# Method for the diagnosis of combinational logic circuits

(57) Abstract:

The invention relates to computing and allows high accuracy to control the combinational logic (CCL). The method is based on measuring the number of logical changes on the output poles of the logic circuits. Characterized in that the modules corresponding to different fault diagnosed KLS determine the coefficients of transparency of the i-th input to output is fed to the input X_{i}the analyzed logical schema meander frequency F

_{m}having a value satisfying resolution of the Registrar logical extremes, on the N - 1 remaining inputs meanders frequencies, most of which must have a duration of a half-cycle pulse, not less than 2 times the duration of the period of the frequency F

_{m}and the transparency coefficient of the real logic is determined from the ratio Z/2 (N - 1) where Z is the number of time intervals in which detected more than two logical periods; N - number of input poles of the circuit. Diagnosis is carried out by comparing the coefficients of transparency obtained for modules of schemes with different faults, with a coefficient of transparency, which can be used when monitoring and diagnosing failures combinational logic (CCL) and nodes.The aim of the invention is to increase the reliability of control KLS.In Fig.1 shows a block diagram of the connection of devices for carrying out the procedure of diagnosing, Fig.2 shows the connection diagram of the experimental device at different stages of the procedure, diagnosis, and Fig. 3 presents diagnosed scheme (object of the experiment; Fig.4 shows time diagrams obtained using the logic analyzer (LA) with the experimental device shown in Fig.2B,and Fig.5 - time diagrams obtained through LA during the experimental device shown in Fig.2B,,Presented on Fig.1 device, with which implemented method, contain unit 1 impact (NI), consisting of a generator (g), 2 - simple generator of rectangular pulses, which can be done using simple logical elements using positive feedback, and using standard chip type GG, and counters-dividers 3, 4, 5 - group four-bit binary counters that meet the frequency requirements fed to the input of synchroneyes previous counter is input to the synchronization follow-up. The number of counters depends on the number of input poles of the object 6 of the experiment (MA) so that for every one to four input poles have one counter. MA 6 can be any KLS, where X is the input pole MA, and Y is the output pole. LA 7 - device for tracking digital signals (Registrar logical extremes), where L is the input channels LA. You can use any LA with the number of input channels at least three capable of tracking in asynchronous mode (i.e. with the internal clock).In Fig.3 presents KLS, she MA 6, each element of which can be the logical elements of type AND, OR, AND NOT, nor, NOT. And if MA 6 has several output poles of Y, then the entire procedure for diagnosis is divided into stages, each of which includes only one of these poles.A specific example of the procedure of diagnosis.For the experiment as MA take 6 circuit malfunction Const 1 at point b shown in Fig.3, is performed on the chip 155 series, where the logical element OR NOT 8 - CLE, the logical element AND a 9 - CLI, the logical element AND-NOT 10 - KLA, the logical element AND 11 KIL having four input the ve LA 7 using the experimental system of logical analysis (SAL - 1) developed in the Institute of automation and electromechanics, Tomsk. Determine the coefficients of transparency for models corresponding to different fault this CCL.From discrete mathematics aware of the concept of Boolean derivative or a Boolean difference. It is denoted as D (i/F) and is in a mathematical form record sets on which the variable of the i-th input is transmitted to the output or, as they say, "custsat path from the i-th input to output.Introduced integrated diagnostic parameter, the transparency coefficient of the i-th input and output is associated with a Boolean of the derived the following relationship: he is equal to the ratio of unit sets the Boolean derivative to the number of possible supplied sets of 2 ** (N-1). Mean that the Boolean derivative takes the value 1 on the set of N-1 inputs provided "manifestations" of the modulating signal of the i-th input to the circuit output.Further KLS consider vector, i.e., multidimensional, transparency coefficient consisting of coefficients transparency of all inputs schema.Because when a significant fault in the circuit is changing feature implemented this scheme, it is natural to expect that a different function is about.On the basis of the above, it is proposed to use this characteristic to distinguish significant fault scheme. The advantage of this approach is, on the one hand, that there is a possibility to compute the coefficient of transparency directly on the model, and on the other hand, this option is relatively easy to obtain experimentally.The procedure for determining the coefficient of transparency for models corresponding to different fault circuit and completing reference table that follows.Building on the block diagram of the orthogonal disjunctive normal form (DNF), which is obtained by superposition of functions describing each element in the form of orthogonal DNF (DNF, in which all of conjunction are pairwise orthogonal).Find the Boolean derivative of the function D (i/F) with respect to the i-th input (moreover, F can be as healthy and faulty function), by the formula

D(i/F)=F

^{1}

_{i}F

^{o}

_{i}= F

^{1}

_{i}VF.Using the properties of orthogonal DNF determine the number of units DNF this Boolean derivative.By dividing the number of units of the Boolean derivative 2 ** (N-1) output. Thus, define the entire dimensional vector of coefficients transparency.For each new input in the model to determine their fault multidimensional transparency coefficient, which is recorded in the reference table.A specific example of obtaining transparency coefficient for the KLS model, shown in Fig.3.Define DNF this healthy

F=BC=(x

_{1}A)()=x

_{1}()(()V)=

< / BR>

According to the formula D(i/F)=F

^{1}

_{i}VF define Boolean derivative D (i/F):

_{D(1/F)=};

_{D(2/F)=};

_{D(3/F)=};

_{D(4/F)=}.Determine the number of units of each of the Boolean derivative:

D

_{1}(F) = 1;

D

_{2}(F) = 1;

D

_{3}(F) = 1;

D

_{4}(F) = 1 and vector transparency coefficient for the proper schema

[1/8, 1/8, 1/8, 1/8].This procedure can be automated and executed in a short period of time.Determine the coefficient of transparency for the KLS model corresponding faults Const 1 at point C.Define DNF

F

^{}

^{}=V=()V=x

_{2}Vx

_{3}V..Define Boolean derivative according to the formula

D(i/F)=F

^{o}

_{i}VF:

D(1/F=0;

D(2/F=()=x

_{STI[0, 1/4, 1/4, 1/4].Consider the equivalence classes of faults of this circuit (fault, for which there is no separating tests).Malfunction Const 0 at point C, Const 0 at the point X1, Const 1 at the point x2, Const 1 at the point X3, Const 1 at the point X4, Const 0 at the point F, Const 1 at point F, Const 0 at point a, Const 0 at point b there is no transparency coefficient[0, 0, 0, 0].Malfunction Const 1 - point, onst 1 - at the point X1 corresponds to the transparency coefficient [0, 1/4, 1/4, 1/4], and so onProceed to the determination of the coefficient of transparency of the actual schema.Internal rate LA 7 is set to 1 MHz. The frequency generator 2 BV 1 set equal to 0.5 MHz, therefore, the signal Fmhas a frequency of 0.25 MHz, which satises resolution asynchronous mode LA to be at least 4 times less than the internal frequency of aircraft and does not exceed the maximum working frequency of the chip 155 series, equal to 100 MHz. The signal Fmthe modulating frequency is removed from the first output of the counter 3, the frequency is 2 times less than the frequency of the generator 2, which is supplied to the synchronization input of this counter. The rest of the frequency F1removed from the first output of the counter 4. Thus, the frequency of signal on the output pole OE 6, equal to not less than 16, for a time equal to the half period of the signal frequency F1(1 = 1). Signal frequency F1(1 = 1) does not necessarily have to be 16 times less than the signal frequency Fm. In order to estimate the number of drops was reliable, the signal frequency F1(1 = 1) must be at least 4 times less than the signal frequency Fm. Condition resolution asynchronous mode LA to be at least 4 times less than the internal frequency LA follows from the following considerations.The asynchronous nature of LA mode is to record the sequence of logical signals in the memory LA synchronously with the internal frequency of the clock pulses C LA, i.e., for each clock C in memory of LA (one input channel) recorded bits of information. The recorded signal as would "cut" the frequency of SI, and recorded will be the information which was at the entrance of LA at the time of arrival of the sync pulse SI. It is obvious that the more "cut" of the input signal, the more are aware of it. But too much frequency "cut" requires large amounts of memory LA and application of high-frequency element base for the creation of LA. To receive the lowest full and true information about the monitored signal, Meuse is the beginning and the end of zero half-cycle and at the beginning and end of a single half-cycle. Hence the condition - satisfying resolution asynchronous mode, LA, ie, to be at least 4 times less than the internal frequency of the aircraft.Make the connection of the experimental device, as shown in Fig.2A-g, so that was produced brute force signal Fmturn on each of the four input poles MA 6, and the other three free pole signals F1(1 = 1, 2, 3). In each experiment, the signals FmF1(1 = 1), Y monitored LA 7.The signal Fmserved on input X1 MA 7 and L1 LA 7, the signal F1served on input x2 OE 6 and L1 LA 7, the signal F2- input pole X3 OE 6, the signal F3- input pole X4 OE 6, the Y signal on the input pole L3 LA 7.Apply power to the BV 1 and OE 6 and conduct an experiment, the result of which is to obtain quasibiennial chart in Fig.4A.Make the connection of the experimental device, as shown in Fig. 2B. The signal Fmserved on input x2 OE 6 and L1 LA 7, the signal F1- on input X1 OE 6 and L1 LA 7, the signal F2- input pole X3 OE 6, the signal F3- input pole X4 OE 6, the signal MA 6 Y - input pole L3 LA 7.Apply power to the BV 1 and OE 6 and experiment, financial p is Sperimentale device, as shown in Fig. 2B. The signal Fmserved on input X3 OE 6 and L1 LA 7, the signal F1- on input X1 OE 6 and L1 LA 7, the signal F2- input pole x2 OE 6, the signal F3- input pole X4 OE 6, the signal MA 6 Y - input pole L3 LA 7.Apply power to the BV 1 and OE 6 and conduct an experiment, the result of which is to obtain quasibiennial chart in Fig.5A.Carry out the connection of the experimental device, as shown in Fig. G Signal Fmserved on input X4 OE 6 and L1 LA 7, the signal F1- on input X1 OE 6 and L1 LA 7, the signal F2- input pole x2 OE 6, the signal F3- input pole X3 OE 6, the signal MA 6 Y - input pole L3 LA 7.Apply power to the BV 1 and OE 6 and conduct an experiment, the result of which is to obtain quasibiennial chart in Fig.5B.Procedure switches feeding signals with BV can be automated.Estimate the number of drops from zero in the unit on the output pole MA Y 6 (Fig.4A) for a period of time equal to the half period of the signal frequency F1. It is evident from Fig.4B shows that at the pole Y for two of the eight time intervals equal to half the signal frequency F1there are more than two drops of zero in e is the number of drops from zero in the unit on the output pole MA Y 6 (Fig.5A) for a period of time, equal to the half period of the signal frequency F1. It is evident from Fig.5A shows that at the pole Y for two of the eight time intervals equal to half the signal frequency F1there are more than two changes from zero to one, therefore, we can conclude that the transparency coefficient K3= 1/4.Estimate the number of drops from zero in the unit on the output pole MA Y 6 (Fig.5B) for a period of time equal to the half period of the signal frequency F1. It is evident from Fig. 5B shows that at the pole Y for two of the eight time intervals equal to half the signal frequency F1there are more than two changes from zero to one, therefore, we can conclude that the transparency coefficient K4= 1/4.Complex or vector transparency coefficient K= [0, 1/4, 1/4, 1/4].Conduct its comparison with the coefficients of transparency for models of fault, it coincides with the transparency coefficient corresponding to the class of equivalent fault belongs and put in a real circuit malfunction Const 1 at point C.Compared with the prototype of the reliability of control procedures and diagnosis of KLS implemented the proposed method is increased due to the other diagnostic parameters) must be performed many experiments, because of the increased likelihood of errors when large volumes of measurements during the preparatory procedure leads to decrease in the reliability of subsequent diagnostic procedures, and the proposed method allows producing minimal calculations on the structure KLS get parameter diagnostic theoretically, eliminating experimental error and error and reduces the time for preparatory procedures of diagnosis (filling in the reference table) for the set of exceptions to this procedure, mechanical operations and human intervention. A METHOD for DIAGNOSING COMBINATIONAL LOGIC CIRCUITS based on measuring the number of logical changes on the output poles of the circuit, characterized in that, in order to increase reliability analysis for models corresponding to different fault diagnosed combinational logic circuit, determine the coefficients of transparency of the i-th input and output (i=), each of which is equal to the ratio of unit sets the Boolean derivative to the amount of potential applied to the N-1 input poles of this scheme sets, the number of which is determined by the formula 2**(N-1) is fed to the input Xiissled the th ability Registrar logical extremes and do not exceed the permissible operating frequency of the circuit, and on the N-1 remaining inputs - the meanders of frequencies, most of which Fl(l= 1) must have a duration of a half-cycle pulse, not less than 2 times the duration of the period of the frequency Fmand the rest of the frequency Fl (l = ) must be a multiple of the greatest, when the output signal is fixed by the Registrar logical differences, determine the coefficient of transparency of the real logic of the ratio,,where Z is the number of time intervals for the output signal Y is equal to the half period of the signal Fl (l=1), which found more than two logical differences, N is the number of input poles of circuit,and diagnosis is carried out by comparing the coefficients of transparency obtained for models of schemes with different faults, with transparency coefficient obtained experimentally. }

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