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From: rb@ccivax.UUCP (rex ballard)
Newsgroups: net.micro,net.micro.atari
Subject: Re: (FASI), SASI, SCSI - General info on SCSI (PLEASE READ)
Message-ID: <311@ccivax.UUCP>
Date: Mon, 14-Oct-85 22:44:23 EDT
Article-I.D.: ccivax.311
Posted: Mon Oct 14 22:44:23 1985
Date-Received: Fri, 18-Oct-85 21:00:31 EDT
References: <123@apr.UUCP> <279@ccivax.UUCP> <268@aum.UUCP>, <297@ccivax.UUCP> <553@oakhill.UUCP>
Organization: CCI Telephony Systems Group,  Rochester NY
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> I would like to correct some misnomers presented in the  following  article
> concerning  the  relationships  of  the  so  called  "FASI"  and  SASI/SCSI
> interfaces.

I would like to thank Brian for Doing so, I had intended to post the correction
myself but was unable to do so.  Brian's posting is much more informative.

> SASI has only one data  bus  used  to  transfer  both  commands  and  data.
> Message  and status information is also transferred over the same data bus.
> I am hopeful that  all  new  products,  including  CD-ROMs,  will  be  SCSI
> compatible.


> The Atari DMA port is just that - a DMA port - and nothing more.  Its  only
> resemblence  to  SASI/SCSI  is  the  REQ/ACK handshake lines and the 8 data
> lines.

> I disagree.  The Atari Port  is  nothing  more  than  a  DMA  channel.  The
> circuit shown below is a SCSI Host Adapter for the Atari.  It might work.

The CS is not under DMA it is triggered only when the CPU has control of the
bus.  This is important, considering that interfacing to a controller requires
at least some non-DMA initialization/set up.  You are correct in stating that
the Atari port is NOT a SCSI/SASI port.

> >BE CERTAIN THE DEVICE IS SCSI, AND NOT SASI, THEY ARE NOT THE SAME!!!!!
> 
> This is not true.  A SCSI controller will  work  as  well  in  a  SASI  bus
> environment  as  will  a  SASI  controller  in a SCSI bus environment.  The
> protocol for the physical aspect of both busses allows for this.  Now it is
> true  that  the firmware aspect of SASI is different from the SCSI but only
> in terms of the command implementation.  For example  both  SASI  and  SCSI
> send  commands over the data bus in 6 byte command blocks (SCSI also has 10
> and 12 byte command blocks which allow for a 32 bit logical  block  address
> and  a  16  bit  transfer length).
> What  all  this  boils  down to is the device drivers for SASI are slightly
> different from the device drivers for SCSI.

The important question here is, what kind of "Boot Rom" is installed?
Would a SASI peripheral respond correctly to SCSI commands?  Once you're
booted, you can use a little of both.  The current ROM doesn't support either.


>>By the way, there are kits to put SCSI on the MacIntosh (Xebec I believe).
>>There are SCSI Adapter boards for most IBM compatibles (from almost anyone).
>>Apple has announced plans to incorporate SCSI into the MAC (probably Jonathan)

> >My guess is that when Peripheral manufacturers see that they can get the
> >IBM, MacIntosh, Atari ST, and the Amiga market with the same product,
> >"SCSI compatibility" will become more important than "IBM compatibility".
> >
> >Fortunately, SCSI compatibility is MUCH easier to accomplish.
> 
> I agree - SCSI is a great interface and would be a boon for  the  types  of
> machines listed.
> 
> ---------------------------------------------------------------------------
> Brian D. Wolf
> Motorola MCU Division
> William Cannon at US 290 West
> Austin, Texas
> ---------------------------------------------------------------------------

Motorola was not on my previous posting of those making support chips for
SCSI.  Obviously, they do support it very well!  Does Motorola offer a
chip that would be Atari compatible in some way?