Logic Switch

9 Key excerpts on "Logic Switch"

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  eBook - ePub

  Electronics

  from Classical to Quantum

  • Michael Olorunfunmi Kolawole(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  2 Functional Logics

  Many tasks in modern computer, communications, and control systems are performed by logic circuits. Logic circuits are made of gates . A logic gate is a physical device that implements a Boolean function that performs a logic operation on one or more logical inputs (or terminals) and produces a single logical output. This chapter examines the basic principles of logic gates: the types—from primitive to composite gates—and how they are arranged to perform basic and complex functions.

  2.1 The Logic of a Switch

  Basic logic circuits with one or more inputs and one output are known as gates . Logic gates (or simply gates ) are used as the building blocks in the design of more complex digital logic circuits. A logic gate is a physical device that implements a Boolean function that performs a logic operation on one or more logical inputs (or terminals) and produces a single logical output. Practically, gates function by “opening” or “closing” to allow or reject the flow of digital information. For any given moment, every terminal is in one of the two binary conditions “0” (low) or “1” (high). These binary conditions represent different voltage levels; that is, any voltage v up to the device threshold voltage, V th , (i.e. 0 ≤ v ≤ V th ); and in the conduction ranges 0 ≤ v ≤ 2.5 V and 2.5 < v ≤ 5 V represent logic states “0” and “1,” respectively.

  Note that machine arithmetic is accomplished in a two-value (binary) number system, but Boolean algebra—a two-value symbolic logic system—is not a generalization of the binary number system. The symbols 0, 1, +, and • are used in both systems but with totally different meanings in each system. (The meanings of these symbols become obvious during discussions in the next paragraphs.) This symbolic tool allows us to design complex logic systems with the certainty that they will carry out their function exactly as intended. Conversely, Boolean algebra can be used to determine exactly what function an existing logic circuit was intended to perform. So, writing Boolean functional expressions allows us to observe the expected output logic of the simple or complex gates’ design or construction.

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  Introduction To Computers NQF2 SB

  TVET FIRST

  • Sparrow Consulting(Author)
  • 2013(Publication Date)
  • Macmillan

    (Publisher)

  A logic gate is a physical electronic component that forms part of the computer’s circuitry which can manipulate an input signal to give a desired output signal. Most logic gates take in two or more inputs of binary values and produce one output with a value of 1 or 0. We usually use the letters A, B, C, and so on, to label inputs, and F, Q or Z to label the output. However, you can use any letters. It is common practice to explain the function of a logic circuit with a related circuit that uses switches with a power source and a light. When the light is on the value is considered to be ‘high’, ‘on’ or ‘1’. When the light is off it indicates a ‘low’, ‘off’ or a ‘0’. Refer to Fig. 1.2 and study the circuits. The first one shows an AND gate. If you look at the AND gate switch representation, you will see that all the switches must be turned ‘on’, (‘high‘ or ‘1’) before the light will light up or become ‘high’. Because it uses four switches as input, the AND gate that is represented here is indicated inside the circuit as an AND gate with four inputs. The second symbol inside the circuit is the IEC (International Electrotechnical commission) symbol for an AND gate. The second circuit explains how the OR gate works. In this case any one of the switches that is turned ‘on’, (goes ‘high’ or ‘1’) will cause the light as the output to go ‘high’. Once again the symbols for the OR gate are shown inside the switch circuit. The last gate is a NAND gate. An easy way of remembering the NAND gate is to read it as a Not AND gate. The Not relates to the little circle on the output side of the gate. The AND part of the gate functions like any AND gate in which all the inputs need to be ‘on’ for an output of ‘1’. The little circle represents an inverter, which turns a ‘1’ into a ‘0’ and a ‘0’ into a ‘1’. The result is that when all the inputs are ‘0’ the output of the NAND gate will be ‘1’.

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  N4 Fault Finding and Protective Devices

  • Raimund Swart(Author)
  • 2024(Publication Date)
  • Future Managers

    (Publisher)

  Calculations can be performed electronically in the binary number system and the answers then displayed in the decimal number system, which we are all used to. The conversion method is discussed in a later section. For binary logic operations we can define the following conditions. Binary state Boolean condition Output condition Switch position Magnetic field Transistor state Voltage level 0 False Off Open Anti- clockwise Non- conducting Low (0V) 1 True On Closed Clockwise Conducting High (5V) Table 3.1: Binary logic operations and conditions 113 N4 Fault Finding and Protective Devices 3.1.1 IEC symbols, electronic circuits, and truth tables Logic operations are defined in terms of the logic functions that are performed. The logic operations can also be drawn as logic gate symbols, usually with two inputs and one output. The operation of a logic function in terms of its inputs and corresponding output can be described by making use of a truth table, consisting of “0” and “1” conditions. A logic function can also be physically realised by making use of an electronic circuit, consisting of switches, diodes and transistors in an “off ” or “on” state. Definition Logic gate – a device that acts as a building block for digital circuits that perform basic logic functions Truth table – a breakdown of all possible truth values returned by a logic expression Logic functions can also be drawn as logic function blocks, each with their own logic symbol, refer to Table 3.2. The logic function blocks make provision for inputs and an output, and they can be drawn in a diagram, similar to an electrical diagram. The logic function blocks and diagrams can further be used to build electrical circuits, or they can be used in computer programming. Logic functions are also called logic gates, which create outputs once certain input conditions are met.

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  Understand Electronics

  • Owen Bishop(Author)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  19 Logic circuits Whether we are reading the time on a digital watch, dialling a call on a cell-phone, listening to a compact disc, using a Smartcard, or sending a fax, we are using logic circuits. More and more of the equipment we use at home and at work depend on electronic logic. Logic is the science of reasoning, and we use its electronic equivalent as the basis for a whole host of so-called 'intelligent' devices. The form of logic most suitable for implementing electronically is binary logic. In binary logic, we constantly deal with two states. A statement is true or it is untrue: there are no half-truths. A digit is 1 or 0: there are no fractions or other values. A transistor is either fully on (saturated) or fully off: it switches rapidly from one state to the other, spending a negligible time in the intermediate states. A voltage is either high or low: intermediate values have no meaning. The on-off, high-low characteristics of binary logic mean that we can design electronic circuits that can model logical statements with absolute accuracy. We need to be concerned with only two voltage levels, not with all the possible levels that exist in (for example) audio circuits. Let us see how a logical situa-tion may be modelled electronically. A garage floodlamp is to be switched on whenever a car approaches the garage, but this is to happen only at night. There is no point in turning on the floodlight during the day. There are two sensors. One of these, perhaps based on a light-dependent resistor (p. 120) responds to light level. It can be arranged, possibly by using a Schmitt trigger circuit (p. 96), that the output voltage of the sensor circuit is low (close to 0 V) when it is daylight and high (close to the supply voltage) at night. The other sensor is a pyroelectric sensor; it responds to the heat radiating from the car. Its circuit is arranged to give a high output when it is triggered.

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  Hardware and Computer Organization

  • Arnold S. Berger(Author)
  • 2005(Publication Date)
  • Newnes

    (Publisher)

  CHAPTER 2 Introduction to Digital Logic Objectives • Learn the electronic circuit basis for digital logic gates; • Understand how modern CMOS logic works; • Become familiar with the basics of logic gates. Remember the simple battery and flashlight circuit we saw in Figure 1.14? The two on/off switches, wired as they were in series, implemented the logical AND function. We can express that example as, If switch A is closed AND switch B is closed, THEN lamp C will be illuminated. Admittedly, this is pretty far removed from your PC, but the logical function implemented by the two switches in this circuit is one of the four key elements of a modem computer. It may surprise you to know that all of the primary digital elements of a modem computer, the central processing unit (CPU), memory and I/O can be constmcted from four primary logical functions: AND, OR, NOT and Tri-State (TS). Now TS is not a logical function, it is actually closer to an electronic circuit implementation tool. However, without tri-state logic, modem computers would be impossible to build. As we'll soon see, tri-state logic introduces a third logical condition called Hi-Z, Z is the elec-tronic symbol for impedance, a measure of the easy by which electrical current can flow in a circuit. So, Hi-Z, seems to imply a lot of resistance to current flow. As you'll soon see, this is criti-cal for building our system. Having said that we could build a computer from the ground up using the four fundamental logic gates: AND, OR, NOT and TS, it doesn't necessarily follow that we would build it that way. This is because engineers will usually take implementation shortcuts in designing more complex functions and these design efficiencies wiU tend to blur the distinctions between the fundamental logic elements. However, it does not diminish the conceptual importance of these four fundamental logical functions.

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  The Silicon Web

  Physics for the Internet Age

  • Michael G. Raymer(Author)
  • 2009(Publication Date)
  • CRC Press

    (Publisher)

  A simple example occurs in a calculator when you press the “add” or “ + ” button. The input data are the two numbers you want to add (18, 5). The calculator carries out several logical operations to produce the resulting sum (18 + 5 = 23), which is the output data. Before we consider the actual electronic circuits that perform the operations, we will discuss the principles behind logic. English mathematician George Boole (1815–1864) was one of the founders of the principles of logic. In his honor, the methods used are called Boolean logic . In the context of modern computing, Claude Shannon was the most influential scientist who contributed to the theory of logic. In 1938, as a graduate student at Massachusetts Institute of Technology, he submitted his master’s thesis that showed how electronic circuits could be used to perform logic. Ten years later Shannon published the paper, “A Mathematical Theory of Communication,” which revolutionized scientists’ under-standing of the concept of information. 6.2 CONCEPTS OF LOGIC What is logic? In everyday life, it means to take in some information, apply certain rules of reasoning, and produce a decision. For example, you might reason that “if the sky is blue then I will take a walk without an umbrella, but if the sky is cloudy then I will take my umbrella.” The color of the sky is the input data and the umbrella decision is the output data. We can make a table showing our logic about the sky and umbrellas: Input: Sky blue? Output: Umbrella? No Yes Yes No The rules we use to process data or information are called logic operations . A logic operation is an elementary rule for arriving at a logical outcome. Three basic opera-tions that can serve as building blocks for all logic operations are NOT, AND, and OR. In considering complex situations, a diagram is useful to help visualize the logic process. Think of this as a flow chart for making a decision.

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  Computers and Microprocessors

  Made Simple

  • George H. Olsen, Ian Burdess(Authors)
  • 2016(Publication Date)
  • Made Simple

    (Publisher)

  They are being used increasingly in consumer products, such as washing machines, sewing machines, toys and television games as well as scientific applications for data acquisition and control. This shift away from the traditional markets has, to a large extent, been due to the evolution and development of the basic logic gates used in their construction. Unlike analogue systems, the digital computer is constructed entirely of switching devices capable of assuming only two states, ON and OFF. As the demands for computers have grown and new markets have opened up, the semiconductor device manufacturers have responded by increasing the speed and reducing the size of the basic logic circuits. A majority of the systems in use today is now based upon the popular transistor-transistor logic (TTL) NAND gate. By using these TTL NAND gates, it is possible to design and construct a logic circuit capable of making decisions based upon the current state of the input signals. These combinational logic circuits may be used to perform such elementary tasks as checking the door interlocks of an automatic washing machine before the wash cycle starts, or they may be used to construct a com-plex and high-speed arithmetic unit of a computer capable of adding numbers together at the rate of hundreds of thousands per second. Combinational logic circuits are, however, incapable of learning by experi-ence and always respond to a given situation in exactly the same manner. Based upon the same TTL NAND gates, but by incorporating feedback, it is possible to construct a circuit which can take into account its past experience. These systems, referred to as sequential logic systems, are very important in computers as they can be used to store information and count events as they occur. Finally, at the centre of any computer is a unit which is capable of perform-ing arithmetic calculations at very high speed.

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  Micropower Electronics

  • Edward Keonjian(Author)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  11. Logic performed by serial and parallel combination of switching elements. 30 P H Y S I C A L R E A L I Z A T I O N O F D I G I T A L L O G I C C I R C U I T S 31 of the states of the individual switching elements, and delivers a quan-tized 0 or 1 output signal accordingly. (iii) The NO Τ function. Physical realization of the N O T function (i.e. the conversion of an 0 signal to a 1 signal, and vice versa) depends primarily on the nature of the physical representation of the information signal. For signals whose 0 and 1 representations are mirror images of each other (such as a pulse of opposite polarities or a sinusoid of 0° and 180° phases) a simple phase-reversal transformer performs the N O T function. For signals in the form of a d.c. level, some circuit element with inversion property (such as a tube or a transistor) is required. (iv) Storage. As sequential operation is a requirement for digital systems, some of the information in the system has to be retained for use at a later time. This operation involves the storage of information signals in some circuit elements or networks, and reproducing the signal some-time after the termination of the input signals. Storage can be achieved by employing a switching element with two remanent states (such as a magnet core), or by a quantizing network with positive feedback (such as a transistor flip-flop). In certain occasions the use of a passive delay line, or even a passive network with large time constant, is adequate. 3. S W I T C H I N G M E L E E N T S T h e heart of an elementary digital network is usually a simple physical component which provides most of the above mentioned properties required of an elementary digital network. Such physical components are commonly known as switching elements. T h e general requirements of a switching element are well-defined thresholds, discriminative gain and limiting characteristics, and adequate unilateral and isolation properties.

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  Embedded Systems Circuits and Programming

  • Julio Sanchez, Maria P. Canton(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 3 Logic Gates and Circuit Components 3.1  Logic Gates

  A logic gate can be a virtual or a physical device. In either case the logic gate takes one or more binary signals as input and produces a binary output as a logical function. The basic logical operations of AND, OR, XOR, and NOT are described in basic electronics and Boolean algebra texts. Although logic gates can be made from electromagnetic relays, mechanical switches, or optical components, nowadays they are normally implemented using diodes and transistors.

  Charles Babbage’s Analytical Engine, devised around 1837, used mechanical logic gates based on gears. Electromagnetic relays were later used for logic gates, and these were eventually replaced by vacuum tubes, as Lee De Forest’s modification of the Fleming valve can be used as an AND logic gate. In 1937, Claude E. Shannon wrote a thesis paper that introduced the use of Boolean algebra in the analysis and design of switching circuits. The first modern electronic gate was invented by Walther Bothe in 1924, for which he received part of the 1954 Nobel prize in physics.

  The primitive types of gate are the AND, OR, and NOT. Additionally, the XOR gate offers an alternative version of the OR. All other Boolean operations can be implemented by combining the three primitive types. However, for convenience, other secondary types have been developed. These are called NAND (NOT plus AND), NOR (NOT plus OR), and XNOR (XOR plus NOT). The advantage of these secondary logic gates is that they require fewer circuit elements for a given function. In fact, the NAND gate is the simplest of all gates, except for the NOT gate. Furthermore, a NAND can implement both a NOT and an OR function; therefore it can replace AND, OR, and NOT. This means that the NAND gate is the only type actually needed in a real system. Programmable logic arrays will very often contain nothing but NAND gates. The symbols for logic gates are shown in Figure 3-1

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