1. DIGITAL LOGIC DESIGN(1)
Course :
DIGITAL LOGIC DESIGN(1)
BY:FLOYD & JAIN
LECTURE # 02
BY:Hira Farman

2. TODAYS TOPIC: BINARY DIGIT LOGIC LEVELS DIGITAL WAVEFORMS (NUMERICALS)
TIMING DIAGRAM
DATA TRANSFER
BY:Hira Farman

3. INTRODUCTION
Digital electronics involves circuits and systems in which there are only two possible states.
These states are represented by two different voltage levels.
(A HIGH and a LOW)
The two states can also be represented by current levels,open and closed switches,or lamps turned on and off.
In digital systems such as computers,combination of the two states,called codes,are used to represent numbers,symbols,alphabetic characters,and other types of information.
BY:Hira Farman

4. 1.BINARY DIGIT
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5. BINARY DIGIT
The two digits in the binary system,1 and 0 are called bits,which is a contraction of the words binary digit.
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6. In digital circuits two different voltage levels are used to represent the two bits.
Generally ,1 is represented by the higher voltage,which we will refer to as a HIGH,and a 0 is represented by the lower voltage level,which we will refer to as a LOW
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7. LOGICS: 1-Positive Logic 2-Negative Logic
Circuit commonly used a combination of positive & negative logic
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8. Which is called positive logic: HIGH=1 and LOW=0
Another system in which a 1 is represented by a LOW and a 0 is represented by a HIGH is called negative logic.
Which is called negative logic:
LOW= and HIGH=0
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9. CODES:
Group of bits (combination of 1s & 0s) called codes,are used to represent numbers,letters,symbols,instructions and anything else required in a given application.
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10. LOGIC LEVELS
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11. BINARY DIGIT AND LOGIC LEVELS
Digital electronics uses circuits that have two states, which are represented by two different voltage levels called HIGH and LOW.
The voltages represent numbers in the binary system.
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12. Logic level ranges of voltage for a digital circuit:
(binary 1)
unacceptable
(binary 0)
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13. EXPLANATION Understand & write yourself… (Read Book page no 4)
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14. BY:Hira Farman

15. DIGITAL WAVEFORM
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17. Digital Waveforms Digital waveforms change between the
LOW and HIGH levels.
A positive going pulse is one that goes from a normally LOW logic level to a HIGH level and then back again.
Digital waveforms are made up of a series of pulses.
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18. (Diagram)
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19. Periodic Pulse Waveforms
Periodic pulse waveforms are composed of pulses that repeats in a fixed interval called the period.
The frequency is the rate it repeats and is measured in hertz.
The clock is a basic timing signal.
BY:Hira Farman

20. DUTY CYCLE
An important characteristics of a periodic digital waveform is its duty cycle.
“The duty cycle is the ratio of the pulse width (tw) to the period(T) and can be expressed as a percentage.
Duty cycle= ( tw )
*100 T
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21. BY:Hira Farman

22. NUMERICALLY WORK
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23. Example of a periodic wave.
NUMERICAL # 01:What is the period of a repetitive wave if f= 3.2 GHz?
Ans: We know that:
T=1/f
T=1/3.2
T=0.3125(ANS)
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24. NUMERICAL 2:
A portion of a periodic digital waveform is shown in fig .The measurements are in milliseconds. Determine the following:
Period (b) frequency (c) duty cycle T tw
t(ms) 10 11 1
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25. SOLUTION:
(a)The period is measured from the edge of one pulse to the corresponding edge of the next pulse.
In this case T is measured from the leading edge to leading edge,as indicated.
T equals 10ms.
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26. SOLUTION: Now find frequency: We know that formula: F=1/T =1/10ms
=100Hz
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27. SOLUTION: Now find duty cycle: We know that formula:
Duty cycle=(tw/T)100%
=(1ms/10ms)100%
=10%.
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28. NUMERICAL # 03:
A periodic digital waveform has a pulse width of 25 milisecond and a period of 150 millisecond. Determine the frequency and the duty cycle.
(Try to solve )
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29. Ans:f=6.67HZ,duty cycly=16.6%
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30. TIMING DIAGRAM
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31. TIMING DIAGRAM
A timing diagram is a graph of digital waveforms showing actual time relationship of two or more waveform and how each waveform charges in relation to the others.
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32. Knowing the period of a waveform, how do you find the frequency?

33. DATA TRANSFER/DATA TRANSMISSION
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34. DATA TRANSFER
Data transmission refers to the movement of data in form of bits between two or more digital device.
This transfer of data takes place via some form of transmission media(For example ,coaxial cable,fiber optics etc).
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35. DATA TRANSFER Binary data are transferred in two ways: Serial Parallel
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36. BY:Hira Farman

37. BY:Hira Farman

38. Which type of data transfer?
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40. BY:Hira Farman

43. Discuss some Pros & Cons of serial & parallel transmission
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44. ADVANTAGES OF SERIAL TRANSFER
An advantage of serial transfer of binary data is that a minimum of only one line is required.
(only one wire is required)
Use of single communication line reduces the transmission line cost by the factor of n as compared to parallel transmission.
DISADVANTAGES OF SERIAL TRANSFER
A disadvantage of serial transfer is that it takes longer to transfer a given no of bits than with parallel transfer.
(For Example):If one bit can be transferred in 1 microsecond,then it takes 8microsecond to serially transfer eight bits ..but only 1 microsecond to parallel transfer eight bits.
Use of conversion devices of source and destination end may lead to increase in overall transmission cost.
This method is slower as compared to parallel transmission as bits are transmitted serially one after the another.
BY:Hira Farman

45. ADVANTAGES OF PARALLEL TRANSFER:
It is speedy way of transmitting data as multiple bits are transmitted simultaneously with a single clock pulse.
In parallel transfer ,a number of lines equal to the number of bits to be transferred at one time is required.
DISADVANTAGES OF PARALLEL TRANSFER:
A disadvantage of parallel transfer is that it takes more lines.
It is costly method of data transmission as it requires n lines to transmit n bits at the same time.
BY:Hira Farman

46. CLASS TASKS:
QNO1:Define the sequence of bits(as and 0s) represented by each of the following sequence of levels:
(a)HIGH,HIGH,LOW,HIGH,LOW
(B)LOW,LOW,LOW,HIGH,HIGH,LOW,HIGH,LOW
QNO2:List the sequence of levels (HIGH nad LOW) that represent each of the following bit sequences
(a)10111
(b)
QNO3:Draw the timing diagram of the following data
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47. BY:Hira Farman

48. Summary # 02:(Tasks) Define binary. What does a bit mean?
(Give only 1 line answer)
Define binary.
What does a bit mean?
What are the bits in a binary system?
Explain what a clock waveform it.
What is the purpose of a timing diagram?
What is the main advantage of parallel transfer over serial transfer of binary data?
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49. Referrences
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