WAGO 750-830, Руководство пользователя

Страница: 275 / 360

List of all BACnet Properties in Native Operation • 275
WAGO-I/O-SYSTEM 750
BACnet/IP Controller
6 List of all BACnet Properties in Native Operation
This section contains a list of all properties of BACnet Objects that can be
used in native operation.
The properties of BACnet Objects are classified as follows:
•
individual, primitive data types
•
complex data types consisting of several data types
•
collection of data elements of the same type
In some cases, the number of data elements of a collection is specified; some-
times the number of elements can vary. In some cases, the elements must be
accessed individually or there is a certain sequence to follow. BACnet pro-
vides two forms of data types for properties that represent a collection of data
elements of one type:
•
"BACnetARRAY"
•
"List of"
The data type " BACnetARRAY " describes a structured field and consists of
data elements of a data type in an ordered sequence. A "field index", i.e. an
unsigned integer value, can be used to access the individual components of a
field property (write or read access). An index of 0 (zero) indicates that the
number of present data elements has been returned. If there is no field index,
this means that all elements of the field can be accessed. A field index of n
greater than zero indicates the nth element of the sequence. When using field
properties with BACnet objects, the designation "BACnetARRAY[N] of data
type" indicates an ordered sequence of data elements with this data type. If the
size of a field can be changed by writing in the field, the field element 0 must
be writable. If the value of the field element 0 is reduced, this is shortened and
all elements of the field with an index greater than the new value of the field
element 0 are deleted. If the value of the field element 0 increases, new ele-
ments of the field with an index greater than the old value of the field element
0 are replaced. Values that are assigned to these elements are local values if
not otherwise indicated. If the size of a field can be changed, writing in the en-
tire field as a single property with a different number of elements leads to a
change in field size. The attempt to write with an index greater than the field
in a field element leads to an error, and the field is not enlarged in order to ac-
cept the element. Fields with a size established in the Standard cannot be
enlarged or reduced in size.
The data type " List of " is a structure list with a sequence of zero or more data
elements of one data type. The length of each "List of" is different. If not re-
quired for a certain purpose, no maximum size should be given for a "List of".
The designation "List of <data type>" indicates a sequence of zero or more
data elements of the corresponding type.