Alioth's Journal: [Z80] Core board hopefully complete

Hopefully I've finished the design for the Z80 core board now. I made a few changes yesterday - moved the bus connector to the left of the board (beside the memory and CPU), realising it was pretty damned stupid to put it on the right hand side (beside the CTC and PIO) in the first place, since that would require a huge via farm in the middle of the board, and then some very creative track routing, to get the rest of the address bus over to that side.

So I did a quick 'Select all', then dragged the entire design over so the PIO/CTC sat on the extreme right of the board, opening up the space to put the 40-pin bus connector on the left. The bus connector exposes all of the Z80's pins.

There are additional connectors for 'optional' things. I wanted to have a 50-pin bus connector, and include things like the sideways memory select outputs and a couple of pins of the I/O address decoder circuit, but routing them was going to be a real pain in the ass (another via farm, and they are fiddly to solder). Since most projects don't need those signals, they instead have their connectors near the circuit itself. The other advantage of using a 40 pin bus connector and having smaller headers for the other functions I might want to take off the board is that I already have plenty of 40-way (and less, I've got a whole assortment) of ribbon cable which saves a fairly significant amount of money. (I can also use IDE CD-ROM cables for bus connectors too.)

I also ordered some tinning chemicals. The chemical is quite expensive (£40 per container or so!), but it'll do approximately 2.5 metres square of PCB (so it won't add much cost to each PCB, and make it look much nicer, and I won't worry so much about those narrow little signal lines eventually corroding through). Also 'low profile' IC sockets - the type which allow the IC to sit very low in the socket, but also the plastic of the socket is about a couple of mm above the board so I can solder the top side as well, because some IC pins double as vias!