Function Code 21 (15H) - Write Configuration Reference Data; Write Restrictions; Request And Response Formats - Honeywell UDC2800 Product Manual

00,27 = Register Address (Standard Access LSP #1 - ID Tag 39)
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 (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)
(CRC16)
Function Code 21 (15h) - Write Configuration
Reference Data
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.
Chapter 11 - Modbus RTU Function Codes 20&21
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