Schweitzer Engineering Laboratories SEL-787, Instruction Manual, Page: 427 / 564

E.13
Date Code 20081022 Instruction Manual SEL-787 Relay
Modbus RTU Communications
Communications Protocol
The relay responses to errors in the query are shown below.
60h Read Parameter
Information
Command
The SEL-787 uses this function to allow a Modbus master to read parameter
information from the relay. One parameter (setting) is read in each query.
2 bytes Number of Registers to Write
1 byte Number of Bytes of Data ( n )
n bytes Data
2 bytes CRC-16
A successful response from the slave will have the following format:
1 byte Slave Address
1 byte Function Code (10h)
2 bytes Starting Address
2 bytes Number of Registers
2 bytes CRC-16
Table E.19 10h Preset Multiple Registers Query Error Messages
Error Error Code Returned
Communication
Counter Increments
Illegal register to set Illegal Data Address (02h) Invalid Address
Illegal Write
Illegal number of registers to set Illegal Data Value (03h) Illegal Register
Illegal Write
Incorrect number of bytes in
query data region Illegal Data Value (03h) Bad Packet Format
Illegal Write
Invalid register data value Illegal Data Value (03h) Illegal Write
Table E.18 10h Preset Multiple Registers Command (Sheet 2 of 2)
Bytes Field
Table E.20 60h Read Parameter Information Command
Bytes Field
Queries from the master must have the following format:
1 byte Slave Address
1 byte Function Code (60h)
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 (60h)
2 bytes Parameter Number
1 byte Parameter Descriptor
1 byte Parameter Conversion
2 bytes Parameter Minimum Settable Value
2 bytes Parameter Maximum Settable Value
2 bytes Parameter Default Value
2 bytes CRC-16