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How Does Device Scan Mode Work?


Last Update: 11/12/2018

Scan Mode allows users to specify both how the server scans the device for data and how to override the client application's update rate when necessary. It is especially helpful with more devices being developed for areas outside process automation. The parameters are:

  • Respect client specified scan rate: This mode uses the scan rate requested by the client.
  • Request data no faster than x: This mode specifies the maximum scan rate to be used.
  • Request all data at x: This mode forces tags to be scanned at the specified rate for subscribed clients.
  • Do not scan, demand poll only: This mode does not periodically poll tags that belong to the device or perform a read to get an item's initial value once it becomes active. It is the client's responsibility to poll for updates, either by writing to the _DemandPoll tag or by issuing explicit device reads for individual items.
  • Respect tag-specified scan rate: This mode forces static tags to be scanned at the rate specified in their static configuration. Dynamic tags are scanned at the client-specified scan rate.
Note: Synchronous and asynchronous device reads and writes are processed as soon as possible; they are not affected by the Scan Mode.
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