Physics
Flip Flop Circuit
A flip flop circuit is a digital electronic circuit that can store one bit of information. It has two stable states and is commonly used in computer memory and digital logic circuits. The circuit can change its output based on the input signals, making it a fundamental building block in digital electronics.
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10 Key excerpts on "Flip Flop Circuit"
- Subir Kumar Sarkar, Asish Kumar De, Souvik Sarkar(Authors)
- 2014(Publication Date)
- Jenny Stanford Publishing(Publisher)
This circuit is called a flip-flop. It can stay in one of two stable states. The flip-flop has two stable states and, hence, is called a bistable multivibrator as it can store 1 bit of information ( Q = 0 or Q = 1), it is called a 1 bit memory or 1 bit storage cell. It is also called a latch because it locks the information between consecutive clock pulses. A logic gate has truth tables, but a flip-flop has an “excitation table,” which provides information about what its (flip-flop) input should be if the outputs are specified before and after the clock pulses. Some flip-flops have preset and clear inputs for some specific purposes. “Clear” input is to clear or reset the output of the flip-flop ( Q = 0) where “preset” input is used to set the output of the flip-flop ( Q = 1). A flip-flop may be triggered in various ways: 1. level triggering 2. master–slave or pulse triggering 3. positive and negative triggering Different Types of Flip-Flops and Their Application 123 In the level triggering scheme, the output of the flip-flop responds to input(s) according to its truth table as long as the clock is present. In the master–slave (pulse) triggering, both negative and positive edges are needed for triggering. In the positive and negative triggering either positive clock pulse or negative clock pulse is required. 2.4 Different Types of Flip-Flops and Their Application 2.4.1 S–R Flip-Flop 1. There are two additional inputs S and R . 2. Feedback path of resistance R B is fed to the base of Transisitor Q 2 S and R are two inputs to the transistors Q 1 and Q 2 respectively, which are used to change the outputs of the flip-flops (Q and Q’). When Q — 1 is ON, Q 2 is OFF and vice versa. Here due to the presence of R B (base resistances) and (R B = 10R C ) the collector swing is ( V CC – V CE, SAT ) = 5 V–0.4/0.2 = 4.6 to 4.8 V, which is nearly equal to logical 1.
eBook - PDFDigital Electronic Circuits
Principles and Practices
- Shuqin Lou, Chunling Yang(Authors)
- 2019(Publication Date)
- De Gruyter(Publisher)
5 Flip-flops and related devices Combinational circuit introduced in Chapter 4 is a type of digital circuits, whose outputs solely depend on the combination of current inputs, without storage being involved. Another kind of digital circuits is sequential logic circuit, in which outputs depend on not only the current inputs but also the previous inputs. Therefore, memory and storage are necessary parts for a sequential logic circuit. This chapter introduces bistable, monostable, and astable multivibration. Bistable multivibration has two stable states called logic 0 (or RESET) and logic 1 (or SET); it can maintain either of these states indefinitely, making it useful as memory devices. The monostable multi-vibration, also called the one shot, only has one stable state. A single controlled-width pulse is generated when a one shot is triggered. The astable multivibration has no stable state and is used to produce a periodic of pulse signal that can be used as a clock pulse source in a sequential logic circuit. In addition, Schmitt trigger and 555 timer are introduced for pulse generating, pulse shaping, and pulse transforming. The objectives of this chapter are to – Explain the operation of a basic S-R latch – Describe the difference between a flip-flop and a latch – Identify four kinds of edge-triggered flip-flops, and their dynamic characteristics – Discuss the application of flip-flops – Explain how a one shot operates – Explain the difference of retriggerable and nonretriggerable one shots – Explain the operation and application of Schmitt trigger – Explain the operation of an astable devices – Describe the function of 555 timer – Apply a 555 timer to construct a one shot and an astable device 5.1 Latches Latch and flip-flop are two categories of bistable multivibrators. Both of them have two stable states, that is, logic 0 and logic 1. Generally, a latch or a flip-flop can only store one-bit binary digit. It is the basic storage element in sequential logic.
- Will Kimber(Author)
- 2016(Publication Date)
- Newnes(Publisher)
6 Sequential systems 1 : Flipflops The term sequential system in logic language means a system in which the resulting output condition is dependent not only on the input but also on the existing output condition. As we shall see later on, the truth tables can be developed from a knowledge of the output state before the application of the inputs. The bistable condition A flipflop is a device that has two stable conditions or states and which can remain in one or other of these states indefinitely. The device can be made to change state when a trigger signal (pulse) is applied. The application of a second trigger pulse will cause the device to revert to its original state. This two-state situation, known as a bistable state, forms the basis of operation of counters and registers. Practical Exercise 6.1 allows you to become familiar with the basic bistable operation. Practical Exercise 6.1 The two-transistor switch For this exercise you will need the following components and equipment: 2 - BC 109 npn transistor 2 - LED (5 mm) 2 -resistor (270 Ω) 2 -resistor (10 kQ) 1 - 5 V dc power supply 1 - dc voltmeter Procedure 1 Connect up the circuit shown in Figure 6.1. The connection diagram for the BC109 transistor is given in Figure 5.16. Continued on p. 90 90 Sequential systems 1: Flipflops Practical Exercise 6.1 (Continued) ι t ο V cc = + 5 V flying lead Figure 6.1 The two-transistor switch: circuit for Practical Exercise 6.1 2 For the moment, leave the free end of the flying lead disconnected. 3 Switch on the supply and note which one of the two LEDs lights up. 4 Switch the supply off and then on. Again, note which LED lights up. (It should be the same LED on both occasions. The actual LED that lights will depend upon the characteristics of the transistors, which are unlikely to be identical, thus causing an unbalance in the circuit).
eBook - PDF- R. Townsend(Author)
- 2014(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 3 Counters and Sequential Circuits The logic circuits described in Chapter 2 have all had the property, when considered as a box with binary digital inputs and outputs, that the output can be represented as a Boolean function of the input at that particular instant, and is not affected in any way by previous events. This class of circuit contains no storage elements of any kind which could preserve any memory of what has gone before, and are termed combinational circuits. The output of a circuit which includes some type of memory as well as logical elements, and is a Boolean function not only of the input, but also of the binary number stored in its memory elements—which itself is also a function of previous events-is known as a sequential circuit. A wide variety of memory devices are used in the design of computers, but, for the purpose of current design of the counters and sequential circuits embodied in the arithmetic and control systems of computers, the flip-flop is in general use for the temporary storage of digital data. It is constructed from similar circuits to those used in the logic gates, with which it is designed to be compatible in voltage, current and power, and has the advantage of providing an output as a dc level which can be used directly as an input to a succeeding network of logic gates. As will be described in Chapter 7 on memories the static RAM consists of a large array of flip-flops formed as microcircuits on a silicon chip. The flip-flops may be set to either the 1 or 0 state and are provided with addressing logic on the chip so that only selected flip-flops are set or reset. Essentially the whole operation of a computer system can be reduced to a problem of transferring digital information from one register to another, usually by way of more or less complicated interacting logic.
eBook - PDF- R. M. Marston(Author)
- 2013(Publication Date)
- Newnes(Publisher)
4 Clocked flip-flops and counters Most digital ICs can be classified into either of two basic types; the first is those based on simple logic gate networks, and many of these have already been described in particular, Chapter 2. The second type is those based on 'clocked' bistable or flip-flop elements, and this group includes simple counter/divider ICs, shift registers, data latches, and complex ICs such as presettable up/down counters, etc. This chapter takes a detailed look at clocked flip-flop basics, and pre-sents practical user information on a variety of popular TTL clocked flip-flop and counter/divider ICs. Clocked flip-flop basics One of the simplest types of digital flip-flop circuit is the cross-coupled NOR-type bistable. This flip-flop has already been briefly described in Chapter 3, but its basic circuit and standard symbol are repeated here in Figure 4.1 , together with its full Truth Table. The circuit's basic action is such that its Q output switches to logic-1 (and NOT-Q goes to logic-0) when the SET terminal is taken to logic-1, T -n RESET J 'JI Q r-» (b) S R Q 5 0 0 no change 0 1 0 1 1 0 1 0 1 1 0 0 (disallowed) (c) Figure 4.1 Circuit (a), symbol (b), and Truth Table of the NOR-type S-R flip-flop. 110 Modern TTL Circuits and then latches into that state even if SET and RESET are both then pulled to logic-0. The only way that the latched output states can be changed is to apply a logic-1 to the RESET terminal, in which case the Q output switches to logic-0 and latches into that state even if SET and RESET are both then pulled to logic-0. The basic SET-RESET (S-R, or R-S) flip-flop thus acts as a simple memory element that 'remembers* which of the two inputs last went to logic-1. Note that if both inputs go to logic-1 simultaneously, both outputs go to logic-0, but if both inputs then simultaneously switch to logic-0 the output states cannot be predicted; the 'both inputs high' con-dition is thus regarded as a 'disallowed' state.
eBook - PDF- R M MARSTON(Author)
- 1995(Publication Date)
- Newnes(Publisher)
7 Clocked flip-flops Modern digital ICs come in two basic types, one of these comprising 'logic' types that are based on simple gate networks of the type already described in Chapter 3, and the other comprising those that are primarily based on clocked flip-flop (bistable or 'memory') elements. This latter category of devices includes simple ICs such as counter/dividers, shift registers and data latches, and complex ICs such as presettable up/down counters and dividers. The present chapter explains how clocked flip-flop circuits work, and then goes on to introduce some simple CMOS flip-flop ICs and show some practical ways of using them. As an immediate follow-up the next two chapters introduce a range of advanced counter/divider ICs and associated devices, together with much applications information. Basic principles The simplest type of flip-flop is the cross-coupled bistable, which has already been briefly described in Chapter 5 (see Figures 5.32 to 5.35). Figure 7.1 shows the basic circuit, symbol and truth table of a NOR-gate version of this flip-flop, which has two input terminals and a pair of anti-phase output terminals (Q and not-Q). The circuit's basic action is such that its Q output immediately switches high (and the not-Q output switches low) if the set terminal is briefly taken high (to logic-I], and the cross-coupling then causes the outputs to latch into this state even when both inputs are pulled low again. The only way that the output states can be changed is to apply a logic-l to the reset terminal, in which case the Q output immediately switches low (and the not-Q output switches high), and the cross-coupling then causes the outputs to latch into this new state even when both inputs are pulled low again. Thus, the basic set-reset (S-R) flip-flop acts as a simple memory element which 'remembers' which of the two inputs last went high.
eBook - PDF- B. Holdsworth(Author)
- 2014(Publication Date)
- Butterworth-Heinemann(Publisher)
5 Single-bit memory elements 5.1 Introduction A digital logic circuit is usually made up of combinational elements such as NAND and NOR gates and memory elements which might be single bit memory elements such as discrete flip-flops or, alternatively, an array of flip-flops such as might be found in a shift register. With the introduction of memory elements as components in digital circuits, an additional variable, time, has been introduced and must be taken into account when dealing with digital circuit problems. In effect, logic operations can now be performed sequentially, information being stored in a memory element and being released at some particular instant so that it can take part in a controlled combinational operation. Circuits operating in this way are called sequential circuits. Some sequential circuits are controlled by a repetitive clock signal, in which case the circuit is called a synchronous or, alternatively, a clock-driven circuit. Other sequential circuits are controlled by random events in which case they are called asynchronous or event-driven circuits. The basic characteristic of any flip-flop is that it has two stable states which can be represented by logical Ό' or logical 'Γ respectively. There are a number of flip-flops in common usage in digital circuits. They are called T, SR, JK and D type flip-flop. This chapter is concerned with the logical behaviour of these various types of flip-flop. 5.2 The T flip-flop This flip-flop is conventionally represented by the diagram shown in figure 5Λ{α). The device has one input Tand complementary outputs ßandß. 91 92 Single-bit memory elements la) 0 T »»I _ I o 0*0 ' f T 0 = 1 (CO T3&-C—j&J^®)— ' (e) Present state Γ ' 0 0 1 1 0> 0 1 0 1 Next 1 state Q**t 1 0 1 1 0 (
eBook - PDFDigital Computer Design
Logic, Circuitry, and Synthesis
- Edward L. Braun(Author)
- 2014(Publication Date)
- Academic Press(Publisher)
4.72. Schematic of a collection unit stored in the flip-flops. The signal S passes through the delay channel, arriving sequentially at the inputs to gates Gi through G4. Thus, at sue- 180 4. SWITCHING AND STORAGE CIRCUITS cessive times, a signal is entered onto the output line by each gate con-nected to a flip-flop in the 1 state. If the period between successive bits is more than a few /xsec, the delay line becomes too large, and distribution and collection are accom-plished by means of reading information from a dynamic store into a shift register and stepping information from the register into the store, respectively. The shift register combines the properties of storage and unit delays. A description of various shift registers is provided next. 4.9. Shift Registers Each stage of a shift register is built around a bistable element, to-gether with control circuitry that, upon command, causes the contents of each stage Ri to be transferred to stage Ä i + i . These elements may be vacuum tube or transistor flip-flops, magnetic cores, ferroelectric cells, or any other form of binary storage device. Shift registers are widely used in computers for storage, shifting, delay, serial-to-parallel and parallel-to-serial conversion, etc. If parallel input lines are provided, it can serve as a parallel-to-serial conversion device. Parallel readout lines enable it to be used as a serial-to-parallel converter. The serial shift register serves principally to provide buffer storage, accepting information when available and delivering it when desired. It can also provide speed buffering by being pulsed at one rate when receiving information and at another when delivering it. Whenever a shift command is received, each stage is cleared and made to accept the previ-ous contents of the preceding stage. If used simply as an external read-in device, shift pulses will be received every time a new bit is to be entered.
eBook - PDFElectronic Systems
Study Topics in Physics Book 8
- William Bolton(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
(b) If input B is high the final output is low. Whether the input is at A or B the circuit 'remembers' which was its last input and remains in that condition until the next input is received. The bistable circuit is thus a circuit having two stable states. Such a circuit is sometimes referred to as a flip-flop. We can modify the input arrangement to the bistable circuit so that instead of having to alternate the high input from input A to input B a circuit will automatically switch the input from A to B, putting the input to whichever of A or B is in the low state. We thus have: 1st high input to the bistable gives a high output. 2nd high input to the bistable gives a low output. 3rd high input to the bistable gives a high output. 4th high input to the bistable gives a low output. 5th high input to the bistable gives a high output, etc. Figure 5.20 shows the circuit that can be used to give the above results. By combining a number of these bistable circuits a counter can be produced. Such a counter will count on a binary rather than a denary scale. A binary scale involves counting to a base of two, a denary scale involves counting to a base of ten. Denary scale 0 1 2 3 4 5 Binary scale 0 1 10 11 100 101 Figure 5.20 Digital compu ters 91 If we call a low output 0 and a high output 1 we have for the bistable circuit: 1 st high input 2nd high input 3rd high input 4th high input 5th high input output high, i.e., output 1 output low, i.e., output 0 output high, i.e., output 1 output low, i.e., output 0 output high, i.e., output 1 A count of 1 on the denary scale means a count of 1 on the binary scale. The bistable circuit indicates a 1 for a 1 pulse input. A count of 2 on the denary scale means 10 on the binary scale. The bistable circuit indi-cates 0, just the second figure of the 10. What we need to indicate the 10 are two bistable circuits so that the second pulse causes the first bistable circuit to indicate a 0 and the second bistable circuit to indicate a 1.
eBook - PDF- B. Holdsworth(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
A diagram illustrating the arrangement is shown in Figure 2.7. Data from the device cannot be transferred to the system interconnecting bus until each of the tri-state gates has been enabled by the signal E. A Output A Output 0 0 High 0 0 High 0 1 0 0 1 1 1 0 High 1 0 High 1 1 1 1 1 0 { / ») Figure 2.6 (a) The tri-state gate and its truth table (b) The inverting tri-state gate and its truth table i i i i i i, i i Data bus Figure 2.7 Device connection to system data bus via tri-state buffers In certain circumstances data may have to be transmitted from the device to the interconnecting bus and also received by the device from the same bus. This will require a bidirectional capability, as illustrated in Figure 2.8. The transmission and receipt of data is controlled by two selection signals, E! and E 2 . When E! = 1 and E 2 = 0, data is transmitted from the device to the bus, and when E x = 0 and E 2 = 1 data can be received from the bus. When = E 2 = 0, both the device and the bus are tri-stated and data can pass in neither direction. Logic 34 The D-type flip-flop 35 Data output Bidirectional data bus line From and to device Data input Figure 2.8 Tri-state connection to bidirectional data bus 2.6 The D-type flip-flop A single-bit memory element is a device that will store one binary digit. The most widely used device of this kind in a microprocessor system is a D-type flip-flop, although it should be noted that other types of flip-flops such as T, SR and JK are also widely available and are sometimes used in microprocessor systems. A D-type flip-flop is a bistable element, which implies that it has two stable states, and conventionally it can be represented by the diagram shown in Figure 2.9(a). For this D-type flip-flop there is one input or data line D and two complementary output lines, Q and Q. The two stable_states are defined as (a) Q = 0 and Q = 1, and (b) Q = 1 and Q = 0. Control of the transfer of data D to the output Q line is achieved via the clock line.
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