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Modbus RTU Function Codes
186 UDC2500 Universal Digital Controller Product Manual 4/07
9.4 Function Code 21 (15h) - Write Configuration Reference Data
Introduction
Function Code 21 (15 Hex) is used in this instrument to allow writes of integer and
floating point values to the configuration database and override values.
The configuration database of this instrument is located in EEROM. The override values
are stored in RAM.
Integer format is used to write to “Digital” configuration items. Floating Point format is
used to write to “Analog” configuration items as defined by the configuration ID tags.
Write Restrictions
Care should be taken not to exceed the 100,000 write limit of the EEROM.
Request and Response Formats
The Request and Response formats for Function code 21 (15 Hex) are shown below.
Details for each block reference follow.
Request Message Format
Slave
Address
Byte
Count
Function
Code 15
Reference
Type
File
Number
Register
Count
Register
Address
CRC
Data
CRC
Data
Data
Data Data Data
File
Number
Response Message Format (echo back of request)
Slave
Address
Byte
Count
Function
Code 15
Reference
Type
File
Number
Register
Count
Register
Address
CRC
Data
CRC
Data
Data
Data Data Data
File
Number
The register address is interpreted as the tag ID configuration number.
For Infrared Transactions, add three BOFs (C0hex) at the beginning of each message and
one EOF (FFhex) at the end of each message.
Reference Type Definitions
The Reference Type definition is always 06.
See examples in Subsection 9.4.1