Designating bundles

Every input and output on every component in the circuit has a bit width associated with it. Many of Logisim's built-in components allow you to customize their inputs and outputs bit widths through attributes. Below, I have inserted two input pins, an AND gate, and an output pin, all customized to deal with three-bit data.

We are currently viewing the AND gate's attributes. Notice how its Bit Width attribute is 3. As a result, the AND gate expects three-bit inputs and outputs. The input pins and the output pin are similarly configured. (Notice that they are drawn containing three bits.)

Wires, however, do not need their bit width specified. Logisim will automatically infer a wire's bit width based on the requirements of the components to which the wire is attached. To connect the input and output pins to the AND gate, we have only to select the wiring tool and draw in three wires.

Given multi-bit inputs, the AND gate computes the bitwise AND of its inputs; in the above screen shot, you can see how the middle bit of the output is 1 because the middle bits of both of the inputs are 1.

Whereas Logisim shows a single-bit wire's value by coloring it either light or dark green, it draws multi-bit wires black. To view the value a wire is currently carrying, probe it with the poke tool .

Next: Splitters.