HBC-56 homebrew 8-bit computer (65C02 + TMS9918A on a backplane)

[visrealm]

Rather than start a new thread for each update on this project, I've decided to create a single thread and update it as required. This is that thread.

Background

This is my second homebrew project after first completing a Ben Eater inspired SAP-1ish on a breadboard. Dipped my toe in 65C02 assembly working on some Commander X16 projects, so decided to do a 65C02 next. Loved the idea of a backplane where I can easily add/replace components of the build at will. I also have a soft spot for the TMS9918A having grown up with a TI-99/4A. So that was my starting point. (Yes, I'm quite a newbie at this - but have a very extensive background in software).

I started out building the project on breadboards, but then designed a backplane and custom proto card to start the build proper. I started out with a graphics LCD:



Then built the TMS9918A card and added support for a NES controller:



It was around this point I started working on the emulator. For this, I wrote my own 65C02 and TMS9918A emulator libraries and built both a desktop and web-based version. You can try the latest web version here (requires keyboard): https://visrealm.github.io/hbc-56/emulator/wasm

Not long after that, I was contacted by PCBWay who were keen to supply me with PCBs in return for mentioning them (nothing more than that). This surprised me as my project / YouTube, etc. has very few followers, but I decided to go ahead anyway. This gave me the perfect opportunity to design custom PCBs to replace the old hand-wired ones.

The brings me to the present day where I've started building out some of these new cards and documenting the process in video form. It's not all smooth-sailing and you might get something out of these. If you're interested in TMS9918A development, I'm planning to do some videos on that specifically soon (probably after the card build series).

All five cards now built. Updates for each to follow in coming weeks.



Updates

28 May 2022

The new RAM/ROM card. It contains 64KB RAM + 32KB ROM with runtime-configurable selection of RAM or ROM in 4KB pages.



23 May 2022

Video covering the schematic, PCB design, assembly and testing of my new TMS9918A display card



16 May 2022

Video covering the schematic, PCB design, assembly, diagnosis, repair and testing of my new 65C02 CPU card



Project links

GitHub: https://github.com/visrealm/hbc-56

YouTube: https://www.youtube.com/playlist?list=PLhBwUsBsKBEMxZFNBWzE2UhNCxNknMrcR

Emulator (live online instance, requires keyboard) : https://visrealm.github.io/hbc-56/emulator/wasm

Hackaday: https://hackaday.io/project/180904-hbc-56-65c02-tms9918a-on-a-backplane

[visrealm]

The next HBC-56 video is now available. This time covering the new RAM/ROM card. It contains 64KB RAM + 32KB ROM with runtime-configurable selection of RAM or ROM in 4KB pages.



The video also covers GAL/PLD programming and touches on future changes to the emulator.

[CJay]

Nice

That's on my playlist now

[Benta]

Very nice, I like it.
As you're using DIP parts, you might be interested in looking at the single-Eurocard sized VME boards from "PEP Modular Computers" (we're talking 80s/90s/00s here)
They were specialists in stacking parts using "elevator sockets". This allowed placing bus buffer ICs, decoder ICs, caps, crystals etc. underneath the larger ICs (24/28/40/64-pins), compacting the board even more.

[visrealm]

A brief montage of mostly unreleased footage covering the first 12 months of my HBC-56. From breadboards to custom protoboards to today.

[SiliconWizard]

Impressive work. Your channel sure deserves more views.

Did you write all the sofware yourself?

[visrealm]

Thanks. Yes, I wrote all of the software except BASIC which is a port of EhBASIC. All of the software is available in my GitHub repo. https://github.com/visrealm/hbc-56