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Chapter 8 Modbus Communication
8-2
8.2.2 Structure of modbus protocol
Modbus protocol
’
s structure is as follows.
.
In case of normal communication, process step is as follows.
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
Server process time
delay
Server takes time to process. Master should request again.
Summary of Contents for XGL-C22A
Page 172: ...Chapter 8 Modbus Communication 8 23 ...
Page 246: ...Chapter 10 Program Examples 10 40 XG 5000 program Sequence Program 1 2 3 4 ...
Page 247: ...Chapter 10 Program Examples 10 41 Sequence Program 5 6 ...
Page 289: ...Appendix A 23 Sub procedure module When port open event occurs perform the next module ...
Page 291: ...Appendix A 25 The lower code shows BCC check setting ...