Several-valued combinational switching circuits

SINCE the introduction of symbolic methods1,2 into the field of digital control, much has been written on the application of Boolean algebra to the analysis and synthesis of 2-terminal electromagnetic (relay and magnetic core) and electronic switching networks. In general, a switching network involves not only the network configuration and the switching elements but also the states of transmission through the network. A survey of the literature will show however, that it is generally (tacitly) assumed that the states of transmission through a switching network are limited to two values. For relays the two states are usually the establishment and the opening of a d-c path through the network; for electronic gate circuits these two states are usually the presence and absence of a pulse. An essentially similar situation prevails on the states of the switching elements in a network. For relays, a relay contact is either open or closed; for electronic gates, an input or output lead either carries a pulse or does not carry one.