CHAPTER FOUR
4-16
bc635VME/bc350VXI Time and Frequency Processor (Rev. E)
Symmetricom Inc
Bit 1
During leap years this path bit must be set to enable the different day counts which represent
leap years.
Note
: Software versions later than 9501128 use the “S” packet to set the year and then
calculates the leap year. In this software the leap year bit has no effect.
Bit 2
Jamsynch is a method employed to match the output 1pps signal to the input time mark. If you
change modes of operation on a warmed up unit and want to rush the re-synchronizing you can
enable jamsynch, then use Packet “C” to force a jamsynch of the unit, which will cause the 1pps
signal to be reset to the time-mark time. There are disadvantages to using this method. If a
strobe was scheduled for a time between the flywheeling time and the jamsynch it will be missed
in the jump to the new time. There is also a break in the lock for a couple of seconds.
Jamsynchs are ineffective on a cold unit that has the oscillator changing frequency at a high rate
during warm up.
Bit 3
Oscillator disciplining might be disabled if you were using an external clock source that requires
a different disciplining routine and you are using the on-board DAC and disciplining through a
Packet “D.”
4.1.14.2 UPPER NIBBLE BIT DESCRIPTIONS
Bit 0
When enabled, packets written to the INPUT FIFO will be automatically echoed to the OUTPUT
FIFO.
Bit 1
This bit is used when you want to report UTC time instead of GPS time. The change is that leap
seconds are added to the time to derive UTC.
Bit 2
When enabled, the RTC data is automatically inserted into the OUT-FIFO every second. This
could be useful if you have a system that is maintaining two different times such as UTC and
local time.
Bit 3
In GPS mode (Mode 5 or 6) you may want to report the time in seconds from the start of the
GPS epoch (seconds from start of January 6, 1980). Some systems may find it easier to deal
with time strictly in seconds. The table below reflects that fields TIME1 and TIME2 contain a
32 bit contiguous binary number representing GPS Epoch seconds. The minor time remains in
decimal sub-seconds as reflected by Table 4-2.
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