24
Startup and Operation
6.1.2
Clock Time, Startup Mode
When the clock first starts, it will not indicate the correct time until it is locked to the GNSS.
Pressing the
TIME/DATE
key before the UNLOCKED LED is extinguished will produce the message:
TIME NOT AVAILABLE
IRIG-B time and the LCD display will not produce a time while the clock is starting up. The
large C display and any serial port broadcast (if turned on), will not produce or broadcast the time
until the clock is locked and stabilized. This method was chosen so that there would be no mistake
in interpreting that the clock was in startup mode.
When the full set of ephemeris data is received by the GNSS receiver from the GNSS (satellites),
the time will be accurate. At this time, the UNLOCKED LED will extinguish and the SPDT relay
will close if set to the out-of-lock function.
6.2
Operating Modes: Model 1201B/C Only
Initially, the very the first time the clock starts up it will be in the promiscuous mode. In this
mode, the clock performs position fixes each second and does not keep track of antenna position
and satellite information. The clock will stay in the promiscuous mode forever unless the learn
mode is initiated. Power cycling the clock has no affect on this. Once the learn mode is initiated
the clock should never again fall back into the promiscuous mode. To enter the Learn mode, see
Section 7.6.
6.2.1
Learn and Normal Modes
During the learn mode, the clock tracks its position over time looking for anomalies, such as a
satellite suddenly appearing or disappearing, and satellites that are out of position. It is during
the learn mode that the clock establishes its basis of operation with the GNSS, and anti-spoofing
protective measures are suspended. After 24 hours the clock should complete the learn mode and
revert to the normal mode in which anti-spoofing protection is operative.
Normal Mode Operation and Re-entry
While operating in the normal mode, the clock should run undisturbed from problems such as GNSS
spoofing, or a faulty antenna. If a problem occurs, the clock will maintain its time and operate with
accuracy based on the internal holdover oscillator. Holdover estimated uncertainty, found under
the TIMING menu, will provide you with an estimate of the timing accuracy for defined periods
during which the clock is not locked to the GNSS. If while operating in the normal mode the clock
is power cycled, it should restart and continue operating in the normal mode.
6.2.2
Faults and Alarms
If a problem occurs, the clock may indicate this as either a fault or an alarm. A fault signifies a
hardware problem inside the clock that may clear on its own or may need attention. An alarm
signifies some external influence that may interfere with the operation of the clock. During an
alarm, the clock will adopt protective measures to guard its integrity until the interference is no
