Apple Article TA21815 has line drawings of divers bits of SCSI gear for use with HDI-30 ports. Several things arise from the article. All of those drawings show CN-50 connectors in addition to the HDI-30 connector on the cable. Host computers (desktop) all have DB-25 connectors. Apple's HDI-30 connector is not switched. There are separate HDI-30 connectors on separate cables for 30-pin (SCSI Disk mode) and 29-pin operation (peripheral device connection). The 30-pin has a dark grey jacket on the cable. I have never seen one of these, and stopped looking for or caring about them when I found switchable third-party adapters. The 29-pin has a standard lighter grey jacket. I have two of the 29-pin, 590-0717-A, but they can be useful only for post-68K PowerBooks, because termination cannot be inserted at their HDI-30 ends. I also have third-party 29-pin HDI-30 cables with DB-25M and -25F connectors. Again, these are useful only for post-68K PowerBooks, although the -25M can be connected directly to desktop host Macs.
Switched adapters (for 30- or 29-pin use) are third-party devices, available with either CN-50F or DB-25F connectors in addition to the HDI-30. Apple's pass-through terminator can be attached only at the host Mac end of an Apple cable, since passthrough terminators are available only in CN-50M/CN-50F form, not DB-25, as far as I know or have seen. Even if these could be directly connected to a host Mac's DB-25 port, having the terminator remote from the PB is not as efffective as having it at the PB end of a cable, which is possible in conjunction with a third-party switched HDI-30M/CN-50F adapter.
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