I think the adaptor you have takes a 'straight through' type cable and set the pins for null modem use together with hardware handshake signals,
You will need a null modem cable for the Siemens so the adaptor should work.
This link explains the conections a bit more in detail.
http://www.cadem.com/ncnet/dnc-detai...merik-802d.pdf
With full handshake usually all the handshake connections are made across the cable, with no handshake they are usually jumpered out inside the connector.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.