E.14
SEL-700G Relay
Instruction Manual
Date Code 20170814
Modbus RTU Communications
Communications Protocol
08h Loopback
Diagnostic Command
The SEL-700G uses this function to allow a Modbus master to perform a
diagnostic test on the Modbus communications channel and relay. When the
subfunction field is 0000h, the relay returns a replica of the received message.
The relay responses to errors in the query are shown in Table E.19.
10h Preset Multiple
Registers Command
This function code works much like code 06h, except that it allows you to
write multiple registers at once, as many as 100 per operation. If you are
accustomed to 4X references with the function code, for six-digit addressing,
simply add 400001 to the standard database addresses.
Table E.18
08h Loopback Diagnostic Command
Bytes
Field
Requests from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (08h)
2 bytes
Subfunction (0000h)
2 bytes
Data Field
2 bytes
CRC-16
A successful response from the slave will have the following format:
1 byte
Slave Address
1 byte
Function Code (08h)
2 bytes
Subfunction (0000h)
2 bytes
Data Field (identical to data in Master request)
2 bytes
CRC-16
Table E.19
Responses to 08h Loopback Diagnostic Query Errors
Error
Error Code Returned
Communications
Counter Increments
Illegal subfunction code
Illegal Data Value (03h)
Invalid Function Code/Op Code
Format error
Illegal Data Value (03h)
Bad Packet Format
Table E.20
10h Preset Multiple Registers Command
(Sheet 1 of 2)
Bytes
Field
Queries from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (10h)
2 bytes
Starting Address
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
Содержание SEL-700G Series
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