Nevion FRS-3G-DUAL - Manual (Page 21)

FRS-3G-DUAL Rev. B
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Figure 11 show how the sync signal and the isync signal would look on an oscilloscope, if
converted to analogue signals. The delay of isync can be given in lines, and samples. The
delay can be negative, see Figure 12.
Figure 12: Negative phase delay
It is not possible to specify a more negative phase delay than -1 frame, or more positive
phase delay than +1 frame. Doing so would be pointless, as the distance between two
start-of-frame pulses for the sync reference must by definition be 1 frame, and the delay will
wrap around. A phase delay of 1 frame + N lines would be completely equivalent to a phase
delay of just N lines. The same applies to a phase delay of -1 frame + (-N lines), it would be
equivalent to just
–N lines.
Strictly speaking, it would suffice to allow the phase delay to be within the interval -1/2
frame to +1/2 frame (or just 0 frames to 1 frame, or even -1 frame to 0 frames); every
possible phase delay could be specified this way. But people like to think of these things in
different ways, and the phase delay can thus be specified in the entire interval -1 frame to
+1 frame.
In addition to the phase delay, the user may specify Additional frame delay. If the input
signal doesn’t have the exact same frequency as the sync reference, the phase between
the input and the reference will vary continuously, and hence the delay must also vary over
time. When the Additional frame delay is set to N frames, the delay through the card will be
somewhere between N and (N+1) frames, and vary over time unless the sync and SDI
input have the same frequency.
Here’s what happens when an external error event occurs:
If video input disappears
Given that a stable sync input exists: If the SDI input disappears, the output picture will
freeze for Hold time and then go to one of the internal video generators (depending on the
module’s configuration).
If video input reappears
Given stable sync input, the video will reappear after the module has had stable lock to the
video input for a duration of Lock time.
If sync input disappears
Given that stable SDI input exists: If the sync signal disappears, the card will revert to frame
delay mode, see Chapter 4.2.2.
NOTE: This will result in a frame roll as the delay changes.