D.2
SEL-587Z Instruction Manual
Date Code 20020903
Modbus RTU Communications Protocol
Modbus Overview
Responses
The slave device sends a response message after it performs the action
requested in the query. If the slave cannot execute the command for any
reason, it sends an error response. Otherwise, the slave device response is
formatted similarly to the query including the slave address, function code,
data (if applicable), and a cyclical redundancy check value.
Supported
Function Codes
The SEL-587Z supports the Modbus function codes shown in
Exception
Responses
The SEL-587Z sends an exception code under the conditions described in
In the event that any of the errors listed in
occur, the relay
assembles a response message that includes the exception code in the data
field. The relay sets the most significant bit in the function code field to
indicate to the master that the data field contains an error code, instead of the
requested data.
Table D.2
SEL-587Z Modbus Function Codes
Codes
Description
01h
Read Coil Status
02h
Read Input Status
03h
Read Holding Registers
04h
Read Input Registers
05h
Force Single Coil
06h
Preset Single Register
07h
Read Exception Status
08h
Loopback Diagnostic
10h
Preset Multiple Registers
64h
Scattered Register Read
Table D.3
SEL-587Z Modbus Exception Codes
Exception
Code
Error Type
Description
01
Illegal Function Code
The received function code is
either undefined or unsupported.
02
Illegal Data Address
The received command contains
an unsupported address in the data field.
03
Illegal Data Value
The received command
contains a value that is out of range.
04
Device Error
The SEL-587Z is in the wrong
state for the requested function.
06
Busy
The SEL-587Z is unable to process the
command at this time due to a busy resource.
Содержание SEL-587Z
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