In a buffer register with a LOAD control, when LOAD is active the input word is captured on the next positive clock edge.

Introduction / Context:
Edge-triggered registers are the fundamental storage elements in synchronous digital systems. A buffer register typically has a LOAD (enable) input that gates whether new data is latched. Understanding exactly when data is captured helps avoid setup/hold violations and ensures correct timing in pipelines and interfaces.

Given Data / Assumptions:

• The register is clocked and edge-triggered.
• The LOAD input is active (asserted).
• “Positive edge” means a transition from logic 0 to logic 1 on the clock signal.

Concept / Approach:
For a positive-edge-triggered register, data present at the inputs is sampled and stored only at the instant of the rising clock edge, provided the LOAD (enable) is asserted. Between edges, the output remains stable. Designers must meet setup and hold times: data must be stable for a minimum time before and after the rising edge to guarantee reliable capture.

Step-by-Step Solution:
Identify the trigger mechanism: positive-edge-triggered register.Check control: LOAD active → register is enabled to accept new data.At the next rising transition of the clock, the input word is sampled and stored.Therefore, the correct word to fill the blank is “clock.”

Verification / Alternative check:
Consult typical timing diagrams for D-type flip-flops with enable: they show sampling on the rising clock edge when enable is high. This behavior underpins synchronous design methodologies and static timing analysis tools.

Why Other Options Are Wrong:
“Pulse” is vague and not the synchronous reference edge; “register” and “transistor” are components, not timing references; “None of the above” fails because “clock” is correct and precise.

Common Pitfalls:
Confusing level-sensitive latches with edge-triggered flip-flops; forgetting to meet setup/hold windows; assuming LOAD changes can occur exactly at the edge—controls must also meet timing requirements.

Final Answer:
clock