Choosing components to clone ZX80

componentscpumemorynon-volatile-memory

I have an idee fixe to make a clone of Sinclair's ZX80 computer.

So now I'm trying to find out which ICs I need for the basic prototype – and here are a few questions:

  • it seems Z84C00xxx is a modern substitution for original Z80 processor, right?
  • for SRAM, will UT62xx or LY62xx be the proper choice (I think of 6264 or 62256 chips, preferably in DIP, though it would not be hard to manage SOIC also);
  • what to use for ROM? FLASH-chips I can find usually contain megabits of memory while I only need few kilobytes – would EEPROM will do instead? Though it seems there are not very much with parallel interface, but I believe I can get along with Atmel's (like AT28C256)? I also had idea that I can use some MCU with enough pin count and internal flash instead, but I suspect it will not give good timing (unless I pump the flash content to RAM at first).
  • what series for discrete logic chips I should prefer, I believe 74HCxx or 74HCTxxx should be ok with the given CPU?

Best Answer

The Z84C00xxx is not exactly 'modern', but it is still available new. Another advantage is that being CMOS it uses much less power than the NMOS version. It is specified to work at TTL logic levels, so for best compatibility I would use HCT logic chips.

For SRAM I would use a 62256 (32kx8) because they are readily available and often cheaper than smaller capacity static RAMs. If you can't get it in DIP then use a SOIC to DIP adapter board.

For ROM you can use either EPROM or (parallel) EEPROM. I prefer EEPROMs because they are quicker to program and don't need a UV lamp for erasing. The AT28C64 (8kx8) is readily available in DIP package at a good price.

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