The Siemens 6ES7901-3DB30-0XA0 is a USB-to-PPI programming cable for the SIMATIC S7-200 PLC family. It connects an S7-200 CPU to a USB port on a PC for program download and online diagnostics, supporting PPI protocol at 10/11 bit framing. The cable is powered from the USB interface, so no external supply is needed at the PC side.
The cable length is 5.63 m, which is enough to reach from a panel-mounted S7-200 to a laptop on the floor without an extension. The maximum transmission rate is 187.5 kbit/s, with auto-baud support for 9.6, 19.2, and 187.5 kbit/s — no DIP switch setting required. That covers the standard S7-200 baud rates; the cable negotiates the speed automatically. Three LED indicators on the cable body give real-time status: Tx (green) for USB send, Rx (green) for USB receive, and PPI (green) for RS-485 send. This is useful during commissioning to confirm the PC is actually driving the bus — if the PPI LED doesn't flash when you try to go online, the issue is on the PLC side, not the cable. A critical constraint: this cable does not support Freeport protocol. Freeport is the S7-200's user-defined serial protocol for custom devices (printers, barcode scanners, third-party displays). If your application uses Freeport communication, you need a different interface — typically the PC/PPI cable with RS-232 or a CP 243-1 communications processor.