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Acutime 2000 Synchronization Kit User Guide A-125
A Trimble Standard Interface Protocol
Leap Second Flag
Leap seconds are inserted into the UTC timescale to counter the effect
of gradual slowing of the earth’s rotation due to friction. The 8F-AD
packet provides extensive UTC leap second information to the user
application.
The Leap Scheduled bit is set by the receiver, when the leap second
has been scheduled by the GPS control segment. The Control
segment may schedule the leap second several weeks before the leap
second takes place.
The Leap Pending bit indicates that the leap second will be inserted at
the end of the current day.
The GPS Leap Warning bit is set while GPS is operating in the leap
exception mode specified in ICD-200.
The Leap in Progress bit is set to 1 at the beginning of the leap
second, and cleared at the beginning of the second following the leap
event. The date rollover is delayed by one second on the day the leap
second is inserted. The date will not increment until the beginning of
the first second following the leap second.
Table A-100 Leap Second Flag Definitions
Bit # Name Meaning if set to 1
0 UTC Flag UTC Time is available
1-3 Reserved N/A
4 Leap Scheduled GPS Almanac’s leap second date is not in the past.
5 Leap Pending 24-hour warning. Cleared before leap second.
6 GPS Leap Warning Set +/- 6 hours before/after leap event.
7 Leap in Progress Leap second is now being inserted.