Date   : Fri, 02 Dec 2005 10:12:23 +0000
From   : Richard Gellman <splodge@...>
Subject: Re: Order of Acorn Computers?

Jules Richardson wrote:

> I also feel that the US-spec BBC B should really go on there as a 
> separate machine, same with the Domesday setup, just for completeness 
> sake (I don't *think* you could buy the bits separately to roll your 
> own Domesday system).

*most* of the Domesday system is standard parts, essentially:

One BBC Master 128, standard issue.
One internal co-processor board, 64K, 65C02/3Mhz fitted to the above, 
standard issue.

One reworked Acorn SCSI hostadapter board. Take the hostadapter board 
from an Acorn winchester unit, and replace one of the buffer chips with 
its non-inverting counterpart. Then wire it into the internal modem/test 
connector on the Master's main board (nasty looking slot-ish connector 
on the left-hand side, next to where you normally put the CMOS batteries).

One Acorn trackerball - You can replace this with an AMX mouse, just 
swap the signals coming from the left and right buttons.

One Acorn VFS ROM - ADFS reworked to use a different memory address for 
the SCSI controller, and lacking floppy disk support. The memory space 
it occupied is now taken up with LV Player * commands.

Acorn "Domesday" Monitor. While somewhat flashy at the time (and 
provides a stonking picture over any 14" TV today) it is essentially 
just a TV with no UHF tuner. Connection at the back is via SCART, and 
takes the composite video from LVROM, and the RGB from the Master 128. 
This is done on a loop through with the LVROM drive so it can GenLock, 
i.e. BBC RGB goes into the LVROM, SCART comes out with LV video on the 
composite line.

Now the hard part: One Philips VP-415 LVROM Player.
This is actually a VP405, with a hack, namely the SCSI interface and the 
data interpreter. Thus, it is possible to obtain a few identical-looking 
uints (the 405s) but increasingly difficult to obtain the VP415 variety. 
The 415s were made for the BBC/Acorn especially for the Domesday system 
(although they also work with the RM Nimbus domesday variant), hence 
their rarity.

To summarise, you could probably build the majority of the Domesday 
system without too much difficulty (a little soldering may be required), 
but you will need to find a VP415 from somewhere.

Incidentally, the SCSI board in the Domesday Master has a second circuit 
on it (separate from the SCSI part) that provides an alternate 16Mhz 
clock through the links near the UHF modulator. Since the Master 128 
already has a 16Mhz clock, anyone have any idea why a second clock is 
provided to override it? Said clock has caused me floppy disk grief by 
the fly-lead coming loose during a disk access (its an old lead....) 
nicely corrupting disks. I have for this reason removed it from the 
system altogether, and reset the links back to M128 defaults, and can't 
see any issues (even with the CoPro board running).

-- Richard