In the logic circuit of Figure (a), there is an added switch to a digital buffer that is called as enabled input indicated by E. Whereas E is low; the output is disconnected from the input circuit. Whereas E is high, the switch is connected and the circuit acts like a digital buffer. All of these states are listed in Truth Table (b). Figure (c) illustrated the symbol of a Tri-state Buffer.
(a) (b) (c)
Figure: (a) Switch Configuration, (b) Truth Table, and (c) Symbol of a Tri-state Buffer