Chapter 1 Introduction 1.2 Software 1.2.1 Program Editor The outline of program editor ISPSoft: There are five types of programming languages, including the instruction list, the structure text, the ladder diagram, the sequential function chart, and the function block diagram. The use of variables which allows the user to define the variable symbol to replace the device name of the PLC not only enhances the readability of the program, but also saves the user a lot of time to allocate the address of the device. 1-9