Fets and Crosses: Tic-Tac-Toe built from 2458 discrete transistors

Fets & Crosses

Overview + Features

An implementation of the classic Tic-Tac-Toe / Noughts and Crosses game built entirely from 2458 discrete transistors.

Simulation / Design

While playing around with a graphical logic simulator during a 'Digital Design' lecture, I came up with a simple Tic-Tac-Toe game, featuring both a player-vs-player and player-vs-computer mode. It is capable of detecting all possible win/draw states, and features a move validator, allowing it to reject invalid inputs from the user.

The 'Engine' against which a player can play was originally implemented using a parallel input/output ROM as a large lookup table: The current board state was applied to the 18-bit address applied to the ROM address input, and the engine's move read from memory. This worked well, but was very inefficient: less than 5% of all possible inputs corresponded to possible game states.

In a second step I replaced this implementation with a purely combinatorial logic-gate based module, also capable of perfect play.

The simulation in LOGISIM.

... continue reading