MULTIPLE SOURCE CONFIGURATIONS

It is common to have multiple sources for a single Network Tag/ONSPEC table location. Problems can occur when both sources are updated at the same time.

An LSO master will accept both updates and store the last one to arrive at the machine in its internal memory mirror. This can cause problems when both sources arrive at or near the same time. This situation can be viewed from the point of view of a distributed database application. When updating information in the master database only one user should be allowed access to the database at a time. All others should be locked out.

LSO does not provide record locking automatically as this would impact the real-time performance of LSO. The user can accomplish record locking in LSO by using conditional transfers. A multiple source tag can be set to output only if a transfer flag has been set to ON. A workstation that wants to update the tag will first turn the transfer flag OFF for other workstations. By using network tags and the LSO configuration mechanism you can avoid having repeated updates offset each other from multiple sources.


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