Digital Systems Functions Set Defining to Select Design Debugging Tests

Digital control systems are considered, the functioning of which can be represented as a sequence of functions from a finite alphabet. For such systems projects debugging by simulation it is necessary to generate some set of tests for the applying on the simulated system to verify that it is functioning correctly. This paper is devoted to the development of test sets for function successions correctness. It is shown that on admissible function successions partly defined semigroup exists. Admissible successions are formally described by the graph of functions. Such a graph defines admissible functions for all digital system states. If the admissibility of two functions fulfillment one after another depends on previously fulfilled functions and the digital system internal state, then some functions should be divided into several subfunctions. The method of such a process is described. The developed graph of functions together with input interaction set for each digital system function define specification for digital system behavior. The proposed method is illustrated on the drawing machine control digital system functions development.