[BBC-Micro] Z80 coprocessor cursor keys

[Jonathan Graham Harston]

>Message-ID: <126200.15461.qm at web27203.mail.ukl.yahoo.com>
 
Greg Cook <debounce at yahoo.co.uk> wrote:
> > > J.G.Harston wrote:
> > > > Challenger introduced 640K double density disks.
> > > Erm, 720K.  :-)  640K was ADFS.
> > 2 sides * 80 tracks * 16 sectors * 256 bytes = 655360 bytes
> 
> Source please?  I was under the impression that Challenger discs were
> identical to DDOS discs[1][2].  Anyway, there was DDOS and quite a few
> other formats that offered 720K capacity.
 
Looks like we're both wrong. The Challenger BIOS contains:
 
.DPB_800k       ;
EQUW &0028      ; SPT=40   Sectors Per Track
EQUB &05        ; BSH=5    Block Shift
EQUB &1F        ; BLM=31   Block Mask
EQUB &03        ; EXM=3    Extent Mask
EQUW &00C3      ; DSM=195  Disk Sector Max
EQUW &00FF      ; DRM=255  Maximum directory entry number
EQUB &C0        ; AL0=&C0  Directory occupies
EQUB &00        ; AL1=&00    first two blocks
EQUW &0040      ; CKS=64   Size of directory checksum vector
EQUW &0003      ; OFF=3    Researved tracks before logical start of disk
; Total disk size is 128*(BLM+1)*(DSM+1)=784k
 
I've got a full disassembly somewhere if I can find it.
 
-- 
J.G.Harston - jgh at arcade.demon.co.uk - mdfs.net/User/JGH
HADFS System Resources - http://mdfs.net/Software/HADFS