Date   : Tue, 13 Jul 1993 08:18:29 +1200
From   : David Andrew Sainty <David.Sainty@...>
Subject: Re: Tube connections (was RE: colour Graphics)

>Date: Mon, 12 Jul 93 11:21:43 +0100 (BST)
From: "I Stephenson" <ian@...>

>I have before me a (slightly illicit) circuit diagram for the Acorn Tube  
>Spiltter. This (officially non-existant) device (which is curently sitting
here  
>looking dead) plugs into the Tube, and allows two 2nd processors to be  
>attached, and switched by software.

>This tells me that A0,1 and 2 are passed on the co-prcessor. RST is an output  
>only (its buffered and switched by this circuit). A3 and 4 are used by the
tube  
>switcher, along with HCS (the name used for NTube). Pins 38 and 40 (A5+6 are  
>not connected).

Output _from_ the computer?

I assume it suffices to isolate the Ntube on a second processor to disable
it.... (Hmmm, and NIRQ I guess).

So, this seems to indicate only the low 8 locations are required by TUBE
hardware. Does the splitter ensure splitter switching writes don't make it
to the second processor? (What I'm really asking is, if a write is make
to a second processor above those bottom 8 locations, does it ignore it,
or might it panic?)

>In addtion to the 8 datalines, the only other pins used are Phi2 (4) and
 R/nW   
>(2). Apart from the data lines, all are output only.

>I was actually planning to start playing around with this circuit today
(I just  
>can't get mine to work!), so I'll report anything intersting.

How many second processors have you got!? :-)

Dave.