ZX81 ULA replacement revisited

[RetroTechie]

MACH210 devices are ancient, are you sure you want to base a new design on those? You may have considerable trouble finding those parts in a few years. Note that in Bodo's .zip mentioned above, file "zx81vid.abl" has the logic equations in ABEL, which are somewhat 'easy' to read & re-produce in whatever programmable logic of your choice.

AFAIK Andy Rea's design is written in Verilog, which should make it (relatively) easy to implement on a modern FPGA board.

In documentation with my ZX81 ULA project, I suggested use of a Xilinx XC9572XL in 64-pin VQFP housing. Such a part would fit nicely inside a 40-pin DIP footprint. And despite its fine pitch (0.5mm) between pins, certainly possible to hand-solder. I've tried hard but so far unable to find a similar 5V-tolerant part from Altera. Unless you're into soldering BGA packages...

And given the prices of PCB services lately, there is another option: take whatever 5V tolerant CPLD you want, and design an entire replacement ZX81 board around it. Gold plated edge connector, a few extra (Flash EP)ROM sockets, re-designed EAR/MIC circuitry, whatever.

[mhudson52]

I guess this is the part where I fully expose my ignorance once again! My real reason for going with the MACH210 design as old as it is, is because it is the only design which I have found the files for the board, schematic, and source file to reproduce with my limited experience.

Naturally I would prefer to go with a better design such as Andy's, but finding the complete documentation needed is proving elusive no matter how many hours I spend searching this forum and others. I would love to see the documentation for your project. My sanity is tenuous enough as it is without even thinking about a BGA package!

[mrtinb]

Reading the links provided, gives you links to zip-files with everything needed.

viewtopic.php?f=8&t=1862&start=10#p21120

viewtopic.php?f=8&t=1862&start=10#p21128

[mhudson52]

Thanks Martin. I had downloaded these zip files previously and looked at the contents, but felt like a hog being shown a wrist watch. I've got a LOT to learn. One thing that threw me off was the absence of an obvious .brd file in the contents. I'll keep studying and hopefully make some progress.

Mike