Specifications

ISU AT Command Reference Modem Overview
Iridium Proprietary Version 2.45
20 June 2011 5
2 Modem Overview
2.1 DTE-ISU Interchange Circuits
The communication between the ISU (Iridium Subscriber Unit) and the DTE (Data Terminal Equipment)
follows the ITU-T V.24 (RS-232) recommendation. Please see reference [4] for details.
2.2 9-Wire and 3-Wire Operation
The ISU supports a full 9-wire interface to the DTE, incorporating hardware handshaking and flow control.
A 3-wire DTE interface, where only transmit, receive, and ground signals are used, is supported in those
ISUs where the AT&D0 command has been revised to ignore the DTR (Data Terminal Ready) signal.
When operating with a 3-wire connection, the following limitations apply:
 AT&Dn must be set to AT&D0 to ignore the DTR input from the DTE, as it will not be present as an
input from the DTE
 AT&Kn must be set to AT&K0 for no flow control or AT&K4 for XON/XOFF software flow control, as
RTS (Request To Send) and CTS (Clear To Send) hardware flow control signals will not be present
 AT&Cn setting will have no affect, as DCD (Data Carrier Detect) output to the DTE will not be present
 AT&Sn setting will have no affect, as DSR (Data Set Ready) output to the DTE will not be present
 RI (Ring Indicate) output to the DTE will not be present
2.3 Configuration Settings
The ISU allows the DTE to configure the communication parameters. The three configuration types are
active, factory default, and stored.
The active configuration is the set of parameters currently in use. They can be changed by the DTE
individually via specific AT commands.
The factory default configuration is stored in permanent memory. This configuration can be recalled at any
time by through use of the AT&Fn command.
Two groups of settings, or “profiles”, can be stored as user-defined configuration. The DTE first creates
desired active configurations and then writes them to memory using the AT&Wn command. These profiles
can be designated to be loaded as the active configuration upon ISU power-up through use of the AT&Yn
command. Similarly, the ISU can be reset without loss of power to these profiles through use of the ATZn
command.
Most of the configuration settings are reflected in “S-register” locations. S-register is the term used by
Hayes-compatible modems for a specific physical location in memory.
2.4 Mode of Operation
The ISU is always in one of two modes: command mode or data mode.
When the ISU is in command mode, AT commands can be entered to control the phone. Note that
command mode can be accessed while on-hook (i.e. not in a call) or in-call.
When in data mode, the ISU is connected to a remote system and any characters sent to it will be
transmitted to the remote system. Note that data mode can be only accessed while in-call.
While in-call, the Escape Sequence (+++) is used to enter the command mode. The Online command