More Complex Systems
Three-, and higher-, input molecular logic gates are considered here. Careful attention is paid to minimize the complexity of the logic device commensurate with its (bio)chemical behaviour. Functional, rather than physical, integration of logic is a guiding principle in this Chapter. We start off with three-input versions of AND, OR, NOR, INHIBIT and IMPLICATION. Cases with an enabling or disabling function, e.g. enabled OR, enabled NOR, enabled IMPLICATION, disabled OR, disabled INHIBIT, disabled XNOR and disabled IMPLICATION, are also detailed. Some of these, which display different logic types upon altering the wavelength of observation, are discussed here even though related examples are taken up for discussion in Chapter 13. Other three-input cases including 2:1 multiplexers (and their corresponding 1:2 demultiplexers) also come under the spotlight. Four-input versions of AND, doubly disabled AND and 4-to-2 encoders (and their corresponding 2-to-4 decoders) come next, followed by a few other four-, and higher-, input devices. Higher arithmetic systems which contain various integrations of half-adders and half-subtractors such as full-adders and full-subtractors are illustrated. Even combinations of the latter pair are available. Intricate molecular logic systems, which are capable of playing games such as ‘tic-tac-toe’ rather sensibly, round off the Chapter.