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Modbus RTU Function Codes
4/07 UDC2500 Universal Digital Controller Product Manual 185
Example #2
The following is another example of a request and response message using Function code
20.
Request Message (Read LSP #1 = ID Tag 39 and LSP #2 = ID Tag 53)
02 14 0E 06 00 03 00 27 00 02 06 00 03 00 35 00 02 (CRC16)
Where:
02 = Address
14 = Function Code 20 (14 Hex)
0E = Byte Count
06 = Reference Type (IEEE Floating Point)
00,03 = File Number (Access Data Value)
00,27 = Register Address (Standard Access LSP #1 - ID Tag 39)
00,02 = Register Count to read (Floating Point Data)
06 = Reference Type (IEEE Floating Point)
00,03 = File Number (Access Data Value)
00,35 = Register Address (Standard Access LSP #2 - ID Tag 53)
00,02 = Register Count to read (Floating Point Data)
(CRC16)
This is the response to the above request.
Response Message
02 14 0C 05 06 43 C8 00 00 05 06 44 60 00 00 (CRC16)
Where:
02 = Address
14 = Function Code 20 (14 Hex)
0C = Byte Count
05 = Data Byte Count (Sub Message Length)
06 = Reference Type (IEEE Floating Point)
43 C8 00 00 = 400.0 (Value of Local Setpoint #1)
05 = Data Byte Count (Sub Message Length)
06 = Reference Type (IEEE Floating Point)
44 60 00 00 = 896.0 (Value of Local Setpoint #2)
(CRC16)