Echelon IzoT BACnet Developes - Manual (Page 14)

The modified or unmodified message is passed back to the LonTalk stack for further
processing as normal at this point (3).
Data Flow during a L ON W ORKS Read of a Network Variable
The BACnet stack does not participate in this task.
Data Flow during an outgoing Network Variable Update
When the application program on the Neuron updates a Network Variable, an outgoing
L ON W ORKS message is generated. This message is intercepted by the BACnet Stack and
passed on for L ON W ORKS processing like always, without any change.
Data Flow during a BACnet Write to a BACnet Object
A BACnet Write operation is effectively a
L ON W ORKS Message with a different Message Code Field.
As shown in Figure 4, when the
L
ON
W
ORKS
message is received by the LonTalk Stack (1) it is routed
through the BACnet stack which extracts the BACnet Properties and values, modifies them to suit a
Network Variable format and passes this new Network Variable information back to the
L ON W ORKS
stack for further processing.
Data Types and BACnet to Lon Mapping
The following BACnet Objects are implemented in the BACnet Interface.
AI Analog Input
AO Analog Output
AV Analog Value (These are BACnet-optional, temporary holding registers, and are of
no value in this scenario.)
BI Binary Input
BO
Binary Output
BV
Binary Value
(These are BACnet-optional, temporary holding registers, and are of
no value in this scenario.)
BACnet Instance Numbering
BACnet Objects are identified by an Object Identifier that comprises a Type and an
Instance Number, the latter being any number between 0 and 2^22-2 (4194302)
inclusive. Object Identifiers have to be unique per BACnet Device, but the Instance
Number only has to be unique per Type. The BACnet Stack on the Neuron uses the
Network Variable Index as part of the BACnet Instance Number.
14 Using BACnet