Date   : Tue, 12 Sep 2006 04:30:32 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: [Fwd: [Fwd: Re: Master AIV SCSI]]

as requested :)


Subject: [Fwd: Re: [BBC-Micro] Master AIV SCSI]
Date: Mon, 11 Sep 2006 17:19:22 +0100 (BST)
From: Richard Gellman <splodge@...>
Reply-To: splodge@...
To: julesrichardsonuk@...

Hi Jules,

Can you forward this to bbc micro list?

I posted it earlier, but I'm on webmail and my default email address
doesn't match the list database :(

To follow up something you said earlier, the ATN line is target to
initiator, rather than initiator (BBC) to target (drive). It is used in a
disconnected transfer for the drive to alert the computer that it has
finished its length operation and is now ready to provide data, so the
computer should reconnect and begin receiving.

The ADFS/VFS code has no such support for this, so the ATN line is
ignored. I think it may not even be connected to anything. Check the
WInchester Disc Service Manual... it has a circuit diagram showing where
ATN is connected.

-- Richard


Subject: Re: [BBC-Micro] Master AIV SCSI
From:    "Richard Gellman" <splodge@...>
Date:    Mon, September 11, 2006 12:45 pm
To:      "Ian Wolstenholme" <BBCMailingList@...>
Cc:      bbc-micro@...


The VFS *is* a modified ADFS, with the floppy code stripped out and the
hardware address changed from the 1Mhz bus to what is labelled in ref
manual pt 1 as "Modem" (FE80-FE84). It also has the logic to invert data
bus reads either removed or insterted... whichever is opposite to the
Acorn
winchester host adpater. The SCSI board in the Master AIV is a cut-down
version of the Winchester host adapter board, but it operates in a
practically identical way (save for the data bus logic above).

You should be able to slip a SCSI hard disk onto the AIV SCSI cable, and
read it as if it were the LV-ROM player. Obviously instructions to seek to
video frames will be met with disappointment, as will any attempt to write
to the disk... all writing code was removed on the basis of being somewhat
useless with a laserdisc.

I've actually tested this under emulator conditions and confirmed it
works. VFS only issues SCSI command 1B (start unit) and the commands for
Read Sectors, so it works fine with hard drives.

-- Richard


> Here's a picture of the resistor pack in my Domesday SCSI Board:
>
> http://www.beebmaster.co.uk/Downloads/SCSITerm.jpg
>
> On a general point about this particular SCSI interface, has anybody
> successfully connected up a SCSI device other than the LV-ROM player?
>
> I would be interested in seeing how VFS accesses the SCSI interface, I
> think if an amended version of ADFS could be made to look at the
> SCSI interface for devices instead of the 1MHz bus then it could open
> up all sorts of possibilities.
>
> Best wishes,
>
>
>
> Ian
>
>





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If you've ever wondered how you get triangles from a cow
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