Echelon IzoT BACnet Developes - Manual (Page 9)

Differences between BACnet and L ON W ORKS
There is a fundamental difference between BACnet and L ON W ORKS “Input” and “Output”
concepts pertaining to physical I/O. For example, when considering a temperature
sensor; when using BACnet, the temperature sensor is viewed as an “Analog Input” and
displayed and processed accordingly. In a L ON W ORKS example, the common approach is
to process the measurement internally and expose the resulting temperature as an
“Analog Output” of a Function Block. Similarly, in the case of a setpoint for example; in
BACnet systems, setpoints are normally considered “Analog Outputs” to be written to a
device, whereas when using L ON W ORKS , setpoints are processed as Analog Inputs to
Function Blocks.
With this in mind, the mapping of the BACnet conceptual model to a L
ON W ORKS model
can easily be achieved by the creation of a “Virtual BACnet Server” model within the
Neuron Chip, and other BACnet devices interact with this virtual device as they would
with any other native BACnet device.
External
LonWorks
Device
External
LonWorks
Device FT 6000 based LonWorks Device
Standard LonWorks Function Block
AO: Temp Setpoint
BACnet Write BACnet Read
BACnet Read
Virtual BACnet Server (New)
nviSpaceTemp
AO: Space Temp
nviSetPoint
nvoSpaceTemp
AI:SpaceTemp
AI
Figure 1. Conceptual Model of a Virtual BACnet Server
Figure 1 shows 3 L ON W ORKS Devices. The central device contains the BACnet Interface,
embodied as the Virtual BACnet Server (VBS) which exists within the Neuron 6050 chip.
It is this interface that a BACnet Client (such as a Building Management System,
Operator Workstation, or perhaps another BACnet Controller) communicates with. The
model of the VBS is such that the BACnet Client can read from and write to BACnet
points in a completely BACnet-compliant fashion. The VBS connects and maps these
BACnet points internally to the L ON W ORKS Network Variables.
Normal L ON W ORKS connections can still be bound, simultaneously, to the L ON W ORKS
Network Variables in the original function blocks as before, and the L
ON
W
ORKS
systems
will continue normal operation.
It should be noted that in some cases a single L
ON W ORKS Network Variable with
multiple SNVT fields will map to Multiple BACnet Objects.
Using BACnet and LONWORKS with the FT 6000 EVK 9