01BEDCSemiconductorsDiodesandDevicesUnivMalasiyaLesson01B backup.pdf

7/30/2019 01BEDCSemiconductorsDiodesandDevicesUnivMalasiyaLesson01B backup.pdf

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ME2255- ELECTRONICS

& MICROPROCESSOR

KARTHIC.K AP/ECE

SSM COLLEGE OF ENGINEERING
http://www.foxitsoftware.com/shopping


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UNIT 1

SEMICONDUCTORS &DIODES


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ELECTRICAL CONDUCTIVITY In order of conductivity: superconductors,

conduc tors, semiconductors, insulators conductors: material capable of carrying

electric current, i.e. material which hasmobile charge carriers (e.g. electrons,ions,..) e.g. metals,

liquids with ions (water, molten ioniccompounds), plasma insulators: materials with no or very few free

charge carriers; e.g. quartz, most covalentand ionic solids, plastics

semiconductors: materials with conductivitybetween that of conductors and insulators;e.g. germanium Ge, silicon Si, GaAs, GaP,InP

superconductors: certain materials havezero resistivity at very low temperature.


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ENERGY BANDS IN SOLIDS: In solid materials, electron energy levels

form bands of allowed energies, separatedby forbidden bands

valence band = outermost (highest) bandfilled with electrons (filled = all statesoccupied)

conduction band = next highest band tovalence band (empty or partly filled) gap = energy difference between

valence and conduction bands, = width ofthe forbidden band

Note:

electrons in a completely filled band cannotmove, since all states occupied (Pauli

principle); only way to move would be tojump into next higher band - needs energy; electrons in partly filled band can move,

since there a re free states to move to.


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CLASSIFICATION OF SOLIDS INTO THREE TYPES,ACCORDING TO THEIR BAND STRUCTURE:

insulators: gap = forbiddenregion between highest filledband (valence band) andlowest empty or partly filled

band (conduction band) is verywide, about 3 to 6 eV;

semiconductors: gap is small -about 0.1 to 1 eV;

conductors: valence bandonly partially filled, or (if it isfilled), the next allowed emptyband overlaps with it


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Band structure and conductivity


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Band structure and conductivity


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INTRINSIC SEMICONDUCTORS

semiconductor = material for whichgap between valence band andconduction band is small;

(gap width in Si is 1.1 eV, in Ge 0.7eV).

at T = 0, there are no electrons in the

conduction band, and thesemiconductor does not conduct(lack of free charge carriers);

at T > 0, some fraction of electronshave sufficient thermal kinetic energyto overcome the gap and jump to theconduction band;

fraction rises with temperature;e.g. at 20o C (293 K),

Si has 0.9x1010 conduction electronsper cubic centimeter; at 50o C (323 K)there are 7.4x1010 .


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Intrinsic semiconductor

electrons moving to conduction bandleave hole (covalent bond withmissing elec tron) behind;

under influence of applied electricfield, neighboring electrons can jump

into the hole, thus creating a newhole, etc. holes can move underthe influence of an applied electricfield, just like electrons; bothcontribute to conduction.

in pure Si and Ge, there are equallymany holes (p-type charge carriers)

as there are conduction electrons (n-type charge carriers);

pure semiconductors also calledintrinsic semiconductors.


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N-Type material

d ono r (n- typ e) im p urities: dopant with 5 valence electrons (e.g.

P, As, Sb) 4 electrons used for covalent bonds

with surrounding Si atoms, one electronleft over;

left over electron is only looselybound only small amount of energyneeded to lift it into conduction band(0.05 eV in Si)

n -t yp e sem ic ond uc to r, hasconduction electrons, no holes (apartfrom the few intrinsic holes)

example: doping frac tionof 10-8 Sb in Si

yields about 5x1016 conductionelectrons per cubic centimeter atroom temperature, i.e. gain of 5x106

over intrinsic Si.


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N-TYPE MATERIAL


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P-TYPE MATERIAL

ac c ep to r (p - typ e ) imp urities: dopant with 3 valence electrons (e.g. B,

Al, Ga, In) only 3 of the 4 covalentbonds filled vacancy in the fourthcovalent bond hole

p -t yp e sem ic ond uc to r, has mobile

holes, very few mobile electrons (onlythe intrinsic ones).

advantages of dopedsemiconductors:

cantune conductivity by choice ofdoping fraction

can choose majority carrier (electronor hole)

can vary doping frac tion and/ormajority carrier within piece ofsemiconductor

can make p-n junctions (diodes) andtransistors


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P-TYPE MATERIAL


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DIODES

p-n JUNCTION: p-n junction = semiconductor in which

impurity changes abruptly from p-type to n-type ;

diffusion = movement due to difference inconcentration, from higher to lowerconcentration;

in absence of electric field across thejunction, holes diffuse towards and acrossboundary into n-type and capture electrons;

electrons diffuse across boundary, fall intoholes (rec om b ina t ion o f m a jor ity c a rrie rs);

formation of adepletion region (=region without free charge carriers)

around the boundary; charged ions are left behind (cannot move):

negative ions left on p-side net negativecharge on p-side of the junction;

positive ions left on n-side net positivecharge on n-side of the junction

electric field across junction which preventsfurther diffusion


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Diode


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PN Junction


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DIODE

diode = biased p-n junction, i.e. p-njunction with voltage applied across it

forward biased: p-side more positivethan n-side;

reverse biased: n-side more positivethan p-side;

forward biased diode: the direction of the elec tric field is from

p-side towards n-side p-type charge carriers (positive

holes) in p-side are pushed towardsand across the p-n boundary,

n-type carriers (negative electrons) inn-side are pushed towards and acrossn-p boundary

currentflows across p-n boundary


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DIODE


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FORWARD BIASED


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REVERSE BIASED reverse biased diode: applied voltage makes n-side more

positive than p-side electric field direc tion is from n-side towards p-side pushes charge carriers away from the p-nboundary depletion

region widens, and no current flows

diode only conducts when positive voltage applied to p-side and negative voltage to n-side

diodes used in rectifiers, to convert ac voltage to


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REVERSE BIASED


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ZENER DIODES


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ZENER DIODES The simplest of all voltageregulators is the zener diodevoltage regulator.

A zener diode is a special

diode that is optimized foroperation in the breakdownregion.


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ZENER DIODE CIRCUIT

The zener diode is typically connected

reverse biased, in parallel with the

load.

Resistor Rs limits current to zener.


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Simplest rectifier

Simplest rectifier resistiveload


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Simplest rectifier


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VOLTAGE REGULATION

A voltage regulator circuitautomatically maintains the outputvoltage of a power supply constant,regardless of

a change in the load

- a change in the source voltage


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SERIES VOLTAGE REGULATOR


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SHUNT VOLTAGE REGULATOR


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Unit-2

TRANSISTORS ANDAMPLIFIERS


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TRANSISTORS

(bipolar) transistor = combinationof two diodes that share middleportion, called base of transistor;other two sections: emitter'' andcollector;

usually, base is very thin and lightlydoped. two kinds of bipolar transistors: pnp

and npn transistors pnp means emitter is p-type,

base is n-type, and collec tor is p-type material;

in normal operation of pnptransistor, apply positive voltage toemitter, negative voltage tocollector;


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TRANSISTORS


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OPERATION OF PNP TRANSISTOR

if emitter-base junction is forward biased,holes flow from battery into emitter, moveinto base;

some holes annihilate with electrons in n-type base, but base thin and lightly dopedmost holes make it through base intocollector,

holes move through collec tor into negativeterminal of battery; i.e. collector currentflows whose size depends on how manyholes have been captured by electrons inthe base;

this depends on the number of n-typecarriers in the base which can becontrolled by the size of the current (thebase current) that is allowed to flow fromthe base to the emitter; the base current isusually very small; small changes in thebase current can cause a big difference inthe collector current;


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PNP TRANSISTOR


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PNP TRANSISTOR

if emitter-base junction is forward biased,holes flow from battery into emitter, moveinto base;

some holes annihilate with electrons in n-type base, but base thin and lightly dopedmost holes make it through base intocollector,

holes move through collec tor into negativeterminal of battery; i.e. collector currentflows whose size depends on how manyholes have been captured by electrons inthe base;

this depends on the number of n-typecarriers in the base which can becontrolled by the size of the current (thebase current) that is allowed to flow fromthe base to the emitter; the base current isusually very small; small changes in thebase current can cause a big difference inthe collector current;


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PNP TRANSISTOR

Operation as amplifier

Transistor acts as ampli fier of base

current, since small changes in basecurrent cause big changes in

collector current.transistor as switch: if voltage applied tobase is such that emitter-base junction isreverse-biased, no current flows throughtransistor -- transistor is offtherefore, a transistor can be used as a

voltage-controlled switch; computers usetransistors in this way.


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Field-effect Transistor (FET)

In a pnp FET, current flowingthrough a thin channel of n-type material is controlled bythe voltage (electric field)

applied to two pieces of p-type material on either sideof the channel (currentdepends on electric field).

Many different kinds of FETs

FETs are the kind of transistormost commonly used incomputers.


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Field-effect Transistor (FET)


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SCRs and Their Characteristics

The silicon controlled rectifier (SCR) isa four-layer pnpn device with threeleads, the anode, gate, and cathode.

An SCR will not conduct until theforward breakover voltage is

reached, even though its anode-cathode is forward-biased.

The gate current in an SCR controlsthe forward breakover voltage.

Once an SCR turns on, the gate losesall control.

The only way to turn an SCR off is toreduce the anode current below theholding current,


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A silicon controlled rectifier(SCR) is a four-layer pnpndevice.

Fig. 32-3 (a) shows thebasic construction of anSCR, and Fig. 32-3 (b)shows the schematicsymbol.

The SCR has three externalleads: the anode,cathode, and gate.


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Triacs

A triac is a bi-directionalthyristor used to control thepower in ac circuits.

A triac has two leadsdesignated MT1, and MT2 or A1and A2.

A triac has a gate lead which isused to control its conduction.

A triac is equivalent to two SCRsin parallel.


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Triacs


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TRIACS


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Unijunction Transistors

The unijunction transistor(UJ T) is athree-terminal semiconductor devicethat has only one p-n junction.

The unijunction transistor (UJ T) has twobase leads, B1 and B2 and an emitter

(E) lead. The interbase resistance, RBB of a UJ T is

the resistance of its n-type silicon bar.

The ratio RB1/(RB1 + RB2) is called theintrinsic standoff ratio, designated .

UJ Ts are used in conjunction with SCRsand Triacs to control their conductionangle.


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Unijunction Transistors operation

The unijunction transistor(UJ T) is athree-terminal semiconductor devicethat has only one p-n junction.

The unijunction transistor (UJ T) has twobase leads, B1 and B2 and an emitter

(E) lead. The interbase resistance, RBB of a UJ T is

the resistance of its n-type silicon bar.

The ratio RB1/(RB1 + RB2) is called theintrinsic standoff ratio, designated .

UJ Ts are used in conjunction with SCRsand Triacs to control their conductionangle.


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Unijunction Transistors symbol


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UNIJUNCTION TRANSISTORS

CHARACTERISTICS Negative resistance is illustrated

in the emitter characteristiccurve shown in Fig. 32-12.

Once VP is reached, theemitter voltage, VE, decreasesas IE increases.


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CHARACTERISTICS


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CIRCUIT DIAGRAM


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Application

Fig. 32-13 shows how a UJ Tcan be used as arelaxation oscillator.

Because the voltagewaveform, VB1 is a sharppulse of short duration, it isthe ideal gate triggering

source for either an SCR ortriac.


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Unit-3

DIGITAL ELECTRONICS


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DIGITAL

Digital system is known asany

electronic system that

handle andprocess electrical signals in

the form of

0s and 1s, no more analogsignals

used here.


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Logic gates

A logic gate is an elementarybuilding block

of a digital circuit. logic gate is

an electroniccircuit can perform specific

processing on the input

signals.

Logic gates have two inputsand one output.


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Basic logic gates

A Y

0 1

1 0


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BASIC LOGIC GATES

A B Y

0 0 0

0 1 0

1 0 0


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EX-OR GATE

A B Y

0 0 0

0 1 1

1 0 1

1 1 0


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A B Y

0 0 1

0 1 0

1 0 0

1 1 0


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NAND GATE

A B Y

0 0 1

0 1 1

1 0 1

1 1 0


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Boolean algebra basics

logic operations symbols:

OR: (+) Plus symbol, e.g.:Y=A+B

AND: (.) Dot symbol, e.g.:Y=A.B

NOT: () a bar is drawn abovethe letter, e.g.: Y= .

XOR: ( ) Plus symbol

surrounded with a circle, e.g.:Y=A B.


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. Commutative

e.g. A+B = B+A, A.B = B.A.

2. Associative

e.g. A+(B+C) = (A+B)+C =A+B+C,

(B.C) = (A.B).C = A.B.C.

3.Distributivee.g. A (B+C) = AB + AC.


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A+1= 1.

A+0= A.

A.0= 0.

A.1= A. A+A= A.

A+= 1.

A.A= A.

A. = 0. A+AB= A.

A+ B= A+B.

A=A.

-De Morgan's law:


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THE 8085 MICROPROCESSORARCHITECTURE & INTERFACING


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The 8085 and Its Buses The 8085 is an 8-bit general purpose

microprocessor that can address64K Byte ofmemory.

It has40 pinsand uses +5V for power. It can

run at a maximum frequency of 3 MHz. The pins on the chip can be grouped into 6

groups: Address Bus.

Data Bus.

Control and StatusSignals. Power supply and frequency.

Externally Initiated Signals.

Serial I/O ports.


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The Address and Data Busses

The address bus has 8 signal linesA8 A15which are unidirectional.

The other 8 address bits are multiplexed

(time shared) with the 8 data bits. So, the bits AD0 AD7 are bi-directional andserve asA0 A7and D0 D7 at the same time.

During the execution of the instruction, these lines carrythe address bits during the early part, then during thelate parts of the execution, they carry the 8 data bits.

In order to separate the address from the data,we can use a latch to save the value before thefunction of the bits changes


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The Control and Status Signals

There are 4 main control and status signals. These are:

ALE: Address Latch Enable. This signal is a pulse that become 1when the AD0 AD7 lines have an address on them. Itbecomes 0 after that. This signal can be used to enable a

latch to save the address bits from the AD lines. RD: Read. Active low.

WR: Write. Active low.

IO/M: This signal specifies whether the operation is a memoryoperation (IO/M=0) or an I/O operation (IO/M=1).

S1 and S0 : Status signals to specify the kind of operation beingperformed .Usually un-used in small systems.


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Frequency Control Signals

There are 3 important pins in thefrequency control group.

X0 and X1 are the inputsfrom thecrystal or clock generating circuit.

The frequency is internally dividedby 2.

So, to run the microprocessor at 3MHz, a clock running at 6 MHzshould be connec ted to the X0and X1 pins.

CLK (OUT): An output clock pin todrive the c lock of the rest of thesystem


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Microprocessor Communication

and Bus Timing To understand how the

microprocessor operatesand uses these different

signals, we should studythe process ofcommunication betweenthe microprocessor and

memory during a memoryread or write operation.


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Steps For Fetching an Instruction

Lets assume that we are trying to fetch theinstruction at memory location 2005. Thatmeans that the program counter is nowset to that value. The following is the sequence of operations:

The program counter places the addressvalue on the address bus and the controller

issues a RD signal. The memorys address decoder gets the

value and determines which memorylocation is being accessed.

The value in the memory location is placedon the data bus.

The value on the data bus is read into theinstruction dec oder inside themicroproc essor.

After decoding the instruction, the controlunit issues the proper control signals toperform the operation.


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Timing Signals For Fetching an

Instruction AtT1 , the high order 8 address bits(20H)are placed on the address linesA8 A15and the low order bitsare placed on AD7AD0. The ALE signal goes high to indicatethat AD0 AD8 are carrying an address. Atexactly the same time, the IO/M signal goeslow to indicate a memory operation.

At the beginning of theT2 cycle, the loworder 8 address bitsare removed from AD7AD0 and the controller sends the Read (RD)signal to the memory. The signal remainslow (ac tive) for two c lock periodsto allowfor slow devices. During T2 , memory placesthe data from the memory location on thelinesAD7 AD0 .

DuringT3 the RD signal is Disabled (goes

high). This turns off the output Tri-statebuffers in the memory. That makes the AD7AD0 lines go to high impedence mode.


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Demultiplexing AD7-AD0

From the above description, it becomesobvious that the AD7 AD0 lines areserving a dual purpose and that theyneed to be demultiplexed to get all theinformation.

The high order bitsof the address remainon the bus for three clock periods.

However, the low order bitsremain foronly one c lock period and they wouldbe lost if they are not saved externally.Also, notice that the low order bitsof theaddressdisappearwhen they areneeded most.

To make sure we have the entire addressfor the full three clock cycles, we will use

an external latch to save the value ofAD7 AD0 when it is carrying the addressbits. We use the ALE signal to enable thislatch.


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Demultiplexing AD7-AD0

Given that ALE operates as a pulseduring T1, we will be able to latch theaddress. Then when ALE goes low, the

address is saved and the AD7 AD0 linescan be used for their purpose as the bi-direc tional data lines.

A15-A8

LatchAD7-AD0

D7- D0

A7

- A0

8085

ALE


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Cycles and States

T- State: One subdivision of anoperation. A T-state lasts for one clockperiod.

An instructions execution length isusually measured in a number of T-states. (clock cycles).

Machine Cycle: The time required tocomplete one operation of accessingmemory, I/O, or acknowledging anexternal request.

This cycle may consist of 3 to 6 T-states.

Instruction Cycle: The time required tocomplete the execution of aninstruction.

In the 8085, an instruction cycle mayconsist of 1 to 6 machine cycles.


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Generating Control Signals The 8085 generates a single RD signal.

However, the signal needs to be usedwith both memory and I/O. So, it mustbe combined with the IO/M signal togenerate different control signals for thememory and I/O.

Keeping in mind the operation of the IO/Msignal we can use the following c ircuitry togenerate the right set of signals:


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The ALU

In addition to the arithmetic &logic circuits, the ALU includesthe accumulator, which is partof every arithmetic & logic

operation.

Also, the ALU includes atemporary register used forholding data temporarily during

the execution of the operation.This temporary register is notaccessible by the programmer.


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The Flags register

S-sign flag The sign flag is set if bit D7 of the

accumulator is set after an arithmetic orlogic operation.

Z-zero flag Set if the result of the ALU operation is 0.

Otherwise is reset. This flag is affec ted by

operations on the accumulator as wellas other registers. (DC R B).

AC-Auxiliary Carry This flag is set when a carry is generated

from bit D3 and passed to D4 . This flagis used only internally for BCDoperations. (Sec tion 10.5 describes BCDaddition including the DAA instruction).

P-Parity flag

After an ALU operation if the result hasan even # of 1s the p-flag is set.Otherwise it is cleared. So, the flag canbe used to indicate even parity.

CY-carry flag Discussed earlier


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The 8085 machine cycles

The 8085 executes several typesof instructions with eachrequiring a different number ofoperations of different types.However, the operations can

be grouped into a small set. The three main types are:

Memory Read and Write. I/O Read and Write. Request Acknowledge.

These can be further dividedinto various operations(machine cycles).


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Opcode Fetch Machine Cycle

Opcode fetch cycle. In this cycle, the microprocessor brings

in the instructions Opcode frommemory.

To differentiate this machine cycle fromthe very similar memory read cycle,the control & status signals are set asfollows:

IO/M=0, s0 and s1 are both 1.

This machine cycle has four T-states. The 8085 uses the first 3 T-states to fetch

the opcode.

T4 is used to decode and execute it.

It is also possible for an instruction tohave 6 T-states in an opcode fetchmachine cycle


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Memory Read Machine Cycle

The memory read machinecycle is exactly the sameas the opcode fetch

except: It only has 3 T-states

The s0 signal is set to 0instead.


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The Memory Read Machine Cycle

To understand the memory readmachine cycle, lets study theexecution of the following instruction:

MVI A, 32

In memory, this instruction looks like: The first byte 3EH represents the

opcode for loading a byte into theaccumulator (MVI A), the second byteis the data to be loaded.

The 8085 needs to read these twobytes from memory before it canexecute the instruction. Therefore, itwill need at least two machine cycles.

The first machine cycle is the opcode fetchdiscussed earlier.

The second machine cycle is the MemoryRead C ycle.

Figure 3.10 page 83.


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The Memory Write Operation

In a memory write operation:

The 8085 places the address(2065H) on the address bus

Identifies the operation as a

memory write (IO/M=0, s1=0, s0=1). Places the contents of the

accumulator on the data bus andasserts the signal WR.

During the last T-state, the contentsof the data bus are saved into thememory location.


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Memory interfacing

There needs to be a lot ofinteraction between themicroprocessor and thememory for the exchange ofinformation during program

execution. Memory has its requirements on

control signals and their timing. The microprocessor has its

requirements as well.

The interfacing operation issimply the matching of theserequirements.


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Memory structure & its

requirements

The process of interfac ing theabove two chips is the same. However, the ROM does not have

a WR signal.

AddressLines

Data Lines

CS

RDOutput Buffer

RAMWRInput Buffer

Data Lines

AddressLines

DateLines

CS

RDOutput Buffer


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Interfacing Memory

Accessing memory can besummarized into the following threesteps:

Select the chip.

Identify the memory register.

Enable the appropriate buffer.

Translating this to microprocessordomain:

The microprocessor places a 16-bitaddresson the address bus.

Part of the address bus will select thechip and the other part will go throughthe address decoder to select the

register. The signals IO/M and RD combinedindicate that a memory read operationis in progress. The MEMR signal can beused to enable the RD line on thememory chip.


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Address decoding

The result of address decodingis the identification of a registerfor a given address.

A large part of the address bus is

usually connected directly to theaddress inputs of the memory chip.

This portion is decoded internallywithin the chip.

What concerns us is the other part

that must be decoded externallyto select the chip.

This can be done either using logicgates or a decoder.


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Interfacing concepts Interfacing concepts

together

A15-A8

LatchAD7-AD0

D7- D0

A7

- A0

8085

ALE

IO/MRDWR

1K ByteMemory

Chip

WRRD

CS

A9

- A0

A15

- A10

Chip SelectionCircuit


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Interfacing the 8155

The 8155 is a special chipdesigned to work with the8085 to demonstrate theinterfacing of the 8085.

the 8155 has256 bytes ofRAM, 2 programmable I/Oportsand a timer.

It is usually used in systems

designed for use inuniversity labs.


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Traffic light controller


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Stepper motor controller

In the PM type stepper motor, a permanentmagnet is used for rotor and coils are put onstator. The stepper motor model which has 4-poles is shown in the figure on the left. In case ofthis motor, step angle of the rotor is 90 degrees.

As for four poles, the top and the bottom andeither side are a pair. coil, coil and coil, coil

correspond respectively. For example, coil andcoil are put to the upper and lower pole. coiland coil are rolled up for the direc tion of thepole to become opposite when applying anelectric current to the coil and applying anelectric current to the coil. It is similar aboutand , too.The turn of the motor is controlled by theelectric current which pours into , , and . The

rotor rotational speed and the direc tion of theturn can be controlled by this control.


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STEPPER MOTOR CONTROLLER


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STEPPER MOTOR CONTROLLER


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TEMPERATURE CONTROLLER

To accurately control process temperaturewithout extensive operator involvement, atemperature control system relies upon acontroller, which accepts a temperature sensorsuch as a thermocouple or RTD as input. Itcompares the actual temperature to thedesired control temperature, or setpoint, andprovides an output to a control element. The

controller is one part of the entire controlsystem, and the whole system should beanalyzed in selec ting the proper controller. Thefollowing items should be considered whenselecting a controller:

Type of input sensor (thermocouple, RTD) andtemperature range

Type of output required (electromechanical

relay, SSR, analog output) Control algorithm needed (on/off, proportional,PID)

Number and type of outputs (heat, cool, alarm,limit)


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There are three basic types of controllers: on-off, proportional and PID. Depending upon thesystem to be controlled, the operator will beable to use one type or another to control theprocess.

On/Off ControlAn on-off controller is the simplest form of

temperature control device. The output fromthe device is either on or off, with no middlestate. An on-off controller will switch the outputonly when the temperature c rosses the setpoint.For heating control, the output is on when thetemperature is below the setpoint, and offabove setpoint. Since the temperature crossesthe setpoint to change the output state, theprocess temperature will be cycling continually,

going from below setpoint to above, and backbelow. In cases where this cycling occursrapidly, and to prevent damage to contactorsand valves, an on-off differential, or hysteresis,is added to the controller operations.


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This differential requires that thetemperature exceed setpoint by a certainamount before the output will turn off oron again. On-off differential prevents theoutput from chattering or making fast,continual switches if the cycling aboveand below the setpoint occurs very

rapidly. On-off control is usually usedwhere a precise control is not necessary,in systems which cannot handle havingthe energy turned on and off frequently,where the mass of the system is so greatthat temperatures change extremelyslowly, or for a temperature alarm. Onespecial type of on-off control used for

alarm is a limit controller. This controlleruses a latching relay, which must bemanually reset, and is used to shut down aprocess when a certain temperature isreached


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T H A N K Y O U

01BEDCSemiconductorsDiodesandDevicesUnivMalasiyaLesson01B backup.pdf

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