Petri nets are a research tool for systems consisting of interacting components. Petri nets are the most interesting in that they allow representation and studying the behavior of evolving parallel processes in a program or in a discrete device. Petri nets are used to describe an asynchronous composition of fine-grained algorithms. To this end a sample model of a Petri net based on a parallel flowchart is created in the form of a parallel substitution algorithm (PSA). A set of cells associated with places within a net is transformed by such an algorithm. Parallel substitutions are associated with transitions within a network. Each such substitution transforms the states of the cells that are set in correspondence with input and output places of the transition that is set. The resulting algorithm can be used to build a network of automata, on which is a control device for the operators included in the composition. This transforms a Petri net into a working system, for example, a control unit of a special-purpose processor.