This is 3 free pin to rs232 set top box software downloading cable. This cable gives you freedom to choose Txd, Rxd and Gnd on the PCB plate of Set Top Box. Because some stb manufecturers have different sequence of these these trans , receive and groud. So it can be used on both type of set top boxes.
If still you wants to have more details about RS232 cables then visit https://www.headendinfo.com/rs232-cables-stbs/