FieldServer FS-8700-08 - Manual (Page 16)

FS-8700-01 Modbus RTU/ASCIIFS-8700-01_Modbus_RTU.doc Driver Manual Page 16 of 21
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Appendix A.1.2. Transferring 32 bit values with two registers
If a Modbus Server sends two consecutive registers to the FieldServer representing either a floating point value or
a 32 bit integer value, the FieldServer can combine and decode these registers back into their original format. To
do this declare Data Array of type Float or UINT32 and set the Map Descriptor Data_Type as ‘Float_Reg’ or ‘32-
Bit_Reg’ etc
Example:
Data_Arrays
Data_Array_Name , Data_Format , Data_Array_Length
DA1
, Float , 20
DA2 , UInt32 , 20
DA3 , Float , 20
DA4 ,UInt32 , 20
// Client Side Map Descriptors
// For Nodes where Address_Type is PDU
Map_Descriptors
Map_Descriptor_Name , Data_Array_Name , Data_Array_Offset , Function , Node_Name, , Data_Type , Address , Length ,Scan_Interval
CMD_AO_01 , DA1 , 0 , Rdbc , MODBUS DEVICE2 , Float_Reg , 0 , 20 ,1.000s
CMD_AO_02 , DA2 , 0 , Rdbc , MODBUS DEVICE2 , 32-Bit_Reg , 0 , 20 ,1.000s
CMD_AI_01 , DA3 , 0 , Rdbc , MODBUS DEVICE2 , Input_Float , 0 , 20 ,1.000s
CMD_AI_02 , DA4 , 0 , Rdbc , MODBUS DEVICE2 , Input_Reg_32Bit , 0 , 20 ,1.000s
Each Map Descriptor will read 20 pairs of registers and store them as 32-bit floating number or 32-bit Integer.
If somehow server device send swapped registers (low value register first) then use corresponding _swap
data_types.
Note: Please note starting addresses per address_type, see section 5.3.2
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.