Pixel Box

It reads as fully lit while emitting nothing, which is the entire idea. It is a display pixel. Signal it and it goes bright without changing the lighting around it, so a grid of them is a screen you can drive from a wiring room.

It wants two signals rather than one. A pulse arriving from above or below does nothing on its own, and neither does one from the side. Both have to land at the same moment. That is an and gate baked into the tile, and it is what lets a row line and a column line together address one box in a grid without a separate gate for every cell. The wire has to sit on the box itself to count, and every one you place starts switched off.