I have a batch of EPM570 3.3V CPLD for quite a while. I plan to use them for a project, but I want to make sure they are working parts, so I built this prototype board to check it out. My batch of EPM570 were checked out good and the project is proceeding nicely with EPM570 as its core logic, but what to do with this prototype board?

Since W65C02 can operate at 3.3V, I thought it may be interesting to find out how fast it can run at 3.3V. So here is a simple design with EPM570 provides the bootstrap ROM, serial port and address decodes which took about 15% of EPM570 macrocells. I don't have fast 3.3V RAM, but the 5V CY7C109 seems to work reasonably OK at 3.3V.

I found this board can boot from serial port, load monitor program and run memory diagnostic successfully at 3.4V at 25.175MHz, but memory test failed around 3.3V. This may still be a memory problem that can be fixed with a proper 3.3V RAM. I found the result quite encouraging; I probably will add a CF disk interface, VGA and PS2 connectors and make this a standalone computer.
Bill

That's a nice dev board. I was going to suggest some Inmos IMS1420/1/3 4k nibble SRAMs as they look cool and are fast (although they 1W of power) but don't know if they work on 3.3V. HOwever I believe this format was popular so you may be able to find fast 3.3V versions.

You might also consider Big Mess of Wires 6502 'alike CPU that probably fits into the CPLD

Arlet has a CPLD-6502 that fits four XC9572XL so it should fit EPM570 with resource left over for SBC support functions. That should be an interesting project in itself.

What I am currently working on is VGA beam racing 6502 at 25.175MHz, an enhanced version of VGA65. It is similar to your cheap video project with 6502 doing actual scanning, PS2 input, audio output at 31.5KHz interrupts and then work on application during the vertical retrace period. The original VGA65 is done with a 64-macrocell CPLD and I/O limited PLCC44; I should have much more CPLD resources with 100-pin 570-macrocell CPLD.
Bill

I am running my selfbuilt machines at 70MHz oscillator, 35MHz pixel clock and 17.5MHz W65816 clock at 3.3V.

It works very well, the most critical part is actually getting data from a RAM through an FPGA back onto the CPU data bus quickly enough.

But the system works fine under heat gun or freeze spray

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Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/