Echelon IzoT BACnet Developes - Manual (Page 13)

BACnet messages that do affect the Network Variables are routed via the Mapping
Functions, and then back to the LonTalk stack, where they are presented to the
Application layer completely transparently to the Application Code.
Note that some BACnet properties can be stored in permanent (Flash) memory.
Data Flow during a L
ON
W
ORKS
Write to a Network Variable
The following figure shows data flow when LONWORKS writes to a Network Variable.
FT 6000 Based LonWorks Device
Lon Application
( User Code)
Lon Network
Variables
BACnet Stack
LonTalk Stack
Static (Flash/
EEPROM)
Dynamic (RAM)
BACnet
Mapping
Function
BACnet to Lon Mapping
Configuration Process
Mapping Table
“Sicbhook” write
intercept
( 2 )
Protocol Layer – IzoT
LonWorks Write
Figure 4. Data Flow during L ON W ORKS Write
A L ON W ORKS Network Variable write arrives at the LonTalk stack in figure 4, this is
noted as (1). During the processing of the write, the BACnet stack is given an
opportunity to examine the message, and if necessary, (2) modify the data content with
higher priority data values (see “write operation resolution” above).
Using BACnet and LONWORKS with the FT 6000 EVK 13