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FS-8700-01_Modbus_RTU_(T28700-01) Driver Manual Page 18 of 21
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
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, the user must read the registers into an
integer data array, and then use the Moves function to move the data to a floating point or
32 bit integer data array. The “function” field in the move must be populated with the correct
move function required. Details of the available function fields are listed in the FieldServer
configuration manual along with a more detailed explanation of moves. Note that functions
also exist to split a floating point value into two integers using the reverse operation.
A diagrammatic representation of this process is depicted below:
The example below shows how a floating point value is retrieved from two Modbus registers
that were placed in an integer data array.
Example
Data_Arrays
Data_Array_Name,
Data_Format,
Data_Array_Length
DA1, int16, 20
DA2, float, 10
Moves
Function, Source_Data_Array, Source_Offset,
Target_Data_Array,
Target_Offset
2.i16-1.float-sw,
DA1, 0, DA2, 6
This Move will cause two integers at offsets 0 and 1 in the integer Data Array DA1 to be
copied to offset 6 in the float Data Array DA2. In the process of copying the values, the
integers will be combined and treated as an IEEE 32 bit floating point number.
Appendix A.5. Connection to York Modbus Microgateway
If connecting the FieldServer to a York Modbus Microgateway, the Node_ID of the
Microgateway is defined by the address DIP switches. If switch 4 is set to ‘On’ and the other
switches are set to ‘off’ then Node_ID of the Microgateway is ‘247’, the parity is ‘Even’, and
the stop bits are 1. Other Node_ID combinations can be found in the York Modbus
Microgateway Installation Manual.
Modbus
Device
Two 16 bit
integers
polled:
e.g: 40001,
length 2
Together, they
combine to
form a 32 bit
IEEE Floating
point number.
Source Data
Array
-------------------------
Offset 0: 40001
-------------------------
Offset 1: 40002
-------------------------
Float Data Array
-------------------------
Offset 40: Float value
-------------------------
Modbus
Poll
Special
Move
Unreadable
content
Sensible data