Chapter 2 0BProgramming Users can see the Prog_Main window on the main screen. The difference between the function block and the main program is that the function block has to be called before it is executed while the main program is executed directly. The creation of the local symbols for the main program is omitted in this example. Please write the following program by means of the skills learned previously. Users can prepare to call the function block. First, click to open the API/FB window. Then, select Function Block in the Type Class box, and select “FB_SPP_Sys” in the API/FB box. Finally, click Insert . 2-29