[OPC]LeaveTagsActive = 1. This means that when a page is displayed, all the tags on that page are added to a list in RSLINX to request continual information on those tags. If you then go to another page (with different tags on it), CitectHMI/SCADA adds those tags to the list in RSLINX without removing the previous tags from the list. This means that tags continue to be added to the list with each page change and with no tags being removed from the list. (this incremental addition of tags causes RSlinx to produce inefficient "optimised packets") Having this option set to 1 ensures fast display times because when you go to a page the tags may already be in the list. Setting this parameter to 0 may cause #COM to be displayed on pages for a short period after opening a page while the tags are added to the list and RSLINX seeks the information for the tags from the field devices.

[OPC]FillCacheOnStartup = 1 means that all tags in the project are added to the list in RSLINX on start-up. Whilst this may mean more items in the list at any one time, because this is done as one operation, RSLINX is able to produce more efficient "optimised packets" which means the network loading is actually less.

In short, Citect recommends the following values for these parameters:

[OPC]LeaveTagsActive = 1
[OPC]FillCacheOnStartup = 1