Circuits

Gates may be connected to build circuits

Valid combinational circuits

The output of a gate may only be attached to the input of another gate.

Think of this as a directed edge from output to input.

There must be no cycles in the circuit (directed graph).

Although the output of a gate may be attached to more than one input,

an input may not have two different outputs attached to it

(This would create conflicting input signals.)

Each input of a gate must come from either the output of another gate or a source.

Source: something which generates either a constant 0 or 1.

Gate delay

Output takes some small amount of time before it changes.

Information can travel at most, at the speed of light.

Gate delay limits how fast the inputs can change and

the output can still have meaningful values.