“staleness” for the item, requested in milliseconds. The server will calculate the number of milliseconds between “now” and the item timestamp. If the item that has not been updated within the last MaxAge milliseconds, the value must be obtained from the underlying device. Or if the item is not available from the cache, it will also need to be obtained from the underlying device. A max age of 0 is equivalent to OPC_DS_DEVICE and a max age of 0xFFFFFFFF is equivalent to OPC_DS_CACHE. Without existence of a cache the server will always read from device. In this case MaxAge is not relevant. Some servers maintain a global cache for all clients. If the needed item is in this global cache, it is expected that the server makes use of it to check the MaxAge value. Servers should not automatically create or change the caching of an item based on a Read call with MaxAge.
Note: Since this is a int of milliseconds, the largest MaxAge value would be approximately 24 days.

Syntax

Requirements

See Also