Date   : Wed, 25 Apr 2007 10:11:34 +0100
From   : dominic@... (Dominic Beesley)
Subject: Z80 coprocessor cursor keys

Hi Jonathan,

Is there any chance you could post it somewhere - I'd be very interested
in having a look through it all.

Cheers

Dominic

----- Original Message ----- 
From: "Jonathan Graham Harston" <jgh@...>
To: <bbc-micro@...>
Sent: Wednesday, April 25, 2007 12:55 AM
Subject: Re: [BBC-Micro] Z80 coprocessor cursor keys


> >Message-ID: <126200.15461.qm@...>
>
> Greg Cook <debounce@...> 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@... - mdfs.net/User/JGH
> HADFS System Resources - http://mdfs.net/Software/HADFS
>
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>
>
> -- 
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> 17:26
>
>