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Browse Prior Art Database

Small Computer System Interface ID Translation

IP.com Disclosure Number: IPCOM000111302D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Buckland, P: AUTHOR

Abstract

The 8 bit Small Computer System Interface (SCSI) drives only support 8 SCSI IDs while the newer SCSI adapters support 16 IDs with 16 bit devices. Users cannot take advantage of the increased IDs of newer adapters when using the older 8 bit drives.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 90% of the total text.

Small Computer System Interface ID Translation

      The 8 bit Small Computer System Interface (SCSI) drives only
support 8 SCSI IDs while the newer SCSI adapters support 16 IDs with
16 bit devices.  Users cannot take advantage of the increased IDs of
newer adapters when using the older 8 bit drives.

      A solution is to build a SCSI converter that does SCSI ID
translation during arbitration, selection, and reselection.  By
adding extra logic that swaps the data lines around during
Arbitration, Selection, and Reselection SCSI phases; the translating
converter can make 8 bit SCSI devices that have IDs of 0 through 6 on
an 8 bit translated SCSI bus appear to an adapter on the 16 bit
adapter SCSI bus as having IDs of 8 through 14.  This allows up to 7
more 8 bit drives to be connected to a 16 bit adapter for increased
system DASD capacity.  In this design, the adapter must be at ID 7
and this bit is not translated.  This allows the translated 8 bit
drives to reselect the adapter.  The data 7 bit is also driven during
arbitration if a SCSI device of ID 0 through 7 or ID 15 is
arbitrating on the adapters SCSI bus.  This forces the lower priority
drives with translated IDs to lose the arbitration.

      This design is not limited to this exact translation.  The
translating converter could be set up to translate drives of SCSI ID
0 through 3 to 0 through 3, or 8 through 11, or 12 through 15;
depending on some jumpers.  Three of the translating converters c...