Getting parallel data from a shift register How can parallel data be taken simultaneously from a shift register built from flip-flops?
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AUse the Q output of the first flip-flop only.
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BUse the Q output of the last flip-flop only.
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CTie all of the Q outputs together.
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DUse the Q output of each flip-flop.
Answer
Correct Answer: Use the Q output of each flip-flop.
Explanation
Introduction / Context:A shift register stores one bit per stage. To expose the entire word in parallel, each stage's Q output is treated as one bit of the bus. This is the basis of SIPO devices and parallel reads from serial streams.
Given Data / Assumptions:
- Register consists of cascaded flip-flops.
- Each flip-flop Q holds one bit.
- We need a simultaneous parallel representation of the stored word.
Concept / Approach:
Parallel readout is accomplished by wiring each flip-flop's Q to a dedicated output pin or bus line. Optionally, an output latch can isolate the internal shifting from the bus, but the fundamental method is one Q per bit line.
Step-by-Step Solution:
Identify number of stages n → n parallel outputs required.Connect Q0..Q(n−1) to the parallel bus lines D0..D(n−1).Read all bits simultaneously on the bus or latch them with a strobe if needed.Verification / Alternative check:
Examine typical SIPO IC pinouts (e.g., 74HC164, 74HC595). Pin names Q0..Q7 expose each flip-flop's output for parallel access.
Why Other Options Are Wrong:
- First/last Q only: yields one bit, not a word.
- Tying all Qs together: creates bus contention/shorts and corrupts data.
Common Pitfalls:
- Forgetting to buffer or latch outputs when long loads or timing integrity is required.
Final Answer:
Use the Q output of each flip-flop.