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L-Proxy User Manual 59 LOYTEC
Version 3.1 LOYTEC electronics GmbH
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Multi-state : A
multi-state
data point represents a discrete set of states. The associated
data type is a signed integer machine variable. Each state is identified by an integer
value, the
state ID
. State IDs need not be consecutive. Meta-data of a multi-state data
point includes human-readable descriptions for the individual states (state texts) and
the number of available states.
•
String : A
string
data point contains a variable-length string. The associated data type
is a character string. International character sets are encoded in UTF-8. A string data
point does not include any other meta-data.
•
User : A
user
data points contains un-interpreted, user-defined data. The data is stored
as a byte array. A user data point does not include any other meta-data. This type of
data point also serves as a container for otherwise structured data points and represents
the entirety of the structure.
6.3.2 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): The value is given in seconds, which specifies that this data point
periodically polls data from the source.
•
Receive Timeout (input): This is a variation on the poll cycle. When receive timeout
is enabled, the data point actively polls the source unless it receives an update. For
example, if poll cycle is set to 10 seconds and an update is received every 5 seconds,
no extra polls are sent.
•
Poll-on-startup (input): 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.
•
Maximum Cache Age (output): This parameter defines if a received poll request to an
output can be answered from the data point cache. Setting it to ‘0’ disables the cache.
Then each poll request is repeated to the other side of the connection. Setting it to ‘-1’
sets the cache age to infinite and polls are never forwarded. A value in milliseconds
defines that a poll is only forwarded, if the last update to the output is older than this
setting. If the polled data point does not respond to a request, the poll request on the
primary side is not answered, either.
6.3.3 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.
6.3.4 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.