The System Backplane contains the system bus. From a hardware point of view, its role is to allow connections from all the different system-core interfaces. There are no electrical components, just some wire paths and some connectors, so the design is rather trivial.
You can download all the schematic and PCB designs below.
The schematic for the System Bus is rather simple. Just a bunch of parallel bus lines connecting to connectors for each module. It almost doesn't really require a schematic, but in the interest of keeping things neat and consistent here it is:
Due to the nature of the system bus, it really doesn't make sense to create the system backplane on a breadboard. It is far more sensible to at least use the protoboard layout.
The protoboard is very simple. The bus is just a bunch of lines, so strip-board is perfect for this use.
Here is a photo of an earlier prototype board I created. There is strip-board on the underside and a white silkscreen on the other (which I colored in with a highlight pen for the different bus lines). I've then attached female pin headers across the strips.
As you can see here, I have evenly spaced out the pin header connecters with plenty of room between each one. Probably overkill for the spacing but it looks cool.
This method is by far the cheapest way to create your system backplane. You don't have to go to the trouble of creating your own PCB for this as it is rather simple. But I did anyway...
The ultimate solution is to create a Printed Circuit Board for the system backplane. Because I'm using the free version of Eagle, there is a limitation on the board size (which is 80mmx100mm). Having the 6 x 35-pin header connectors placed on the board was a challenge as it only just fits within this restriction.
I sent off my design to BreadBoardKillers and a few weeks later 5 shiny Whizz80 system backplane boards arrive.