Date   : Mon, 12 Jul 1993 11:21:43 +0100 (BST)
From   : "I Stephenson" <ian@...>
Subject: Re: Tube connections (was RE: colour Graphics)

>Certainly does! Pin 4 is the clock we need. With 7 address lines, that
>should be enough to map some control registers to addresses not used by
>2nd processors, so it needn't be the case that you could only have one or
>the other plugged in. Strange though, I assume the NTUBE line indicates
>an address space of 127 bytes is being addressed, within Sheila?

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).

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.

Ian