Introduction:
Parallel loading is a foundational capability of many shift registers and register files. The idea is that each flip-flop in the register receives its own data input line (a parallel bus), and when the correct control and clock conditions occur, all flip-flops capture their assigned bits at the same instant. This item asks you to confirm that “parallel load means to load all flip-flops at the same time.”
Given Data / Assumptions:
- A register contains multiple flip-flops, typically one per bit.
- A control input (often labeled LOAD or SHIFT/LOAD) selects between parallel load and shift modes.
- Loading occurs on a specified active clock edge if the control selects parallel load.
Concept / Approach:
In parallel load mode, each stage’s D input is driven by the corresponding bit of the parallel data word. When the clock edge arrives (synchronous design), the entire word is sampled and stored simultaneously, eliminating the per-bit skew that would appear if bits were shifted serially over multiple cycles.
Step-by-Step Solution:
Identify the control: when LOAD=active, the input multiplexers route the external data bus to each flip-flop.On the active clock edge, every flip-flop samples its D input.Because the same edge triggers all stages, capture is simultaneous for the whole word.
Verification / Alternative check:
Datasheets for universal shift registers (e.g., 74195 family) describe “parallel load” as synchronous, single-edge capture across all stages.
Why Other Options Are Wrong:
Incorrect: Contradicts standard register operation.Only true for ripple registers: Ripple refers to asynchronous carry or clocking in counters, not parallel load behavior.Depends on duty cycle: Duty cycle does not alter the fact of simultaneous sampling at an edge.
Common Pitfalls:
Confusing parallel load with serial shift (which takes multiple clocks).Assuming “simultaneous” means “asynchronous”; it is synchronous to a single edge.
Final Answer:
Correct
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