Polling rules

General rules apply for polling Network Variable (nvi and nvo) values.

A Network Variable (nv) is subscribed if it is being viewed or has a proxy point which is subscribed. A proxy point that is subscribed if it is viewed, if it is linked to control logic if it has an alarm or history extension.
When a nv is first subscribed, the driver reads its value (if the device is in a valid state). The poll thread handles further reads. The Poll Service must be enabled for polling to function normally.
Adding a proxy point creates a local connection to the associated nv. each proxy point for a Network Variable Output (nvo) or a writable proxy point for a Network Variable Input (nvi), appears as one entry (row) in the Lon Link Manager.
The Bound To Local property on nv Props container is set when an output nv with a proxy is bound. An output nv is not polled when it is bound locally. Instead, nv updates are received from the device.
The Poll Enable property is set to true if there are unbound links and the nv is not bound locally. To prevent polling on an nv, set its Poll Enable property to false. The driver still performs the initial read when the nv is first subscribed, but subsequent polling by the poll service does not occur.

This table provides polling rules for nvs with specific connection scenarios

Type of nv, connection	Update rules
nvi with writable proxy	Poll when nv or proxy point subscribes.  If proxy value changes update nv.
nvi with read-only proxy	Poll when nv or proxy point subscribes.
nvo with writable proxy	<Not allowed>
nvo with read-only proxy (unbound)	Poll when nv or proxy point subscribes.
nvo with read-only proxy (bound)	Receive nv updates (No polling).
polled nvo with read-only proxy bound	Poll when nv or proxy subscribed.
nvi linked	Poll when subscribed.
nvo linked unbound	Poll when subscribed. If nvo changes push value to linked nvi. Write nvi value to device.
nvo linked bound	Poll when subscribed.

NOTE: Input nvs (nvi) with read-only proxy points are never bound, and do not show up in the Lon Link Manager.