Schweitzer Engineering Laboratories SEL-749M - Table D.15 Responses to 60 H Read Parameter Information Query Errors; Table D.16 61 H Read Parameter Text Command; Table D.17 61 H Read Parameter Text Query Error Messages

D.7
Date Code 20080918 Instruction Manual SEL-749M Relay
Modbus RTU Communications Protocol
Communications Protocol
Use Equation D.1 to calculate the actual (not scaled) value of the parameter
(setting):
Equation D.1
Use Equation D.2 to calculate the scaled setting value:
Equation D.2
The relay response to errors in the query are shown Table D.15:
61h Read Parameter
Text Command
The SEL-749M 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:
Table D.15 Responses to 60h Read Parameter Information Query Errors
Error Error Code Returned
Communication
Counter Increments
Illegal parameter to read Illegal Address (02h) Invalid Address
ParameterValue Offset+()Multiplier•
Divisor
---------------------------------------------------------------------------------------------------------
--=
value
value Divisor•
Multiplier Base•
---------------------------------------------- O f f s e t–=
Table D.16 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
Ta b l e D .17 61 h Re a d Pa r a m et er Tex t Qu er y E r ro r M e ss a g es
Error Error Code Returned
Communication
Counter Increments
Illegal parameter to read Illegal Address (02h) Invalid Address
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