Which diagnostic tool is commonly used to verify basic functionality of serial (RS-232) and parallel ports by looping signals back to the interface?

Introduction / Context:
When troubleshooting legacy serial and parallel interfaces, a quick way to validate the physical port and UART/printer port circuitry is to use a loopback device. Understanding the correct tool speeds diagnosis without needing external peripherals.

Given Data / Assumptions:

• Interfaces: RS-232 serial and Centronics/IEEE-1284 parallel.
• Goal: Verify that transmitted signals can be received back at the same port (self-test).

Concept / Approach:
A loopback (wrap) plug routes specific output pins to corresponding input pins so the host's transmitted data or status lines are returned to the receiver side. Passing loopback tests indicates the port hardware and driver stack are functional. Cable scanners and sniffers serve other purposes (cable mapping, network packet capture), and high-voltage probes are for power electronics, not I/O port testing.

Step-by-Step Solution:
Connect the appropriate loopback plug to the port.Run a loopback test utility to transmit data and verify correct reception.Confirm that successful loopback indicates a working port; otherwise, suspect hardware, driver, or cable.

Verification / Alternative check:
Many vendor diagnostics ship with loopback test options; RS-232 pinouts (e.g., shorting TXD to RXD) are standard practice.

Why Other Options Are Wrong:

• Cable scanner: Maps cable conductors; not a loopback of the port logic.
• Sniffer: Captures network packets; unrelated to local port wiring tests.
• High-voltage probe: For measuring HV; not for serial/parallel diagnostics.
• None of the above: Incorrect since loopbacks are the correct tool.

Common Pitfalls:
Testing with a peripheral of unknown condition; always validate the port first with a loopback to isolate issues.

Final Answer:
Loop backs (wrap plugs)