Consider next how a typical 7-segment common anode LED might be interfaced via an I/O port. Here each segment of the display is driven via an inverting tri-state buffer so that a "1" on the corresponding data bus line will cause that segment to light. Will the display operate properly if connected as illustrated below? What happens when the port is de-selected? The problem with this circuit is that when the port is not selected (via the address bus), all the buffer outputs go to the high impedance state ("Hi Z") and hence all the segments will go off. Remember, the port is only selected at most a couple of microseconds! The conclusion is that, since the data is displayed for only a few fleeting moments, the display will not be visible.

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