Electronics Module by Sam Kinyera OBWOYA - HTML preview

were 32 bits long and most arithmetic instructions supported 32-bit arithmetic,

and 24-bit in that the address bus was 24 bits long.

v A 16-bit integer can store 216 (or 65536) unique values. In an unsigned re-

presentation, these values are the integers between 0 and 65535; using two’a

component, possible values range from −32768 to 32767.

Activity 6.4.3 32-Bit Systems

The key learning points here are that:

(i) In computer architecture, 32-bit integers, memory addresses, or other data

units are those that are at most 32 bits (4 octets) wide. Also, 32-bit CPU and

ALU architecture are those that are based on registers, address buses, or data

buses of that size. 32-bit is also a term given to a generation of computers in

which 32-bit processors were the norm.

(ii) The range of integer values that can be stored in 32 bits is 0 through

4,294,967,295 or −2,147,483,648 through 2,147,483,647 using two’s comple-

ment encoding. Hence, a processor with 32-bit memory addresses can directly

access 4 gigabytes of byte-addressable memory memory.

Activity 6.4.4 Kibibyte vs Kilobyte

In this activity we will differentiate between kibibyte and kilobyte. First, we define the kibibyte. That is,

A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, established by the International Electrtechnical Commission in 2000.

Its symbol is KiB.

1 kibibyte = 210 bytes = 1 024 byte

You should note that:

The kibibyte is closely related to the kilobyte, which can be used either as a

synonym for kibibyte or to refer to 10³ bytes = 1,000 bytes, whereby

1 kilobyte = 103 = 1000 byte

Thus, the term kibibyte has evolved to refer exclusively to 1,024 bytes.

African Virtual University

You should note that:

If one expects power-of-two values to refer to capacity, and manufacturers use power-

of-ten values, the difference could be substantial.

(i) With a kilobyte (1024 versus 1000), the difference is 2.4%.

(ii) With megabyte (1024² or 1,048,576, versus 1,000,000 - a difference of 4.9%.

(iii) With “gigabytes”, if one uses 1024³, the size of a drive would be expected to

be 1,073,741,824 bytes per gigabyte versus a mere 1,000,000,000 - a difference

of 7.4%.

This should tell you that, confusion can be compounded by the use of both 1,024 and

1,000 in a single definition.

The quoted capacity of 3½ inch HD floppy disks is 1.44 MB, where MB

stands for 1000 times 1024 bytes. The total capacity is thus 1474560 bytes,

or approximately 1.41 MiB.

Example

The above relation can be shown as follows:

1.44 MB = 1.44 × 1000 × 1024 = 0 bytes

Divide this by 1,048,576, i.e.

1.44 × 1000 × 1024

= 1.40625 MiB

1,048,576

Thus, 1.44 MB floppy disks can store 1474560 bytes of data when MB means 1000

times 1024 bytes.

Self Evaluation 6

1. Explain the meaning of the term program in computing.

2. Find the number of input lines that can be coded to 32 bit word

3. Explain what is meant by an instruction and register in computing.

4. Express 3.7 MB in (i) bytes (ii) MiB

African Virtual University

Solution to Self Evaluation 1

1. (a) n = 6.1144 ×1017

i

m−3

(b) 0.01859 s/m

2. This is because, by addition of donor impurity, the number of electrons avail-

able for conduction purposes becomes more than the number of holes available

intrinsically. But the total charge of the semiconductor does not change because

the donor impurity brings in as much negative charge (by way of electrons) as

positive charge (by way of protons in its nucleus).

3. Barrier voltage depends on doping density, electronic charge and temperature.

For a given junction, the first two factors are constant, thus making depending

on temperature. With increase in temperature, more minority charge carriers

are reduced, leading to their increased drift across the junction. As a result,

equilibrium occurs at lower barrier potential. It is found that both for Ge and Si,

decreases by about 2mV / ºC.

Solution to Self Evaluation 2

1. Physical features BJT are that

- The base is lightly doped, with high resistivity material.

- The collector surrounds the emitter region, making it almost impossible for the

electrons injected into the base region to escape being collected, thus making

the resulting value of α very close to unity, and so, giving the transistor a large

β. A cross section view of a BJT indicates that the collector–base junction has

a much larger area than the emitter–base junction.

- The bipolar junction transistor, unlike other transistors, is not a symmetrical

device. This means that interchanging the collector and the emitter makes the

transistor leave the forward active mode and start to operate in reverse mode.

Because the transistor’s internal structure is usually optimized to forward-mode

operation, interchanging the collector and the emitter makes the values of α

and β in reverse operation much smaller than those found in forward operation;

often the α of the reverse mode is lower than 0.5. The lack of symmetry is

primarily due to the doping ratios of the emitter and the collector. The emitter

is heavily doped, while the collector is lightly doped, allowing a large reverse

bias voltage to be applied before the collector–base junction breaks down.

The collector–base junction is reverse biased in normal operation.

- The reason the emitter is heavily doped is to increase the emitter injection

efficiency: the ratio of carriers injected by the emitter to those injected by the

base.

African Virtual University

- For high current gain, most of the carriers injected into the emitter–base

junction must come from the emitter.

Small changes in the voltage applied across the base–emitter terminals causes the

current that flows between the emitter and the collector to change significantly. This effect can be used to amplify the input voltage or current. BJTs can be thought of

as voltage-controlled current sources, but are more simply characterized as current-

controlled current sources, or current amplifiers, due to the low impedance at the

base.

NPN is one of the two types of bipolar transistors, in which the letters “N” and “P”

refer to the majority charge carriers inside the different regions of the transistor. Most

bipolar transistors used today are NPN, because electron mobilty is higher than hole

mobility in semiconductors, allowing greater currents and faster operation.

NPN transistors consist of a layer of P-doped semiconductor (the “base”) between

two N-doped layers. A small current entering the base in common-emitter mode is

amplified in the collector output.

The arrow in the NPN transistor symbol is on the emitter leg and points in the direction

of the conventional current flow when the device is in forward active mode.

A convenient mnemonic device for identifying the symbol for the NPN transistor

and, by elimination, the PNP transistor is “NPN is Not Pointed iN.”

Solution to Self Evaluation 3

1. A specific op-amp may be chosen for its: open loop gain, bandwidth, noise

performance, input impedance, power consumption, or a compromise

between any of these factors.

2. 84.42 mV

3 The output voltage is

⎛ 330

330 ⎞

V = −

V +

V

(

+ 33V )

0

1

2

2

⎝⎜ 33

10

⎠⎟ = − 10V1

= − 1

⎡ 0 50sin 1000

⎤

⎣ (

(

t) + 33 10sin 3000

(

(

t)

⎦

= ⎡0.5sin 1000

⎣

(

t) + 0.33sin 3000

(

t)⎤

⎦

African Virtual University

Soultions to Self Evaluation 4

1. The following four steps will be used for this purpose.

Step 1.

0

1

1

1

Step 2.

½

¼

1/8

Step 3.

½

¼

1/8

Step 4.

½ + ¼ +1/8 = 0.875

∴0.111 = 0.875

2

10

2. 0.77 = 0.110001

10

2

3. 25.625 = 11001.101

10

2

4. i- 13 and 26;

ii- 13 and 6.5

This implies that shifting binary point to right is equivalent to multiplying the

number by 2, while shifting the binary point to the left is equivalent to dividing the

number by 2

5. a. 111 2

b 0010 2

c. 0011 2

6. (i) 11101000

(ii) 1001111

7. (c) i. X = AB + C

ii. X = 1; and X = 1

8 The logic equation which provides the switching function is given by

F = C A.B + C .A.B + C .A.B + C .A.B

0

1

2

3

African Virtual University

For A = B = 0, we get F = C ,0

For A = 0, B = 1, we get F = C1

For A = 1, B = 0, we get F = C2

For A = 1, B = 1, we get F = C3

Thus for C to be selected AB = 10, which enables and will appear at the

2

X 2

C2

output F

Solution to Self evaluation 5

1. (a) -Finite Aperture Time: The sample and hold takes a period of time to capture a sample of the sensor signal. This is called the aperture time. Since the signal

will vary during this time, the sampled signal can be slightly off.

-Signal Feedthrough: When the sample and hold is not connected to the signal,

the value being held should remain constant. Unfortunately, some signal does

bleed through the switch to the capacitor, causing the voltage being held to change

slightly.

-Signal Droop: The voltage being held on the capacitor starts to slowly decrease

over time if the signal is not sampled often enough.

(b) The main solution to these problems is to have a small aperture time relative to

the sampling period. This means that if the HCI designer uses a high sampling

rate, the aperture time of the sample and hold must be quite small.

2 - Magnetic isolation is primarily used for coupling power from the computer or

the wall outlet to the sensor. This is done through the use of a transformer.

- Optical isolation is used for coupling the sensor signal to the data acquisition

input. This is usually done through the use of a light emitting diode and a pho-

todetector. This can be integrated into a single IC package such as the 6N139.

The Basic Theory Optical isolation has two basic elements: a light source (usually

a light emitting diode) and a photo-sensitive detector. These two elements are

positioned facing one another and inserted in an electrical circuit to form an op-

tocoupler. The key property of an optocoupler is that there is an insulating gap

between the light source and the detector. No current passes through this gap,

only the desired light waves representing data. Thus the two sides of the circuit

are effectively «isolated» from one another. Primary Application In data com-

African Virtual University

munications, the primary application for optical isolation is in a point-to-point

data circuit that covers a distance of several hundred feet or more. Because the

connected devices are presumably on different power circuits, a ground potential

difference likely exists between them. When such a condition exists, the voltage

of «ground» can be different, sometimes by several hundred volts.

Where a ground potential difference exists, a phenomenon called ground loop-

ing can occur. In this phenomenon, current will flow along the data line in an

effort to equalize the ground potential between the connected devices. Ground

looping can, at the very least, severely garble communications--if not damage

hardware!

Optical isolation solves the problem of ground looping by effectively lifting the

connection between the data line and «ground» at either end of the line. If an

optically coupled connection exists at each end, the data traffic «floats» above

the volatility of ground potential differences.

Solution to self Assessment 6.

1. In computing, a program is a specific set of ordered operations for a computer

to perform. In the modern computer, the program contains a one-at-a-time se-

quence of instructions that the computer follows. Typically, the program is put

into a storage area accessible to the computer. The computer gets one instruction

and performs it and then gets the next instruction. The storage area or memory

can also contain the data that the instruction operates on. (Note that a program

is also a special kind of “data” that tells how to operate on “application or user

data.”)

Programs can be characterized as interactive or batch in terms of what drives them

and how continuously they run. An interactive program receives data from an

interactive user (or possibly from another program that simulates an interactive

user). A batch program runs and does its work, and then stops. Batch programs

can be started by interactive users who request their interactive program to run

the batch program. A command interpreter or a Web browser is an example of an

interactive program. A program that computes and prints out a company payroll

is an example of a batch program. Print jobs are also batch programs.

When you create a program, you write it using some kind of computer language.

Your language statements are the source program. You then “compile” the source

program (with a special program called a language compiler) and the result

is called an object program. There are several synonyms for object program,

including object module and compiled program. The object program contains

the string of 0s and 1s called machine language that the logic processor works

with.

The machine language of the computer is constructed by the language compiler

with an understanding of the computer’s logic architecture, including the set

African Virtual University

of possible computer instructions and the length (number of bits) in an instruc-

tion

2. For 32-bit word, the total number of input lines = 232 − 1 = 4294967295

3. Instruction

An instruction is an order given to a computer processor by a computer program. At

the lowest level, each instruction is a sequence of 0s and 1s that describes a physical

operation the computer is to perform (such as “Add”) and, depending on the parti-

cular instruction type, the specification of special storage areas called registers that

may contain data to be used in carrying out the instruction, or the location in com-

puter memory of data. In a computer’s assembler language, each language statement

generally corresponds to a single processor instruction. In high-level languages, a

language statement generally results (after program compilation) in multiple pro-

cessor instructions

Register.

In a computer, a register is one of a small set of data holding places that are

part of a computer processor. A register may hold a computer instruction, a storage address, or any kind of data (such as a bit sequence or individual charac-

ters). Some instructions specify registers as part of the instruction. For example,

an instruction may specify that the contents of two defined registers be added

together and then placed in a specified register. A register must be large enough

to hold an instruction - for example, in a 32-bit instruction computer, a register

must be 32 bits in length. In some computer designs, there are smaller registers

- for example, half-registers - for shorter instructions. Depending on the processor

design and language rules, registers may be numbered or have arbitrary names.

4. (i) 3788800 bytes (ii) 3.61 MiB

African Virtual University

XI. Compiled list of all key concepts

Intrinsic conductivity- Is the conductivity of a semiconductor that is associated with

the semiconductor itself and is not contributed by impurities. At any given temperature

equal numbers of charge carriers: electrons and holes are thermally generated, and

it is these which give rise to the intrinsic conductivity.

Intrinsic semiconductor - Is a pure semiconductor in which the electrons and hole

densities are equal under condition of thermal equilibrium. In practice absolute purity

is unattainable and the term is applied to nearly pure materials.

Extrinsic semiconductor – Is asemiconductor in which the charge carrier concen-

tration is dependent is dependent upon impurities or other imperfections.

Depletion layer: Is a space-charge region in a semiconductor in which there is a net

charge due to insufficient mobile charge carriers. Depletion layers are formed, for

example, at the interface between a p-type and n-type semiconductor in the absence

of an applied field. They are also formed at the interface of a metal and a semicon-

ductor.

Rectifier- Is an electrical device that permits current to flow in only one direction

and can thus make alternating into direct current. It operates either by suppressing or

attenuating alternate half-cycles of the current waveform or by reversing them. The

most common rectifiers are semiconductor diodes.

Threshold voltage- Is the voltage at which a particular characteristic of an electric

device first occurs. For an insulated-gate field-effect transistor, it is the voltage at

which channel formation occurs.

Leakage- Is the flow of an electric current, due to imperfect insulation, in a path

other than that intended.

Leakage current- Is a fault due to leakage. It is small in magnitude compared with

that of a short circuit.

Amplifier- Is a device for reproducing an electrical input at an increased intensity.

If an increased e.m.f.is produced operating into a high impedance, the device is a

voltage amplifier, and if the output prodvides an appreciable current flow into a re-

lativiely low impedance, the device is a power amplifier. The most commonly used

amplifiers operate by transistors.

Logic circuit- Is a circuit designed to perform a particular logical function based on

the concepts of “and”, “either-or”, etc. Normally these circuits operate between two

discrete voltage levels, i.e. high and low logic levels, and are described as binary logic

circuits. Logic using three or more logic levels is possible, but not common.

African Virtual University 0

Logic gates- Is a device used to implement the elementary logic functions. These

basic gates include among others: AND gate; Inverter (NOT gate); NAND gate;

NOR gate…

Transducers- Is any device for converting a nonelectrical signals (or vice versa), the

variations in the electrical signal being a function of the input. The transducers are

used as measuring instruments and in the electroacoustic field, the term being applied

to gramophone pick-ups, the microphones, and loudspeakers. The physical quantity

measured by the transducer is the measurand, the portion of the transducer in which

the output originates is the transducer elements, and the nature of the operation is

the transduction principle. The device in the transducer that responds directly to the

measurand is the sensing element and the upper and lower limits of the measurand

value for which the trandsucer provides a useful output is the dynamic range.

Microprocessor- Is the integration of a number of useful functions into a single IC

package. These functions are the ability to execute a stored set of instructions to carry

out user defined tasks, and the ability to be able to access external memory chips to

both read and write data from and to the memory.

PREV   NEXT