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Modbus RTU Function Codes
182 UDC2500 Universal Digital Controller Product Manual 4/07
9.3 Function Code 20 (14h) - Read Configuration Reference Data
Description
Function code 20 (14 Hex) is used in this instrument to read information stored in its
configuration database. Each configuration item is explicitly addressed by a file number
and register address. IEEE 32-bit floating point and 16-bit integer formats are supported.
Request and Response Formats
The Request and Response formats for Function code 20 (14 Hex) are shown below.
Details for each block reference follow.
Request Message Format
Slave
Address
Byte
Count
Reference
Type
Function
Code 14
Reference
Type
File
Number
Register
Count
Register
Address
Reference
Type
File
Number
Register
Count
Register
Address
CRC
Data
CRC
Data
Response Message Format
Slave
Address
Byte
Count
Reference
Type
Function
Code 14
Reference
Type
Data
Reference
Type
Data
Byte
Count
Data Data
Data
Data
Byte
Count
Data Data Data Data
CRC
Data
CRC
Data
Byte Count
The Byte Count equals the number of bytes transmitted in either the request or response
message and will be the minimum number required to transmit all requested data.
Data Byte Count
The Data Byte Count is the number of data bytes of the sub response including the
Reference Type but not including itself. A floating point sub response has four bytes of
data and one byte representing the reference type making the data byte count equal to
five.