Modbus RTU Function Codes 
9.3.1 Read Configuration Examples 
Example #1 
The following is an example of a request to read the Gain 1 value using Function code 
20. 
Request Message (Read (Gain 1) = ID Tag 001) 
  02 14 07 06 00 03 00 01 00 02 (CRC16) 
Where: 
 02 =  Address 
  14  =  Function Code 20 (14 hex) 
  07  =   Byte Count 
  06  =   Reference Type 
  00,03  =   File Number (Access Data Value) 
  00,01      =   Register Address (Standard Access  Gain 1 - Tag ID #1)  
  00 02  =   Register Count (Floating Point Data) 
 (CRC16) 
This is the response to the above request. 
Response Message 
  02 14 06 05 06 3F C0 00 00 (CRC16) 
Where: 
 02   = Address 
  14    = Function Code 20 (14 Hex) 
  06    = Byte Count 
  05    = Sub Message Length 
  06    = Reference Type (IEEE Floating Point) 
  3F C0 00 00  = 1.50 (Value of Proportional Band) 
 (CRC16) 
 
180  UDC3200 Universal Digital Controller Product Manual  12/04