When is multiplexing required? In digital systems, multiplexing of signals is usually required under which circumstance?

Introduction / Context:
Multiplexing (time, frequency, or code division) allows multiple signals to share a limited physical medium. It is widely used to reduce wiring and channel count where links are constrained.

Given Data / Assumptions:

• Long-distance links are expensive or have limited conductors.
• On-chip internal data movement often has abundant parallel paths, but board-to-board or long-cable runs are scarce.

Concept / Approach:
Over long distances, sending many parallel wires is costly and prone to skew. Serial or multiplexed schemes combine many signals over fewer lines, then demultiplex at the destination, conserving bandwidth and conductors.

Step-by-Step Solution:
Identify the scenario most constrained by physical media: long distance links.Multiplexing combines multiple signals over one or a few channels.Therefore, option “moving data over long distance transmission lines” is most accurate.

Verification / Alternative check:
Standards like TDM in telecom, SERDES on backplanes, and network links exemplify multiplexing for distance or pin-count constraints.

Why Other Options Are Wrong:
Internal CPU buses often use wide parallel paths; multiplexing may occur but is not “usually required.”Memory/register transfers are typically parallel on short distances to maximize throughput.Option d restates a typical internal case, not the primary driver for multiplexing.

Common Pitfalls:
Assuming multiplexing is always better; for short distances with tight timing, parallel buses can be superior.

Final Answer:
Moving data over long distance transmission lines.