Grass Valley 2200 - Manual (Page 106)

5-16
Section 5 Ñ Digital Effects Interface
With no ßags set, the Unsubscribe command cancels the speciÞed service
information. For example, when unsubscribing from a select group of parameters,
only those parameters identiÞed in the parameter service data will be cancelled.
When the cancel service ßag is set, the subscription associated with the speciÞed
request address, request ID, and service ID is cancelled. It should be noted that a
control point can have more than one subscription to the same service. This can be
accomplished by using a different request ID with each service request. The cancel
service ßag will not cancel all subscriptions to the speciÞed service, but only the
one associated with the given request address and request ID. The cancel
subscription ßag is used to cancel all subscription services associated with the
speciÞed request address and request ID. The clear subscriptions ßag is used to
clear all subscriptions associated with a control point. Finally, the clear all
subscriptions ßag is used to clear out all control point subscriptions, including
those for other control points. If any one of the Unsubscribe ßags is set, the service
speciÞc data is ignored.
Issue
An Issue status message is sent to a control point as the result of a subscription
request (a subscribe command) or a change in the value of a parameter with an
active subscription. When a request is received, an issue is delivered to the
subscribing control point. Another issue is not delivered until the requested
information changes. As shown on the following page, there are Þve Þelds of data
associated with the Issue status message.
The request ID is a user deÞned request identiÞer. It is passed in the data portion
of the Subscribe command and is sent back to a control point as part of the Issue.
The request ID is typically used by a control point to route issue data to the correct
handler.
The serial number Þeld provides the mechanism by which unwanted issue data
can be ignored
1 . This Þeld is followed by the service ID Þeld. The service ID
speciÞes the type of issue. Only parameter issues are supported for the switcher/
DPM interface.
The service ID is followed by a pad Þeld which 32-bit aligns the service data. The
service data itself contains service speciÞc information.
Table 5-6. Issue Message Data:
Field Size Value
Request ID 2 bytes matches Request ID of Subscribe
message
Serial Number 2 bytes any (requestor’s choice)
Service ID 2 bytes 3 = Parameter Article
alignment pad 2 bytes any
Service Data variable refer to Parameter Article section below
1. Refer to the Subscribe command for more information.