AT Command Set: Resetting a Modem When using the standard AT command set, which command resets the modem to its default profile?

Introduction / Context:
The classic Hayes-compatible AT command set is still referenced in embedded systems and legacy troubleshooting. Knowing the reset command is useful for clearing unexpected states, restoring defaults, and re-establishing known modem behavior.

Given Data / Assumptions:

• A Hayes-compatible modem accepts text commands prefixed with AT.
• The task is to reset the modem to a default profile without power cycling.
• We are not changing serial control signals (like DTR) but issuing a command.

Concept / Approach:

ATZ is the canonical software reset that loads the stored default profile and re-initializes settings. It is distinct from hardware control signals and other AT commands that query or set parameters. Using ATZ is a quick, non-disruptive way to standardize the modem state.

Step-by-Step Solution:

Verification / Alternative check:

After ATZ, most modems respond with OK and revert to default settings. If persistent profiles are used (AT&F or AT&Y), behavior can be confirmed by printing active settings.

Why Other Options Are Wrong:

ATR: Not the standard reset command. DTR: A hardware serial control line (Data Terminal Ready), not an AT text command. DCE: Refers to the device role (Data Communication Equipment), not a command. None of the above: Incorrect because ATZ is valid.

Common Pitfalls:

Confusing ATZ with AT&F (factory defaults). ATZ loads the stored profile; AT&F loads factory defaults. Both may be used in sequence if required.

Final Answer:

ATZ