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FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 19 of 21
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Appendix A.6. 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.
Example:
Nodes
Node_name, Node_ID, Protocol, Node_Offline_Response, port
DEV11, 11, Modbus_rtu, No_Response, -
DEV12, 12, Modbus_rtu, Old_Data, -
DEV15, 15, Modbus_rtu, Zero_Data, -
DEV16, 16, Modbus_rtu, FFFF_Data, -