I have found no reference to DC in the existing specification of impedance values. The original SAS work included the following with regards to impedance measurement:

All impedance measurements shall be TDR measurements except where the receiver termination being tested includes inductive components such as transformers.  When inductive components exist in the receiver termination, a swept frequency Return Loss or VSWR measurement may be more appropriate.  The frequency sweep shall cover the range Bit rate/10 to Bit rate/2.

As far as I can tell from the SAS perspective, the term DC is first used in Kevin's proposal. It may have resulted from the issue that we have not specifically stated how the measurements are to be made (an item that Kevin Witt has indicated that we need in the SAS-2 specification) or it may be a carry-over from another specification (non-SAS). Appendix B is very general in its measurement descriptions.

Alvin Cox
Seagate Technology, LLC
Tel 405-350-7424
Cell 405-206-4809
E-Mail  alvin.cox@seagate.com