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Understanding the PowerLogic Drivers (PWRMODBUS, PLOGIC, SEPAM, MICROLOGIC) as Backend Drivers Which Use a Cache and Poll All Configured Variable Tags Continuously

It is important to note that PowerLogic SCADA's PowerLogic drivers (PWRMODBUS, MICROLOGIC, PLOGIC, SEPAM) are "backend" drivers, that is to say, they poll I/O devices through a cache. Previously, with most Citect drivers, one could configure the Cache and Cache Time parameters for a given I/O device. With the PowerLogic drivers, caching is the default operation.
When Runtime is started, all I/O devices using the PowerLogic drivers attempt to populate the cache with data for all Variable Tags configured for those devices. This is why a user may see some delay between Runtime is started and when data is available on all graphic pages. Once the cache is fully populated, the drivers attempt to keep that data updated based on the interval specified by the CacheRefreshTime citect.ini parameter. Settings like the scan time and poll time do not affect the device polling as they did for previous drivers. Regardless of the presence of alarm tags, variable tags are polled based on a combination of the CacheRefreshTime and Bandwidth parameters. Values are always taken from the driver's cache. More information about the aforementioned parameters can be found in the PowerLogic SCADA System Integrator's Manual.

Keywords: PLS, PL SCADA, PLSCADA, PowerSCADA, 7.10, 7.20, v7.10, v7.20, 710, 720, back end, poll all tags all the time

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