Echelon IzoT BACnet Developes - Manual (Page 8)

BACnet Terminology
The following terms are a brief summary of BACnet terminology.
BACnet Network – A group of BACnet Devices on a single network, which may be
any of BACnet’s physical layer options, namely Ethernet, RS-485,
LonTalk, and now IzoT, identified by a Network Number.
BACnet Internetwork – A collection of connected BACnet Networks connected via
BACnet Routers. The resulting devices are all able to communicate
with one another. Every BACnet Device is required to have a unique
BACnet Device Instance and Device Object Name to unambiguously
distinguish it, and every BACnet Network must have a unique Network
Number.
BACnet Device – A controller, operator workstation, etcetera, that supports
BACnet communications
BACnet Object – A data point, measurement or some other value in a BACnet
Device
BACnet Object Identifier – An identifying parameter for each object in a Device
which is unique on a Device basis, which comprises the Object Type and
the Object’s Instance Number.
BACnet Property – A BACnet Object contains multiple Properties, some optional
and some mandatory. For example, Properties such as Present Value
could reflect the value of a physical input such as temperature, the Object
Identifier Property of an Object identifies the Object.
BACnet Device Instance – More exactly, the Instance Number of the Object
Identifier of the Device Object that every BACnet device is required to
contain. It has to be unique across the whole of the BACnet Internetwork.
BACnet Router – A standard BACnet component that allows the interconnection of
different BACnet Networks. They may effect a physical and logical
change between networks of different physical types and different
Network Numbers, or sometimes only a logical change between different
BACnet Network Numbers.
Priority Array – An array of 16 values for some BACnet output Objects, (e.g.
Analog Output), which allows multiple systems to control a single output,
by writing to the Priority Array, with predetermined results. The value of
the resulting highest Priority Array item is transferred to the Present
Value
Present Value – One of a BACnet Object’s Properties, usually containing a physical
input or output value.
Relinquish Default – A value that is transferred to the Present Value when the
Priority Array does not contain any values at all.
BACnet Priority – Specified when writing a value to the BACnet Priority Array.
8 Using BACnet