Specifications

ISU AT Command Reference Phase III AT Commands
Iridium Proprietary Version 2.45
20 June 2011 60
7.17 -MSSTM - Request System Time
Exec Command: -MSSTM
Query the latest system time received from the network. The response is the form:
-MSSTM: <system_time>
<system_time> can take one of the following forms:
no network service The ISU has not yet received system time from the network.
XXXXXXX Where XXXXXXXX is the current Iridium system time available from
the network. The system time as received through the Iridium Air
Interface, is a 32 bit integer count of the number of 90 millisecond
intervals that have elapsed since the epoch. The return value is
formatted as an ASCII hexadecimal number. The counter will rollover
approximately every 12 years or be changed to prevent a rollover and
as a result should not be used as a time source for user applications .
Iridium system time epoch: March 8, 2007, 03:50:21.00 GMT. (Note: the original Iridium system
time epoch was June 1, 1996, 00:00:11 GMT, and was reset to the new epoch in January, 2008).
Iridium system time source: The system time is available and valid only after the ISU has registered with
the network and has received the Iridium system time from the network. Once the time is received, the ISU
uses its internal clock to increment the counter. In addition, at least every 8 hours, or on location update or
other event that requires re-registration, the ISU will obtain a new system time from the network.
Time localization: None. The system time value is always expressed in GMT time.
Resolution and accuracy: The resolution of the system time is one Iridium frame tick, or 90 ms. Accuracy
as measured by the difference between the time reported and the actual time it is sent out the ISU’s serial
port should not exceed 4 frame ticks (.36 seconds) and in most cases will be one frame tick (.09 seconds) or
less.