Start the step7-micro /WIN32 programming software and write the ladder diagram in the user window. Before programming, you must first determine the host model and select PLC model according to the actual application: right-click the "project 1 (CPU221)" icon, click the "type" in the pop-up button, or use the "PLC" menu to select the "type" command, and then select the PLC model to use in the pop-up dialog box. This article selects PLC224 and then writes the ladder diagram.