Combinational Logic

A combinational circuit has inputs, gates and outputs.

The logic shown below is called a full adder, where the s output is the sum of inputs a, b, and c_in (carry in), and c_out output is the carry out.

Note that for a given combinational circuit, each output is some function of the inputs, and nothing else. Not of time, and not of its previous inputs. Appling a particular input combination gives the same output every time.

You can open the full_adder.circ file in Logisim and verify this by toggling the inputs.

Visually, when the inputs are on the left side and the outputs on the right side, a combinational circuit can be constructed without any of its wires going from right to left. The signals would flow in the left-right direction without any loops.