M e r i d i a n I I U s e r M a n u a l
194
A P P E N D I X J
195
M e r i d i a n I I U s e r M a n u a l
S I M U L A T O R U S E
Command:
clearalmanac
MeridianII reply:
Clearing GPS Almanacs
resetlastgpswn
The GPS Subsystem is designed to autonomously handle future rollovers of the 10-bit GPS week
number received in data from the satellites. To do that, it maintains a record in non-volatile memory
of the unambiguous, full GPS week number when it was last locked to the GPS system, i.e. the Last
GPS Week Number. If this information is not available, then the full GPS week number correspond-
ing to the build date of the GPS receiver firmware will be used as the Last GPS Week Number.
This Last GPS Week Number is the minimum possible full GPS week number. The Meridian II will
never allow the date and time to be set prior to the date and time corresponding to this Last GPS
Week Number. For example, setting the simulator time to a date two weeks in the past will result in
the Meridian II setting the date 1022 weeks in the future.
This means that a simulator should not be set to a date in the past.
Doing so will cause the time to
be set a multiple of 1024 weeks in the future relative to the simulator time. If lock to the simulator
is then achieved, this future time will then be saved to non-volatile memory as the Last GPS Week
Number. Subsequent runs with the simulation time set in the past would cause this time to continue
to advance.
Following simulator operation, it is imperative that the non-volatile Last GPS Week Number be reset
to the firmware build date. This is accomplished by running the
resetlastgpswn
command prior
to reconnecting to live GPS signals.
SUMMARY
The simulator should not be set to a date in the past, and you MUST execute the
resetlastgpswn
command before reconnecting the receiver to a live GPS signal.
IMPORTANT
This command should not be used unless you have reason to believe that operation with a GPS simulator
has previously taken place. Arbitrary usage of this command could compromise the effectiveness of the
algorithm in autonomously handling the GPS week number rollover events.
The command must be issued with one argument:
TRUE
Command:
resetlastgpswn TRUE
MeridianII reply:
Resetting Last GPS Week Number
resetleaphistory
The GPS Subsystem performs extensive integrity/sanity checking on the data received from the GPS
satellites. In particular, the current and future UTC leap second values received in the almanac data
Summary of Contents for Meridian II
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