Before executing an on-line simulation, the user can click [Tools] [On-line Simulation] or click the icon in the Layout Bar, or use the system hotkey [Ctrl+F4]. The system will ask the user to set the number of the communication port at the PC end that corresponds to the HMI, as shown in the figure below. If the box next to Ask on every time is not checked, the system will execute the on-line simulation directly without opening the Com Port Setting dialog first. When the system has entered into the On-line Simulation dialog, the user can right click the mouse to open the drop-down menu as shown in the figure below. After clicking Com Setting, the Com Port Setting dialog opens again. Once the Com Port Setting dialog is displayed, the user can set and modify the number of the communication port. When all the settings are correctly set, the On-line Simulation represents the communication between the HMI and PLC.