Neo6502 Chess 0.1: chess in assembly, online
Our chess program for the Neo6502 is out in beta on Prophet. Written in 6502 assembly, it plays against you, against itself, or puts you in front of another board over the Internet.
Since 10 November, Neo6502 Chess can be downloaded from prophet.3617.fr, our program server for the Neo6502, in the "in development" category. One file, chess.neo, to copy to the board and run. The same engine also runs on the Oric: it has an article of its own.
The published version
| Neo6502 Chess | |
|---|---|
| Version | 0.1.0 (beta), 10 November 2026 |
| File | chess.neo, 62,986 bytes |
| Machine | Neo6502 (W65C02), Trinity firmware |
| Where | Prophet, "in development" category (id chess-neo) |
| Tried | on a real board and in the Phosphoneo emulator |
1. An engine written for the 6502
The engine is written in assembly and kept apart from the machine by an abstraction layer: the same code plays on the Neo6502 and on the Oric. It searches with alpha-beta and quiescence, killer moves and null move, keeps a transposition table, and evaluates positions with tables we tuned ourselves with Texel's method, from games it played against itself.
Every routine is checked against a twin written in Go: move generation verified by perft, searches replayed identically, position by position. The program knows checkmate, stalemate, threefold repetition and the fifty-move rule.
2. What you see on screen
A colour board with pieces drawn in relief. You play with the keyboard (arrows and Enter) or the mouse. The machine's first five levels give it a fixed time per move, from one second; the next ones are 13 time controls from 1 to 90 minutes, with or without increment. Each side has its clock.
The menu offers one or two players, random colour, computer against itself, French or English. Playing aids switch on when asked: a suggested move, possible moves, movable pieces, attacked squares, a warning before a risky move. You can take back, replay the game, save it, and set up a position with the editor. The H key shows the help.
3. Playing another board
With a Pico W modem, two Neo6502 boards play each other through a relay we host, chessrooms.3617.fr, over an encrypted link. You enter a public room to face a stranger, or a private room with a shared code. Takeback, draw offer and resignation are negotiated between both boards.
We played this way on a real board, in both directions, against a PC client.
4. What we do not claim
This is a beta: 0.1.0 is the first published version. We have not measured the program's Elo strength against human players; our measurements pit it against other engines, at a fixed budget. Prophet's "Play" button runs the emulator, not the board. The game record stops at 150 half-moves. Correction of 10 November: a first version of this article announced a 3D view of the board, removed before publication, and a 230 half-move record, which comes after 0.1.0. The code has no public repository yet.
Sources & links
- Neo6502 Chess on Prophet (play in the browser)
- prophet.3617.fr — the program server
- Oric Chess: the same engine on the Oric Atmos
- Using Phosphoneo, the Neo6502 emulator
- Get started with the Neo6502
← Neo6502 · Manoir NG → · Phosphoneo → · Prophet 0.25 → · SWD → · Prophet → · AsteroNeo → · Neo6502 →