• CELL
  • Intermediate
  • 5 min
  • Serial CLI

Recipe · Intermediate · CELL

How to send a USSD request

Use CELL mode to send USSD codes from a cellular modem after SIM and network registration checks.

Cellular modem with SIM card and radio signal.
Start with read-only checks, then move to write, replay or automation only when the setup is understood.
Step 1

Commands

Use the shortest command path that matches the documented firmware workflow. When a mode needs setup, follow the prompts shown on first entry.

Result

What it means

The command path is working when the target responds and the firmware prints the expected menu, status or captured data.

Troubleshooting

  • Re-enter the mode setup when pins or peripherals are not already initialized.
  • Check common ground and target voltage before blaming software.
  • Prefer Serial CLI for long captures or high-volume output.
  • Repeat the read or capture to confirm stability.

Next steps

  • Save the output in your project notes.
  • Compare the result with the full wiki page for mode-specific details.
  • Create a shorter alias if you repeat this workflow often.

cellular USSD FAQ

What is USSD useful for?

USSD sends short operator service codes for things like balance, plan status or menu-style carrier services, depending on the SIM and network.

Why does a USSD code fail on one SIM but work on another?

USSD codes are operator-specific. A valid code on one carrier may be unsupported, blocked or different on another carrier or modem mode.

What should a USSD response tell me?

A USSD response should return operator-side text for a short service code, such as balance or account information where supported. It confirms modem, SIM and network service interaction.

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