Grass Valley Switcher Products - Manual (Page 117)

Switcher Products — Protocols Manual 117
Message Format
is also needed to unsubscribe from it. The primary difference between the
Subscribe and Unsubscribe command data is the value that the flags field
may assume. As shown below, the Unsubscribe command flags may be set
to one of four values.
With no flags set, the Unsubscribe command cancels the specified service
information. For example, when unsubscribing from a select group of
parameters, only those parameters identified in the parameter service data
will be cancelled. When the cancel service flag is set, the subscription asso-
ciated with the specified request address, request ID, and service ID is can-
celled. 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 dif-
ferent request ID with each service request. The cancel service flag will not
cancel all subscriptions to the specified service, but only the one associated
with the given request address and request ID. The cancel subscription flag
is used to cancel all subscription services associated with the specified
request address and request ID. The clear subscriptions flag is used to clear
all subscriptions associated with a control point. Finally, the clear all sub-
scriptions flag is used to clear out all control point subscriptions, including
those for other control points. If any one of the Unsubscribe flags is set, the
service specific data is ignored.
Issue
An Issue status message is sent to a control point as the result of a subscrip-
tion 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 deliv-
ered to the subscribing control point. Another issue is not delivered until
Table 109. Unsubscribe Command Data:
Field Size Value
Request Address 16 bytes (not used)
Request ID 2 bytes
any (requestor’s choice)
echoed in Issue message
Serial Number 2 bytes any (requestor’s choice)
Service ID 2 bytes 3 = Parameter Service
Flags 2 bytes
1 = Cancel Service
2 = Cancel Subscription
4 = Clear Subscriptions
8 = Clear All Subscriptions