Grass Valley 2200 - Manual (Page 100)

5-10
Section 5 Ñ Digital Effects Interface
The activity check is optional. The interface behaves normally even if the DPM
never responds to the switcherÕs query. However, the switcher will not be able to
recover from link failures, patching or routing without a reset from one of the two
devices.
The switcher queries the DPM approximately every 20 seconds.
Running Effects
During initialization, the switcher subscribes for the DPMÕs current effect number.
When a switcher effect is learned, the DPMÕs current effect number is stored as
part of the effect.
When that effect is recalled at the switcher (DPM 1 level enabled), the switcher
will send out a command to recall the DPM effect. (SET,
PID_CURRENT_EFFECT).
At the time of the recall, the switcher also issues a SET, PID_EFFECT_POSITION.
The time value sent is zero if REVERSE on the switcher E-MEM effect memory
system is turned off; or to the ending time of the switcherÕs effect if REVERSE is
on.
As an effect is running, the switcher sends out commands every Þeld to the DPM
to SET the effect position (PID_EFFECT_POSITION). This same mechanism
supports runs via the RUN button as well as the switcherÕs run lever arm. Other
time positioning controls on the switcher panel (PREV KF, NEXT KF, REWIND,
etc. also result in the sending of a new effect position to the DPM. In this way, the
DPM exactly follows the timeline of the switcherÕs effect.
Subscription
Status information is gathered indirectly as a result of a ÒsubscriptionÓ request.
The request tells the other device where to send changes to the speciÞed
parameter. The changes are delivered to the requestor in an ÒissueÓ message
which may contain several parameter ÒarticlesÓ. Many articles may be contained
in one subscription. Consider a magazine subscription: The reader subscribes to
the magazine and whenever new information is available, a new issue is delivered
to the readers home. The reader does not have to speciÞcally request each new
issue of the magazine. The Òsubscribe immediateÓ mechanism is like requesting a
trial magazine issue - you only get one. Subscriptions may be canceled at any time.
The requestor can also modify the terms of delivery at will.
The switcher subscribes to information using several request IDs. It is important
for the DPM to include the proper request ID in the status update issue messages.
Different parameter articles may be sent in the same issue as long as the
subscriptions for all the data had the same request ID. Articles destined for
different request IDs must be placed in separate issue messages.
It is also important to limit issue messages to less than 256 bytes or the message
will be discarded by the switcher.