Date   : Thu, 20 Oct 2005 00:57:20 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: Programming the 8271 and 1770 FDC's from BASIC

"Ian Wolstenholme" <BBCMailingList@...> wrote:
> communicate with the floppy disc controller.  "Officially" OSWORD &72 is
> the ADFS one and &7F is the DFS one but I suspect that this probably
> has more to do with whether the controller is being used in FM or MFM
> mode as far as the 1770 is concerned.  Pages J.11-12 to J.11.15 of
 
No OSWORD &7F is the single density one and OSWORD &72 is the
double density one. It is incidental that the single density call
is within DFS which uses single density floppies and OSWORD &72 is
within ADFS which uses double density floppies.
 
> You would need the 8271 and 1770 data sheets (available somewhere on
> the internet) for details of the commands available and the parameters they
> take.
 
No. For OSWORD &7F (Single density disk access) you need the
OSWORD &7F documentation. For OSWORD &72 (Double density disk
access) you need the OSWORD &72 documentation. The whole point of
MOS APIs is that they translate whatever you give the to the
appropriae hardware access without you having to know what the
hardware is.
 
OSWORD &7F takes a control block that looks like an 8271 FDC
control block and uses its contents to do single density access to
floppy disks, using whatever controller the DFS you are using has
been written for.
 
OSWORD &72 takes a control block that looks like a SCSI control
block and uses its contents to do double density access to floppy
disks using whatever double density controller the ADFS you are
using has been written for. The only official ADFSs use the 1770.
OSWORD &72 will also access a hard drive.
 
Annoyingly, OSWORD &72 will only work if ADFS is the currently
selected filing system, *and* the disk you are accessing has a
valid ADFS filesystem written to it.
 
See http://mdfs.net/Docs/Comp/BBC/Osword
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC BASIC for Windows and Internationalisation
  See http://mdfs.net/Software/BBCBasic/Windows/ProgTips