Acorn Second Processors (was: Re: Quick survey on equipment)

[Rob]

On 26/04/07, Ensor <classiccmp at memory-alpha.org.uk> wrote:
>
[on Z80 add-on processors]
>
> I suppose I could always make one, assuming the necessary ROM images are
> available somewhere? I don't recall there being any custom logic in the 6502
> Second Processor and my memory of the Torch Z80 2nd processor is waaay to
> hazy.

Acorn used a custom "ULA" chip to handle communications between the
second processor, of whatever flavour, and the host BBC computer.
This provided a handfull of FIFOs and signal lines in both directions.

Torch used a pair of PIO chips connected back-to-back to provide
simular but incompatible functionality; only their ROM software could
understand it.

The Acorn one has definiatly been emulated, in Sprow's AEM7TDMI
co-processor for example: <http://www.sprow.co.uk/bbc/armcopro.htm>


>
>
> Which brings me onto a second point. I actually have at least one BBC
> "Master" too, I have a vague recollection that these have a connector for an
> internal, as well as an external, second processor?

They do.  You can connect up to both, and *CONFIGURE the system to use
which ever one you want (or neither, but not both.)

>
> Do you know of any websites where I could get more info?
>

Sprow's page above has a link to Acorn's Tube application notes - that
should get you started on how the tube actually /worked/ ..

Whilst not wishing to remove an 8-bit thread from cc, you are probably
best asking for technical info over on the bbc micro mailing list -
gioto <http://lists.cloud9.co.uk/mailman/listinfo/bbc-micro> for
subscription machine.


Rob