L-VIS User Manual
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LOYTEC
Version 6.2
LOYTEC electronics GmbH
SNVT_time_stamp:
This type of data point can be connected to date controls.
SNVT_str_asc:
This and other string data types (string registers) may be directly
connected to a text control. The string received via these data points will be
displayed directly on the text control, without a lookup in a mapping table. If the
data point is used as output, the string selected from the mapping table is directly
assigned to the data point, without converting to a number first. If the string
contains non-ASCII characters, they are represented in the ISO-10646 character
set and are transferred in UTF-8 encoded format. This way, it is possible to
exchange strings in any language between two L-VIS devices.
The
data point object
is the L-Vis object created when
Add Data Point…
is selected from
the context menu of a control to assign a data point to it. The reason why the assignment of
data points to controls is done via a separate object; instead of directly connecting a data
point to the control has a number of reasons. The most important ones are:
1.
Data points represent communication objects which exist on the device. They
must be independent of the existence of any control or other user interface object.
If a data point was to be connected to a control and the control is deleted, the data
point would be deleted as well. Using a reference object to link the control to an
existing data point solves this problem. Deleting the control will also delete the
reference object (the data point object), but not the data point itself.
2.
Many projects need to link multiple controls to the same data point, for example
to display a temperature which is received from the network on a bar control and
on a numeric control at the same time. This would not be possible if the data
point would be directly connected to a control, since it could only be in one place
of the object tree at a time. A separate link or reference object is required, which
points to the data point from which the control should receive its value updates.
3.
Sometimes it is required to apply simple linear transformations to the value
received from the data point before it can be displayed. For example, a data point
may receive a temperature value from the network in degrees Celsius, but the
temperature displayed on the device should show degrees Fahrenheit, or a data
point provides a speed in meters per second, but the display should read mph or
km/h. Such translations can be done by the data point object on the fly, while
passing values between the control and the data point. This makes it easy to
display for example a temperature from an input data point both in degree Celsius
and in degree Fahrenheit side by side, using two data point objects referencing
the same data point, but using different value translations.
It is important to understand this concept to understand what can be configured on the
Data
Point
property page of L-Vis data point objects. The key is that there can and usually will
be multiple data point objects in the L-Vis object tree, referencing the same data point in
the data point configuration.
9.6.1 Data Point Properties
The following properties can be set on the
Data Point
property page:
Value Translation:
If the unit of the data point is known and there are some commonly used
translations available for this unit, one of the pre-defined translations can be selected from
the drop down list. A custom translation can be defined by filling out the formula below the
drop down list. In this formula, NV stands for the value on the network side (Network
Value), that is, the value of the data point, and DP stands for the value of the data point as
seen by controls or other objects which are connected via this data point.
