In tri-state (three-state) logic, when the output of a shift register is disabled, into what electrical condition is its output placed?

Introduction / Context:
Tri-state outputs allow multiple devices to share a common bus. Besides logic 0 and logic 1, a third state disconnects the output driver so that it neither sources nor sinks bus current. Recognizing this state is critical for avoiding bus contention when several devices might otherwise drive the same line.

Given Data / Assumptions:

• A shift register with an enable (OE) or output control pin.
• Bus-oriented design where only one device should drive the line at a time.
• Disabled output should not affect bus level.

Concept / Approach:
The disabled or tri-stated condition is called the high-impedance (Hi-Z) state. In Hi-Z, the output behaves electrically like an open circuit, effectively removing the device from the bus. This permits another enabled device to drive the line without conflict, and also allows external pull-ups/pull-downs to set the idle level.

Step-by-Step Solution:
Assert OE so that the output drivers turn off.Measure bus current contribution: It becomes negligible (no active drive).Observe that bus level is determined by the enabled driver or bias resistors.Therefore, the output is in a high-impedance state.

Verification / Alternative check:
Datasheets specify output leakage currents (e.g., ±10 µA) in Hi-Z, confirming near-open-circuit behavior. Timing diagrams also show OE controlling transitions into and out of Hi-Z to prevent overlap driving.

Why Other Options Are Wrong:

• LOW or intermediate bias: These imply the device is still driving; not true for Hi-Z.
• Float state: Informally used, but the precise engineering term is high impedance; floating is a symptom, not the defined output mode.
• Float + Hi-Z: Redundant/confusing; the canonical term is Hi-Z.

Common Pitfalls:

• Leaving a bus with all drivers tri-stated and no bias resistors, causing undefined levels and noise susceptibility.
• Enabling more than one driver simultaneously, leading to destructive contention currents.

Final Answer:
high impedance state