ATAPI Shadow Registers on Non-existent Slave Drives

Ken Wolfgang kenw at
Wed Apr 29 07:38:15 PDT 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* Ken Wolfgang <kenw at>
It appears that several of the newer ATAPI drives (especially DVD-ROM =
drive) are no longer following the specification for shadowing the =
registers of a non-existent slave drive.  It appears they are either =
tri-state in the reads of the non-existent drives register or are =
driving FFH as the shadow register.  Has this requirement been removed =
|from the specification?  And if so, is there a new specification that =
deals with this situation?

Ken Wolfgang
Cirrus Logic
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