Sierra Video Yosemite - Manual (Page 95)

SPECIFICATIONS
89
The fielddelay value applies to the entire router, not just to the control port on which the “F”
command is received. It is therefore recommended that a single value be settled on for the
fielddelay
value, rather than changing the value constantly depending on needs. Once changed,
the router records the value in non-volatile memory and uses it each time it is powered up, so it is
only necessary to change it one time.
Even though a crosspoint isn’t changed until the fielddelay time has elapsed, the router records
the new crosspoint state immediately upon receiving the crosspoint change request, so a
controlling device may receive a report of a crosspoint change before the change has actually
taken effect, and this is more likely to happen the larger fielddelay is. Since routers currently
make no guarantees about when they will report a crosspoint change anyway, this behavior is
usually of no concern. There is a case where this could cause problems. If the fielddelay value
were to be changed while two different devices were changing the same output, it is possible for
the router to report the incorrect input value for that output. This would happen if the earlier
device that changed the output did so before the fielddelay value was changed, and the later
device that changed the output did so after the fielddelay value was reduced but soon enough
that its input value would be sent to the crosspoint hardware before that of the earlier device. A bit
later, the earlier device’s input value is sent to the crosspoint hardware, but the router has
recorded the later device’s input value as being the one in effect. To prevent this scenario, we
recommend that an appropriate fielddelay value be chosen, set, and left alone.
Here is an example of an “F” command:
** F5 Y1,5 X2,6,3 !!
This says that input 5 is to be connected to output 1 on all levels and input 6 is to be connected to
output 2 on level 3, after a delay of 5 fields from the beginning of the field that follows receipt of
the “!” character.