NOR logic

For example, the first embedded system, the Apollo Guidance Computer, was built exclusively from NOR gates, about 5,600 in total for the later versions.

Today, integrated circuits are not constructed exclusively from a single type of gate.

Instead, EDA tools are used to convert the description of a logical circuit to a netlist of complex gates (standard cells) or transistors (full custom approach).

Again, note that a NOR gate is equivalent to a NOT with its inputs joined.

This construction entails a propagation delay three times that of a single NOR gate.

Alternatively, an XNOR gate is made by considering the conjunctive normal form

An XOR gate is made by considering the conjunctive normal form

Alternatively, the 4-gate version of the XNOR gate can be used with an inverter.