Hayes AT command set basics: Which standard AT command is used to hang up (disconnect) a modem connection?

Introduction / Context:
Classic dial-up and many embedded modems use the Hayes-compatible AT command set for control. Technicians often need to drop an existing call from a terminal session or script; the correct command prevents confusion and unintended resets.

Given Data / Assumptions:

• Modem is Hayes-compatible and currently connected or in command mode.
• Goal is to terminate the connection and go on-hook.
• Familiar AT mnemonics: D for dial, H for hook, Z for reset.

Concept / Approach:

The hook control command is “H”. With the AT prefix, “ATH” instructs the modem to go on-hook (disconnect). If the modem is in data mode, you may need to escape to command mode (for example, +++ with guard times) before issuing ATH.

Step-by-Step Solution:

Verification / Alternative check:

Vendor manuals and terminal tests confirm ATH drops carrier reliably.

Why Other Options Are Wrong:

• ATD: dials; it is the opposite of hang-up.
• ATZ: resets the modem, not the canonical hang-up.
• ATR: not the hang-up command; function varies by device.
• None of the above: incorrect because ATH is correct.

Common Pitfalls:

Forgetting the escape sequence; confusing reset with hang-up; scripts that issue ATZ unnecessarily and alter profiles.

Final Answer:

ATH