I've recently started porting the Harlequin over to a Xilinx CPLD, specifically the hardware that replicates the ZX Spectrum ULA. The intention is to migrate this into two additional projects:
- A Replacement ULA project
- A Low Cost Spectrum Clone
A replacement ULA will have many benefits, from keeping the many Spectrum's out there in the World alive when the last few remaining ULA spares disappear, to improving the video output and perhaps adding extra video modes.
Creating a low cost Spectrum Clone is desirable for those people who like having real hardware! There are plenty of original ZX Spectrum's available on eBay, but a new design implemented using a CPLD or FPGA would allow for improved video output, memory modes, video modes, sound etc. Andrew Owens has expressed particular interest in moving the Spectrum SE out of it's prototype phase and into something that people could build, or even buy. Without reducing the Harlequin's chip count, this would not be practical.
Over the coming months I will be documenting progress here, but first I have the task of finishing:
- A Dynamic Memory Controller to replicate the ULA behaviour
- My mini-book "The ZX Spectrum ULA", in which I provide a wealth of information about the Ferranti ULA and the Sinclair ULA design itself.