Date   : Mon, 28 Sep 2009 20:20:13 +0100
From   : mfirth@... (Michael Firth)
Subject: Couple of Tube operation queries

Michael Firth wrote:

<snip>
> Interesting. The Watford book is the only (semi) official documentation 
> that
> doesn't make a differentiation between reading and writing the status 
> register.
> Both the AppNote, and the 6502 Second Processor Service manual (one other
> source that describes the Tube ULA operation) talk about the behaviour being
> different for reading and writing.
> That said, there are several obvious clangers in the Watford book - 
> referring
> to the Tube as "", which plainly isn't true, for example.
>
>   
Oops - that's what happens when the phone rings half-way through writing 
an e-mail - I forget to go and insert the relevant reference before sending!

That was supposed to say "referring to the Tube as 'a pair of 
proprietary chips coupled to the respective processors, and 
communicating with one another over a 2MHz asynchronous bus', which 
plainly isn't true".

Another interesting quote from this book's Tube section is "The ARM 
second processor architecture is slightly different from that of the 
other language processors as it is provided with its own peripheral 
controller chips and communicates directly with the video and audio 
outputs" - this is the only reference I've found to suggest that Acorn 
may have been thinking of productising a BBC add-on that gave an ARM 
processor plus improved graphics and sound, rather than just the ARM 
Evaluation system, which was just a standard second processor.

Regards

Michael