Appendix A.2. Node_Offline_Response - FieldServer FS-8700-01 Driver Manual

FS-8700-01 Modbus RTU/ASCIIFS-8700-01_Modbus_RTU Driver Manual

Appendix A.2. Node_Offline_Response

This function is specific to the Modbus RTU driver.
In systems where data is being collected from multiple Server Nodes and made available on a FieldServer
configured as a Modbus RTU Server, when a Server Node goes offline the default behavior of the FieldServer
would be to stop responding to polls for this data. This might not be what the user wants. Various options exist
making it possible to signal that the data quality has gone bad without creating error conditions in systems
sensitive to the default option.
The following options can be configured under the Node parameter, Node_Offline_Response, to set the response
of the FieldServer to the Modbus RTU Client when the Server Node supplying the data is offline:

No_Response - this is the default option. The FieldServer simply does not respond when the
corresponding Server Node is offline.

Old_Data - The FieldServer will respond, but with the last known value of the data. This maintains the
communication link in an active state, but may hide the fact that the Server Node is offline.

Zero_Data - The FieldServer will respond, but with the data values set to zero. If the user normally expects
non-zero values, this option will signal the offline condition without disrupting communications.

FFFF_Data - The FieldServer will respond, but with the data values set to FFFF (hex). If the user normally
expects other values, this option will signal the offline condition without disrupting communications.
When configured as a Server this parameter can force a desired exception response as follows:

Node_Offline_Message or Exception_4 -

Gateway_Path_Unavailable or Exception_A -

Gateway_Device_Failed or Exception_B -
Example:
Nodes
Node_Name , Node_ID
DEV11 , 11
DEV12 , 12
DEV15 , 15
DEV16 , 16
DEV17 , 17
DEV18 , 18
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
FieldServer's response will be Exception 4
FieldServer's response will be Exception B
, Protocol , Node_Offline_Response
, Modbus_RTU , No_Response
, Modbus_RTU , Old_Data
, Modbus_RTU , Zero_Data
, Modbus_RTU , FFFF_Data
, Modbus_RTU , Exception_4.
, Modbus_RTU , Gateway_Path_Unavailable
FieldServer's response will be Exception A
, Port
, -
, -
, -
, -
, -
, -
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