A hobby hardware project · 2020–2021
A homebrew GPU, built from logic chips
It started as a copy of Ben Eater's breadboard VGA card during the 2020 lockdown. A year later it was a tile-based graphics card with 256 colours and hardware scrolling, on its own PCBs, driven by a 6502 computer.
The finished GPU
- Resolution
- 400 × 300
- Colours
- 256 (8-bit RRRGGGBB)
- Tiles
- 256 tiles of 16 × 16 pixels
- Tile map
- 256 × 128 tiles (4096 × 2048 px)
- Scrolling
- Hardware, 12-bit X and Y
- Clock
- 20 MHz
- Output
- VGA, 800 × 600 @ 60 Hz
- Interface
- 8 data + 5 control lines
The build, in five parts
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Building the video card
Rebuilding Ben Eater's VGA card on breadboards at twice the clock speed, trimming the sync logic, getting 16 colours out of an EEPROM, and ordering a first PCB.
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From video card to GPU
Game Boy–style tiles and a tile map, 256 colours, RAM instead of EEPROM, and an interface so another computer can draw to the screen.
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The final design
Hardware scrolling, a multiplexed five-line control interface, an EPROM-driven counter and a PCB in the shape of a PCI-E card.
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Connecting it to a 6502
Splitting the GPU into a three-board stack with Ben Eater's 6502 computer on top, first demos in 6502 assembly, and an emulator for both.
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The EPIC 6502
Everything on one big purple board: the computer, the GPU and four expansion ports, plus swappable cartridges and Enhanced BASIC drawn in tiles.
About the project
I'm a programmer by trade, and electronics is a hobby I'm teaching myself. After watching Ben Eater's “world's worst video card” series I set out to build my own: first on breadboards, then with higher resolution and better logic, and finally on custom PCBs.
Writing a Game Boy emulator over Christmas 2020 gave me the main idea: store the screen as tiles plus a map of which tile goes where, not one byte per pixel. A slow 8-bit CPU can drive that, and moving a viewport across a bigger map gives scrolling almost for free.
These pages are my original build logs, written as the work happened, with the original photos, diagrams and videos.