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Recently found Z80 video of how a guy makes ZX Spectrum computer from ground up, fixes bugs and problems as he proceeds. Video is in Russian, but still amazing even if you don't understand it!

https://www.youtube.com/watch?v=8rWCYo1UcOQ

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A lot of the ZX Spectrum functionality and logic is in the ULA, an ASIC.

There's a whole book on the ULA - http://www.zxdesign.info/book/theZXSpectrumULA.shtml

Actually there is now design out of 74ls series logic that replicates functionality of the ULA (it is probably completely bug-for-bug compatible), IIRC it was designed by author of said book.

Nice, I'm thinking about making it possible to connect it directly to a display/TV and keyboard. Now, I have to have a terminal or laptop + terminal emulator.

It seems hard to drive a vga display without resorting to fpgas or an avr.

If composite is enough, the NES PPU could be a fun addition to that design :)

Apparently, it can be done with a bunch of TTL logic chips.

http://forum.6502.org/viewtopic.php?f=4&t=3329

Yes, the composite solutions sounds more fun :-)

A Propeller Chip does this easily.

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