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CPP100
SECTION 6
CPP1OPS
25/10/06
www.snellwilcox.com
Version 1 Issue 6
6.34
Reference Format
The reference signal should be a normal composite
video signal of either PAL-I or NTSC formats. The
burst information has no effect on the operation of
the synchroniser.
The nominal input level is 1-volt peak to peak.
If the loop-through facility is not required the signal
should be terminated here by using a 75 Ohm BNC
terminator.
Genlock Offsets
Provision has been made to allow the horizontal
and vertical timing of the output to be varied in
relation to the “referenced” signal, whether it be the
input or the reference. This facility is useful when
the output needs to be in sync with other units such
as in a studio system. This will allow clean switching
between multiple sources which may have different
phase relationships.
H-Lock
This changes the Horizontal Genlock Offset
525 line standards
Range 0ns to 63455 ns
Step
37 ns
Preset 0 ns
625 line standards
Range 0 ns to 63899 ns
Step
37 ns
Preset 0 ns
V-Lock
This changes the Vertical Genlock Offset
525 line standards
Range 0 lines to 524 lines
Step
1 line steps
Preset 0 lines
625 line standards
Range 0 lines to 624 lines
Step
1 line
Preset 0 lines
Genlock Status
This displays the current Genlock status
---
Unable to Genlock.
Check the reference signal is valid or
that the input is valid.
Off
Genlock Off
Input
Genlocked to input if a valid
reference input is not present.
Ref
Genlocked to reference input
Status information about Genlock is also indicated
by the status LED on the Genlock button and on the
front panel LED display.
Using the Synchroniser
Prefix contains a frame-synchroniser which is
essentially just a variable delay which has a little in
excess of 1 frame capacity. The purpose of the
variable delay is to allow each unit to provide an
output picture which is cotimed with other units in a
studio system. Normally this is achieved by
applying a studio reference signal to each unit in the
studio and the variable delay automatically adjusts
the output so it is horizontally and vertically phased-
up with the studio reference.
The purpose is to allow clean switching between
multiple sources which may have different phase
relationships.
Another advantage of a synchroniser is that the
stability of the output clock is directly related to the
quality of the reference signal. This is fundamental
as the output video rate must be phase locked to
the reference video signal. In some cases this is
also important as it guarantees output clock
stability even if the input disappears or is noisy.
The penalty of using a synchroniser is that the input
and output sides of the synchroniser are running at
different clock rates and sooner or later the
synchroniser will be forced to repeat or drop a video
frame. A complete frame must be dropped to avoid
interlace errors. This is fundamental and will almost
certainly be undetectable.
If no reference is applied then the unit will
automatically phase lock to the input as long as
Genlock ON is selected. In this case there will be
no necessity to repeat or drop a video frame and
the output of each unit will be a fixed delay relative
to the input.
With Genlock OFF the frame synchroniser will once
again be running with different clock rates on each
side and therefore will either repeat or drop a frame
as necessary. The output clock stability will be very