VZ-DOOM

A Wolfenstein-style, first-person 3D maze shooter for the 1983 VTech / Dick Smith VZ200 — a Z80 home computer running at 3.58 MHz with 2 KB of video RAM and four colours. Real-time raycasting, doors, chasing demons, sound, and a DOOM-style status face, all in hand-written Z80 assembly on the original hardware.

Rendered by the game's own engine — a demon dead ahead, pistol drawn, health bar and Doomguy's face at the bottom.

Yes, it really runs on a stock VZ200:

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What it does

• Raycast 3D — 32 columns cast through a 16×16 grid map with integer DDA, perspective wall slices, fisheye correction, two-tone wall faces.
• 128×64, 4-colour MC6847 graphics mode (Mode 1), ~15–30 fps depending on how much of the maze is visible.
• Move & fight — walk, turn, strafe, open doors (they auto-close behind you), and shoot. Three demons hunt you through the maze; they slide along walls and come through open doors.
• Status HUD — health pips, kill tally, and a five-state DOOM-style face that gets bloodier as you take damage, flashes when bitten, and X-eyes when you die. At full health his eyes glance left and right, just like the original.
• Sound — footsteps, door whoosh/thunk, pistol zap, pain grunt, death wail, all on the VZ's 1-bit speaker.

All of it is plain Z80 machine code executing on the actual CPU — no emulator, no coprocessor doing the heavy lifting.

Play it

The quick way: copy dist/VZDOOM.VZ to an SD card for a BennVenn SD Loader, then on the VZ200:

LOAD "VZDOOM"

It autostarts.

Controls

Key	Action
W / S	forward / back
A / D	turn left / right
, / .	strafe left / right
E	open door
SPACE	fire
Q	quit to BASIC

Requirements

• A VZ200 (or VZ300 / Laser 200/210/310) with at least ~28 KB of RAM — the BennVenn SD Loader provides this. The game's code lives in base RAM and its data tables load into expansion RAM at $9000.
• Any way to get a .VZ file onto the machine (the SD Loader is the easy path).

If you don't have the RAM expansion, the game won't fit — see DESIGN.md for the memory map.

Build it yourself

You need sjasmplus (a Z80 cross assembler) and, optionally, Python 3.10+ (only to regenerate the lookup tables).

1. Download sjasmplus and put sjasmplus.exe in the tools/ folder.
2. (Optional) regenerate tables — needed only if you change the map, art, or engine constants:

   python tools/gen_tables.py
   

3. Assemble and wrap into a .VZ:

   .\build.ps1 src\vzdoom.asm VZDOOM

   The playable file lands in build/VZDOOM.VZ.

The committed src/tables.inc is pre-generated, so you can build the game with sjasmplus alone — Python is only for changing the data.

How it was built (the interesting part)

Every binary in this project ran correctly on the first hardware attempt, because nothing reached the VZ200 without passing a byte-exact simulator check first:

• tools/gen_tables.py is a Python reference implementation of the entire renderer, using exactly the same integer math (8.8 fixed point, 8-bit angles) the Z80 performs. It also generates the trig, fisheye, wall-height, sprite, and HUD tables.
• tools/z80sim.py is a small Z80 interpreter that executes the real assembled binary.
• tools/doom_test.py drives the binary in the simulator with scripted keyboard input and compares the emulated video RAM against the Python reference, byte for byte, across ~17 scenarios (movement, wall collision, doors, demon AI, hitscan kills, damage, death, and an 88-position projection sweep).

This caught bugs that would have been maddening to debug on a CRT — including a Z80 division routine that dropped a carry bit and made demons flicker and teleport. See DESIGN.md for the full milestone-by-milestone story.

Repository layout

src/
  vzdoom.asm      the game (current build)
  wavedemo.asm    milestone 1 — column renderer
  raycast.asm     milestone 2 — the raycaster
  walk.asm        milestone 3 — movement
  tables.inc      generated data tables (map, trig, sprites, HUD)
tools/
  gen_tables.py   Python reference renderer + table generator
  z80sim.py       minimal Z80 interpreter (the verifier)
  doom_test.py    byte-exact test suite
build.ps1         assemble + wrap a .VZ file
dist/VZDOOM.VZ    prebuilt, ready to play
DESIGN.md         design notes and development history

Credits & thanks

• Claude Code Fable5 (All code written by Claude)
• Built for the VZ200 using BennVenn's SD Loader and his CPLD bus-export firmware — the SD Loader is what makes loading (and the RAM expansion) painless. https://bennvenn.myshopify.com/products/vz300-sd-loader
• Assembled with sjasmplus.
• The VZ/Laser community: https://www.facebook.com/groups/4609469943

DOOM is a trademark of id Software. This is an affectionate homebrew tribute, not affiliated with or endorsed by id/ZeniMax/Microsoft. It shares the genre and the grinning-face HUD idea, none of its code or assets.

License

MIT — do what you like, have fun, and if you get it running on your own VZ, post a video for the group. 🕹️