The diode

The diode

We’ll now look at how to make a diode: in other words, how to allow electrons to flow only one way along a wire.

It’s worth noting that we don’t actually use the diode much in practice, as it is very rare for a wire to be used to communicate in both directions; however, it’s instructive to look at and lets us review the rules of Wireworld.

The picture shows two wires. The upper one has a diode facing forwards, while the lower one has a diode facing backwards. As you can see, the diode blocks electrons flowing in the opposite direction to the way it is facing.

How does it work?

Recall from the rules that a copper cell becomes an electron head if it has just one or two neighbours that are electron heads. If three neighbours are electron heads, the cell will remain copper. This is the key to the operation of the diode. As an electron attempts to flow through the diode, there comes a point (generation number 1 in this case) when a column of three cells simultaneously become electron heads. In the top case in the picture above, the electron heads can propagate to the next column to the right, as each copper cell in that column is only adjacent to two of the heads. In the bottom case, however, the copper cell in the next column is adjacent to three heads, and so the flow stops.

Next we shall look at how to perform logical operations on Wireworld signals.

<Previous page  Wireworld index  Next page>