>> I've been looking at the pin-out documents, and don't see many (if any)
>> uncommitted lines, then again.. I'm not really following Chris Jones'
>> documents that well.

Don't worry, I have that problem too :-)

> Moving away from the Samtec pinout and looking deeper at the schematic,
> I see that the samosa bus might be useful for my application.

Although the standard Balloon 3 FPGA code implements the Samosa bus on 
those pins, they're intended to be re-used for other purposes. I've got 
a Balloon 3 board here with some special stuff in the FPGA which 
connects to a custom USB transceiver board via the Samosa connector. 
It's not using the Samosa bus, just the connector as a handy way into 
the FPGA.

> I'd started to think that the D0-31, A0-24 lines on the Samtec were
> pretty much uncommitted, but I now note they are the same data-lines
> used by the CF socket.

They're a buffered (by the FPGA) version of the system bus, if I 
remember correctly.

> Can anyone who's constructed motherboards or accessories for the
> Balloon comment as to how extra functionality such as Ethernet
> controllers are added, and what IO pins are used? I realise can't share
> in my application (I need control over the line), but can the address
> and data lines of the CF socket be shared with other addressed and
> chip-selected devices?

David Bisset is the expert on the current expansion boards, but as far 
as I am aware Ethernet controllers and so on live on the system bus. A 
little address decoding should allow your application to live on the 
bus, too.

I hope this is some help,
Chris

-- 
Chris Jones - chris@martin-jones.com
Martin-Jones Technology Ltd, makers of Solidlights
148 Catharine Street, Cambridge, CB1 3AR, UK
Phone +44 (0) 1223 655611 Fax +44 (0) 870 112 3908
http://www.solidlights.co.uk/