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Iridium Communications, Inc.
Iridium 9523 Product Developers' Guide
Revision 2.6
3.5.3
Modes of Operation
The serial interface is always in one of three modes: command mode, SBD data mode or SBD session
mode. When the data port is in command mode, AT commands can be entered to control the Iridium
9523. In command mode, flow control has no effect, with the RTS input ignored and the CTS output
driven ON (low). When in SBD data mode, the Iridium 9523 is transferring binary or text SBD message
data to or from the FA.
In SBD data mode:
All characters from the FA not forming part of the message data are ignored (i.e. no AT
commands may be entered)
No unsolicited result codes are issued
RTS/CTS flow control, if enabled, is active. When RTS is OFF (high), the Iridium 9523
suspends transfer of data to the FA; when CTS is OFF (high), the Iridium 9523 expects the FA to
suspend transfer of data.
When in SBD session mode, the Iridium 9523 is attempting to conduct an SBD session with the network.
In SBD session mode:
The FA must wait for the +SBDI [X][A]session result code
All characters from the FA are ignored
Unsolicited result codes are issued where those codes have been enabled
Transitions between the modes of operation are performed automatically by the Iridium 9523 in response
to the SBD AT Commands; the FA has no other control over the mode.
3.5.4
Serial port signal levels
The inputs on the Iridium 9523 Data/Fax serial port (RTS, DTR and TXD) will operate correctly at 3.3V
digital signal levels.
The five outputs from the Iridium 9523 Data/Fax serial port (DCD, DSR, CTS, RI and RXD) are all at 3.3V
digital levels.
RS-232 interface chips can be fitted to the FA board if connection to an external RS232 link is required.
3.6 SIM interface
The Iridium 9523 needs an external Iridium SIM card and socket to be connected to its SIM interface. The
signals operate at 3.3V logic levels, so an external SIM level converter such as the ONSemi NCN4555
must be connected between the Iridium 9523 and the SIM connector/socket to allow 3V or 1.8V SIM
cards to be used.
An external SIM card reader may also be interfaced as a peripheral to the Iridium 9523 via the DPL
interface. A SIM card in the external reader will take precedence over the SIM chip connected to the SIM
interface when both are present.
3.7 GPIO Signals
There are four GPIO signals to the Iridium 9523, as described in this section.
Iridium Communications, Inc.
Proprietary & Confidential Information
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Information Contained in this Guide
is Subject to Change Without Notice
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