Hayes AT command set — manual dialing: Which command will manually dial the telephone number 123-4567 using a tone-dial modem?

Introduction / Context:
Classic dial-up modems use the Hayes AT command set. Understanding basic commands such as dialing is essential when testing, scripting, or troubleshooting dialers and communications software.

Given Data / Assumptions:

• We are using a Hayes-compatible modem.
• Tone dialing is requested (as opposed to pulse dialing).
• The number to dial is 123-4567 (hyphen is ignored by the modem).

Concept / Approach:

The generic dialing command format is ATD followed by a dialing modifier. ATDT specifies tone mode; ATDP specifies pulse mode. The digits of the phone number follow immediately, with optional punctuation ignored.

Step-by-Step Solution:

Verification / Alternative check:

Most terminal emulators and modem manuals show ATDT for tone dialing and ATDP for pulse. Issuing ATDT followed by a number audibly triggers touch-tone sequences on an analog line.

Why Other Options Are Wrong:

• AT1234567: Missing the D (dial) and tone/pulse specifier.
• AT1234567DL: Not a recognized form for dialing.
• ATM 1234567: M controls speaker; the space and syntax are invalid for dialing.
• None of the above: Incorrect because ATDT1234567 is correct.

Common Pitfalls:

Forgetting the T (tone) or using ATDP on tone-only lines; including spaces where none are allowed; and mistaking ATZ (reset) or ATH (hang up) for dialing commands.

Final Answer:

ATDT1234567