In this paper is described the design and implementation process f the STL compiler for the PLC-UD, the which is in charge of generating executable code for the PLCs, starting from the structured language STL. The work consists of two fundamental parts, the administration of the hardware and the compilation process. For the first part, is defined the routines in object language necessary in the compilation, and for second part it shows the used compilation techniques, and the way in that the compiler was implanted using the C++ language.