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The combinational logic design method is suitable for designing digital control programs. It involves logical analysis and synthesis of control tasks, treating the on/off states of components as logical functions with the on/off states of contacts as logical variables. For the simplified logical functions, PLC logic instructions can be used to develop efficient and concise programs that meet the required specifications. This approach has a clear design concept, and the programs written using it are easy to optimize. Programming using the combinational logic design method generally involves the following steps: 1) Define the control tasks and requirements; by analyzing the manufacturing process, draw diagrams of the working cycles and the distribution of sensing elements, and obtain a functional table for the electrical actuating elements. 2) Draw a detailed system state transition table. It usually consists of four parts: the output signal status table, the input signal status table, the state transition command table, and the intermediate memory device status table. The state transition table presents in a comprehensive and complete manner the states of various components of the system at different times, as well as the relationships and transitions between these states. It is very intuitive and greatly helps in understanding the overall structure of control systems and the concept of dynamic changes; it serves as an effective tool for analyzing and designing such systems. 3) Perform the logical design of the system based on the state transition table, including writing the logical function expressions for the intermediate memory elements and those for the actuating elements (output values). These two functional sets are not only expressions of the internal logical relationships and patterns of change in manufacturing machinery or production processes, but also the specific programs that constitute control systems to achieve control objectives. 4) Convert the results of the logical design into a PLC program. The results of logical design (logical function expressions) can be easily converted into PLC programs, especially in the form of statement lists; their structure and format are very similar to those of logical function expressions, making it straightforward to convert them directly from logical function expressions. Of course, if the designer needs a ladder diagram program as a transition, or if the programmer for the selected PLC has graphic input capabilities, it is also possible to first convert it from a logical function form into a ladder diagram program.