Although this is the most important part of the whole computer, this is the simplest of the PCBs.  Basically, just a breakout board for the Z80 processor the only other components are a 3k3 resistor to keep the INT pin held high and header pins


First edition of this board was just made on Veroboard.  It works fine, but it’s bit more delicate than the PCB version


Click the image below for schematics in PDF format


Early iterations of this board had WAIT, NMI and BUSRQ tied to 5v.  Later versions have these broken out to header pins along with RFSH and BUSAK.  These later versions need links soldered from WAIT, NMI and BUSRQ to 5v, or connections other devices that take them high.  [Note that an error on the silkscreen indicates that BUSAK should also be linked across to 5v.  It should not, although doing so may result to damage to the CPU only if BUSRQ is pulled low]



Buy one here

Bill of materials

  • PCB
  • 34 pin R/A header
  • 4o pin wide DIL socket
  • Z80 CPU
  • 3k3 resistor