Lohmeyer, John JLOHMEYE at
Thu Sep 26 08:56:00 PDT 1996

* From the SCSI Reflector (scsi at, posted by:

>* From the SCSI Reflector (scsi at, posted by:
>* Takaharu Ai <aiai at>
>Does it means:
>-the SCSI-2 device can be used in the FAST-20 system


>-the negotiation of the nexus should be as FAST or slow synchronous

The SCSI-2 device should negotiate for slow synchronous.  SCSI-2 does not   
strictly prohibit single-ended Fast SCSI, but it recommends against it.   
 Some manufacturers of SCSI-2 devices read drafts of the SPI standard and   
have implemented single-ended Fast SCSI (10 MegaRepetitions/Sec).

>-it does not influence the transfer rate of the other FAST-20 deviced?

Two Fast-20 (Ultra SCSI) devices on the same bus with one or more slower   
devices should work okay.  The Fast-20 devices should negotiate for   
Fast-20 data rates when transferring between themselves.  They will   
negotiate slower rates with the other devices.  Please note that the   
Fast-20 bus rules must be met for this configuration to work.  Some   
manufacturers allow the system integrator to 'slow down' their Fast-20   
device so it can be used on older buses -- it will then not negotiate for   
a higher data rate.

John Lohmeyer                 E-Mail: john.lohmeyer at
Symbios Logic Inc.             Voice: 719-533-7560
4420 ArrowsWest Dr.              Fax: 719-533-7036
Colo Spgs, CO 80907-3444    SCSI BBS: 719-533-7950 300--14400 baud

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