Date   : Sat, 03 Dec 1988 05:09:11 GMT
From   : eve.usc.edu!mlinar@oberon.usc.edu (Mitch Mlinar)
Subject: Disk Controllers, Info on.

In article <10644@s.ms.uky.edu> simon@ms.uky.edu (Simon Gales) writes:
>
>I could probably construct an SCSI port given some references to good 
>books/articles.  How about SCSI --> St506/412 conversion?  Would it be
>easier to build an St506/412 interface?  Any references for making an 
>st506/412 interface?  

I admire your enthusiasm, but I think you are underestimating the
difficulties of building your own ST506 interface.  I mean, would you
build your own floppy disk controller?  The hard drive controller (ST506
side of things) is a whole lot more difficult due to the timing.  The extra
10-pin cable which carries the read/write data is separate for a reason:
data is moving awful damn fast at 3600rpm.  They make chips to handle this
interface, but I can't think of any off-hand.

The SCSI port side is almost as difficult.  SCSI is a command language of
sorts: you say which LOGICAL sector you want to read/write, and the
controller card computes the actual head/track/sector, seeks to it, and
read/writes it.  You tell it to format the drive, and off it goes.  This can
get pretty sophisticated if it supports disconnect/reconnect.  There is a
nice chip that takes care of this side pretty well made by NCR; number might
be 5830, but I am not positive.  However, this chip is made to interface and
be operated by a microprocessor and is not a stand-alone converter.

So, you need a microcontroller, SCSI (maybe on the same chip) and ST506
stuff.  Plus, all the microprogram to make it work.  And that is how the
commercial products do it for the most part.  The hardware gurus I know
refuse to mess with this due to the difficulty and buy completed boards
(usually at swap meets).

Anyway, good luck, but thought I would warn you.

-Mitch