L-VIS User Manual
242
LOYTEC
Version 6.2
LOYTEC electronics GmbH
10.16 Data Points in L-Vis Projects
When referencing a data point of the data point configuration via an L-Vis data point
object, the initial direction is taken over from the referenced data point, with value data
points being used for read access by default. If needed, the data flow may be reversed by
setting an option in the L-Vis data point object. This is important because the data flow
direction determines how a data point will be used by other objects in the tree. For example,
a mathematic object will assign variable names (v1, v2…) to all input data points and write
the result of the calculation to all output data points. For controls, the direction of the
attached data points determine if the control will be selectable (to input new data) or not.
NOTE:
The direction is defined from the point of view of the L-VIS device in question, referring to
the network side, not the application side. Therefore, an input data point will receive new
data from the network and deliver this data to the L-Vis application, whereas an output
data point will write new data from the L-VIS application to the network.
Data points in an L-Vis project fall into one of the following categories:
Favorite:
A favorite is a symbolic link to another data point. It can be used to
define a virtual data interface which can be connected to real data points during
integration. It may be helpful to build reusable templates or collect data from
different base folders into one favorite folder.
System Register:
System registers cannot be created by the user. They are
provided by the device to modify certain internal system parameters, like the time
zone, IP address, BACnet device instance number, or others, or read the current
value of a system parameter like the current time, CPU load, free memory, and so
on. A system register object is either a read-only or a write-only value, and is
accessed via a system register data point of the appropriate direction.
User Register:
A user register is a place to store data internally, instead of
communicating with other devices on a network. Registers are used to internally
transfer data between objects, for example when a mathematic object calculates a
value which should be displayed on a control, the result of the calculation is
stored to a register and the control reads the value from the register for display. A
register is therefore always represented either by a data point of type value (r/w)
or by two separate data points. One to write a new value to the register and one
by which the current value of the register can be read.
Local Network Object:
A local network object refers for example to a static or
dynamic network variable (CEA-709 models) or a BACnet server object
(BACnet models) which exists on the device. Most of these communication
objects are either write-only (output NV, BACnet input object) or read-only
(input NV, BACnet output object). They are therefore represented by one data
point with the appropriate direction. One exception to this rule are BACnet value
objects, which may be read and written and which are therefore represented like
user registers (either one value data point or two separate read and write points).
Remote Network Object:
A remote network object is a reference to some object
existing on a remote device on the network. Such a reference is called a
client
mapping
on BACnet devices, since it maps the value of the existing data point on
the L-VIS device to a communication object on a remote device. Depending on
the direction of data flow, the mapping can be either read (poll or COV) or write.
There may be more client mappings for the same remote object, for example to a
remote BACnet value object, which can be read and written and is therefore
represented by two client mappings. On CEA-709 devices, external network
objects are called
external NVs
since they are references to NVs located on other
devices. A remote network object is usually only constructed from data retrieved
