From this you can see that Init Channel starts the driver, which then begins to download tags. Init Unit will check back to see if the Driver is polling every watchtime. Projects with a large number of tags (approx 5000+) tend to take more time to download and subscribe the tags, so Init Unit may need to check back a few times. This is where extending the value for the watchtime may be useful. You do however need to be careful in doing this as the watchtime is also the check to see if the PLC is still online - so if you have a large watchtime and your PLC goes offline, it may take the entire watchtime to attempt to re-establish comms (which is the entire process of downloading tags, subscribing them and polling them takes place - hence potential additional delays).

Lack of idle time in the PLC processor is also a possible throttle point. If there is insufficient idle time in the PLC processor, then Citect driver requests are split up to fit into the small idle time that exists. This means that for all of the Citect driver request can be stretched out over a significant period of time when you consider that it is attempting to download tags, subscribe them and finally poll them. Customers are advised to aim to have sufficient overhead timeslice in the PLC processor to allow for the Citect driver to establish and maintain comms.