9.13
Date Code 20120126
Instruction Manual
SEL-2032 Communications Processor
Protocols
Modbus RTU Protocol
For successful operations, the response message will have the same format as
the request message. For error responses, the message format will be as
follows:
1 byte.
Slave Address (echo of received)
1 byte.
Exception Function Code (function code with high-bit set)
1 byte.
Exception Code (see below)
2 bytes.
CRC–16 code for message
Whenever multiple-byte values are sent over Modbus, they are sent most
significant byte first.
The function codes supported by the SEL-2032 are listed in
Read Coil Status (Function Code 01h)
The SEL-2032 uses function code 01h to read the status of various bits. You
may read up to 1000 bits at once.
The master request must have the following format:
1 byte.
Slave Address
1 byte.
Function Code (01h)
2 bytes.
Starting Bit Address
2 bytes.
Number of Bits to Read
2 bytes.
CRC–16 for Message
A successful SEL-2032 response will have the following format:
1 byte.
Slave Address
1 byte.
Function Code (01h)
1 byte.
Byte Count
n bytes.
Data
2 bytes.
CRC–16 for Message
The data response contains 8 bits per data byte, with the LSB of the first byte
corresponding to the addressed bit.
summarizes the supported bit addresses. Control points are detailed
Table 9.4
Supported Function Codes
Function Code
Description
01h
Read Coil Status
02h
Read Input Status
03h
Read Holding Register
04h
Read Input Register
05h
Force Single Coil
06h
Preset Single Register
10h
Preset Multiple Registers
11h
Report Slave ID
Содержание SEL-2032
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