I have now got my DS1501 real time clock working. The DS1501 also comes with some 256 bytes of RAM — this won't be accessible in this design as it takes up 16 IO ports and is fairly useless, when I've already got 512Kb of RAM. I haven't wired the battery backup into the RTC yet, so you have to set the time every times the computer starts up.

I've also been trying to get the CP/M version of BBC BASIC running on here. I started building some of the CP/M functions which it uses (as I don't actually have CP/M running, and I was hoping to get a ROM BASIC working), but at the moment it succesfully calls three of my CP/M functions and then dies elsewhere.