In case of abnormal communication, process step is as follows.
When receiving the abnormal frame from client, server transmits error code and exceptional code. Error
code is function code adding 80(Hex) and exceptional code indicate the specific error content. Each
code has following content.
Code Code name Meaning
01 Function code error Function code error
02 Address error Exceeds allowed address range
03 Data setting error Not allowed data value
04 Server error Server(slave) is error
05
Server requesting
re-transmission
Now server is too busy to process and requests re-transmission later
06