The paper presents the authors' original contributions to the synthesis of embedded systems based on programmable logic arrays. An embedded system has one or more central units with a program structure. This allows the optimized design of the instruction set for that central unit. The paper presents the method used to design central units with a dedicated set of instructions. The advantages and disadvantages of the method are discussed and the design steps are presented. We discuss the shortcomings regarding the portability of the programs and we also show the methods of solving this. In the paper there is also an analysis of the structure used for the dedicated set of instructions.