The Homebrew Handwired Z80 Computer - H2Z80

A 64K Z80 computher that you cand build by yourself only with perfboards, wires and some components

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This little computer idea was born from my desire to better understand how computers really works and how they can do everything they actually do. The things started very slow... as anyone can imagine, understending how to build it from zero is quite defficult and I don't have any training to do that.
At that momment, the computer is already working, running Small Computer ROM Monitor and CP/M 2.2, has a usable videocard and a almost good Compact Flash card. The controller and PS/2 keyboard card is unfinished yet, even the schematic isn't finished.

  • Main Board - The Motherboard:  It's contains the Z80 processor running at 4 MHz, 32K ROM and 64K RAM (two 65256 with 32K each), the Z80 SIO chip witch interfaces the serial up to 19200 baud rate by a RS2323 adapter, the clock generators for the Z80 CPU, and for the Z80 SIO, the I/O decoder with a 74HC154, this one supports up to 16 I/Os, the LM7805 regulator, three expansions slots with 31 2.54mm pins each one, a 10 LEDs bar that help to monitore some CPU control pins and a simple reset circuit. I can easily modify the baud by selecting from 2400 to 19200 in the dipswitch and the CPU crystal clock can be exchanged by hands;
  • Expansion Slot 0 - The VDP: This board is basically a TMS9918 VDP, 16K RAM and some glue logic to uses a 62256 instead of multiple 4116 SRAMs chips. This board also provides the connections for stereo audio and power to a small RCA monitor that I have here. This board has it's own 5 volts regulator due the high VDP consumption;
  • Expansion Slot 1 - The CF card: This one is a Compact Flash card interface to allow the computer to run CP/M and provides much more space than the 32K ROM, Its also has a 10 LEDs bar that is mapped to I/O 0x00h and acts as a status monitor. In the future, I want to wire up the seccond PATA connector to be able to connect a IDE cable and a hard drive directly to the computer in addition to the CF card;
  • Expansion Slot 2 - The Keyboard and Controllers interface: This board is on development yet, its will provide a PS/2 keyboard interface directly for the computer and two NES/SNES compatible controllers interfaces to play some games like the colecovision library. I would like to turn H2Z80 indeppendent from my computer terminal, using this board to interface the keyboard and the CP/M to uses the VDP as a terminal;
  • Display: It's not more than a simple 4,3 inch display that works with RCA video, I modified a little to add a sound output with one PAM8403 amplifier and two speakers opering on mono;
  • Frame: A 3D printed frame that I make on Fuzion360 to match with the boards and add some structure sopport to then.

H2Z80 Schematic 13MAIO2024.pdf

Schematic for the Maind Board and all the Expansion boards

Adobe Portable Document Format - 152.90 kB - 05/13/2024 at 22:39


  • Now workable Controller interface and Sound board!

    Jorisclayton7 days ago 0 comments

            Today I started working with the controller board and, after some headacha, I came with this workable design. At first, I thought the the clock and the latch signals would be send by the controller (something like the PS/2 protocol) and until understand that I need to send it to the joystick I lost some time... As I'm using a pseudo SNES controller that, in practice, works like a NES controller with turbo A and B mapped to X, Y R and L buttons, this also give me some pain, as I was waiting 16 bits and the controller only send 8 to me with a "strange noise" on some buttons. Its was what I thought until realize that it is a NES not a SNES protocol. My controllers also came with Start and Select button inverted for some reason but it wasn't a problem.
            Finally, after much tests, there is the result, a board that get the 8 bits serial informatin from the controller and shows it as one byte, all the 8 bits at a time, for the Z80 CPU at the ports E0h and E1h, the Z80 just need to read it and all the pressed keys will be there. I will update the schematic with some other changes, like IO addresses and some expansion slots pins changes.

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Peabody1929 wrote 05/09/2024 at 18:31 point

Check out Small Computer Central SC131.

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Jacob David C Cunningham wrote 05/08/2024 at 15:26 point

very compact nice

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Jorisclayton wrote 05/08/2024 at 19:16 point

Thanks, I like to well use the board space

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