Combinational circuits are logic circuits whose outputs respond immediately to the inputs. Gatelevel test generation for sequential circuits people. Design of synchronous counters, shift registers and their e applications. On potential fault detection in sequential circuits. Another tool in the design and analysis of sequential circuits is the transition table. Fault modeling of combinational and sequential circuits at. The use of feedback in a device can introduce problems which are not found in strictly combinational circuits. It is assumed that all testing must be performed on the external terminals of the circuits. Block diagram flip flop flip flop is a sequential circuit which generally samples its. Because the current state is being constantly fed back a glitch during a. The figure above shows a theoretical view of how sequential circuits are made up from combinational logic and some storage elements.
Basic memory cell operation sr latch jk latch d latch flipflops clocked cmos logic cascode voltage. Give a precise definition of synchronous sequential circuits. Pdf a fault detection method for combinational circuits. A discussion of the construction of stateoutput tables or diagrams from a word description or flow chart.
Sequential circuits use current input variables and previous input variables by storeing the information and putting back into the circuit on the next clock activation cycle. Examples for sequential digital circuits are registers, shift register, counters etc. Big data architect in companies such as santander, daimlerbenz, telefonica, etc through my company synthetic data. Sequential circuits a sequential circuit consists of a combinational circuit and a feedback through the. This thesis is concerned with the detection of non transient faults in linear sequential circuits lsc over gf2 8. It is in contrast to combinational logic, whose output is a function of only the present input. This paper describes the design of experimental procedures for determining whether or not a sequential switching circuit is operating in accordance with a given statetable description. Fault modeling of combinational and sequential circuits at register transfer level. Sequential circuit it is a type of logic circuit whose output depends not only on the present value of its input signals but on the past history of its inputs. Analysis of clocked sequential circuits and mealy and moore models of finite state machines 6 hours 6. In this course material we design and analyze only synchronous sequential logic. Multivalued circuits in fault detection of binary logic circuits. Elec 326 1 sequential circuit analysis sequential circuit analysis objectives this section introduces synchronous sequential circuits with the following goals. This solution is based on the combination of a bist structure with a scanbased design to apply delay test pairs to the circuit under test.
Test pattern generation for sequential circuits on single stuckat fault model. Sequential circuit analysis electrical and computer. Basic concept of fault detection and location in sequential. Sequential circuit design university of pittsburgh. Fault diagnosis in sequential circuits sciencedirect. Input sequence to set z to 0 in the faultfree circuit. A synchronous sequential circuit usually has a clock pulse clocked sequential circuits.
Test generation for sequential circuit using podem algorithm. This paper proposes a novel approach to the delay fault testing problem in scanbased sequential circuits. It has state memory while combinational logic does not. As the asynchronous sequential circuit has become more and more important to digital systems in recent years high reliability and simple maintenance of the circuit is stressed. Microelectronics and reliability vol15 supplement pp. Chuang, a unified approach to the realization of failsafe sequential machines, ieee proceedings of the fourth annual international symposium on faulttolerant computing, 1974, pp. Flip flop is a sequential circuit which generally samples its inputs and changes its outputs only at particular instants of time and not continuously. But sequential circuit has memory so output can vary based on input. The significance of proposed work lies in the design of reversible sequential circuits and their equivalent circuits for maximum fault coverage. The removal of hazards requires the addition of redundant gates to the circuit. Lecture 11 27 modulo3 counter cyclic structure sequential depth is undefined.
Digital electronics part i combinational and sequential logic. Sequential circuit analysis last week we started talking about memory. This type of circuits uses previous input, output, clock and a memory element. Deterministic test pattern generation techniques for sequential circuits ilker hamzaoglu and janak h. There are many creative ways to assign binary numbers to state labels, here. Flipflops inclusion of masterslave, characteristics equation and state diagram of each ffs and conversion of flipflops. In general, hazard s in combinational circuits can be removed by cove ring any two minterms that may produce a hazard with a product term common to both. Digital electronics part i combinational and sequential. Deterministic test pattern generation techniques for. Upon the completion of electrical circuit and simulation practical course, the student will be able to attain the following.
Delay testing that requires the application of consecutive twopattern tests is not an easy task in a scanbased environment. Sequential logic sequential circuits simple circuits with feedback latches edgetriggered flipflops timing methodologies cascading flipflops for proper operation clock skew asynchronous inputs metastability and synchronization basic registers shift registers simple counters hardware description languages and sequential logic. Multivalued circuits in fault detection of binary logic circuits zvonko g. Department of computer engineering and information technology amirkabir university. The outputs of a sequential circuit depend on not only the inputs, but also on whats stored in the circuits memory.
Yet virtually all useful systems require storage of. Demonstrate by example how to analyze synchronous sequential. Combinational and sequential logic circuits hardware. Asynchronous circuits must be hazard free along their path through the input state space.
These procedures are particularly easy to apply when the given state table is reduced, stronglyconnected, and has a distinguishing sequence, and when the actual circuit has no more states than the given table. One bit memory cell the simplest sequential circuit or storage element is a bistable multivibrator, which is constructed with two inverters connected sequentially in a loop as shown in figure below. Conservative logic gates can be designed in any sequential circuits and can be tested using two test vectors. We will now study the behavior of sequential circuits where their output values are computed using both the current and past input values. Consequently the output is solely a function of the current inputs. The design of a synchronous sequential circuit starts from a set of specifications and culminates in a logic diagram or a list of boolean functions from which a logic diagram can be obtained. We must develop efficient fault detection and location methods in order to reduce.
In contrast to a combinational logic, which is fully specified by a truth table, a sequential circuit requires a state. Basically, sequential circuits have memory and combinational circuits do not. In a sequential logic circuit the outputs depend on the inputs plus its history. Block diagram flip flop flip flop is a sequential circuit which generally samples its inputs and changes its outputs only at. Read, highlight, and take notes, across web, tablet, and phone. Fault diagnosis in sequential circuits 19 which distinguishes the most faults which have not yet been distinguished, should be selected first. Ser in sequential circuits compared to the number of methods proposed for modeling. All sequential circuits contain combinational logic in addition to the memory elements. The scanpath technique for testable sequential circuit design copy free download as powerpoint presentation. Fault detection in sequential circuits by vladimir frantisek berka. A scanbist structure to test delay faults in sequential. Jul 19, 2015 apr 15, 2020 basic concept of fault detection and location in sequential circuits notes edurev is made by best teachers of.
A combinational logic circuit is a circuit whose outputs only depend on the current state of its inputs. A discussion of the construction of stateoutput tables or diagrams from a word description or flow chart specification of sequential behavior. Concurrent error detection in sequential circuits using. Modeling and optimization for softerror reliability of. The sequential test generation algorithm, which is e ective for small and medium sized sequential. The probability of error detection in sequential circuits.
Right from a simple mobile memory card to a bulky computer memory modules are the rocksolid example of application of seq. Automatic test pattern generation for sequential circuits. Latches and flipflops are basic onebit memory units. A thesis in electrical engineering submitted to the graduate faculty of texas tech university in partial fulfillment of the requirements for the degree of master of science in electrical engineering approved c accepted may, 1975. That is, a detection test in this case must consist of applying certain signals at the circuit s external input terminals and ob. This document is highly rated by students and has been viewed 3462 times. Hazards in combinational circuits and sequential circuits. Fault detection in logical circuits by samprakash majumdar, b. The circuit is partitioned into three parts, the input and output combinational logic and the memory. For more examples and detailed description of the material in the lecture notes, please refer to the main textbook. In this article a method is presented for evaluating the probability of detecting pd a single stuckfault in a sequential circuit as a function of the number of random input test vectors. Apr 15, 2020 basic concept of fault detection and location in sequential circuits notes edurev is made by best teachers of.
Asm chart, timing considerations, control implementation design with multiplexers, pla controlasynchronous sequential circuits. The storage capability in sequential circuits is normally achieved by means of flipflops. Publication date 1975 topics electric fault location data processing, digital integrated circuits testing, sequential machine theory. Later, we will study circuits having a stored internal state, i. Ripple counter increased delay as in ripplecarry adders delay proportional to the number of bits. Multivalued circuits in fault detection of binary logic.
The sequential test generation algorithm, which is e ective for small and medium sized sequential circuits, is based on the podem algorithm. Elec 326 1 sequential circuit design sequential circuit design objectives this section deals with the design of sequential circuits including the following. Binary counters simple design b bits can count from 0 to 2b. These functions can be described using logic expressions, but is most often at least initially using truth tables. In designing asynchronous sequential circuits, care must be taken to conform to certain restrictions and precautions to ensure that the circuits operate properly.
Autumn 2003 cse370 vi sequentai llogci 1 sequential logic sequential circuits simple circuits with feedback latches edgetriggered flipflops timing methodologies cascading flipflops for proper operation clock skew asynchronous inputs metastability and synchronization basic registers shift registers simple counters hardware description languages and sequential logic. Logic gates are the simplest combinational circuits. Consist of a combinational circuit to which storage elements are connected to form a feedback path. Sequential circuit analysis university of pittsburgh.
Flip flop is a sequential circuit which generally samples its inputs and changes its outputs only. Fault detection methods in sequential systems sciencedirect. Hughes, virgil willis, fault diagnosis of sequential circuits 1969. Automated error prediction for approximate sequential circuits. Similar to combinational circuits, the alternative to simulation is analyticalsymbolic modeling. Easy to build using jk flipflops use the jk 11 to toggle. It contains the same information as the state table, except that all labels have been replaced by binary numbers. Vranesic departments of electrical engineering and computer science university of toronto toronto, ontario, canada abstract the paper considers two possibilities of. Me vlsi design materials,books and free paper download. Fault detecting experiments for sequential circuits. Experimental section1 you will build an adder using 7400nand and 7402nor gates, as an example of combinational logic circuit. A fault detection method for combinational circuits. They do not remember the history of past inputs and, therefore, do not require any memory elements. A fault detection method for combinational circuits aliabbasszoraghchian1, moslem didehban2, mohammadreza mehrabian3 1.
The scanpath technique for testable sequential circuit. Digital design 3rd edition, by morris mano, publisher prentice hall, 4th edition. Sample of the study material part of chapter 5 combinational. Input signals change one at a time and only when the circuit is in the stable state. What are the applications of sequencial logic circuits. A discrete parameter markovmodel is used in the analysis to obtain closedform expressions for pd. The circuit must be operated in fundamental mode with only one input changing at any time and must be free of crit. Pdf on potential fault detection in sequential circuits. In mathematical terms, the each output is a function of the inputs.
However, while in case of logic circuits one pass through the circuit is enough to evaluate its susceptibility to given particle hit, in the case of sequential circuits this evaluation becomes much more difficult. Testing digital systems i lecture 11 14 copyright 2010, m. For fault detection, the test which detects the most faults which have not yet been detected, is the best choice. We now consider the analysis and design of sequential circuits. Fault detection in asynchronous sequential circuits. Introduce several structural and behavioral models for synchronous sequential circuits. Combinational circuits are the class of digital circuits where the outputs of the circuit are dependent only on the current inputs.
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