Model 5601MSC
Model 5601MSC Master SPG/Master Clock System
OPERATION
Revision 2.2
Page - 47
Every time the daily jam event occurs, the 5601MSC will attempt to bring the dropframe timecode as
close to system time as possible, while optionally maintaining color frame alignment. The amount of
frames adjusted depends on the error accumulated from the previous daily time jam. See Figure 2-19
for an example of a week worth of daily time jams on a dropframe 29.97Hz timecode output. The
pattern of 2 frame and 4 frame adjustments runs over a period of a couple months.
If multiple timecode outputs are set to dropframe counting mode, it is possible that they may jam
differently from each other at the daily time jam event, even if they are set to jam at the exact same
time. This can occur if they were initialized at different times. To prevent this from happening, use the
“Jam all VitcLtc” menu item which forces all timecode outputs to jam at the same instant. This manual
jam is typically done at an innocuous time of day. There is currently no method of forcing multiple units
to jam together at the same time. It can be expected that eventually a 2-frame offset may appear
between dropframe timecode across multiple 5601MSC units.
Figure 2-19: Dropframe Timecode with Respect to Real-time over One Week
2.3.4.2.3.
Color Frame Alignment to PAL
Color frame alignment to PAL video can be enabled for 25Hz LTC timecode and for any PAL sync
(VITC) output or PAL analog TG output (burn-in window). The 25Hz timecode runs at exactly real time
which means it is always possible to
jam
the timecode output exactly to the
system clock
. However,
the color frame alignment rule adds additional complexity. The color frame sequence in PAL runs over
4 frames (8 fields), which does not divide evenly into a 25 frame per second count. This means that
color frame 1 lines up with the same frame count only once every four seconds. Therefore color frame
alignment occurs once every 4 seconds.
When a time
jam
event occurs, the timecode output clock is jammed to the
system clock
and then may
be adjusted up or down one or two frame counts to match the color frame phase of the reference or
particular black burst sync output. If the frequency reference to the 5601MSC is not phased correctly
with respect to the time reference this can cause a static one or two frame shift for 25Hz timecode
outputs, with respect to the
system clock
.