User Guide

FS-8700-21 LonWorks Manual Page 9 of 62
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5 IMPLICIT CONFIGURATIONS
5.1 Special considerations
Implicit addressing is used when a Network Management Tool such as LonMaker® is used to connect a FieldServer to other
LonWorks nodes - the FieldServer is assigned its data transfer (binding) parameters by the Network Management Tool.
5.1.1 Map Descriptor Names (Network Variable Names)
When using Implicit configuration, 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.
5.1.2 Implicit Lon functions
Implicit Map Descriptors are distinguished from Explicit 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 implicit functions are available as
follows (NOTE: function field MUST pair up with the Lon_Function field as shown in the table):
Lon_Function
Description
Function Field
NVUI
Network Variable Update Input
PASSIVE
NVPO
Network Variable Polled Output
NVPIIMC
Network Variable Polled Input Implicitly addressed Continuously sent
RDBC
NVUOIMC
Network Variable Update Output Implicitly addressed Continuously sent
WRBC
NVUOIMX
Network Variable Update Output Implicitly addressed and sent on Change
WRBX
NVUOIMT
Network Variable Update Output Implicitly addressed sent in Throttling Mode
WRBC See Appendix A.3
CFG_NVUI
Configuration Network Variable Update Input
PASSIVE
5.1.3 SNVT_Index
For implicitly addressed Client Map Descriptors and all Server side Map Descriptors the driver will assign an index to each
one, starting from 0 and incrementing to 4095, in the order they appear in the configuration file.
5.1.4 Address Table Limit
It is important to note the limitation within LonWorks Implicit addressing that the Address Table used for storing the
addresses of all active connections made with the FieldServer is limited to 16 Device Addresses including that of the
FieldServer. This is a LonWorks limitation, not a FieldServer limitation, and it means that the FieldServer can only make active
implicit connections to 15 other devices . If active connections to more than 15 devices are required, then it is necessary to
use Explicit Configuration (NMFETCHC is recommended).
Devices that write to passive Map Descriptors in the FieldServer only are not placed in this table and therefore this limitation
does not apply. (A Passive Map Descriptor is recognized by the Passive Parameter in the Function Field).