SASI device <-> PC ?

[Allison]

>
>Subject: Re: SASI device <-> PC ?
>   From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
>   Date: Thu, 30 Jun 2005 19:45:19 +0000
>     To: cctalk at classiccmp.org
>
>On Thu, 2005-06-30 at 12:14 -0700, Lyle Bickley wrote:
>> It's been a while since I used the controller, but IIRC it was an old ISA 
>> controller card like a WD7000 or Seagate ST-01/ST-02.  Any early SCSI-1 
>> controller should do - that was before SCSI became "smart" - and the 
>> messaging between the controller and the device (HDD) was minimal.  A SASI 
>> device on such a controller will respond "well enough" to "look like" SCSI-1.
>> 
>> As I said before - DO NOT mix a SASI device with a SCSI device on the same 
>> controller - or strange things can happen (don't ask).
>
>Yep - far as I remember, SASI's single target only, so I expect if you
>have a SASI target on the same bus as a SCSI target all sorts of things
>would happen! :-)
>
>Most classic SASI controllers seem to be little more than a handful of
>buffer and latch ICs though (only about 6 chips total) - hence I was
>wondering if someone had chucked together something to hang off a PC
>parallel port (and just drive it all in software). Not especially
>complex - my worry would be that the SASI target would timeout on
>certain ops if the PC parallel port isn't quick enough though.
>
>cheers
>
>Jules


The deal is that SASI is almost SCSI.. the differences are very 
small at the hardware level (interface).  However the protocal and 
instruction set of the SASI bridge controllers is different from 
SCSI.  That difference in instructions and protocal does not 
allow for mixing the two nor simple substitution of one for the 
other. SCSI was not standardized till the late 80s so there are
a number of SASI/SCSI devices that predate the widespread acceptance
of SCSI.  There are a few systems that have a SCSI interface that
were SASI or SCSI subset (DEC uVAX2000 for one).  I've also done 
the reverse, used SCSI on older SASI machine but, it required a 
new bios to even talk to the SCSI disk.  The later was due to the 
SCSI vs SASI bridge board (Xybec) instruction/protocal differences.


Allison