Allen-Bradley Ethernet Driver
Rate. The data is not saved if the server removes the item (such as when the server is reinitialized). The default
is No.
Notes:
1. This System tag (_Simulated) is read only and cannot be written to for runtime protection. The System
tag allows this property to be monitored from the client.
2. In Simulation mode, the item's memory map is based on client update rate(s) (Group Update Rate for
OPC clients or Scan Rate for native and DDE interfaces). This means that two clients that reference the
same item with different update rates return different data.
Simulation Mode is for test and simulation purposes only. It should never be used in a production envir-
onment.
Device Properties - Scan Mode
The Scan Mode specifies the subscribed-client requested scan rate for tags that require device com-
munications. Synchronous and asynchronous device reads and writes are processed as soon as possible; unaf-
fected by the Scan Mode properties.
Scan Mode: specifies how tags in the device are scanned for updates sent to subscribed clients. Descriptions of
the options are:
l Respect Client-Specified Scan Rate:This mode uses the scan rate requested by the client.
l Request Data No Faster than Scan Rate:This mode specifies the maximum scan rate to be used. The
valid range is 10 to 99999990 milliseconds. The default is 1000 milliseconds.
Note:When the server has an active client and items for the device and the scan rate value is
increased, the changes take effect immediately. When the scan rate value is decreased, the changes do
not take effect until all client applications have been disconnected.
l Request All Data at Scan Rate:This mode forces tags to be scanned at the specified rate for sub-
scribed clients. The valid range is 10 to 99999990 milliseconds. The default is 1000 milliseconds.
l Do Not Scan, Demand Poll Only:This mode does not periodically poll tags that belong to the device
nor 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 indi-
vidual items.
For more information, refer to "Device Demand Poll" in server help
.
l Respect Tag-Specified Scan Rate:This mode forces static tags to be scanned at the rate specified in
their static configuration tag properties. Dynamic tags are scanned at the client-specified scan rate.
Initial Updates from Cache: When enabled, this option allows the server to provide the first updates for newly
activated tag references from stored (cached) data. Cache updates can only be provided when the new item ref-
erence shares the same address, scan rate, data type, client access, and scaling properties. A device read is
used for the initial update for the first client reference only. The default is disabled; any time a client activates a
tag reference the server attempts to read the initial value from the device.
Device Properties - Timing
The device Communications Timeouts properties allow the driver's response to error conditions to be tailored to
fit the application's needs. In many cases, the environment requires changes to these properties for optimum
performance. Factors such as electrically generated noise, modem delays, and poor physical connections can
influence how many errors or timeouts a communications driver encounters. Communications Timeouts prop-
erties are specific to each configured device.
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