From the operator environment, you can enter the data through any datalink that allows data entry. Typically this is done from a faceplate or detail display, but it can also be done from a primary control display.
When you enter the data, the workstation writes the value to the parameter in the extended block (sometimes called a shadow block) in the control module in the controller. The extended block communicates data to and from the block in the fieldbus device. When the extended block receives the write request from the workstation, it does not immediately update its own parameter value. Rather, it passes the write down to the fieldbus device. On the next scan of the control module in the controller, the extended block asks the block in the device for its dynamic view list parameter data. If ST_REV, the static revision, has incremented since the previous scan, the field block updates the extended block with its static view list parameter data. ST_REV is incremented any time a static parameter is written. At this point, the extended block parameter values match those in the field block. After the next unsolicited reporting of data by the control module to the workstation and update of the display in DeltaV Operate, the value that had been written is visible on the display.
Display update times may appear slower following writes to parameters in field blocks as compared to writes to controller-resident blocks because of the additional communication over the fieldbus segment. The delay can become significant when there are more than 10 devices are the segment.