Sel 551 - Table G.14 64 H Scattered Register Read Command

G.10
SEL-551 Relay Instruction Manual Date Code 20110408
Modbus RTU Communications Protocol
Modbus RTU Communications Protocol
The relay responses to errors in the query are shown below:
64h Scattered
Register Read
The SEL-551 uses this function to allow a Modbus master to read
noncontiguous registers in a single request. A maximum of 100 registers can
be read in a single query.
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 G.14 64h Scattered Register Read Command
Bytes Field
Requests from the master must have the following format:
1 byte Slave Address
1 byte Function Code (64h)
1 byte Query Data Length
1 byte Subfunction Code (04h)
a
a
Only subfunction 04h is supported.
1 byte Transmission Number
2 bytes Address of First Register
2 bytes Address of Second Register
••
••
••
2 bytes Address of nth Register
2 bytes CRC-16
A successful response from the slave will have the following format:
1 byte Slave Address
1 byte Function Code (64h)
1 byte Response Data Length
1 byte Subfunction Code (04h)
a
1 byte Transmission Number
2 bytes Data from First Register
2 bytes Data from Second Register
••
••
••
2 bytes Data from nth Register
2 bytes CRC-16