PPT Slide
7 – Sequential Logic Examples
The third value
- logic values: "0", "1"
- don't care: "X" (must be 0 or 1 in real circuit!)
- third value or state: "Z" — high impedance, infinite R, no connection
Tri-state gates
- additional input – output enable (OE)
- output values are 0, 1, and Z
- when OE is high, the gate functions normally
- when OE is low, the gate is disconnected from wire at output
- allows more than one gate to be connected to the same output wire
- as long as only one has its output enabled at any one time (otherwise, sparks could fly)