Three-state buffer purpose in bus systems What is the primary purpose of using a three-state (tri-state) buffer in a shared data bus architecture?
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Ato provide isolation between the input device and the data bus
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Bto provide the sink or source current required by any device connected to its output without loading down the output device
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Ctemporary data storage
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Dto control data flow
Answer
Correct Answer: to control data flow
Explanation
Introduction / Context:In bused systems, many devices share lines. A three-state buffer lets only one device drive the bus at a time, preventing contention. Understanding its primary role helps in designing reliable bus interfaces.
Given Data / Assumptions:
- Shared data bus with multiple potential drivers.
- Buffers can be enabled or disabled to present high impedance.
Concept / Approach:Tri-state buffers have an enable control. When enabled, they pass data; when disabled, they present a high-impedance output (effectively disconnected). This gating of drive onto the bus is fundamentally about controlling data flow and bus access.
Step-by-Step Solution:
Identify the bus requirement: only one active driver at a time.Use the buffer’s enable to grant or revoke bus drive.Therefore, the primary purpose is controlled data flow (arbitration) on the bus.Verification / Alternative check:System timing diagrams show OE (output enable) signals orchestrating which device drives the bus in each time slot—core to data flow control.
Why Other Options Are Wrong:
- Isolation (a): A tri-state does isolate when disabled, but isolation is a consequence; the primary system-level goal is controlled data flow.
- Provide sink/source current (b): That is a line-driver strength consideration, not the defining purpose of tri-state behavior.
- Temporary storage (c): Buffers do not store like latches/flip-flops.
Common Pitfalls:
- Equating tri-state drivers with simple buffers and overlooking the OE-controlled high-Z state.
Final Answer:to control data flow