IS 151 Lecture 1
- 1. IS 151 Digital Circuitry Aron Kondoro IS 151 Digital Circuitry 1
- 2. Materials, Assessment and Contact IS 151 Digital Circuitry 2 • Book – Digital Fundamentals, Floyd, T.F – Available in the Unit’s library – contact Mr. Mathew Mndeme • Laboratory Software – Deeds Digital Circuit Simulator – TC lab http://www.esng.dibe.unige.it/deeds/ • Assessment: – 60% exam – 40% coursework • Contact – My contact is through your Class Representative
- 3. Materials, Assessment and Contact • Additional recommended materials – Book: Bebop to the Boolean Boogie, Clive Maxfield – Website: http://www.allaboutcircuits.com/vol_4/ IS 151 Digital Circuitry 3 – Google
- 4. 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 IS 151 Digital Circuitry 4
- 5. Digital vs. Analog Quantities • Diagram: Temperature graph (page 2) IS 151 Digital Circuitry 5 100 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 P.M Temperature (F) Time of Day
- 6. Digital vs. Analog Quantities • Suppose temperature values are taken every hour (sampling), the graph will look like: IS 151 Digital Circuitry 6
- 7. Digital vs. Analog Quantities • Diagram: Sampled Temperature graph (page 3) IS 151 Digital Circuitry 7 100 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 P.M Temperature (F) Time of Day
- 8. Digital vs. Analog Quantities • The sampled values represent the temperature at discrete points over a 24- hour 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 IS 151 Digital Circuitry 8
- 9. 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) IS 151 Digital Circuitry 9
- 10. 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. IS 151 Digital Circuitry 10
- 11. 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. IS 151 Digital Circuitry 11 – 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.
- 12. Binary Representation • One bit can either be 0 or 1. – Therefore, one bit can represent only two things – 1 IS 151 Digital Circuitry 12 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.
- 13. 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) IS 151 Digital Circuitry 13
- 14. Codes and Characters IS 151 Digital Circuitry 14 • 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.
- 15. 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 IS 151 Digital Circuitry 15
- 16. 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 IS 151 Digital Circuitry 16
- 17. 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. IS 151 Digital Circuitry 17
- 18. Logic Levels • Diagram: Logic level ranges (page 5) Uncertain • 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. IS 151 Digital Circuitry 18 HIGH (1) LOW (0) VH(max) VH(min) VL(max) VL(min)
- 19. Logic Levels IS 151 Digital Circuitry 19 • 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
- 20. Questions • 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 IS 151 Digital Circuitry 20 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
- 21. • End of Lecture IS 151 Digital Circuitry 21