E.17
Date Code 20100129
Instruction Manual
SEL-751A Relay
Modbus RTU Communications
Communications Protocol
61h Read Parameter
Text Command
The SEL-751A uses this function to allow a Modbus master to read parameter
text from the relay. One parameter text (setting name) is read in each query.
The relay responses to errors in the query are shown below.
62h Read
Enumeration
Text Command
The SEL-751A uses this function to allow a Modbus master to read parameter
enumeration or bit enumeration values (setting lists) from the relay. One
parameter enumeration is read in each query.
Table E.24
61h Read Parameter Text Command
Bytes
Field
Queries from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (61h)
2 bytes
Parameter Number
2 bytes
CRC-16
A successful response from the slave will have the following format:
1 byte
Slave Address
1 byte
Function Code (61h)
2 bytes
Parameter Number
16 bytes
Parameter Text (setting name)
4 bytes
Parameter Units (e.g., Amps)
2 bytes
CRC-16
Table E.25
61h Read Parameter Text Query Error Messages
Error
Error Code Returned
Communication
Counter Increments
Illegal parameter to read
Illegal Address (02h)
Invalid Address
Table E.26
62h Read Enumeration Text Command
(Sheet 1 of 2)
Bytes
Field
Queries from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (62h)
2 bytes
Parameter Number
1 byte
Enumeration Index
2 bytes
CRC-16
Summary of Contents for 751A
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