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Petersburg State Transport University Automation and Remote Control on Railways department A. Blyudov, D. Efanov, V. Sapozhnikov, Vl. Sapozhnikov

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Properties of code with summation for logical circuit test organization, EWDTS`2012 2

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S(n,m)-codes Properties of code with summation for logical circuit test organization, EWDTS`2012 3

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The errors of an even multiplicity, which have the number of distortions of the informational bits of the type 1 0 equal to the distortions 0 1, cannot be detected in the S(n,m)-code. Formula for calculating the number of undetected errors d – multiplicity of undetectable error; m – length of informational word r – weight of informational word S(8,5)-code In S(8,5)-code 160 undetectable errors with d=2 & 60 undetectable errors with d=2 Properties of code with summation for logical circuit test organization, EWDTS`2012 4

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In the S(n,m)-code the share of undetectable errors β d doesnt depend on the number of informational bits and it is constant The Berger code has a great number of undetectable errors. Particularly, it doesnt detect 50% of distortions of multiplicity 2 Properties of code with summation for logical circuit test organization, EWDTS`2012 5

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Decreasing a number of check bits in the code with summation could be reached if the calculation of ones in the informational vector is carried out by some modulo M (M=2 i <2 k, i=1,2,…) SM(n,m)-codes There are modulo codes, besides the S(n,m)-code, for any value of m. There are modulo codes, besides the S(n,m)-code, for any value of m. Properties of code with summation for logical circuit test organization, EWDTS`2012 6

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All the errors of information bits of the odd multiplicity are detected in the modulo codes, but the errors of the even multiplicity may not be detected. The share of the undetectable errors β d for a modulo code doesnt depend on the number of informational bits and it is a constant value. Any S2(n,m)-code (a parity code) doesnt detect 100% of errors of informational bits of any even multiplicity. Any S4(n,m)-code doesnt detect 50% of errors of informational bits of any even multiplicity. The SM(n,m)-code has the same number of errors of multiplicity d

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Values of the characteristic β d Properties of code with summation for logical circuit test organization, EWDTS`2012 8

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1. The S(n,m)-code is formed for the current m. 2. The modulo M is fixed: M=2,4,8,…,2 b ; b=]log 2 (m+1)[-2. 3. For the current informational word the number of ones q is counted, which is converted to the number W=q(mod M). 4. The special coefficient α is determined. 5. If ( ), then α=0, otherwise α=1. 6. Then the resultant weight of an informational word is counted. 7. The check word is a binary notation of V. 1. The S(n,m)-code is formed for the current m. 2. The modulo M is fixed: M=2,4,8,…,2 b ; b=]log 2 (m+1)[-2. 3. For the current informational word the number of ones q is counted, which is converted to the number W=q(mod M). 4. The special coefficient α is determined. 5. If ( ), then α=0, otherwise α=1. 6. Then the resultant weight of an informational word is counted. 7. The check word is a binary notation of V. The method of forming a RSM(n,m)-code is: RSM(n,m)-codes Properties of code with summation for logical circuit test organization, EWDTS`2012 9

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The analysis tables for different codes allows to deduce the following conclusions: 1. The RS(n,m)-codes have the best characteristics to detect errors. For example, the RS(21,16)-code has about by two times less undetectable errors in comparing with the Berger code, and this concerns to the errors of any multiplicity. 2. Any modulo modified code with M4 has the better detection characteristics than any non-modified code. 3. The modulo non-modified codes have an advantage in detecting errors among all the codes with the number of check bits d=2. The analysis tables for different codes allows to deduce the following conclusions: 1. The RS(n,m)-codes have the best characteristics to detect errors. For example, the RS(21,16)-code has about by two times less undetectable errors in comparing with the Berger code, and this concerns to the errors of any multiplicity. 2. Any modulo modified code with M4 has the better detection characteristics than any non-modified code. 3. The modulo non-modified codes have an advantage in detecting errors among all the codes with the number of check bits d=2. Properties of code with summation for logical circuit test organization, EWDTS`2012 11

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The table of codes, in which the main characteristics of all the available codes with summation with a current number of informational bits are given, allows to choose a code more reasonably at organizing the check of a combinational circuit. Herewith there is a possibility to consider the properties of a control circuit, for example, the possibility of appearing errors of the determined multiplicity at the outputs of the circuit. A. Blyudov, D. Efanov, V. Sapozhnikov, Vl. Sapozhnikov Petersburg State Transport University Automation and Remote Control on Railways department Properties of code with summation for logical circuit test organization, EWDTS`2012 12

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