IDEC WindSRV - Manual (Page 46)

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can be obtained from Read cache for those items and whether or not they are included in the IAdvise
subscription to the group. Deactivating items will not result in a callback, since by definition callbacks do not
occur for inactive items. Activating items will generally result in an IAdvise callback at the next UpdateRate
period.
 SetClientHandles - Changes the client handle for one or more items in a group. In general, it is expected that
clients will set the client handle when the item is added and not change it later.
 SetDataTypes - Changes the requested data type for one or more items in a group. In general, it is expected
that clients will set the requested datatype when the item is added and not change it later.
 ValidateItems - Determines if an item is valid and could be added without error. It also returns information
about the item such as canonical datatype. It does not affect the group in any way.
IOPCItemDeadbandMgt
Force a callback to IOPCDataCallback::OnDataChange for all active items in the group, whether they have changed or
not. Inactive items are not included in the callback. The MaxAge value will determine where the data is obtained. There
will be only one MaxAge value, which will determine the MaxAge for all active items in the group. This means some of
the values may be obtained from cache while others could be obtained from the Device depending on the "freshness" of
the data in the cache.
 SetItemDeadband - Overrides the deadband specified for the group for each item.
 GetItemDeadband - Gets the deadband values for each of the requested items.
 ClearItemDeadband - Clears the individual item PercentDeadband, effectively reverting them back to the
deadband value set in the group.
IOPCItemSamplingMgt
This optional interface allows the client to manipulate the rate at which individual items within a group are obtained
from the underlying Device. It does not affect the group update rate of the callbacks for OnDataChange.
 SetItemSamplingRate - Sets the sampling rate on individual items. This overrides the update rate of the group
as far as collection from the underlying Device is concerned. The update rate associated with individual items
does not affect the callback period.
 GetItemSamplingRate - Gets the sampling rate on individual items, which was previously set with
SetItemSamplingRate.
 ClearItemSamplngRate - Clears the sampling rate on individual items, which was previously set with
SetItemSamplingRate. The item will revert back to the update rate of the group.
 SetItemBufferEnable - Requests that the server turns on or off, depending on the value of the bEnable
parameter, the buffering of data for the identified items, which are collected for items that have an update rate
faster than the group update rate.
 GetItemBufferEnable - Queries the current state of the servers buffering for requested items.
IOPCSyncIO
IOPCSyncIO allows a client to perform synchronous Read and Write operations to a server. The operations will run to
completion.
 Read - Reads the value, quality and timestamp information for one or more items in a group. The function runs
to completion before returning. The data can be read from cache in which case it should be accurate to within the
'UpdateRate' and percent deadband of the group. The data can be read from the Device, in which case an actual
Read of the physical Device must be performed. The exact implementation of cache and Device Reads is not
defined by the specification.
 Write- Writes values to one or more items in a group. The function runs to completion. The values are written to
the Device, meaning that the function should not return until it verifies that the Device has actually accepted or
rejected the data. Writes are not affected by the active state of the group or item.
IOPCSyncIO2
This interface was added to enhance the existing IOPCSyncIO interface.
 ReadMaxAge - Reads one or more values, qualities and timestamps for the items specified. This is functionally
similar to the OPCSyncIO::Read method except no source is specified (Device or cache). The server will make
the determination as whether the information will be obtained from the Device or cache. This decision will be
based upon the MaxAge parameter. If the information in the cache is within the MaxAge, then the data will be
obtained from the cache, otherwise the server must access the Device for the requested information.
 WriteVQT - Writes one or more values, qualities and timestamps for the items specified. This is functionally
similar to the IOPCSyncIO::Write except that Quality and Timestamp may be written. If a client attempts to write
VQ, VT or VQT it should expect that the server will Write to all or none.
IOPCAsyncIO
IOPCAsyncIO allows a client to perform asynchronous Read and Write operations to a server. The operations will be