The methods of fault-tolerant coding are often used in the designing of reliable and safety components of automatic control systems: both in the data transmission between system nodes, and at the level of hardware and software architecture.
The redundant coding is widely used in the management of combinational logic devices control. In this case, codes, which are oriented to the error detection rather than correction of this, are in use. Such features of codes make it possible to implement the checkable automation systems with acceptable redundancy, which does not exceed the redundancy in the situation of duplication using.
The paper highlights the method of the synthesis of self-checking combinational devices, which makes it possible to take into account the features of the source devices architecture, as well as the properties of error detection by redundant codes in solving the problem of the synthesis of technical means for diagnosis. The paper gives the basic information on the theory of the checkable digital systems synthesis on the basis of redundant codes with summation.
The basic stages of the analysis of the diagnosis objects topologies are determined with the selection of groups of outputs — groups of structurally and functionally symmetrically independent devices outputs. The formulas are given to determine the presence or the absence of a symmetrical dependence of the diagnosis object outputs. The example illustrating the calculation process is given. The main stages of the analysis of the redundant codes application in the error detection on the functionally symmetric dependent outputs are formulated. The algorithm of the synthesis of the self-checking combinational devices with taking into account the object of diagnosis structure features and the redundant codes properties is proposed.
The paper describes research results of features of error detection in data vectors by sum codes. The task is relevant in this setting, first of all, for the use of sum codes in the implementation of the checkable discrete systems and the technical means for the diagnosis of their components. Methods for sum codes constructing are described. A brief overview in the field of methods for sum codes constructing is provided. The article highlights codes for which the values of all data bits are taken into account once by the operations of summing their values or the values of the weight coefficients of the bits during the formation of the check vector. The paper also highlights codes that are formed when the data vectors are initially divided into subsets, in particular, into two subsets. An extension of the sum code class obtained by isolating two independent parts in the data vectors, as well as weighting the bits of the data vectors at the stage of code construction, is proposed.
The paper provides a generalized algorithm for two-module weighted codes construction, and describes their features obtained by weighing with non-ones weight coefficients for one of data bits in each of the subvectors, according to which the total weight is calculated. Particular attention is paid to the two-module weight-based sum code, for which the total weight of the data vector in the residue ring modulo M = 4 is determined. It is shown that the purpose of the inequality between the bits of the data vector in some cases gives improvements in the error detection characteristics compared to the well-known two-module codes. Some modifications of the proposed two-module weighted codes are described. A method for calculating the total number of undetectable errors in the two-module sum codes in the residue ring modulo M = 4 with one weighted bit in each of the subsets is proposed. Detailed characteristics of error detection by the considered codes both by the multiplicities of undetectable errors and by their types (unidirectional, symmetrical and asymmetrical errors) are given. The proposed codes are compared with known codes. A method for the synthesis of two-module sum encoders on a standard element base of the single signals adders is proposed. The classification of two-module sum codes is presented.
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