Date   : Tue, 14 Mar 2006 21:50:24 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: SASI/SCSI <>IDE, distracting thoughts.

>Message-ID: <44144C1C.3080500@...>
 
Jules Richardson <julesrichardsonuk@...> wrote:
> Personally I'd much rather someone with the necessary knowledge invest time
in
> getting "modern" (as in 512 byte sectored, parity) SCSI drives (and
> documenting the process) working with old Acorn hardware than futzing around
> with 'orrible IDE stuff!
 
How is IDE 'orrible?
 
It's just:
  REPEAT UNTIL ready
  ?Count=number
  ?Sector=sector
  ?CylinderLo=cylinderlo
  ?CylinderHi=cylinderhi
  ?Head=head
  ?Command=read or write
  REPEAT UNTIL dataok
  FOR byte=0 TO 255:mem?byte=?Data:NEXT (for reading)
  result=?Result
 
>From digging around in the ADFS code and from reading background
material on low level SCSI I/O protocols, *SCSI* is horrible.
 
> Can't see the difference between building an IDE buffer / control board and
a
> SCSI one, myself. Surely they'll be the same level of complexity really?
 
IDE interface: two ICs minimum.
 
SCSI interface: six ICs minimum and lots of bus spaghetti.
 
See http://mdfs.net/Info/Comp/BBC/SCSI and
http://mdfs.net/Info/Comp/BBC/IDE/8bit for circuit diagrams.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
Our chief weapons are 'who', 'ps -aux', 'kill -9', and a fanatical devotion
to 'reboot -q'.