Grass Valley Switcher Products - Manual (Page 95)

Switcher Products — Protocols Manual 95
Overview
the Learn command. When a Recall command is received, the controlled
device should look up the effect that was active at the time and recall that
effect. For example, if the controlling device sends a learn 5 command and
the controlled device's current effect is 37, then when the controlling device
sends a recall 5 command, the controlled device should recall its effect 37.
The cross reference between PBus II register numbers and the controlled
device's effect number should be retained in nonvolatile memory and some
provision for saving this information to disk for transport to another
system should be provided.
Grass Valley Group switchers use PBus II effect numbers 0 through 99, cor-
responding to the switcher's E-MEM register numbers 0 through 99. The
controlled device must provide storage for all 100 PBus II effect numbers
when interfacing to a Grass Valley Group switcher. Grass Valley Group
switchers never send learn or recall commands for register numbers above
99 (0x63).
Some controlled devices (e.g., Kaleidoscope) run effect timelines as part of
the Recall command. We do not recommend this practice, or at least sug-
gests a user preference be available on the controlled device to control
running the effect on Recall. In general, the controlled device should first
recall an effect and prepare to run it when a Recall is received. A Trigger
should then be employed to cause the effect to run.
Trigger Interactions
The switcher can also be set to send triggers to controlled devices over the
peripheral bus. Triggers act like GPIs. They can trigger any controlled
device function that has been programmed for control via the peripheral
bus. The switcher can send a trigger to a controlled device when it recalls
an effect (the trigger is on the first keyframe), or the trigger can be placed
anywhere on the switcher effect’s timeline to send triggers during the
running of an effect.
It is important to understand the purpose of triggers relative to recalls. A
peripheral bus Recall can be sent when the controlling device recalls one of
its effects. The Recall instructs the controlled device to recall an appropriate
effect or return to a specific state. Triggers are intended to cause some
activity to occur within the controlled device.
An example of using recalls and triggers is having a controlled device that
feeds video to the switcher select an output signal when a specific switcher
effect is recalled (a Recall command is sent out the peripheral bus), and then
change its output at specific times when the switcher runs the effect (send
Trigger commands at specific keyframes).
The Peripheral Bus II protocol does not define or recommend which func-
tion is associated with a specific trigger number. It is recommended that a
Digital Video Effects system implement Run, Rewind, and Stop triggers at