Editing Verilog (section)

==Four-valued logic==
The IEEE 1364 standard defines a [[four-valued logic]] with four states: 0, 1, Z ([[high impedance]]), and X (unknown logic value). For the competing VHDL, a dedicated standard for multi-valued logic exists as [[IEEE 1164]] with nine levels.<ref>{{cite book|first1=D. Michael |last1=Miller|first2=Mitchell A. |last2=Thornton|title=Multiple valued logic: concepts and representations|year=2008|publisher=Morgan & Claypool |isbn=978-1-59829-190-2|series=Synthesis Lectures on Digital Circuits and Systems|volume=12}}</ref>