Getting parallel data from a shift register How can parallel data be taken simultaneously from a shift register built from flip-flops?

Difficulty: Easy

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.

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