Oscilloscope triggering best practice for digital troubleshooting: In general bench work on synchronous digital systems, the oscilloscope should be triggered by which signal source to obtain a stable display?

Introduction / Context:
Reliable oscilloscope triggering is key to visualizing repeatable waveforms in digital systems. Without a stable trigger source, the trace will drift, making timing relationships and logic levels difficult to evaluate. Selecting the correct trigger improves measurement quality and speeds up troubleshooting.

Given Data / Assumptions:

• System under test is synchronous, governed by a master clock.
• Goal is to observe data lines, control strobes, or edges relative to the clock.
• Standard bench oscilloscope with external trigger capabilities is available.

Concept / Approach:
In synchronous systems, most signals are time-aligned to a common clock. Triggering on the system clock phase-locks the oscilloscope acquisition to that reference, producing a stable display and preserving edge relationships. This is superior to generic channel-triggering or line sync, which may not correlate with the logic timing and can obscure real behavior.

Step-by-Step Solution:

Verification / Alternative check:
Compare displays while triggering on random data vs. the clock. Only clock-based triggering consistently stabilizes periodic synchronous activity across captures, revealing setup/hold margins and timing skew.

Why Other Options Are Wrong:

• A channel or channel 1: Arbitrary data lines may be pseudo-random and won’t lock the display.
• Vertical input mode: Not a trigger source; it is a front-end setting.
• Line sync: Aligns to mains frequency, unrelated to digital timing.
• Arbitrary free-running trigger: Produces unstable, drifting traces.

Common Pitfalls:
Triggering on noisy or jittery derived signals; neglecting proper termination; ignoring clock inversion or duty cycle that affects trigger level; forgetting to use probe bandwidth and ground lead practices to avoid ringing.

Final Answer:
the system clock