Apple ][ boards -- what have I found?

From: Derek Peschel <dpeschel_at_eskimo.com>
Date: Wed Jul 25 19:29:53 2001

On Wed, Jul 25, 2001 at 10:28:19PM +0100, Tony Duell wrote:

> > > There was a thing sold in the UK called a Torch Graduate. It was an
> > > add-on for the BBC micro that was essentially a complete PC motherboard
> > > (8088) + a few interface chips and a BBC Micro ROM. It also had 2
> > > built-in 5.25" drives, It ran MS-DOS (IIRC the normal PC version) The BBC
> > > was used as the keyboard and video display only for a PC system...
> >
> > How is this different from the BBC Master 512K (or whatever the
> > PC-compatible second processor was)? Did the Torch Graduate use the Tube?
>
> No, Torch rarely used the Tube interface. Probably because the Tube ULAs
> were a custom Acorn part and were not that easy to obtain in quantity,
> unless you were Acorn :-)
>
> Both of the Torch Coprocessors that I've seen use the 1MHz bus. The Z80
> one needs a ROM installed in one of the BBC's sideways ROM sockets. The
> Graduate (8088) does not. It uses a trick where if the Beeb detects NMI
> shortlry after a reset, it runs code in a ROM connected to the 1MHz bus
> (this is not documented in any Acorn manual that I've seen, but it is
> intentional, and works on all Beebs I've ever seen). Of course you can
> only map 256 bytes of the ROM in at a time (the 1MHz bus has 8 address
> lines, A0-A7 and 2 page select lines, page FCxx and page FDxx, only one
> page is used for this ROM). After a few shenanigans mapping in different
> parts of the ROM and copying code into the BBC RAM, the machine is booted.

I remember reading about this trick the last time the subject of the Torch
came up.

> > Just in case anyone doesn't know... The normal system bus on the BBC runs at
> > 1 MHz which is only half the CPU speed. The Tube runs at 2 MHz and is
> > designed to be connected (through a semi-custom Acorn chip, some cables, and
> > a matching chip) to one of a number of "second processor" units.
>
> No, you only need 1 Tube ULA. There is no ULA associated with the Tube
> inside the Beeb -- it's just TTL buffers, address decoders, etc. The ULA
> goes in the second processor unit, and is basically a pair of FIFOs to
> transfer data between the BBC micro and the other processor and back again.

Oops, sorry. I knew there were two FIFOs but I didn't realize they were on
one chip.

What exactly are the MOS routines designed to offer the second processor? I
know they can copy software over the Tube and do some relocation (and that
the relocation was enhanced in the Master). But what are the
functions/memory locations/etc. avaialble to each side? And how does the
whole thing get booted (and then stay running)?

> For the beneift of non-UK classiccmpers, the name 'Tube' was chosen both
> because it was a 'tube' through which data could be passed to the copro
> and back, but also because the name 'tube' is a common slang name for the
> London Underground (Subway), which is, of course, an alternative to the
> bus :-)

Also, ULA = Uncommitted Logic Array, a semi-custom PLA-like thing. Was
it made by Ferranti? Acorn used a few different ULAs and so did some other
vendors. I think Sinclair was one.

And MOS = Machine OS = the ROM routines in the BBC, including the abstract
filesystem interface but not any filesystems (which could be added or
removed as desired) and an astonishing number of places for the user to
extend the code.

-- Derek
Received on Wed Jul 25 2001 - 19:29:53 BST