EXPERT Standard Series User Manual
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of Modbus, and the application protocol data unit in the following refers to these two
parts. Description on frame format in the following takes RTU mode as an example,
and ASCII mode application layer protocol data unit’s length needs to be doubled.
Read drive parameters’ application layer protocol data unit as follows:
Request format is as follows:
Application Layer Protocol
Data Unit
Data Length(Bytes)
Value or Range
Function code
1
0x03
Start register address
2
0x0000～0xFFFF
Register number
2
0x0001～0x0004
Response format is as follows:
Application Layer Protocol
Data Unit
Data Length(Bytes)
Value or Range
Function code
1
0x03
Read bytes
1
2* Register number
Read contents
2* Register number
If operation request fails, response should be error codes and abnormal codes.
Error code is equal to (function code ＋ 0x80), and abnormal code indicates error
reasons. Abnormal codes are listed as follows:
Abnormal Code
Abnormal Code Significance
0x1
Illegal function code.
0x2
Illegal register address.
0x3
Data error, data exceeds upper limit or lower limit.
0x4
Slave operation fails (including data within the range of upper
limit and lower limit, but errors caused by invalid data)
0x5
Command valid, under transaction, mainly used in storing data
to non-volatile storage.
0x6
Slave is busy, please try later, mainly used in storing data to
non-volatile storage.
