microcontroller:

Pins 1-8: Port 1 Each of these pins can be configured as an input or an output.

Pin 9: RST A logic one on this pin disables the microcontroller and clears the contents of

most registers. In other words, the positive voltage on this pin resets the microcontroller.

By applying logic zero to this pin, the program starts execution from the beginning. Pins10-17: Port 3 Similar to port 1, each of these pins can serve as general input or output.

Besides, all of them have alternative functions:

Pin 10: RXD Serial asynchronous communication input or Serial synchronous

communication output.

Pin 11: TXD Serial asynchronous communication output or Serial synchronous

communication clock output.

Pin 12: INT0 Interrupt 0 input. Pin 13: INT1 Interrupt 1 input.


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Pin 14: T0 Counter 0 clock input.

Pin 15: T1 Counter 1 clock input.

Pin 16: WR Write to external (additional) RAM.

Pin 17: RD Read from external RAM.

Pin 18, 19: X2, X1 Internal oscillator input and output. A quartz crystal which specifies

operating frequency is usually connected to these pins. Instead of it, miniature ceramics

resonators can also be used for frequency stability. Later versions of microcontrollers

operate at a frequency of 0 Hz up to over 50 Hz.

Pin 20: GND Ground pin, it is connected to the ground in the circuit.

Pin 21-28: Port 2 If there is no intention to use external memory then these port pins are

configured as general inputs/outputs. In case external memory is used, the higher address

byte, i.e. addresses A8-A15 will appear on this port. Even though memory with capacity of

64Kb is not used, which means that not all eight port bits are used for its addressing, the

rest of them are not available as inputs/outputs.

Pin 29: PSEN If external ROM is used for storing program then a logic zero (0) appears

on it every time the microcontroller reads a byte from memory.

Pin 30: ALE Prior to reading from external memory, the microcontroller puts the lower

address byte (A0-A7) on P0 and activates the ALE output. After receiving signal from the

ALE pin, the external register (usually 74HCT373 or 74HCT375 add-on chip) memorizes

the state of P0 and uses it as a memory chip address. Immediately after that, the ALU pin is

returned its previous logic state and P0 is now used as a Data Bus. As seen, port data

multiplexing is performed by means of only one additional (and cheap) integrated circuit.

In other words, this port is used for both data and address transmission.

Pin 31: EA By applying logic zero to this pin, P2 and P3 are used for data and address

transmission with no regard to whether there is internal memory or not. It means that even

there is a program written to the microcontroller, it will not be executed. Instead, the program written to external ROM will be executed. By applying logic one to the EA pin,

the microcontroller will use both memories, first internal then external (if exists).

Pin 32-39: Port 0 Similar to P2, if external memory is not used, these pins can be used as

general inputs/outputs. Otherwise, P0 is configured as address output (A0-A7) when the

ALE pin is driven high (1) or as data output (Data Bus) when the ALE pin is driven low

(0).

Pin 40: VCC +5V power supply.


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Fig. 3.2 Pin configuration of 8051

3.6 Registers of 8051 Microcontroller:

Basic Registers:

The Accumulator:

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 8051 has due to

the sheer number of instructions that make use of the accumulator. More than half

of the 8051s 255 instructions manipulate or use the accumu lator in some way. This

is one of the two registers in CPU of 8051.


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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 by two 8051 instructions:

MUL AB and DIV AB. Thus, if you want to quickly and easily multiply or divide A byanother number, you may store the other number in "B" and make use of these two

instructions. Aside from the MUL and DIV instructions, the B register are often

used as yet another temporary storage register much like a ninth "R" register.

The Program Counter (PC):

The Program Counter (PC) is a 2-byte address which tells the 8051

where the next instruction to execute is found in memory. When the 8051 is initialized PCalways starts at 0000h and is incremented each time an instruction is executed. It is

important to note that PC is not always incremented by one. Since some instructions

require 2 or 3 bytes 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 an instruction,

PC=2430h is not a valid one. On the other hand, an instruction of LJMP 2430h can be

effectively accomplished to do the same thing.

The "R" registers:

The "R" registers are a set of eight registers that are named R0, R1,

etc. up to and including R7.These registers are used as auxiliary registers in many

operations.

The Data Pointer (DPTR):

The Data Pointer (DPTR) is the 8051s only user-accessible 16-bit(2-byte) register. The Accumulator, "R" registers, and "B" register are all 1-byte values.

DPTR, as the name suggests, is used to point to data. It is used by a number of commands

which allow the 8051 to access external memory. When the 8051 accesses external

memory it will access external memory at the address indicated by DPTR. While DPTR is

most often used to point to data in external memory, an advantage that it is the only true

16-bit register available is very helpful in programming. It is often used to store 2-byte

values which have nothing to do with memory locations.


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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 8051 first increments the value of SP and then stores the value atthe resulting memory location. When you pop a value off the stack, the 8051 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 8051 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. 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 8051 by

six instructions: PUSH, POP, ACALL, LCALL, RET, and RETI. It is also used

intrinsically whenever an interrupt is triggered.

Special Function Registers:

The 8051 is a flexible microcontroller with a relatively large number

of modes of operations. The program may inspect and/or change the operating mode of the

8051 by manipulating the values of the 8051's Special Function Registers (SFRs).SFRs are

accessed as if they were normal Internal RAM. The only difference is that Internal RAM is

from address 00h through 7Fh whereas SFR registers exist in the address range of 80h

through FFh. Each SFR has an address (80h through FFh) and a name. The following chart

provides a graphical presentation of the 8051's SFRs, their names, and their address.

Fig. 3.3 Special function Registers in 8051.


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Although the address range of 80h through FFh offers 128 possible

addresses, there are only 21 SFRs in a standard 8051. All other addresses in the SFR range

(80h through FFh) are considered invalid. Writing to or reading from these registers may

produce undefined values or behaviour.

It is recommended that you not read or write to SFR addresses that

have not been assigned to an SFR. Doing so may provoke undefined behaviour and may

cause your program to be incompatible with other 8051-derivatives that use the given SFR

for some other purpose.

SFR Types:

As mentioned in the chart itself, the SFRs that have a blue

background are SFRs related to the I/O ports. The 8051 has four I/O ports of 8 bits, for a

total of 32 I/O lines. Whether a given I/O line is high or low and the value read from the

line are controlled by the SFRs in green. The SFRs with yellow backgrounds are SFRs

which in some way control the operation or the configuration of some aspect of the 8051.

For example, TCON controls the timers, SCON controls the serial port. The remaining

SFRs, with green backgrounds, are "other SFRs." These SFRs can be thought of as

auxiliary SFRs in the sense that they don't directly configure the 8051 but obviously the8051 cannot operate without them. For example, once the serial port has been configured

using SCON , the program may read or write to the serial port using the SBUF register.

The SFRs whose names appear in red in the chart above are SFRs

that may be accessed via bit operations (i.e., using the SETB and CLR instructions). The

other SFRs cannot be accessed using bit operations. As you can see, all SFRs that whose

addresses are divisible by 8 can be accessed with bit operations.

SFR Descriptions:P0 (Port 0, Address 80h, Bit-Addressable):

This is input/output port 0. Each bit of this SFR corresponds to one

of the pins on the microcontroller. For example, bit 0 of port 0 is pin P0.0, bit 7 is pin P0.7.

Writing a value of 1 to a bit of this SFR will send a high level on the corresponding I/O pin

whereas a value of 0 will bring it to a low level.


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8051 has four I/O port (P0, P1, P2, and P3), if your hardware uses

external RAM or external code memory (i.e., your program is stored in an external ROM

or EPROM chip or if you are using external RAM chips) you may not use P0 or P2. This is

because the 8051 uses ports P0 and P2 to address the external memory. Thus if you are

using external RAM or code memory you may only use ports P1 and P3 for your own use.

SP (Stack Pointer, Address 81h):This is the stack pointer of the microcontroller. This SFR indicates

where the next value to be taken from the stack will be read from in Internal RAM. If you

push a value onto the stack, the value will be written to the address of SP + 1. That is to

say, if SP holds the value 07h, a PUSH instruction will push the value onto the stack ataddress 08h. This SFR is modified by all instructions which modify the stack, such as

PUSH, POP, LCALL, RET, RETI, and whenever interrupts are provoked by the

microcontroller.

DPL/DPH (Data Pointer Low/High, Addresses 82h/83h):The SFRs DPL and DPH work together to represent a 16-bit value

called the Data Pointer. The data pointer is used in operations regarding external RAM andsome instructions involving code memory. Since it is an unsigned two-byte integer value, it

can represent values from 0000h to FFFFh (0 through 65,535 decimal).

DPTR is really DPH and DPL taken together as a 16-bit value. In

reality, you almost always have to deal with DPTR one byte at a time. For example, to push

DPTR onto the stack you must first push DPL and then DPH. You can't simply plush

DPTR onto the stack. Additionally, there is an instruction to "increment DPTR." When you

execute this instruction, the two bytes are operated upon as a 16-bit value. However, there

is no instruction those decrements DPTR. If you wish to decrement the value of DPTR, you

must write your own code to do so.

PCON (Power Control, Addresses 87h):

The Power Control SFR is used to control the 8051's power control

modes. Certain operation modes of the 8051 allow the 8051 to go into a type of "sleep"

mode which requires much less power. These modes of operation are controlled through

PCON. Additionally, one of the bits in PCON is used to double the effective baud rate ofthe 8051's serial port.


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TMOD (Timer Mode, Addresses 89h): The Timer Mode SFR is used to configure the mode of operation of

each of the two timers. Using this SFR your program may configure each timer to be a 16-

bit timer, an 8-bit auto reload timer, a 13-bit timer, or two separate timers. Additionally,you may configure the timers to only count when an external pin is activated or to count

"events" that are indicated on an external pin.

Fig. 3.4 TMOD Register in 8051 microcontroller.

TCON (Timer Control, Addresses 88h, Bit-Addressable): The Timer Control SFR is used to configure and modify the way in

which the 8051's two timers operate. This SFR controls whether each of the two timers is

running or stopped and contains a flag to indicate that each timer has overflowed.

Additionally, some non-timer related bits are located in the TCON SFR. These bits are

used to configure the way in which the external interrupts are activated and also contain the

external interrupt flags which are set when an external interrupt has occurred.

Fig. 3.5 TCON Register in 8051 microcontroller.

TL0/TH0 (Timer 0 Low/High, Addresses 8Ah/8Ch): These two SFRs, taken together, represent timer 0. Their exact

behavior depends on how the timer is configured in the TMOD SFR; however, these timers

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

Fig. 3.6 TL0/TH0 Registers for timer control in 8051.


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Fig. 3.7 TL1/TH1 Registers for timer control in 8051.

TL1/TH1 (Timer 1 Low/High, Addresses 8Bh/8Dh): These two SFRs, taken together, represent timer 1. Their exact

behavior depends on how the timer is configured in the TMOD SFR; however, these timers

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

P1 (Port 1, Address 90h, Bit-Addressable): This is input/output port 1. Each bit of this SFR corresponds to one




SCON (Serial Control, Addresses 98h, Bit-Addressable):

The Serial Control SFR is used to configure the behavior of the

8051's on-board serial port. This SFR controls the baud rate of the serial port, whether the

serial port is activated to receive data, and also contains flags that are set when a byte is

successfully sent or received.

To use the 8051's on-board serial port, it is generally

necessary to initialize the following SFRs: SCON, TCON, and TMOD. This is

because SCON controls the serial port. However, in most cases the program will

wish to use one of the timers to establish the serial port's baud rate. In this case, it is

necessary to configure timer 1 by initializing TCON and TMOD.

Fig. 3.8 SCON Register in 8051 microcontroller.


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SBUF (Serial Control, Addresses 99h):The Serial Buffer SFR is used to send and receive data via the on-

board serial port. Any value written to SBUF will be sent out the serial port's TXD pin.

Likewise, any value which the 8051 receives via the serial port's RXD pin will be deliveredto the user program via SBUF. In other words, SBUF serves as the output port when

written to and as an input port when read from.

P2 (Port 2, Address A0h, Bit-Addressable):




whereas a value of 0 will bring it to a low level .

IE (Interrupt Enable, Addresses A8h):

The Interrupt Enable SFR is used to enable and disable specific

interrupts. The low 7 bits of the SFR are used to enable/disable the specific interrupts,

where as the highest bit is used to enable or disable ALL interrupts. Thus, if the high bit of

IE is 0 all interrupts are disabled regardless of whether an individual interrupt is enabled by

setting a lower bit.

P3 (Port 3, Address B0h, Bit-Addressable):





IP (Interrupt Priority, Addresses B8h, Bit-Addressable):

The Interrupt Priority SFR is used to specify the relative priority of

each interrupt. On the 8051, an interrupt may either be of low (0) priority or high (1)

priority. An interrupt may only interrupt interrupts of lower priority. For example, if we

configure the 8051 so that all interrupts are of low priority except the serial interrupt, the

serial interrupt will always be able to interrupt the system, even if another interrupt iscurrently executing. However, if a serial interrupt is executing no other interrupt will be


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able to interrupt the serial interrupt routine since the serial interrupt routine has the highest

priority.

Other SFRs:

The chart above is a summary of all the SFRs that exist in a standard

8051. All derivative microcontrollers of the 8051 must support these basic SFRs in order to

maintain compatibility with the underlying MSCS51 standard. A common practice when

semiconductor firms wish to develop a new 8051 derivative is to add additional SFRs to

support new functions that exist in the new chip. For example, the Dallas Semiconductor

DS80C320 is upwards compatible with the 8051. This means that any program that runs on

a standard 8051 should run without modification on the DS80C320. This means that all the

SFRs defined above also apply to the Dallas component. However, since the DS80C320

provides many new features that the standard 8051 does not, there must be some way to

control and configure these new features. This is accomplished by adding additional SFRs

to those listed here. For example, since the DS80C320 supports two serial ports (as

opposed to just one on the 8051), the SFRs SBUF2 and SCON2 have been added. In

addition to all the SFRs listed above, the DS80C320 also recognizes these two new SFRs

as valid and uses their values to determine the mode of operation of the secondary serial

port. Obviously, these new SFRs have been assigned to SFR addresses that were unused inthe original 8051. In this manner, new 8051 derivative chips may be developed which will

run existing 8051 programs.

The Program Status Word (PSW)

Every microcontroller contains flags that may be used for testing the

outcome of an instruction's execution. For example, the carry flag may be used to test the

outcome of an 8-bit addition to see if the result is greater than 255. Some microcontrollers

use a special bit to indicate whether the contents of the accumulator are zero or not (the

PIC microcontroller, for example). This flag is usually called the zero or Z flag and

conditional jump instructions that test its value can be used to branch (jump to another

location in code memory) if the accumulator is zero or if the accumulator is not zero (if Z

is set, the accumulator contains zero, if Z is clear the accumulator contains a number other

than zero). The 8051 does not have such a bit. To test the status of the accumulator the

instructions JZ rel (jump if (A) = 0) and JNZ rel (jump if (A) 0) are used. However, the

8051 contains a number of flags, in the special function register called the Program Status


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Word (PSW). These flags can be tested by conditional jumps. Before we go into the

functions of these flags, it would first be useful to understand how positive and negative

numbers are stored in binary.

Fig. 3.9 PSW Register in 8051 microcontroller.

Functions of the PSW:

Bit Symbol Address Description

PSW.7 CY D7H Carry flag

PSW.6 AC D6H Auxiliary carry flag

PSW.5 F0 D5H Flag 0

PSW.4 RS1 D4H Register bank select 1

PSW.3 RS0 D3H Register bank select 0

PSW.2 OV D2H Overflow flag

PSW.1 -- D1H ReservedPSW.0 P D0H Even parity flag

Table 3.3 Functions of PSW Register in 8051.

Carry Flag:The carry flag has two functions. Firstly, it is used as the carry-out in

8-bit addition/subtraction. For example, if the accumulator contains FDH and we add 3 tothe contents of the accumulator (ADD A, #3), the accumulator will then contain zero and

the carry flag will be set. It is also set if a subtraction causes a borrow into bit 7. In other

words, if a number is subtracted from another number smaller than it, the carry flag will be

set. For example, if A contains 3DH and R3 contains 4BH, the instruction SUBB A, R3

will result in the carry bit being set (4BH is greater than 3DH).

The carry flag is also used during Boolean operations. For

example, we could AND the contents of bit 3DH with the carry flag, the result being

placed in the carry flag - ANL C, 3DH


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Auxiliary Carry Flag (AC):

The auxiliary carry flag is set or cleared after an add instruction

( ADD A , operand or ADDC A, operand) only. The condition that result in AC being is: If a

carry was generated out of bit 3 into bit 4 of the accumulator. In other words, if there is acarry out from the lower nibble. This flag may be tested after an addition to see if the value

in the accumulator is outside the BCD range. If it is, the instruction DA A (decimal

adjust A) can be used to change the HEX code in A to BCD.

The above code adds 8 to 9, leaving 17 in the accumulator. 17 10 =

11H. This is outside the BCD range. The lower nibble is not between AH and FH, however

if you perform this addition in binary you will see there is a carry from bit 3 into bit 4.

Therefore AC will be set and the following instruction ( DA A) will change A from 11 to 17.

Flag 0:Flag 0 is a general-purpose flag available to the programmer.

Register Bank Select Bits:Bits 3 and 4 of the PSW are used for selecting the register bank.

Since there are four register banks, two bits are required for selecting a bank, as detailed

below.

Table 3.4 Bank selection in 8051.

PSW.4 PSW.3 RegisterBankAddress of RegisterBank

0 0 0 00H to 07H

0 1 1 08H to 0FH

1 0 2 10H to 17H

1 1 3 18H to 1FH


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Overflow Flag (OV):The overflow flag is bit 2 of the PSW. This flag is set after an

addition or subtraction operation if the result in the accumulator is outside the signed 8-bit

range (-128 to 127). In other words, if the addition or subtraction of two numbers results ina number less than -128 or greater than 127, the OV flag is set. When signed numbers are

added or subtracted, software can check this flag to see if the result is in the range -128 to

127.

Parity Bit:The parity bit is automatically set or cleared every machine cycle to

ensure even parity with the accumulator. The number of 1-bits in the accumulator plus the parity bit is always even. In other words, if the number of 1s in the accumulator is odd then

the parity bit is set to make the overall number of bits even. If the number of 1s in the

accumulator is even then the parity bit is cleared to make the overall number of bits even.

For example, if the accumulator holds the number 05H, this is 0000 0101 in binary => the

accumulator has an even number of 1s, therefore the parity bit is cleared. If the

accumulator holds the number F2H, this is 1111 0010 => the accumulator has an odd

number of 1s, therefore the parity bit is set to make the overall number of 1s even. Parity

bit is most often used for detecting errors in transmitted data.


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4. CIRCUIT OF THE PCB DRILLING MACHINE

Fig. 4.1 Circuit of PCB drilling machine.

4.1 Parts of the circuit:

Transformer:

The transformer is a step down transformer. The Primary side of it

has an input voltage of 220 V AC and the secondary side of the transformer gives an output

voltage of 9V AC. It steps down the voltage from 220V to 9V. Then this 9v AC signal is

converted into 9V dc by a bridge rectifier.

Regulator Circuit:

The regulator circuit has four resistances to control the voltage and

current out from the secondary side of the secondary side of the transformer. The

resistances are followed by Capacitor to store charge to maintain the voltage at the required

level (about 9v). The capacitor is followed by a regulator that controls the voltage to a 5V


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signal which is the required voltage input for the microcontroller. Before the voltage signal

reaches the microcontroller some of the current flows through a set of another 4 resistors

and to an LED that indicates the power input and then to a filter circuit (Capacitors) that

reduces any disturbances in the 5V signal.

Fig. 4.2 Regulator circuit.

The main microcontroller AT89C51 (8051):

The microcontroller 8051 acts as the main controller of the entire

circuit and hence gives signals to the Key board, LCD unit, three secondary

microcontrollers (that give signals to the driver circuit to run the three stepper motors that

control the table movement and drilling machine movement via driver circuit).


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Fig. 4.3 Schema of main 8051 microcontroller.

Fig. 4.4 Key board pin connections from main 8051 microcontroller.

The pins of the main microcontroller are used as follows: The regulated supply of 5 V is given to the VCC (40 th pin). The entire Port 0 (pin 32 (0.0) to 39 (0.7)) is connected as the data lines to the LCD

data input pins I(D0 to D7) Pins 2.5, 2.6, 2.7 are connected to the three control pins of the LCD unit, RS, R/W,

Enable respectively.

The pins 2.1, 2.2, 2.3, 2.4, are connected to the four keys on the keyboard namely

Select, Increment, Decrement, Run respectively.

The pins 18 and 19 namely XTAL2 and XTAL1 respectively are connected to

oscillator for clock control of the timers of the 8051 microcontroller.

The pin 20 is connected to the ground. The pins P1.0 and P1.1 are connected to 20 pin microcontroller for X direction

stepper motor. Similarly P1.2, P1.3 and P1.4, 1.5 are connected to the other two

secondary (20 pin) microcontrollers.


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Secondary microcontroller AT89C2051:

Fig. 4.5Secondary microcontroller.

Apart from the main microcontroller 8051 which has the main

control of the circuit, there are three more microcontrollers, each of them a 20 pin

microcontrollers (AT89C2051). They can be thought of as 20 pin 20 pin 8051s. The pin

connections discussed above shows that there are only 12 more pins free to be used in the

main microcontroller, but the three stepper motors need six pins each to give the driving

signal. This necessitates the requirement of three 20 pin microcontrollers, one for each

stepper motor. The signaling will be done to the Stepper Motor driving circuit by the mainmicrocontroller via respective secondary microcontrollers.

The Driver Circuit:

Fig. 4.6 Driver circuit for stepper motors.


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The driver circuit gets the pulse signals from the secondary

microcontrollers to run the three stepper motors that execute the table movement and the

drilling machine upward and downward movement. The driver circuit is comprised of

optocouplers, transistors SL100 and TIP 122 and LEDs.

The components of the driver circuit and their role:(i) Optocoupler:

Fig. 4.7 Optocoupler.

There are many situations where signals and data need to betransferred from one subsystem to another within a piece of electronics equipment, or from

one piece of equipment to another, without making a direct ohmic electrical connection.

Often this is because the source and destination are (or may be at times) at very different

voltage levels. In this case the microcontroller is operating from 5V DC but being used to

control a Stepper motor which is getting a 12V DC input from the SMPS. In this situation

the link between the two must be an isolated one, to protect the microcontroller from

overvoltage damage. Relays can provide this kind of isolation, but even small relays tend

to be fairly bulky compared with ICs and many of other miniature circuit components.


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Because they are electro-mechanical, relays are also not as reliable and only capable of

relatively low speed operation. Where small size, higher speed and greater reliability are

important, a much better alternative is to use an Optocoupler. These use a beam of light to

transmit the signals or data across an electrical barrier, and achieve excellent isolation.

Optocouplers typically come in a small 6-pin or 8-pin IC package,

but are essentially a combination of two distinct devices: an optical transmitter, typically a

gallium arsenide LED (light-emitting diode) and an optical receiver such as a

phototransistor. The two are separated by a transparent barrier which blocks any electrical

current flow between the two, but does allow the passage of light. The basic idea is shown

in diagram, along with the usual circuit symbol for an optocoupler. Usually the electrical

connections to the LED section are brought out to the pins on one side of the package and

those for the phototransistor to the other side, to physically separate them as much as

possible. This usually allows optocouplers to withstand voltages of anywhere between

500V and 7500V between input and output. Optocouplers are essentially digital or

switching devices, so they.re best for transferring on-off control signals. Analog signals

can be transferred by means of frequency or pulse-width modulation.

(ii) Transistors:

The voltage signal transmitted from the secondary microcontrollers

to the drivers circuit via optocoupler is boosted by two transistors, namely SL 100 and TIP

122.

Fig. 4.8 SL 100. Fig. 4.9 TIP122.


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Amplification is the process of increasing the strength of a SIGNAL.

A signal is just a general term used to refer to any particular current, voltage, or power in a

circuit. An amplifier is the device that provides amplification (the increase in current,

voltage, or power of a signal) without appreciably altering the original signal. The final

output after amplification is around 12 V.

Each of the three stepper motors used are connected to a set of four

TIP122 transistors, four SL100 transistors, four Optocouplers. So, the total number of

Optocouplers, Transistors SL100 and TIP 122 as 12 of each kind. Three are also four LEDs

for each stepper motors indicating the functioning of a particular stepper motor at a

particular instant.

(iii) Switched Mode Power Supply (SMPS):

The power required for the operation of the Stepper motors is

supplied through a Switched Mode Power Supply. Switched-mode power supply is an

electronic power supply that incorporates a switching regulator in order to be highly

efficient in the conversion of electrical power. An SMPS transfers power from a source

like the electrical power grid to a load while converting voltage and current characteristics.An SMPS is usually employed to efficiently provide a regulated output voltage, typically at

a level different from the input voltage.

Unlike a linear power supply, the pass transistor of a switching

mode supply switches very quickly (typically between 50 kHz and 1 MHz) between full-on

and full-off states, which minimizes wasted energy. Voltage regulation is provided by

varying the ratio of on to off time. In contrast, a linear power supply must dissipate the

excess voltage to regulate the output. This higher efficiency is the chief advantage of a

switch-mode power supply.
http://en.wikipedia.org/wiki/Power_supplyhttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Power_supply


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Fig. 4.10 SMPS Circuit.


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4.2 Schematic diagrams of the circuit:

Fig. 4.11 Schematic part-1, Main microcontroller.


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Fig. 4.13 Schematic part-3, Stepper motor for Y axis travel.


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Fig. 4.14 Schematic part-4, Stepper motor for X axis travel.


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5. INSTRUCTION SET TO PROGRAM 8051 MC IN

ASSEMBLY LANGUAGEThere are a number of useful instructions in assembly language that

enable us to program the 8051 microcontroller to perform the required task. The most

widely used and important of those instructions are as follows:

5.1 MOV Instructions:

MOV: MOV copies the value of operand2 into operand1. The value

of operand2 is not affected. Both operand1 and operand2 must be in Internal RAM. Noflags are affected unless the instruction is moving the value of a bit into the carry bit in

which case the carry bit is affected or unless the instruction is moving a value into the PSW

register (which contains all the program flags).

Instructions Op Code Bytes

MOV @R0,#data 0x76 2

MOV @R1,#data 0x77 2

MOV @R0,A 0xF6 1

MOV @R1,A 0xF7 1

MOV @R0,iram addr 0xA6 2

MOV @R1,iram addr 0xA7 2

MOV A,#data 0x74 2

MOV A,@R0 0xE6 1

MOV A,@R1 0xE7 1

MOV A,R0 0xE8 1

MOV A,R1 0xE9 1

MOV A,R2 0xEA 1

MOV A,R3 0xEB 1

MOV A,R4 0xEC 1

MOV A,R5 0xED 1

MOV A,R6 0xEE 1

MOV A,R7 0xEF 1


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MOV C,bit addr 0xA2 2

MOV DPTR,#data16 0x90 3

MOV R0,#data 0x78 2

MOV R1,#data 0x79 2

MOV R2,#data 0x7A 2

MOV R3,#data 0x7B 2

MOV R4,#data 0x7C 2

MOV R5,#data 0x7D 2

MOV R6,#data 0x7E 2

MOV R7,#data 0x7F 2

MOV R0,A 0xF8 1

MOV R1,A 0xF9 1

MOV R2,A 0xFA 1

MOV R3,A 0xFB 1

MOV R4,A 0xFC 1

MOV R5,A 0xFD 1

MOV R6,A 0xFE 1

MOV R7,A 0xFF 1

Table 5.1 MOV instruction.

MOVC: MOVC moves a byte from Code Memory into the Accumulator. TheCode Memory address from which the byte will be moved is calculated by summing the

value of the Accumulator with either DPTR or the Program Counter (PC). In the case of

the Program Counter, PC is first incremented by 1 before being summed with the

Accumulator.


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MOVC A,@A+DPTR 0x93 1

MOVC A,@A+PC 0x83 1Table 5.2 MOVC instruction.

MOVX: MOVX moves a byte to or from External Memory into or from theAccumulator.

If operand1 is @DPTR, the Accumulator is moved to the 16-bit External Memory

address indicated by DPTR. This instruction uses both P0 (port 0) and P2 (port 2) to output

the 16-bit address and data. If operand2 is DPTR then the byte is moved from External

Memory into the Accumulator.

If operand1 is @R0 or @R1, the Accumulator is moved to the 8-bit External Memory

address indicated by the specified Register. This instruction uses only P0 (port 0) to output

the 8-bit address and data. P2 (port 2) is not affected. If operand2 is @R0 or @R1 then the

byte is moved from External Memory into the Accumulator.


MOVX @DPTR,A 0xF0 1

MOVX @R0,A 0xF2 1

MOVX @R1,A 0xF3 1

MOVX A,@DPTR 0xE0 1

MOVX A,@R0 0xE2 1

MOVX A,@R1 0xE3 1

Table 5.3 MOVX instruction.

5.2 The Accumulator as a Shift and a Rotate Register:

As we shall see, the ability to use the accumulator as a shift register

is very useful in assembly programming. Almost all microcontrollers allow the

programmer to use some register in this fashion. The 8051 has a number of instructions,

known as the rotate instructions that rotate the bits around the accumulator.


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RR A:

This instruction is rotate right the accumulator. Its operation

is illustrated below:

Fig. 5.4 Rotate right instruction.

Each bit is shifted one location to the right, with bit 0 going to bit 7.

RL A:

This instruction is rotate right the accumulator. Its operation

is illustrated below:

Fig. 5.5 Rotate left instruction.

Each bit is shifted one location to the left, with bit 7 going to bit 0.

Rotating through the Carry:

There are two instructions that, in effect, create a 9-bit rotate

register.

RRC A:

Rotate right through the carry.

Fig. 5.6 Rotate right through carry instruction.


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Each bit is shifted one location to the right, with bit 0 going into the carry bit in

the PSW, while the carry was at goes into bit 7 (i.e. if the carry was set prior to

the execution of RRC A, then bit 7 of the accumulator will contain 1 after

execution of RRC A. Similarly, if the carry was clear prior to execution of RRCA, then bit 7 of the accumulator will contain 0 after execution of RRC A).

RLC A:

Rotate left through the carry.

Fig. 5.7 Rotate left through carry instruction.

Each bit is shifted one location to the left, with bit 7 going into the carry bit in

the PSW, while the carry goes into bit 0.

5.3 Arithmetic instructions:

ADD:ADD and ADDC both add the value operand to the value of the

Accumulator, leaving the resulting value in the Accumulator. The value operand is not

affected. ADD and ADDC function identically except that ADDC adds the value of

operand as well as the value of the Carry flag whereas ADD does not add the Carry flag to

the result.


ADD A,#data 0x24 2

ADD A,@R0 0x26 1

ADD A,@R1 0x27 1ADD A,R0 0x28 1


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ADD A,R1 0x29 1

ADD A,R2 0x2A 1

ADD A,R3 0x2B 1

ADD A,R4 0x2C 1ADD A,R5 0x2D 1

ADD A,R6 0x2E 1

ADD A,R7 0x2F 1

ADDC A,#data 0x34 2

ADDC A,@R0 0x36 1

ADDC A,@R1 0x37 1

ADDC A,R0 0x38 1

ADDC A,R1 0x39 1

ADDC A,R2 0x3A 1

ADDC A,R3 0x3B 1

ADDC A,R4 0x3C 1

ADDC A,R5 0x3D 1

ADDC A,R6 0x3E 1

ADDC A,R7 0x3F 1

Table 5.4 Add instruction.

SUB:SUBB subtract the value of operand from the value of the

Accumulator, leaving the resulting value in the Accumulator. The value operand is not

affected.


SUBB A,#data 0x94 2

SUBB A,@R0 0x96 1

SUBB A,@R1 0x97 1

SUBB A,R0 0x98 1

SUBB A,R1 0x99 1

SUBB A,R2 0x9A 1SUBB A,R3 0x9B 1


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SUBB A,R4 0x9C 1

SUBB A,R5 0x9D 1

SUBB A,R6 0x9E 1

SUBB A,R7 0x9F 1Table 5.5 Subtract instruction.

MUL:Multiples the unsigned values of the Accumulator by the unsigned

value of the B register. The least significant byte of the result is placed in the

Accumulator and the most-significant-byte is placed in the "B" register.


MUL AB 0xA4 1

Table 5.6 Multiply instruction.

DIV:Divides the unsigned value of the Accumulator by the unsigned

value of the "B" register. The resulting quotient is placed in the Accumulator and the

remainder is placed in the "B" register.


DIV AB 0x84 1

Table 5.8 Division instruction.

5.4 Increment and Decrement:

INC:

INC increments the value of register by 1. If the initial value

of register is 255 (0xFF Hex), incrementing the value will cause it to reset to 0. Note: The

Carry Flag is NOT set when the value "rolls over" from 255 to 0.


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In the case of "INC DPTR", the value two-byte unsigned integer value of DPTR is

incremented. If the initial value of DPTR is 65535 (0xFFFF Hex), incrementing the value

will cause it to reset to 0. Again, the Carry Flag is NOT set when the value of DPTR "rolls

over" from 65535 to 0.


INC A 0x04 1

INC @R0 0x06 1

INC @R1 0x07 1

INC R0 0x08 1

INC R1 0x09 1

INC R2 0x0A 1INC R3 0x0B 1

INC R4 0x0C 1

INC R5 0x0D 1

INC R6 0x0E 1

INC R7 0x0F 1

INC DPTR 0xA3 1

Table 5.9 Increment instruction.

DEC:DEC decrements the value of register by 1. If the initial value

of register is 0, decrementing the value will cause it to reset to 255 (0xFF Hex). Note: The

Carry Flag is NOT set when the value "rolls over" from 0 to 255.


DEC A 0x14 1

DEC iram addr 0x15 2

DEC @R0 0x16 1

DEC @R1 0x17 1

DEC R0 0x18 1

DEC R1 0x19 1

DEC R2 0x1A 1


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DEC R3 0x1B 1

DEC R4 0x1C 1

DEC R5 0x1D 1

DEC R6 0x1E 1DEC R7 0x1F 1

Table 5.10 Decrement instruction.

5.5 SETB, CLR and CPL:

SETB:Sets the specified bit to 1.


SETB C 0xD3 1

SETB bit address 0xD2 2

Table 5.11 Setbit instruction.

CLR:CLR clears (sets to 0) all the bit(s) of the indicated register. If the

register is a bit (including the carry bit), only the specified bit is affected. Clearing the

Accumulator sets the Accumulators value to 0.

Instructions Op Code Bytes CLR bit address 0xC2 2

CLR C 0xC3 1

CLR A 0xE4 1

Table 5.12 Clear instruction.

CPL:

CPL complements (1 is set to zero and 0 is set to 1) operand, leavingthe result in operand. If operand is a single bit then the state of the bit will be reversed.


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If operand is the Accumulator then all the bits in the Accumulator will be reversed. This

can be thought of as "Accumulator Logical Exclusive OR 255" or as "255-Accumulator."

If the operand refers to a bit of an output Port, the value that will be complemented is based

on the last value written to that bit, not the last value read from it.


CPL A 0xF4 1

CPL C 0xB3 1

CPL bit address 0xB2 2

Table 5.13 Compliment instruction.

5.6 JUMPS and CALLS:

JMP:

JMP jumps unconditionally to the address represented by the sum of

the value of DPTR and the value of the Accumulator.


JMP @A+DPTR 0x73 1

Table 5.14 Jump instruction.

SJMP:

SJMP jumps unconditionally to the address specified related

address. Related address must be within -128 or +127 bytes of the instruction that follows

the SJMP instruction.


SJMP related address 0x80 2

Table 5.15 Short Jump instruction.

LJMP:

LJMP jumps unconditionally to the specified code and address.


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LJMP code address 0x02 3

. Table 5.16 Long Jump instruction.

AJMP:

AJMP unconditionally jumps to the indicated code address. The new

value for the Program Counter is calculated by replacing the least-significant-byte of the

Program Counter with the second byte of the AJMP instruction, and replacing bits 0-2 of

the most-significant-byte of the Program Counter with 3 bits that indicate the page of the

byte following the AJMP instruction. Bits 3-7 of the most-significant-byte of the ProgramCounter remain unchanged.


AJMP page0 0x01 2

AJMP page1 0x21 2

AJMP page2 0x41 2

AJMP page3 0x61 2

AJMP page4 0x81 2

AJMP page5 0xA1 2

AJMP page6 0xC1 2

AJMP page7 0xE1 2

Table 5.17AJump instruction.

JZ:JZ branches to the address indicated by related address, if the

Accumulator contains the value 0. If the value of the Accumulator is non-zero program

execution continues with the instruction following the JZ instruction.


JZ related address 0x60 2

Table 5.18 Jump Zero instruction.


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JNZ:

JNZ will branch to the address indicated by related address if the

Accumulator contains any value except 0. If the value of the Accumulator is zero program

execution continues with the instruction following the JNZ instruction.


JNZ related address 0x70 2

Table 5.19 Jump Not Zero instruction.

JB:

JB branches to the address indicated by related address if the bitindicated by bit address is set. If the bit is not set program execution continues with the

instruction following the JB instruction.


JB bit address , related address 0x20 3

Table 5.20 Jump Bit instruction.

JNB:JNB will branch to the address indicated by related address if the

indicated bit is not set. If the bit is set program execution continues with the instruction

following the JNB instruction.


JNB bit address , related address 0x30 3

Table 5.21 Jump Not Bit instruction.

JC:

JC will branch to the address indicated by related address if the

Carry Bit is set. If the Carry Bit is not set program execution continues with the instruction

following the JC instruction.


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JC related address 0x40 2

Table 5.22 Jump Carry instruction.

JNC:

JNC branches to the address indicated by related address if the carry

bit is not set. If the carry bit is set program execution continues with the instruction

following the JNB instruction.


JNC related address 0x50 2

Table 5.23 Jump Not Carry instruction.

JBC:JBC will branch to the address indicated by related address if the bit

indicated by bit address is set. Before branching to related address the instruction willclear the indicated bit. If the bit is not set program execution continues with the instruction

following the JBC instruction.


JBC bit address , related address 0x10 3

Table 5.24 Jump Bit Carry instruction.

CJNE:CJNE compares the value of operand1 and operand2 and branches

to the indicated relative address if operand1 and operand2 are not equal. If the two

operands are equal program flow continues with the instruction following the CJNE

instruction.


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CJNE A,# data , related address 0xB4 3

CJNE @R0,# data ,related address 0xB6 3

CJNE @R1,# data ,related address 0xB7 3

CJNE R0,# data ,related address 0xB8 3

CJNE R1,# data ,related address 0xB9 3

CJNE R2,# data ,related address 0xBA 3

CJNE R3,# data ,related address 0xBB 3

CJNE R4,# data ,related address 0xBC 3CJNE R5,# data ,related address 0xBD 3

CJNE R6,# data ,related address 0xBE 3

CJNE R7,# data ,related address 0xBF 3

Table 5.25 Conditional Jump.

ACALL:LCALL calls a program subroutine. LCALL increments the program

counter by 3 (to point to the instruction following LCALL) and pushes that value onto the

stack (low byte first, high byte second). The Program Counter is then set to the 16-bit value

which follows the LCALL op code, causing program execution to continue at that address.


LCALL code address 0x12 3

Table 5.26 Acall instruction.

LCALL:

LCALL calls a program subroutine. LCALL increments the programcounter by 3 (to point to the instruction following LCALL) and pushes that value onto the


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stack (low byte first, high byte second). The Program Counter is then set to the 16-bit value

which follows the LCALL op code, causing program execution to continue at that address.

Instructions Op Code Bytes LCALL code address 0x12 3

Table 5.27 Long Call instruction.

RET:

ET is used to return from a subroutine previously called by LCALL

or ACALL. Program execution continues at the address that is calculated by popping thetopmost 2 bytes off the stack. The most-significant-byte is popped off the stack first,

followed by the least-significant-byte.


RET 0x22 1

Table 5.28 Return instruction.

Stack related Instructions:

PUSH:

PUSH "pushes" the value of the specified internal ram address ontothe stack. PUSH first increments the value of the Stack Pointer by 1, then takes the value

stored in internal ram address and stores it in Internal RAM at the location pointed to by

the incremented Stack Pointer.

Instructions Op Code Bytes Cycles Flags

PUSH internal ram address 0xC0 2 2 None

Table 5.29 Push instruction.


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POP:

POP "pops" the last value placed on the stack into the internal ram

address specified. In other words, POP will load internal ram address with the value of the

Internal RAM address pointed to by the current Stack Pointer. The stack pointer is thendecremented by 1.

Instructions Op Code Bytes Cycles Flags

POP internal ram address 0xD0 2 2 None

Table 5.30 Pop instruction.


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6. INTERFACING THE MICROCONTROLLER TO A

LCD UNIT AND A KEYBOARD

Using the Assembly language a four key keyboard and an LCD

screen are interfaced to the microcontroller 8051. The keyboard is used to select the time

for which each stepper motor is to be run to bring the work table to a required position

such that a hole can be made at the required location on the PCB. The LCD display guides

the user about which stepper motors time is the user is setting and to how much value, the

time is it being set.

6.1 Four keys on keyboard:

Select key:

Select key is used to select the data that is to be fed into the memory

of the microcontroller (Time of running for each stepper motor) or to select the

stepper motor for which the data is to be set.

Increment Key:

Increment key is used to increase the value of time of running of the

selected stepper motor.

Decrement key:

Decrement key is used to decrease the value of time of running of

the selected stepper motor.

Run key:

Run key is used to finally execute the program with the data that is

given as input and to drill a hole at a desired point on the PCB.

The input to the keyboard is always guided in the LCD display by

showing what data is being fed as input to the microcontroller at a particular time.


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7. OPERATION OF THE PCB DRILLING MACHINE

7.1 Operation steps:

1. Place the prototype of the PCB drilling machine on a table with sufficient space and

of reasonable height.

2. Give the connections of the circuit to the three stepper motors using RS 232 cables.

3. Connect the plugs of the main Circuit, SMPS and Hand drilling machine to the 220

V power supply.

4. Switch on the switch of the main circuit and observe that the LED that indicates the

power supply to the circuit is glowing. The Display screen reads as PROJECT_.

5. Press the SELECT button on the keyboard and holding it press the RUN button

wait for 5 seconds and leave the run button first and then leave the Select button.

6. Then it proceeds to a screen reading PROJECT 1 010_, the cursor at the end will

be blinking.

7. Set the first motor (controlling X direction of the table) running time to a value

above or below the 10 using the INCREMENT or DECREMENT keys and press

the select button.


be blinking.

9. Set the second motor (controlling Y direction of the table) running time to a value

above or below the 10 using the INCREMENT or DECREMENT keys and press

the select button.


be blinking.

11. Set the second motor (controlling Z direction of the drilling machine) running time

to a value above or below the 10 using the INCREMENT or DECREMENT keys

and press the select button.

12. Press SELECT button to complete the drilling project. Now the cursor stops

blinking.

13. Switch ON the 220 V supply to the SMPS. All the LEDs of the Driver Circuit will

glow.

14. On the hand drilling machine and keep it in hold position.


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15. Press start the process by pressing RUN button to start the table movement and

finally drilling of the hole is done. Then, the stepper motors operate in reverse

direction and the table reaches the initial position.

16. Repeat the process with different motor timings to drill at a different location.


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8. PROGRAM FOR MICROCONTROLLER OF

PCB DRILLING MACHINE

8.1 PROGRAM:

TICK DATA 7FH

DIGIT1 DATA 7EH

DIGIT2 DATA 7DH

DIGIT3 DATA 7CH

DIGIT4 DATA 7BH

SEC DATA 7AH

PERIOD1 DATA 79H

PERIOD2 DATA 78H

PERIOD3 DATA 77H

FLAG1 BIT 01

;--------------------------------------

M1_FOR BIT P1.0

M1_REV BIT P1.1

M2_FOR BIT P1.2

M2_REV BIT P1.3

M3_FOR BIT P1.4

M3_REV BIT P1.5

;--------------------------------------

ENTER BIT P2.0

UP_BTTN BIT P2.1

DOWN_BTTN BIT P2.2

RUN BIT P2.3

;--------------------------------------

; ***LCD CONTROL***

DAT EQU P0

RS BIT P2.5; LCD REGISTER SELECT LINE

RW BIT P2.6; LCD READ / WRITE LINEEN BIT P2.7; LCD ENABLE LINE


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;-------------------------------------------------------

ORG 00H

JMP START

;-------------------------------

ORG 01BH

JMP ISR1

;-------------------------------

ORG 030H

START:

MOV SP,#30H; POSITION STACK ABOVE BUFFER

MOV P1,#0FFH

MOV TMOD,#10H

MOV TICK,#20

MOV TH1,#0C5H

MOV TL1,#0BDH

MOV PERIOD1,#10

MOV PERIOD2,#10

MOV PERIOD3,#10

SETB UP_BTTN; INIT as input pin

SETB DOWN_BTTN; INIT as input pin

SETB ENTER; INIT as input pin

SETB RUN; INIT as input pin

SETB EA

SETB ET1

CLR TR1

CALL INIT_LCDMOV DPTR,#MSG1

CALL DISP

CHECK_KEY:

JNB RUN,CHECK

CALL DEBOUNCE

JMP CHECK_KEY

;------------------------------CHECK:


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JB ENTER,BEGIN

JMP SET_PERIOD1

;--------------------------------

BEGIN:

MOV DPTR,#MSG2

CALL DISP

CLR M1_FOR; m1 forward run

MOV SEC,PERIOD1

SETB FLAG1

SETB TR1

JB FLAG1,$

SETB M1_FOR; m1 stop


MOV SEC,PERIOD2

SETB FLAG1

SETB TR1

JB FLAG1,$

SETB M2_FOR; m2 stop


MOV SEC,PERIOD3

SETB FLAG1

SETB TR1

JB FLAG1,$

SETB M3_FOR; m3 stop;-------------------------------------------------


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CLR M3_REV; m3 reverse run

MOV SEC,PERIOD3

SETB FLAG1

SETB TR1

JB FLAG1,$

SETB M3_REV; m3 stop


MOV SEC,PERIOD1

SETB FLAG1

SETB TR1

JB FLAG1,$

SETB M1_REV; stop m1


MOV SEC,PERIOD2

SETB FLAG1

SETB TR1

JB FLAG1,$

SETB M2_REV; m2 stop

JMP CHECK_KEY

;-------------------------------------------

;-------

;-------------------------------------------

SET_PERIOD1:JNB ENTER,SET_PERIOD1


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CALL DEBOUNCE

MOV B,#1

CALL PLACECUR2

CALL PRTLCD4

DB 'PERIOD-1>',0

WAIT_PER1:

JNB UP_BTTN,UP_PER1

JNB DOWN_BTTN,DOWN_PER1

JNB ENTER,DURATION_PER1

MOV SEC,PERIOD1

CALL UPDATE1

JMP WAIT_PER1

UP_PER1:

JNB UP_BTTN,UP_PER1

INC PERIOD1

JMP WAIT_PER1

DOWN_PER1:


DEC PERIOD1

JMP WAIT_PER1

DURATION_PER1:


CALL DEBOUNCE

MOV SEC,PERIOD1

; JMP BEGIN

;---------------------------------------;---------------------------------------

SET_PERIOD2:

JNB ENTER,SET_PERIOD2

MOV B,#1

CALL PLACECUR2

CALL PRTLCD4

DB 'PERIOD-2>',0WAIT_PER2:


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JNB UP_BTTN,UP_PER2



MOV SEC,PERIOD2

CALL UPDATE1

JMP WAIT_PER2

UP_PER2:

JNB UP_BTTN,UP_PER2

INC PERIOD2

JMP WAIT_PER2

DOWN_PER2:


DEC PERIOD2

JMP WAIT_PER2

DURATION_PER2:


CALL DEBOUNCE

MOV SEC,PERIOD2

;---------------------------------------

SET_PERIOD3:

JNB ENTER,SET_PERIOD3

MOV B,#1

CALL PLACECUR2

CALL PRTLCD4

DB 'PERIOD-3>',0

WAIT_PER3:JNB UP_BTTN,UP_PER3



MOV SEC,PERIOD3

CALL UPDATE1

JMP WAIT_PER3

UP_PER3:JNB UP_BTTN,UP_PER3


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INC PERIOD3

JMP WAIT_PER3

DOWN_PER3:


DEC PERIOD3

JMP WAIT_PER3

DURATION_PER3:


CALL DEBOUNCE

MOV SEC,PERIOD3

JMP CHECK_KEY

;-------------------------------

;----------SUBROUTINES

;-------------------------------

; LOOKUP TABLE USED BY WRITE_BCD.

;-------------------------------

UPDATE1:

MOV A,SEC

MOV B,#100

DIV AB

MOV DIGIT1,A ;100S INDIGIT1

MOV A,B

MOV B,#10

DIV AB

MOV DIGIT2,A ;10S in digit2

MOV DIGIT3,B ;1s in digit3

MOV B,#10

CALL PLACECUR2

MOV A,DIGIT1

CALL FIND

MOV B,#11CALL PLACECUR2


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MOV A,DIGIT2

CALL FIND

MOV B,#12

CALL PLACECUR2

MOV A,DIGIT3

CALL FIND

RET

;-------

Cnc Automatoc Drilling Machine

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