case 04 · Personal · 2024 – 2025
6502 breadboard computer+ discrete-logic VGA graphics card
A working 8-bit computer based on the 6502 microprocessor, wired up from scratch with SRAM, EEPROM, and address-decoding logic — paired with a TTL-logic video card that generates real VGA signals to a monitor.
code/repo coming soonThe computer
A MOS 6502 microprocessor wired up with SRAM, an EEPROM-based ROM, and discrete address-decoding logic. Programs are written in 6502 assembly, hand-assembled, and burned to the EEPROM. On power-up the CPU fetches the reset vector and runs straight out of ROM.
The video card
A separate breadboard handles video output. It's a discrete-logic VGA generator built from TTL counters and shift registers — generating HSYNC, VSYNC, and a pixel clock at standard VGA timings, scanning a tiny framebuffer out to the monitor. The output works on a real VGA monitor with no driver chip in between.
Why do it
The 6502 is the CPU that ran the Apple II, Commodore 64, and the NES. Wiring one up by hand teaches you how an old computer actually worked at the bus level — when /RD goes high, when the address bus changes relative to the clock, how memory-mapped IO works. Then building a video card from logic gates demystifies how anything ever showed up on a screen before GPUs.
Parts list
Bill of materials for the 6502 computer — drawn from Ben Eater's published list at eater.net/6502. Quantities only; prices omitted. (The discrete-logic VGA card uses a separate BOM, not listed here.)
CPU & memory
- 1×W65C02 — 6502 CPU
- 1×28C256 — 32K EEPROM (ROM)
- 1×62256 — 32K SRAM (RAM)
I/O & glue logic
- 1×W65C22 — Versatile Interface Adapter (VIA)
- 1×74HC00 — quad 2-input NAND (address decode)
Display & controls
- 1×16×2 character LCD (yellow backlight)
- 1×10 kΩ potentiometer (LCD contrast)
- 8×Tact switch
- 10×Red LED
Clock
- 1×1 MHz crystal oscillator can
Passives
- 10×220 Ω resistor
- 10×1 kΩ resistor
- 10×0.1 µF capacitor
Breadboards & wiring
- 3×BB830 breadboard
- 40×20 cm jumper wires
- 1×Hookup wire — assorted colors & lengths
Not in the kit BOM — sourced separately: EEPROM programmer (Ben Eater's Arduino-based programmer, or equivalent), and a 5 V power supply.
- CPU
- MOS 6502
- Memory
- SRAM (RAM) + EEPROM (ROM)
- Programming
- 6502 assembly → hand-assembled → EEPROM
- Video
- TTL-logic VGA generator (HSYNC, VSYNC, pixel clock)
What's next
- Monitor program — write a ROM-resident monitor that lets you inspect and modify memory, enter programs via keyboard, and run them — the classic 6502 development environment
- PS/2 keyboard — decode PS/2 scan codes in software and map them to ASCII so the system has real input
- VGA character mode — tile the display into a character grid backed by a small RAM region; text output becomes a memory write rather than pixel manipulation
- SPI / SD card — bit-bang SPI to an SD card for persistent storage; programs would survive power cycles
- Expand to W65C02S — the CMOS W65C02S is in production and adds useful instructions (STZ, PHX, PHY); a drop-in upgrade for the breadboard