Date   : Wed, 21 Feb 2007 23:45:32 +0000
From   : mike@... (Mike Tomlinson)
Subject: Some Beeb addons

In article <45DB7B24.2030007@...>, Kris Adcock
<beeb@...> writes

>There's a Computer Village LVL DOS board, labelled "CVX7 Disc 
>Interface". The controller on it is an FDC 1797, and there's a ROM 
>marked "LVL DOS 1.00". How does this compare with the more usual 8271 or 
>1770 interfaces?

Not very well.  Pretty obscure and wasn't very good.  It's a double
density DFS.

>There's a Watford Electronics 32K RAM card, with an accompanying ROM. 
>The board holds the 6502 processor - there's a short ribbon cable to 
>connect it where the 6502 would normally go. Does this RAM card add 
>another 32K (making it a 64K machine) or is the extra 32K used as 
>Sideways RAM?

Neither. It's shadow RAM, so it sits alongside the existing memory.
When it's enabled with *SHADOW, selecting screen modes which normally
eat up main memory will result in HIMEM staying at &7FFF - i.e. no user
memory is lost to the screen.

It supports the Master's *FX commands (*FX121 comes to mind) for
manipulating shadow RAM.

The board also comes with buffering software to allow, for example, a
large print buffer to be created.

The manual's on bbcdocs.com.

>There's a Computer Village sideways ROM board, with sockets for 16 ROMs 
>- that can't be right, can it?

Why not?  Either the CV board replaces the on-board ROM sockets (in
which case they shouldn't be used), or some of the ROM positions on the
board are intended for sideways RAM (i.e. there will be two sockets for
a ROM position, to take two 8k x 8 static RAM chips).  Are the ROM
sockets numbered?

> There is also a row of 15 jumpers, each 
>of which can be set north or south. Anyone know what they are for?

Dunno.  They'll most likely be: i) to select 8k/16k ROMs, ii) to enable
the R/W line so a static RAM chip can be fitted for sideways RAM, or
iii) if the board is very old, to select slow ROM access for older,
slower EPROMs.

> Also, 
>the 6502 processor and ULA are held on this board - the boards connect 
>to where they should be on the main board. Is this just to make the 
>board secure, or is the board doing something special that requires 
>these ICs moving?

The ULA is simply used to secure the board.  The 6502 socket is used as
it's a convenient spot to pick up the data and address buses, plus the
R/W line if the board does support sideways RAM.

>Does anyone have scans of the docs for these items? The Beeb isn't 
>really working properly (it never gets to a prompt - just makes a 
>constant beep tone) and I'd like to remove them to clean the machine and 
>help narrow down where the fault is - but I'm not sure about what 
>jumpers I'd need to change on the board when I remove the ROM board.

Very probably none.  Whip out the board and reinstate the 6502 (you
needn't refit the ULA).  Check the jumpers on S21 and S22 to make sure
they're in the default positions.  I can't remember if the CV board uses
the S21/22 jumpers to pick up the ROM select lines, or whether it does
its own decoding.


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