Z80 SBC Respin Ideas

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Trying to avoid Creeping Featuritis

A small rant on the subject of creeping featuritis

Basic objectives

  • Fix all existing errors (obviously)
    • Board works correctly :)
  • Add CF socket on board?
    • Everything on one board
    • Only SMT sockets available
  • Switching power supply?
    • Wider input range
    • Better on battery operation (more efficient)
    • More board space
    • Raises cost
    • Parts may be harder to find
  • Expansion connector?
    • Good way to add Ethernet, video and keyboard support
    • More user flexibility
    • Additional board space
  • All connectors, etc to one end for case?
    • Wiring comes out cleaner
    • May need larger than desired case
  • Possible video option?
    • What Z80 single chip solutions exist?
    • NTSC or VGA output?
    • Having video implies there ought to be a keyboard
  • Ethernet?
    • Connectivity
    • SMT parts
    • More board space
  • All parts available single supplier (Jameco or Mouser)
    • Single source ordering
    • Parts cost may be slightly higher than shopping around

Considerations

VGA would be easy using some SMT packages. Even an LPC2138 configured as a VGA controller with it's own on-board memory. The GPIO ports should be fast enough to provide a standard Z80 I-O space accesses. But it is SMT, something I think I want to avoid as much as possible for this project, given the target audience. Offering it as a completed expansion card would be an option.

The problem with the above is rampant feature creep. We go from a simple little Z80 system that's amusing to play with to something much more complicated. At some point you ask yourself, "Why not just stuff all this in an FPGA?" Which would, indeed, be cool. But it defeats the concept of a simple, easy to understand, minimalist Z80 system that's fun to play with, and still useful. After all, do you really NEED a meg of bank switched memory, video, keyboard, Ethernet, etc? And how many people can put down a 480 pins BGA package, anyway?

One idea would be an add-on card that has video, keyboard and Ethernet.

Another option for the CF socket would be a riser card that plugs on to the IDE connector. Improving on that, perhaps there are two offerings, a riser card for CF-only, and a riser card with CF and a socket for a 2.5" IDE (the advantage in the CF-only being a smaller card).