Date   : Thu, 23 Sep 1993 23:48:52 +1200
From   : David Andrew Sainty <David.Sainty@...>
Subject: Re: Beebs and bits

Date: Thu, 23 Sep 93 10:46:55 +0100 (BST)
From: "I Stephenson" <ian@...>
Comments: BBC Mailing List

> Anyone looked seriously at BUILDING a second processor? Can you get
> the ULA?  Does anyone have a definative idea of the tube protocol?

I think the ULA is different for each type of processor. The TUBE bus
is very simple, and only runs at 2MHz. The tricky bit would be the
buffering of the interface, but lets face it, that could be done in
software with most modern CPU's. :-)

The protocol is reasonably simple I think, to allow it to work on any
processor type, with extra bits for special purpose processors, like
the 80186 PC emulation, dealt with by an extra layer on top of the
tube protocol. The New Advanced user guide goes into it in enough
detail I think....

You could probably get a 2nd processor up and running with a register
file and some interrupt control hardware, or maybe just a bunch of
8 bit latches.

Dave.