This document provides an overview of the IS 151 Digital Circuitry course, including materials, assessment, and contact information. It discusses the differences between analog and digital quantities, how analog signals can be converted to discrete digital signals through sampling. It also covers binary representation of data, logic levels for representing 1s and 0s, and some example exercises distinguishing analog and digital systems.

1. IS 151
Digital Circuitry
Mercy Mbise (PhD, Essex)
Aron Kondoro
IS 151 Digital Circuitry
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2. Materials, Assessment and Contact
• Book
– Digital Fundamentals, Floyd, T.F
– Available in the Unit’s library – contact Mr. Mathew Mndeme
• Laboratory Software
– Deeds Digital Circuit Simulator – TC lab
– Laboratory Instructor – Mr. Mwasita (TA)
• Assessment:
– 60% exam
– 40% coursework
• Contact
– My contact is through your Class Representative
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3. Digital vs. Analog Quantities
• Electronic circuits can be divided into two
broad categories
– 1. Analog Quantities
• Quantities with continuous values (most things that
can be measured quantitatively). E.g. air
temperature changes over a continuous range of
values; temperature does not change from, say 70
to 71 instantaneously; it takes on all infinite values
in between: see graph
• Other examples: time, pressure, distance and
sound
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4. Digital vs. Analog Quantities
• Diagram: Temperature graph (page 2)
Temperature (F)
100
95
90
85
80
75
70
1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
A.M
Time of Day
P.M
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5. Digital vs. Analog Quantities
• Suppose temperature values are taken every
hour (sampling), the graph will look like:
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6. Digital vs. Analog Quantities
• Diagram: Sampled Temperature graph (page 3)
Temperature (F)
100
95
90
85
80
75
70
1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
A.M
Time of Day
P.M
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7. Digital vs. Analog Quantities
• The sampled values represent the
temperature at discrete points over a 24hour period.
– i.e. 1,2,3 etc, which are discrete
• The analog quantity (temperature) have
been converted to a form that can be
represented in digital form
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8. Digital vs. Analog Quantities
– 2. Digital Quantities
• Quantities with discrete values
• Data can be processed and transmitted
more efficiently and reliably
• Useful in data storage: e.g. music when
converted to digital can be stored more
compactly (e.g.mp3 music)
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9. Data Representation Basics
• Computing systems are complex
devices, dealing with a variety of information
categories
• Computing systems store, present, and modify:
–
–
–
–
–
Text
Audio
Images and graphics
Video
Etc.
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10. Binary Representation
• Why binary representation (as opposed to
decimal or octal, etc..)?
– Cost
• Devices that store and manage digital data are far less
expensive and complex for binary representation.
– Reliability
• More reliable when they have to represent one out of only
two possible values.
– Handling
• Electronic signals are easier to maintain if they carry only
binary data.
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11. Binary Representation
• One bit can either be 0 or 1.
– Therefore, one bit can represent only two things – 1
and 0
• To represent more than two things, multiple bits
are needed
– Two bits can represent four things because there are
four combinations of 0 and 1 that can be made from
two bits: 00, 01, 10, 11.
• In general, n bits can represent 2n things
because there are 2n combinations of 0 and 1
that can be made from n bits.
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12. Data Formats - How to Interpret
Data
• Internal representation must be
appropriate
– E.g. Images, sound, and video: have to be
digitized
• Images – need detailed description of the
data, how color is represented at each data point
• Sound – need sampling, digitizing
• Video – need sampling and digitizing in space and
time (because of motion)
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13. Codes and Characters
• The problem:
– Representing text strings, such as
Hello, world in a computer
• Each character is coded as a byte (8 bits)
– including blank spaces, commas, full stops
• Most common coding system is ASCII
• To represent alphanumeric characters – 8 bits per character
– 7-bit code : 27 = 128 codes are used (128 characters can be
represented)
– 8th bit is unused (or used for a parity bit)
• Two types of codes:
– 95 are “Graphic” codes (visible)
• Alphabetic, numeric and punctuation characters
– 33 are “Control” codes (control features)
• Shift, delete, enter, etc.
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14. Binary Digits
– In digital electronics, there are only two
possible states and can be represented by
• two different voltage levels: HIGH and LOW
• current levels: OPEN and CLOSED
• lamps: ON and OFF
– The two states are called codes, and
combinations of the two are used to represent
numbers, symbols, alphabetic characters and
other types of information
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15. Binary Digits
– The two-state number system is called
binary, and the two digits in the binary system
are 0 and 1.
• A binary digit is called a bit (binary digit).
– In digital circuits, two voltage levels are used
to represent the two bits
• 1 – represented by a high voltage level (HIGH)
• 0 – represented by a low voltage level (LOW)
– POSITIVE LOGIC – will be used throughout!
– C.f. NEGATIVE logic:, 1 – LOW, 0 – HIGH
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16. Logic Levels
– Logic levels are voltages used to represent a
1 and a 0.
– One voltage level represents a HIGH and one
voltage level represents a LOW.
– Practically, a HIGH or a LOW can be any
voltage between a specified minimum value
and a specified maximum.
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17. Logic Levels
• Diagram: Logic level ranges (page 5)
VH(max)
HIGH (1)
VH(min)
Uncertain
VL(max)
LOW (0)
VL(min)
• From the figure, VH(max) and VH(min) represent the maximum and
minimum HIGH voltage values, respectively
• VL(max) and VL(min) represent the maximum and minimum LOW
voltage values, respectively.
• The range of voltages between VL(max) and VH(min) is a range of
uncertainty; a voltage in the range of uncertainty can appear as
either a HIGH or a LOW.
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18. Logic Levels
• Examples:
– The high values of a certain digital circuit may
range from 2 V to 5 V and the LOW values
from 0 V to 0.8 V.
– If a voltage of 3.5 is applied, the circuit will
accept it as a HIGH (or binary 1); a voltage of
0.5 V will be accepted as a LOW (binary 0); a
voltage of 1 V will be uncertain
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19. Exercises
• Differentiate between a digital and an analog quantity
• Give examples of digital and analog systems
• Classify the following into analog (continuous) or digital
(discrete)
– (a) Shades of colours in a TV program about landscapes
– (b) TV screen test pattern, white background, black dots
only
– (c) Days in a week, Mon, Tues, Wed, Thurs, Fri, Sat, Sun.
– (d) Sine wave
– (e) A musical symphony
– (f) Chairs/seats in a room
– (g) Integers -2, -1, 0, 1, 2, 3,...
– (h) All real numbers
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20. • End of Lecture
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