The Siemens 6ES7901-2BF00-0AA0 is a PC/MPI cable with an RS-232 interface, 5 meters long. It connects a programming device (PG/PC) to the MPI port of a SIMATIC S7-300, S7-400, or C7 CPU, or to a PC-based controller like the Microbox. The cable handles the RS-232-to-MPI protocol conversion internally, so no external adapter is needed.
This cable is in a mature lifecycle stage — still available through normal Siemens distribution channels, not subject to a last-time-buy notice.
