| 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. | |||||||||||||