Grass Valley Switcher Products - Manual (Page 118)

118 Switcher Products — Protocols Manual
Section 4 — DPM CPL Protocol
the requested information changes. As shown on the following page, there
are five fields of data associated with the Issue status message.
Request ID
The request ID is a user defined request identifier. 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 field provides the mechanism by which unwanted issue
data can be ignored
1
. This field is followed by the service ID field. The
service ID specifies the type of issue. Only parameter issues are supported
for the switcher/DPM interface.
The service ID is followed by a pad field which 32-bit aligns the service
data. The service data itself contains service specific information.
Parameter Article
The parameter subscription service data consists of one or more parameter
articles. Each article contains the value of one parameter. Multiple articles
may be included in the same issue as long as the request address and
request ID for all articles are the same. Remember that the request address
and ID are provided by the requesting control point and must be returned
with the issue.
The data associated with each parameter article is shown below.
The parameter ID field identifies which parameter is contained in the
article. The pad field 32-bit aligns the device field. The device field itself
identifies the device associated with the specified parameter. The last field
contains the parameter value. In order to accommodate parameters of
varying size, the value field is variable length. When parameter service
Table 110. Issue Message Data:
Field Size Value
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.
Table 111. Parameter Article Data
Field Size Value
Parameter ID 2 bytes refer to Appendix B
alignment pad 2 bytes any
Device 4 bytes refer to Appendix B
Parameter value variable refer to Appendix B