L-DALI User Manual
111
LOYTEC
Version 5.2
LOYTEC electronics GmbH
6.1.2
Timing Parameters
Apart from the meta-data, data points can be configured with a number of timing
parameters. The following properties are available to input or output data points,
respectively:
Pollcycle
(input, value): The value is given in seconds, which specifies that this data
point periodically polls data from the source. This is referred to as static polling.
Receive Timeout
(input, value): This is a variation on the poll cycle. When receive
timeout is enabled, the data point must receive a value update within the receive
timeout period. If it does not receive a value, a technology may actively poll the source.
If no value has been received after another period, the data point is set offline and
triggers a fault alarm, if configured. Writing data from any source (network technology,
connection, logic program) the receive timeout is reset.
Poll-on-startup
(input, value): If this flag is set, the data point polls the value from the
source when the system starts up. Once the value has been read, no further polls are
sent unless a poll cycle has been defined.
Minimum Send Time
(output): This is the minimum time that elapses between two
consecutive updates. If updates are requested more often, they are postponed and the
last value is eventually transmitted after the minimum send time. Use this setting to
limit the update rate.
Maximum Send Time
(output): This is the maximum time without sending an update.
If no updates are requested, the last value is transmitted again after the maximum send
time. Use this setting to enable a heart-beat feature.
Dynamic polling is a feature that some network technologies offer. With static polling the
pollcycle is used to permanently poll values over the network. This is required for data
points that require constant value updates a fixed pollcycle (for example to trend the data).
For other data points that do not need permanent value updates, so-called dynamic polling is
activated, as soon as the values are needed (for example displayed on the data pont Web UI
or in L-WEB). If dynamic polling is active, the data points are polled using the configured
pollcycle. When the data is no longer needed, polling stops and no longer puts a burden on
the network. The advantage is that a few data points can be refreshed at a higher rate at a
time compared to static polling, where all data points must permanently share the available
network bandwidth.
Background polling can be enabled in the project settings. With this feature enabled, all
input data points, which rely on polling depending on the underlying network technology,
are polled one-by-one in a round-robin fashion. This happens even if no pollcycle is set or
dynamic polling is activated on those data points. The frequency of the background polling
can be defined in the project settings. The default is 60 polls per minute.
6.1.3
Default Values
Default values can be defined for data points when needed. The value of a data point will be
set to the defined default value, if no other value source initializes the data point. Default
values are beneficial, if certain input data points are not used by the network and need a pre-
defined value, e.g., for calculations. Default values are overridden by persistent values or
values determined by poll-on-startup.
6.1.4
Persistency
Data point values are by default not persistent. This means that their value is lost after a
power-on reset. There exist different strategies for initializing data points with an
appropriate value after the device has started.
For input data points, the value can be actively polled from the network when starting up.
Use the Poll-on-Startup feature for this behavior. Polling the network values has the
advantage that intermediate changes on the network are reflected. An input data point can
