G.9
Date Code 20110408 Instruction Manual SEL-551 Relay
Modbus RTU Communications Protocol
Modbus RTU Communications Protocol
The relay responses to errors in the query are shown below:
10h Preset Multiple
Registers Command
This function code works much like code 06h, except that it allows you to
write multiple registers at once, up to 100 per operation. If you are
accustomed to 4X references with the function code, for 6-digit addressing,
simply add 400001 to the standard database addresses.
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
Error Error Code Returned
Communication
Counter Increments
Illegal subfunction code Illegal Data Value (03h) Illegal Function Code/Op Code
Format error Illegal Data Value (03h) Bad Packet Format
Table G.12 08h Loopback Diagnostic Command (Sheet 2 of 2)
Bytes Field
Table G.13 10h Preset Multiple Registers Command
Bytes Field
Requests 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
2 bytes Number of Registers
2 bytes CRC-16
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