Grass Valley 2200 - Manual (Page 105)

5-15
Message Format
NOTE: Subscribe immediate results in only one issue with the current value(s).
A subscription for changes is not activated.
Parameter Service
The parameter ID field identifies the parameter of interest 1 . This is followed
by a pad field which 32-bit aligns the Device field. The Device field further
qualifies the parameter or group of parameters being requested. In some
instances, the device field contains a mask which may be used to request the
parameter value of each device specified in the mask. For other parameters, a
separate parameter service request is necessary
2 .
Unsubscribe
The unsubscribe command cancels all or part of a subscription. As one might
expect, the same command data necessary to subscribe to a service, is also needed
to unsubscribe from it. The primary difference between the Subscribe and
Unsubscribe command data is the value that the ßags Þeld may assume. As shown
below, the Unsubscribe command ßags may be set to one of four values.
Table 5-4. Parameter Service Data
Field Size Value
Parameter ID 2 bytes refer to Appendix B
alignment pad 2 bytes any
Device 4 bytes refer to Appendix B
1. Refer to “Parameters” on page 5-19 for a complete list of parameters used for this interface.
2. Refer to “Parameters” on page 5-19 for the device types associated with each parameter.
Table 5-5. 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