How can we transform a usb port to a RS232? How to do the hard communication and how to make the cable?

يوجد هذا النوع من الكابل في السوق واعتقد تكلفة عمله لاول مرة لن تكون بالجودة المطلوبة  

there is converter with software to working with almost operating systems to convert from USB port to RS232 port and if we want to make comnucation between computer'usb port and  device with RS232 interface we maste make cable with tow 9 poles  DBI connectors Male and Femal we connect like this M                                    F 2 _TX________________RX__3 3__RX_______________TX__2 7_________GND___________7 we install the software of the converter on the computer then custmised the vertual COMe port number and Baud rate and this conveniant with the device baud rate then we connect the RS232 cable one side F to the USB converter to USB computer port and other side M to the device RS232 port and make the connectin through the software of the divce (PLC- INVERTER- satellait riecever ..etc )

there is a usb-RS232 cable in the markets ..........
not expensive

usb to rs232 connector available in market mostly works on old laptops or pc