The task of this bachelor thesis was to develop a program block for generating a reference signal of variable amplitude and frequency. The program block provides the possibility of defining four different signal types, namely, a saw-tooth wave, sine wave, square wave and triangle wave. A sine wave enables defining of a phase shift. Program development, simulation and visualization are done using “Step 7” and “CoDeSys” software tools. These software tools are used for programming of PLCs (Programmable Logic Controllers), computer devices that control automation processes inside of a plant. The task in “Step 7” is carried out in following way. Inside of “OB35” (Organization Block), which provides cyclic execution of the block in fixed intervals, a call of FB (Function Block), named “SIG_GEN”, is carried out with given parameters. The function block, based on the input parameter “MODE”, makes a call of one of four FCs (Function). Functions, aided by mathematical operations, calculate values of a saw-tooth wave, sine wave, square wave, or triangle wave, after which these values are recursively written in the output global variable “OUT_value”. The drawn values of individual signals are shown in “S7TrendValues” software. The program is written in LAD (Ladder Diagram) programming language. In a similar way, the program is developed using “CoDeSys” programming tool. The difference is in calling the function block “SIG_GEN” and assigning of real parameters being done using “PLC_PRG” program. The other difference is that function blocks are used for calculating signal values instead of functions. Visualization is available in the embedded tools called “Sampling Trace” and “Visualization”, while the program is written in CFC (Continuous Function Chart Editor) programming language.