Date   : Sun, 21 Dec 1997 11:49:50 +0000
From   : Mike Tomlinson <jasper@...>
Subject: Re: Hard Drives

In article <3.0.3.32.19971221015601.006a29d8@...>,
Crispin Boylan <viewtronix@...> writes

> I have been reading a lot of messages
>about someone who produced an SCSI controller board for the BBC, so that
>any SCSI device could be connected, the total cost then was about 35, so
>it should have fallen a bit by now.

Discussion of that board here has suggested it might be SASI, a
forerunner to SCSI, and therefore unlikely to work with modern hard
drives.

>Anyway, I was wondering, is anyone still on here that knows how to make/has
>a controller board for the BBC, and if so what drives are compatible?

You need more than one 'controller'.  You need a 1Mhz bus host
interface, an Adaptec SCSI-to-MFM card, and an MFM drive.  This is how
people making hard drives for the BBC (Acorn, Watford, Viglen etc) built
them.  The 1Mhz bus card implements a simple SCSI-ish interface which is
then used to run the Adaptec SCSI-to-MFM adapter, which then controls
the drive.  You therefore need to supply power to two cards as well as
the drive.

> so all I need is the board, a 1770 controller, an SCSI
>controller, ADFS, and some money - is this correct?

You might as well buy a secondhand hard disc complete.  I sold my self-
built 20Mb unit a few years ago for ukp180.

>Also, I want to add two 3 1/2 inch drives to the beeb, will it work with
>1.44mb drives in 720k mode?  

Some do, some don't.  Wiring the 720/1.44 detection switch closed might
help.  Beware that most PC 3.5 drives use CMOS and you might have to use
buffering to make them work.

>My ultimate aim is to have 2 3 1/2 inch
>drives, and then one 5 1/4 inch drive to run the old software which can't
>be copied.  Can I add three drives in to the beeb, which can be used at the
>same time? 

No.  The Beeb separates 'drives' out into disc surfaces. You will need
to limit yourself to one 3.5 drive and one 5.25, which will give you
drives 0,1,2,3 in DFS and drives 0 and 1 in ADFS.

> Or do I have to add in a selector switch to add in the 5 1/4
>inch drive at the expense of one of the 3 1/2 inch drives, so I could
>either have 1 3 1/2 inch, and 1 5 1/4 inch drive, or two 3 1/2 inch drives.
> Can someone help me with this?

It shouldn't be difficult - get the BBC circit diagram from Acorn's web
site and with a bit of lateral thought it could work.  Is it worth the
effort though?

>One last thing - does anyone have the information to build the Micro User
>real time clock? A scanned copy would do, the article is in the Feb 1984
>Micro user if anyone has got that.

I believe Mike Cook's Body Building articles from Micro User are still
available on the web.  They're on Manchester University's web site
somewhere, I think.  Try a search for Mike Cook, Body Building, etc.

Alternatively, I have a Solidisk RTC module somewhere with the manual
and ROM.  It plugs into a ROM socket and worked the last time I tried
it.  You would be welcome to purchase it for a small sum.


-- 
Mike Tomlinson