Modbus RTU Function Codes
338 UDC3500 Universal Digital Controller Product Manual 3/07
9 Modbus RTU Function Codes
9.1 Overview
This section describes the function codes needed to upload and download the
configuration from a host computer into the instrument.
What's in this section?
The following topics are covered in this section.
TOPIC See Page
9.1 Overview 338
9.2 General Information 338
9.3 Function Code 20 340
9.4 Function Code 21 344
9.2 General Information
This instrument uses a subset of the standard Modbus RTU function codes to provide
access to process-related information. Several MODICON function codes are
implemented. It is appropriate to define instrument-specific "user-defined" function
codes. Where differences occur between the two protocols it will be noted. Several
standard Modbus RTU function codes are supported.
Configuration ID Tags
Function codes 20 and 21 use the RS422/485 tag IDs for accessing configuration and
process-related data. These tags are fully explained in
Section 10.
The tag IDs represent the
register addresses used in the Request Message.
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