We can make any kind of computer circuit we want out of AND, OR, and NOT gates. To do this, it is necessary to wire many gates together. Let's see how this is done. In a drawing we show that two gates are wired together by drawing lines between them. First, we need a couple of gates. Click the following button to add some gates to our drawing area. As in Lesson 1, we are using a schematic editor to draw our illustrations.
Now let's draw a wire joining these two gates. Click on this button to do this.
The schematic editor has named our new wire WR1. WR1 is an output wire of GT0 and an input wire of GT1. This means that ones and zeros will come out of gate GT0 and go into GT1. In a real computer circuit, ones and zeros flow through a series of many different gates to perform different computations.
As in Lesson 1, you can change this drawing. Try clicking on the wires and moving them. Notice that ports change color when a wire is attached to them. Also notice that when you move a gate, the wire attached to it moves with it. The ports that you see in this drawing are not really part of the schematic. They are just a drawing aid that our schematic editor uses to help you draw wires. Before we can see how a gate works, we must look at a couple of other things that our schematic editor needs.
To test a circuit and see how it works, we need bring ones and zeros into the circuit from the outside. To do this, we need to tell the schematic editor where these values will appear in the circuit. This is done using the primary input symbol. Click the following button to see the primary input symbol. The primary input symbol acts like a gate, but is actually part of the wire attached to it.
By the same token, we need to show where ones and zeros come out of the circuit. This is done using the primary output symbol. Click on the following button to see this symbol.
Play around with the drawings a little bit. When you are familiar with moving gates and wires, click here to go to lesson 3.