“Siemens 200 PLC data line selection” problem?

PC/PPI programming cable, RS-232/PPI multi-master programming cable and USB/PPI multi-master programming cable What are the differences between the three S7200PLC data cable models, what is PPI, what is multi-master programming

The Siemens S7-200 programming communication cable is divided into two types:
Programming communication cable, PC/PPI, RS232/485 conversion, with optical isolation, maximum 187.5K baud rate, support for multiple master stations;
Programming communication cable, PC/PPI, USB/RS485 conversion, with optical isolation, maximum 187.5K baud rate, support for multiple master stations;

The order numbers are 6ES7901-3CB30-0XA0, 6ES7901-3DB30-0XA0