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FS-8700-21 LonWorks Manual Page 14 of 62
FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web: www.fieldserver.com
Tel: (408) 262 2299 Fax: (408) 262 2269 Toll Free: (888) 509 1970 email: support@fieldserver.com
6 EXPLICIT CONFIGURATIONS
6.1 Special considerations
With Explicit configuration, the FieldServer communicates directly with other devices by specifying the remote device address
in the FieldServer configuration.
All the Servers and their Clients need to be on the same domain to be able to communicate. If the LonWorks device’s Node
ID is not known, it may be read using a utility program e.g. NodeUtil or using a LonWorks Analyzer. All the Client Node CSV
files need to have their Subnet_ID and Node_ID parameters set to point to their respective Server Subnet and Node ID values.
Once the FieldServers are restarted the network should function correctly.
6.1.1 Map Descriptor Names (Network Variable Names)
As a Server, the LonWorks driver provides a table of Network Variables for other Nodes to read. These Nodes access the
variables according to Index numbers which are automatically assigned by the driver according to the Map Descriptor
definition order in the configuration file. The driver also creates an identification table for configuration nodes to read the
name and types of variables available on the FieldServer. Within the LonWorks protocol, this table size is limited to 64K
bytes. If the application requires a large number of Server mappings (up to 4096), it will be necessary to limit the variable
name length. Each Server mapping requires 4 bytes plus the length of the name from this 64K block.
6.1.2 Lon functions
Explicit Map Descriptors are distinguished from Implicit Map Descriptors by the function used in the Lon_Function field of the
Map Descriptor. Depending on the nature and direction of Data Transfer needed different explicit functions are available as
shown below
NOTE:
Function field MUST pair up with the Lon_Function field as shown in the table
NMFETCHC is the preferred Lon Function for most applications. See Section 6.1.5
Lon_Function
Description
Function Field
NVUI
Network Variable Update Input
SERVER
NVPO
Network Variable Polled Output
NVPIEXC
Network Variable Polled Input Explicitly addressed Continuously sent
RDBC
NVUOEXC
Network Variable Update Output Explicitly addressed Continuously sent
WRBC
NVUOEXX
Network Variable Update Output Explicitly addressed and sent on Change
WRBX
NVUOEXT
Network Variable Update Output Explicitly addressed sent in Throttling Mode
WRBC
NMFETCHC
Network Management Network Variable Fetch Continuously sent (Explicit Addressing only)
RDBC
CFG_NVUI
Configuration Network Variable Update Input
SERVER
6.1.3 SNVT_Index
The SNVT_Index field must be specified for all explicitly addressed Client Map Descriptors. These Client Map Descriptors use
this field to index their relevant Map Descriptors on the Server side.