Echelon IzoT BACnet Developes - Manual (Page 15)

BACnet Object to L ON M ARK SNVT Mapping – The “Mapping
Table”
1. Network Variables
The first issue is that SNVTs are “Structures” and BACnet objects are effectively single
point values, this means that often there is one-to-many mapping required between
L
ON
W
ORKS
and BACnet.
For example, in the VAV template, nvoUnitStatus is numbered nv4, and it is a
SNVT_hvac_status which has 7 fields, which means this single NV needs to expand into
7 BACnet Objects with the following Object IDs.
SNVT Map Status
SNVT_hvac_status.mode maps to Analog Input
SNVT_hvac_status.heat_output_primary maps to Analog Input
SNVT_hvac_status.heat_output_secondary maps to Analog Input
SNVT_hvac_status.cool_output maps to Analog Input
SNVT_hvac_status.econ_output maps to Analog Input
SNVT_hvac_status.fan_output maps to Analog Input
SNVT_hvac_status.in_alarm maps to Analog Input
2. Normal Variables
If normal variables (as opposed to Network Variables) are to be mapped, then alternative
mapping macros need to be used.
Examples of both mapping methods are found in the BAClon\mapping.nc file in both the
BACevb and BACsimple sample projects.
BACnet Object Properties
Object Name Property
The BACnet Object Name Property is automatically determined from the LonWorks
Network Variable name.
Queue Management
If there are more incoming messages than the BACnet stack can handle, these messages
will back up in the Neuron incoming queue, and eventually messages will be discarded
just like any other LonTalk message overrun. This condition can be diagnosed using
familiar tools such as Nodeutil.
Using BACnet and LONWORKS with the FT 6000 EVK 15