E.15
Date Code 20100129
Instruction Manual
SEL-751A Relay
Modbus RTU Communications
Communications Protocol
The relay responses to errors in the query are shown below.
60h Read Parameter
Information
Command
The SEL-751A uses this function to allow a Modbus master to read parameter
information from the relay. One parameter (setting) is read in each query.
The Parameter Descriptor field is defined in
.
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.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
Table E.21
60h Read Parameter Descriptor Field Definition
(Sheet 1 of 2)
Bit
Name
Description
0
RO: Read-only
1 when the setting is read-only
1
H: Hidden
1 when the setting is hidden
2
DBL: 32-bit
1 when the following setting is a fractional value of this setting
3
RA: RAM-only
1 when the setting is not saved in nonvolatile memory
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