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Freeway
Range
Pro-Bel
ltd
6 Routing
This section describes the me
chanisms
for setting cross points and reading
handshakes .
• 6. 1 Setting crosspoints
Indi
vidual crosspoints
are
set
via a parallel bus which issues from the 2440 card
and is accessible to all cards fitt
ed
in the
Freeway
frame. The order of events is as
follows
:
1.
The SYNCS signal leaving the 2440 card is interrupted
2. Level,
Destination
and Audio bits (if applicable) are written to the parallel bus
3. The Source bits are written to the parallel bus
4. The source and dest data is strobed into first-stage latches
5. SYNCS are resumed
This ability to interrupt SYNCS is particularly useful for salvo switching, as
multiple routes can be set up while the SYNCS are disabled and then set all at once
when SYNCS are enabled and a SYNC pulse occurs; or when forced to crash switch.
The switching position will be fixed in hardware and conforms to SMPTE
specification.
If a TTL level pulse is selected as the crosspoint trigger then it must be present for
cross points to be made. No crosspoints will be made if it is absent. This is
different
to cross points using 625 or 525 video references
.
In these instances the
crosspoints are
Forced
if a field pulse has not been detected within a certain
period. In other words, without a video reference (and provided the TTL trigger
has not been set up) the switcher will continue to respond to switch commands in
an asynchronous manner. If a
TTL
level pulse is selected th
en
525 or 625 video
references cannot be used.
The non-volatile RAM on the 2440 is considered the master store for crosspoint
information. This being the case a slow background update of the cross points is
performed, such that if a slave router is connected into the system after the
master router has been
powered
up, any expected cross points are
set.
6540T-00 Nov 97
46
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