ISU AT Command Reference

ISU AT Command ReferenceModem Overview2.5 Hardware Failure ReportingIf the ISU detects a hardware problem during initialisation, the ISU may be unable to function correctly.The ISU notifies the DTE of this situation by issuing an unsolicited result code at the end of initialisation:HARDWARE FAILURE:,where identifies the software subsystem that detected the error, and is thesubsystem-specific error code.Any AT commands that cannot be handled in the failure condition will terminate with result code 4(“ERROR”).2.6 Ring Indicate SignalPrior to Implementation Phase VI (see section 4), the RI (Ring Indicate) signal was used only to indicatethe presence of an incoming telephony call. From Phase VI, it is also used to indicate reception of an SBDRing Alert. This section describes the behaviour of the RI signal in devices supporting both telephony andSBD ring alerts.The Ring Indicate signal indicates that an incoming telephony call is ringing, or that an SBD ring alert hasbeen received. It is accompanied by the unsolicited announcements RING or SBDRING.In the case of an incoming telephony call, which may be a voice, data or fax call, the RI signal is active foras long as the call is offered. The RI signal is deactivated when the call is answered or when it is no longeroffered (e.g. the originator terminates the call before it is answered). A RING announcement is issued ifthe DTE interface is in command mode. (This behaviour is identical to pre-phase VI versions of 9505Aand 9522A).In the case of an SBD ring alert, which indicates that there is at least one SBD message at the gatewayawaiting collection, then provided that SBD ring alerts are enabled (see +SBDMTA), the RI signal isactivated on reception of the SBD ring alert. It is held active for a period of 5 seconds from reception ofthe SBD ring alert, or until the DTE initiates an SBD session to retrieve the waiting message, whicheveroccurs first. An SBDRING announcement is issued if the DTE interface is in command mode, or when itnext returns to command mode. (This behaviour is identical to the 9601).If the ISU receives an SBD ring alert at the same time as an incoming telephony call, the RI signalcombines both of the above behaviours, remaining active as long as required by either the telephony orSBD criteria.The +CRIS command may be used to query the ISU as to the reason for the most recent assertion of the RIsignal.Version 2.6March 30, 2006 5